Masters Degrees (Agrometeorology)

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Development of an air quality early warning system for the eThekwini and Msunduzi municipalities.
(2023) Sithole, Siphesihle Fortunate.; Mabhaudhi, Tafadzwanashe.; Botai, Joel.
The aim of this study was to assess the source and concentration of criteria air pollutants, as conditioned by the weather and climate conditions, in the eThekwini and Msunduzi Local Municipalities, in the KwaZulu-Natal Province. The outcomes of this assessment will contribute towards the establishment of an appropriate early warning system for the two municipalities, in order to reduce the risk of exposure to air pollution and to avoid the associated health risks. For this purpose, the study adopted various methods and tools to determine the status of air pollution within the municipalities, in terms of the exceedance of particles with an aerodynamic of less, or equal to, 2.5 micrometres (PM2.5) and less than 10 micrometres (PM10) of sulphur dioxide (SO2), ozone (O3) and nitrogen dioxide (NO2). The National Ambient Air Quality Standards (NAAQS) and World Health Organisation (WHO) guidelines were used as a threshold for determining these exceedances. In addition, GIS software was used to determine the spatial distribution of the air pollutants, while the IBM SPSS Statistics Version 27 was used to determine the Pearson correlation between the meteorological parameters and the air pollutant concentration levels within the municipalities. The Openair package in R-Studio was used to determine the wind direction and wind speed within the areas, while the US EPA method was adopted to determine the Air Quality Index (AQI). The results of the exceedance study indicated that most of the air pollutants that were emitted exceeded those of the WHO and NAAQS thresholds, especially PM2.5 and PM10, mostly during the winter period, when temperature inversion is at its strongest. A positive relationship was determined between the air pollutants and meteorological conditions. It is worth noting that the meteorological conditions were not the only factors influencing the concentration levels, but the emissions from industries and vehicles, the burning of fossil fuels for domestic purposes and landfill sites were also observed to be contributing factors to the air pollutant concentration within the municipalities. The results of the proposed AQI showed that most of the people living in eThekwini, especially those living south of Durban, were exposed during winter season to high concentrations of PM10, PM2.5 and SO2, while those of the proposed AQI in the Msunduzi Municipality were, in most cases, observed to be moderate throughout the seasons. In two cases, the Pietermaritzburg CBD and at the Pietermaritzburg Airport, the AQI was recorded as hazardous during spring and summer, respectively. According to the proposed AQI, the most dominant air pollutants are NO2 and SO2. The findings of the study suggest that people living in eThekwini and Msunduzi communities may breathe air harmful to their health and well-being, especially those living near industries and national highways. The overall findings of the study showed that the constitutional right of those living within these municipalities, “to live in an environment that is not iv harmful to their health and wellbeing”, is being violated, since they are being exposed to high air pollutant concentrations.
Assessment of maize crop health and water stress based on multispectral and thermal infrared unmanned aerial vehicle phenotyping in smallholder farms.
(2021) Brewer, Kiara Raynise.; Clulow, Alistair David.; Sibanda, Mbulisi.; Mabhaudhi, Tafadzwanashe.
Abstract available in PDF.
Assessment of vulnerability of cattle farming to climate variability and change in South Africa.
(2021) Masemola, Makgethwa Jillie.; Savage, Michael John.; Tongwane, Mphethe Isaac.
Livestock are dependent upon weather for their comfort and food supplies. Sometimes, adverse weather conditions can cause production losses, especially if experienced during critical stages of growth. Heat stress is a major cause of production losses in the dairy and beef industries. Heat stress occurs when the temperature of the environment increases above the comfort zone of cattle as a result of solar irradiance. Heat stress decreases grazing and feed intake in cattle, while drought can limit pasture availability for grazing cattle. The temperature-humidity index (THI), a combination of air temperature and relative humidity, was used to determine the influence of heat stress on the productivity of cattle. The aim of the study was to investigate the air temperature and relative humidity conditions over South Africa accountable for high THI values for cattle farming for the period 1985 to 2015. The standard precipitation index (SPI) and normalised difference vegetation index (NDVI) at three months were computed to assess the soil moisture conditions and vegetation greenness for the season with high THI averages. The THI data analysis was performed seasonally, using a 15-year average and daily values from 75 weather stations in South Africa. Monthly rainfall data from 192 weather stations were used to compute SPI at three months. The NDVI used MODIS satellite information to create vegetation images for the three summer months. Results indicated summer as a season when cattle are vulnerable to heat stress. The periods (2005/06, 2007/08, 2012/13, 2013/14) experienced high seasonal averages (THI > 80) compared to the remaining years. Daily THI extremes were prevalent in February in South Africa. The SPI results indicated that the North West, the western Free State and east of the Eastern Cape provinces were vulnerable to dry conditions for the four summer periods. The NDVI results indicated that the eastern and coastal parts of South Africa were areas of high vegetation activity and greenness for all the summers. The Northern Cape, Limpopo, North West and Free State provinces had vegetation that was vulnerable to dry conditions. Heat stress and a healthy vegetation activity were a problem for the Northern Cape and Limpopo provinces, while KwaZulu-Natal and Mpumalanga had heat stress as their only challenge. The northern and eastern parts of South Africa were heat stress areas with air temperature as the main driver in THI. New smaller areas were developing as heat stress zones, and areas that were identified as heat stress zones in the past were increasing in size for South Africa. Natural grazing areas indicated no significant relationship with THI but showed a relationship with SPI. Cattle farmers situated in the heat stressed regions of South Africa and new heat stress developing areas need to take the necessary precautions to make profitable decisions for their cattle production.
Testing and evaluation of a newly installed Agrometeorology Instrumentation Mast (AIM) web-based system in a rural school in Swayimana, KwaZulu-Natal, South Africa.
(2019) Dlamini, Zibuyile.; Savage, Michael John.
Rural communities in South Africa are the most vulnerable to the effects of climate change and adverse weather due to their heavy reliance on natural resources. Agricultural adaptation is therefore essential. However, there is very little evidence of efforts to build the capacity of rural communities to adopt climate-smart agricultural and environmental practices. Education and public awareness on a community scale are the most important strategies for dealing with climate change and adverse weather. Climate change and adverse weather communication both present challenges because of their complexities. An Agrometeorology Instrumentation Mast (AIM) system was installed at Swayimana High School in Swayimana near Wartburg in KwaZulu-Natal, South Africa. The AIM system is unique in South Africa and was developed to enhance teaching and learning and facilitate research. The system was installed to provide the scholars with real-time weather data and weather hazard warnings using selected information and communication technology (ICT) methods. The emphasis is placed on the use of visualisation to simplify complex elements of adverse weather by displaying measurements graphically. The aim of this study was to investigate whether using the AIM system is an effective tool to promote agrometeorological literacy and over time improve adverse weather resilience in Swayimana. It explores how the web-based system enhances scholars learning and their response to it. It also investigates scholars’ attitudes and perceptions of climate variability and climate change. The target sample was scholars of Swayimana High School in Grades 10 to 12. A combination of purposive and simple random sampling was used to select the participants. Predominantly qualitative research methods were used to obtain an understanding of opinions and perceptions. Content and descriptive analysis was employed to analyse open-ended questionnaires and group interviews. The baseline study conducted demonstrated that scholars felt adverse weather was an important issue but that they were not aware but were poorly equipped to adapt to adverse weather. A lack of computer literacy presented a challenge for scholars when using the system at the school. The alternative option of accessing the website through a web-enabled phone proved to be of advantage. The system improved their understanding of technical and scientific terms that were absent in their language. Web-based learning encouraged critical thinking, active participation in lessons ability to read and analyse visual representations of statistical data. Further, the system improved their awareness of adverse weather, global climate variability and change and adaptation strategies. The results demonstrated the attractiveness of the AIM system as an education tool. However, there is a need for a much larger and longer-term research study on the usability of the system.
Using agrometeorological data to equip local farmers for sustainable food production in Swayimane, KwaZulu-Natal.
(2019) Popoola, Adesegun Quam.; Savage, Michael John.
Abstract available in pdf.
Temperature dynamics within a low-cost aquaponic system and the possibe effects of climate change.
(2019) Mkhize, Minenhle Godslove.; Clulow, Alistair David.; Taylor, Simon Michael.; Lagerwall, Gareth.
The agricultural sector is facing impeding challenges due to climate change. There is enough evidence showing that climate change has a significant impact on agricultural production. Marginalized communities that lack financial resources and depend on agricultural crop production, are the most vulnerable to climate change effects, which further exacerbates 5 their food insecurity. Existing literature hypothesizes that aquaponics, using Tilapia, has potential in addressing climate change effects in agriculture. However, the low average winter temperature hinders successful adoption of low-cost aquaponic systems using Tilapia fish. The implication of cool conditions (South African temperatures) are more extreme for a low-cost, poorly resourced aquaponic users because they lack temperature regulation 10 systems to maintain optimal temperatures and are simply subject to the surrounding environmental conditions. Therefore, the purpose of this study was to understand the temperature dynamics of a low-cost aquaponic system and the possible effects of future climate change. A study was conducted at KwaDeda, a poor rural community in the Ndwedwe area of 15 KwaZulu-Natal. The two objectives were to (1) understand how the surrounding environmental air temperature affects the water temperature of a low-cost aquaponic system and, to (2) assess the implications of future climate change on a low-cost aquaponic system. Two weather stations (22 km apart) were installed, one to measure hourly environmental air temperature conditions and the other to measure the conditions within the plastic tunnel of 20 a low cost aquaponic system (from June – November 2019). The environmental air temperature had no immediate relationship with water temperature. However, there was an observed lag of 4 hours from the environmental air temperature peak to water temperature peak, which varied slightly with seasonality. The conditions within the tunnel were generally hotter than the outside environmental conditions during the day, 25 however, at night, the tunnel air temperature dropped to be the same and sometimes even lower the outside environmental temperature. The air temperatures in winter and resulting water temperatures of the low-cost aquaponic system was well below the optimum range for Tilapia (22-32 °C). Low-cost systems provide limited means to control water temperature. Therefore, further investigation into low-cost methods to reduce the cooling of the tunnels 30 at night, which later results in cooling of the water, is required. The projected future climate was shown to be both advantageous and disadvantageous for the low-cost aquaponic system. The projected increase in average air temperature due to climate change will be positive for South African conditions, which are generally quite cool for Tilapia. However, extreme weather conditions such as intense storms, high wind speed and hail, that are predicted with climate change, may be a threat to low-cost aquaponic infrastructure. Research into improving the design of low-cost tunnels that can withstand adverse weather conditions is recommended.
Runoff simulation using the SWAT model for flood frequency analysis and design flood estimations in the Luvuvhu River catchment, South Africa.
(2018) Thavhana, Mulalo Precious.; Moeletsi, M'aseapa Mookho Violet.; Savage, Michael John.
Abstract available in PDF file.
Rainy season characteristics with reference to maize production for the Luvuvhu river catchment, Limpopo Province, South Africa.
(2017) Tshililo, Fhulufhelo Phillis.; Savage, Michael John.
In arid and semi-arid regions, crop yields are mainly dependent on the amount and spatio-temporal distribution of rainfall. For most smallholder farmers in rural areas of southern Africa, rainfall is a critical input to agricultural production of most staple crops such as maize. To effectively plan for agricultural development, it is of utmost importance that the spatial distribution and temporal variation of rainfall is understood as it govern the type of farming systems that can be practiced in any region. Therefore, a detailed understanding of rainfall is necessary before any farming activities can commence. The study investigated rainy season characteristics with reference to maize production in the Luvuvhu River Catchment. Rainy season characteristics assessed included aridity index, onset, cessation, length of the season, false onset, dry spells, seasonal rainfall, number of rainy days and monthly rainfall. Historical daily rainfall and minimum and maximum air temperature data (1923-2015) were obtained from the Agricultural Research Council. Twelve meteorological stations that were evenly distributed and represented different climatic regions within the catchment were chosen. An aridity index for different areas of the catchment was calculated using the United Nations Environment Programme equation. Evapotranspiration was calculated using the Hargreaves and Samani equation. Annual rainfall was calculated by summing daily rainfall from 1st January to 31st December. The Instat+ v 3.36 statistical programme was utilized to calculate onset, cessation, and length of the season, the number of rainy days, dry spells, seasonal rainfall and monthly rainfall. The Statistica software was used to generate descriptive statistics as well as to calculate probability of exceedance and non-exceedance for the rainy season characteristics. The Anderson-Darling goodness of fit test was performed to determine the distribution model that best represents the data. The resultant probabilities of exceedance were then computed from the distribution models that best fit the data. A non-parametric Spearman rank correlation coefficient test was used to analyze data for trends in rainy season characteristics as well as monthly rainfall. The results from the study showed that monthly rainfall at the Luvuvhu River Catchment during the rainy season varies temporally and spatially. In the high rainfall areas of the catchment, the rainy season commences early from the third week of October and ends the first week of April the following year. For dry areas of the catchment, the rainy season commences in the second week of November and ends early in the third week of February. The results further show a decrease in length of the rainy season, the number of rainy days, and seasonal rainfall further away from wet to dry areas of the catchment. There was no significant change on the onset of the rainy season on the catchment for the past 27-90 years. There is a high risk of both short and medium dry spells at most stations during the month of October, with, Folovhodwe, Phafuri and Sigonde being at highest risk. Farmers are therefore advised to use the first onset for land preparation and plant after the second onset in November and December to avoid the high risk of dry spells and false onset in October and November, depending on the location at the catchment. Folovhodwe, Mampakuil, Phafuri and Sigonde have a mean length of rainy season of less than 120 days and seasonal rainfall of less than 500 mm per rainy season. Hence, these areas are not suitable for rain-fed maize in the current climate. However, they are suitable for the production of other crops which may be sold in order to purchase maize. The most favourable sites for maize production within the catchment are Entabeni, Levubu, Lwamondo, Thathe, Tshiombo, and Vreemedeling. Therefore, production should be maximized at these areas so that there is sufficient maize for the whole catchment. In dry years, stations situated in the low-lying areas in the north-eastern and eastern parts of the catchments receive less rainfall which does not permit planting of maize. In normal and wet years, rainfall is sufficient for the production of various crops. However, in semi-arid areas of the catchment, plans should be made for supplementary water due to high evapotranspiration rates in order to maximize maize production. Stations in the middle/south western parts of the catchment can receive significant rainfall in both dry, normal and wet years. Trend analysis for long-term rainfall data did not show any significant changes in monthly rainfall except for Lwamondo and Levubu where an increasing trend is notable in January rainfall. In December, the rainfall trend was significant at Entabeni, Folovhodwe and Lwamondo. An increase in rainfall is notable at Lwamondo and a decrease in rainfall at Entabeni and Folovhodwe.
Microclimate modification to improve productivity of ‘Carmen®-Hass’ avocado orchards using shadenet under subtropical conditions of Limpopo Province, South Africa.
(2016) Malapana, Clarance Kgethego.; Savage, Michael John.
The agricultural environment is a complex and dynamic system. Microclimate, the crop, biosphere, and management practices interact to determine the best yield production. South Africa is a water-scarce country, with high variability in annual rainfall. Thus, water quality and quantity are major limiting factors in agriculture. Hence, shadenetting can be used to modify the orchard microclimate to make the environment more conducive for fruit production. The South African avocado industry is export-oriented, so there is a commercial need to optimise the exportable percentage of avocado fruit. Sunburn, wind and hail damage and small fruit size as a result of water stress are the major cull factors for the industry. It is believed that shadenetting, with changes in management practices, can counter these limiting factors. There is no literature on growing avocado fruit under shadenetting. Therefore, the aim of the research was to determine the effects of a 20% white shadenet on ‘Carmen®-Hass’ avocado orchards and productivity. The long term objective is to improve avocado fruit quality and profitability in the Mooketsi Valley, Limpopo province, South Africa, a subtropical environment by reducing abiotic stress, particularly, solar irradiance, heat and wind. The trial was conducted at Goedgelegen Estate in the Mooketsi Valley on ‘Carmen®-Hass’ trees planted in 2007/8 season. A 1-ha shadenet structure (6 m high) was used, with 20% white shadenet over the roof and 40% green shadenet on the sides. Air and canopy temperature, relative humidity, wind speed, solar irradiance and leaf wetness duration (LWD) and sap flow were monitored at a sub-hourly rate. Evapotranspiration was calculated from the above mentioned parameters. Irrigation was monitored five times per week using tensiometers at 300- and 600-mm soil depths. The comparison between open and shadenet leaf areas showed that leaves in the open treatment were reduced as a result of the abiotic stress. Fruit water content under the shadenet compared to the open was greater, such enabled fruit under the shadenet to reach maturity two weeks earlier when compared with open treatment. Air and canopy temperature and relative humidity were slightly reduced under the shadenet, with the greatest difference occurring during the flowering period in mid-winter. The modification in air temperature and relative humidity was beneficial for bee activity and pollination in 2015 compared to the 2014 season. ‘Carmen®-Hass’ flowers in mid-winter when temperature conditions are not conducive for pollination. Canopy temperature was also reduced under shadenetting compared to the open treatment. The reduction was due to differences in tree density and the role that shadenetting plays. The infrared thermometer measurements were uniform with dense canopies compared to sparse tree canopies. The midday incoming solar irradiance was reduced by 18% under the shadenet compared to the open treatment. Calm conditions were experienced under the shadenet. Hence, windspeed was reduced to negligible levels. Also, the shadenet resist air flow to a certain height compared to the open treatment. LWD was extended by 12% under shadenet. An infestation of the insect pest citrus leaf roller (Archips occidentalis) caused severe damage to the fruit during the 2014/15 season due to the high plant density used. Significant results were that evapotranspiration was reduced by 14 and 29% less water was applied under the shadenet to maintain an adequate soil water content compared to the open treatment. Fruit reached minimum maturity two weeks earlier under shadenet compared to the open treatment. Fruit quality and pack-out were improved under the shadenet due to reduction in sunburn, wind damage and small fruit. But poor yields were experienced during the 2014 season due to poor bee activity, pollination and fruit size distribution were reduced under the shadenet compared to the open treatment. But following the improved bee activity in 2015, the 2016 normal season yield is likely to be improved under the shadenet than in the open treatment. Data collected in the Mooketsi Valley showed that 20% white shadenet has modified the microclimate and improved fruit quality. The water use under the shadenet was improved compared to the open treatment. But a thorough investigation on bee management under shadenet is required to optimise pollination in order to obtain greater yields under the shadenet.
Investigating possible impact of climate change on sugarcane production in KwaZulu-Natal, South Africa.
(2016) Sithole, Bonga Benson.; Savage, Michael John.
The KwaZulu-Natal Department of Agriculture, Environmental Affairs and Rural Development in 2010 undertook to investigate the vulnerability of KwaZulu-Natal to climate change which identified various sectors of the economy in the region that are impacted by climate change. The aim of the current study was to investigate the possible impact of climate change on sugarcane production in KwaZulu-Natal. The main objective of the study was to identify and synthesize current knowledge, scientific literature and data relating to specific aspects of climate change in KwaZulu-Natal, South Africa. In order to achieve the objectives of the study, a questionnaire was developed to ascertain sugarcane farmers’ awareness about climate change. Based on questionnaire data, the study reveals that sugarcane farmers are aware of the effect of climate change on sugarcane production. Cane growers are also aware of their activities that contribute to climate change. Climatological data for the region were collected and analyzed through the Decision Support System Agro-tech Transfer (DSSAT) daily crop model to assess possible climate change impacts on sugarcane production. Daily rainfall, solar radiation, wind-speed, air temperature (minimum and maximum) and dew point temperature data for various sugarcane mill supply areas were collected from the South African Sugar Research Institute. RClimDex (1.0) software was used to determine if climate change did occur for the period 1966 to 2016. The climate data sets were positive to climate change with respect to daily maximum air temperature, daily minimum air temperature, daily rainfall, daily dew point temperature and daily solar radiation. The impact of climate change on sugarcane production in KwaZulu-Natal has been recognized as the main cause for yield reduction. No major decline in sugarcane production has been noted in KwaZulu-Natal for those farmers practicing irrigation and improved management. The study also demonstrates an increase in the amount of trash on sugarcane in the latter years of the study period. In general, the approach presented in this study encompassed and assessed the effect of climate change on sugarcane production with inclusion farmers perception can be considered as a strategic issue on existing climate change concern in KwaZulu-Natal province. Further research about what measures have been implemented by other countries in addressing climate change is recommended.
The radiation balance of Midmar Dam in KwaZulu-Natal, South Africa.
(2016) Myeni, Lindumusa.; Savage, Michael John.
Abstract available in PDF file.
Investigation of microclimate for human comfort in the natural environment and in a car parked in the open.
(2016) Luthuli, Sithandiwe Ignatia.; Savage, Michael John.
Abstract available in PDF file.
Irrigation control system with a web-based interface for the management of Eucalyptus planting stock.
(2015) Kaptein, Nkosinathi David.; Savage, Michael John.
Commercial forestry nurseries use large quantities of water to irrigate the planting stock to meet the annual forestry industry planting demands. However, South Africa is a water scarce country and there is high competition for this limited resource with other sectors. Thus, sustainable water management strategies should be put in place to preserve this precious resource. In commercial forestry nurseries, sustainable water use may be achieved by carefully managing irrigation schedules, such as accurately measuring growing media water content and then replenishing the depleted soil water. Improved nursery irrigation management may not only save water, but also has the potential to reduce the prevalence of pests and diseases, excessive leaching of nutrients, irrigation costs and may produce robust planting stock that is better suited to adapt to field conditions. Growing media water content can be directly measured by the gravimetric method. However, this method is laborious, time consuming, costly and does not allow for near real-time monitoring and control. Several indirect methods for estimating soil water content have been developed and are in use today. Some common methods are: frequent domain reflectometry, time domain reflectometry, time domain transmission and the dual-needle heat pulse method. However, each method has advantages and disadvantages. Considerations for choosing the most appropriate method are the ability to automate, accuracy and precision, skills required to use and the costs to purchase. The main objective of this study was to calibrate the low cost commercially available Decagon EC-5 soil water content sensors using nursery growing media. The calibration equation was then used to measure and control irrigation for Eucalyptus grandis x Eucalyptus urophylla and Eucalyptus dunnii planting stock grown in seedling trays in a greenhouse. A web-based data and information system was utilised to share measurements and display greenhouse environmental conditions in near real-time. The data could be viewed or downloaded using the internet1. Decagon EC-5 soil water content sensors were laboratory-calibrated, using nursery growing media, against the standard gravimetric method. Four nursery growing media were used for calibrations: coir/perlite mix (CP), coir/pine bark/vermiculite mix (CPBV), pine bark (PB) and sandy soil. The calibration relationships between gravimetric water content and sensor output for each growing media were established, and the manufacturer supplied calibration equation was evaluated against laboratory calibration equations. The appropriate laboratory calibration equation was programmed in the datalogger to measure and control irrigation. Greenhouse microclimate measurements of air temperature, relative humidity and solar irradiance were conducted. Hourly grass reference evaporation (ETo) was calculated by the datalogger. The greenhouse microclimate measurements were compared against an open area automatic weather station at the University of KwaZulu-Natal Agrometeorology Instrumentation Mast (UKZN AIM) system measurements. The EC-5 soil water content sensors were used to schedule irrigation for E. grandis x E. urophylla hybrid clones (GxU) (Experiment 1) and E. dunnii seedlings (Experiment 2) grown in seedling trays inside a fully air temperature controlled greenhouse. Irrigation was controlled in three treatments: low, medium and high watering. All treatments were treated the same except for differing irrigation application. Total daily irrigation and drainage were measured per treatment. Irrigation scheduling for GxU was programmed at a set point and E. dunnii seedlings at lower and drained upper limits. Seedling measurements conducted were root collar diameter (RCD), heights, stomatal conductance (gs), root-to-shoot ratio and total leaf area. Total drainage and its electrical conductivity (EC) was also measured. The calibration relationship showed a linear relationship between gravimetric water content and sensor output for all four growing media with an R2 greater than 0.92. The manufacturer supplied calibration equation poorly estimated growing media water content compared to the laboratory calibration. Poor estimation exceeded the 5% error specified by the manufacturer. Air temperature was consistently less than 25°C inside the greenhouse. The external air temperature, as measured by the UKZN AIM system, fluctuated and reached a maximum of 36.6°C during the study period. Solar irradiance inside the greenhouse was 60% lower than that measured by the UKZN AIM system. The relative humidity was consistently higher inside the greenhouse compared to that measured by the UKZN AIM system. Greenhouse grass reference evaporation was consistently lower than the UKZN AIM system due to low air temperature and high RH inside the greenhouse. For Experiment 1, the GxU clones were irrigated too frequently for short periods. This led to over- and under- irrigation in high and low watering treatments, respectively. However, these challenges were addressed in Experiment 2 using E. dunnii seedlings irrigated at lower and drained upper irrigation limits. In Experiment 2, variability in sensor measurements within each treatment were observed at drained upper limit and decreased at lower limit. This was likely caused by a change in the pore space volume from dry to wet growing media. The web-based system was successfully used as an early warning system to monitor soil water content measurements and greenhouse microclimate, averting experimental failure due to lack of irrigation on one occasion. Seedlings in the high watering treatment had the highest RCD, heights and gs followed by the medium and low watering treatments. Although the low watering treatment had the lowest growth rates and gs these seedlings were more robust, hardy and resistant to water stress. The root-to-shoot ratio showed no statistically significant differences between treatments. However, seedlings in the high watering treatment had slightly greater root volume. This was probably due to the increased total seedling leaf area for this treatment which facilitated increased photosynthetic activity and carbohydrates production, enabling increased root growth. The highest EC measurements were recorded in the low watering treatment. This was likely due to low irrigation and therefore nutrients were not washed off the growing media. Medium watering treatment EC was 30% lower than the low watering treatment whilst high watering EC was almost equivalent to the irrigation water. The analysis of economics showed that implementing the fully automated system could be costly. However, there are many potential benefits that may be offered by this system such as reduction in water use, pumping costs and management time. The early warning offered by this system could potentially help avoid the loss of planting stock if there is a problem with the irrigation system. The study showed that irrigation may be automatically scheduled for nursery seedlings trays using low cost Decagon EC-5 soil water content sensors with reasonable accuracy. However, medium-specific calibration is important to improve the soil water content measurement accuracy. The study also showed that reducing irrigation may result in reduced growth rates of seedlings. However, other benefits such as seedling resistance to water stress, robust seedlings, irrigation water savings and a reduction in washing off nutrients may be achieved.
Monitoring fire danger in near real-time using field-based agrometeorological measurement systems.
(2014) Strydom, Sheldon.; Savage, Michael John.
Africa has been termed the ‘Fire Continent’ due to its high annual fire frequency. Wildfires are considered one of the most common disasters in South Africa resulting in a high number of human fatalities and financial loss on an annual basis. It is believed that increased population growth, as well as more concentrated settlement planning is likely to result in increased fire disasters and increased human fatalities as a direct result of wildfires. The high number of human fatalities and high financial loss associated with wildfires served as the main motivation for the research throughout all studies. While wildfires may provide beneficial environmental service, increased wildfire activity can result in a number of adverse effects on the environment, for example the removal of vegetation, fascilitating/aggravating floods and soil erosion but do bring with them positive effects such as nutrient recycling and removal of alien species. In order to better understand the spatial and temporal variations and characteristics of wildfires in South Africa an 11-year dataset of MODIS-derived Active Fire Hotspots was analysed using an open source geographic information system. The study included the mapping of national fire frequency over the 11-year period. Results indicate that the north-eastern regions of South Africa experience the greatest fire frequency, in particular the mountainous regions of KwaZulu-Natal, Mpumalanga and the Western Cape. Increasing trends in provincial fire frequency was observed in eight out of the nine provinces with Mpumalanga being the only province where a decrease in annual fire frequency over the study period was observed. Temporally, fires have been observed in all months for all provinces although distinct fire seasons were observed, largely driven by rainfall seasons. The South-Western regions of South Africa (winter rainfall patterns) experienced higher fire frequencies during the summer months with the rest of the country (summer rainfall) experiencing higher fire frequencies during the winter months. Regions which experience bi-modal rainfall seasons did not display distinct fire seasons. The study included an investigation into the likely effects of climate change on South African fire frequency. Three of the 11 years were identified as being climatologically anomalous. Fire frequencies in 2005 and 2010 (two of the warmest years in recent history) were significantly greater than normal years. Observed fire frequencies in 2008 were also significantly greater. The increased fire frequency was attributed to a severe La Niña event which may have resulted in increased vegetation growth prior to the dry season. A current issue with the mitigation of wildfires is the lack of proper real-time monitoring and measurement systems which can aid decision makers in the timing of controlled fires. The development of a system for improved monitoring of meteorological conditions conducive to fire was investigated. The traditionally used nomogram and lookup table used by Lowveld fire danger index (LFDI) system was replaced by mathematical functions which were then programmed into an automatic weather station datalogger. Near real-time results of the calculated LFDI were displayed in a web-based teaching, learning and research system found at: http://agromet.ukzn.ac.za:5355/?command=RTMC&screen=Fire%20danger%20index. Warm, dry mountain winds known as Berg winds have a direct link to fire weather, enhancing the danger of uncontrollable fires. Berg winds are associated with periods of increased air temperature, decreased relative humidity and increased wind speeds. This increases the potential for the development and spread of wildfires. The effects of Berg winds on the microclimate and fire danger were quantified. For this purpose, historic hourly meteorological data, local and international, were used together with a fuzzy logic system for determining Berg wind conditions in near real-time. This included the use of modelled diurnal sinusoidal functions for solar irradiance, air temperature, relative humidity, wind speed and direction, for various locations. Application of the system demonstrated that out of four sites in the KwaZulu-Natal Midlands, South Africa, Baynesfield was the most vulnerable to Berg wind occurrences, followed by Ukulinga (near Pietermaritzburg) and lastly Cedara. Boulder in Wyoming, USA, experienced a larger frequency of Berg wind events compared to Sidney in Montana, USA, despite being located at a higher altitude. The McArthur Fire Danger Meters (FDM) have been used to monitor and measure fire danger in Australia since the 1950s when they were first developed following severe wildfires. The McArthur FDM has traditionally made use of nomograms to calculate grassland and forest fire danger. In the 1980s mathematical descriptions of the McArthur FDM were developed. These then allowed for the sub-daily and near real-time measurement of grassland and forest fire danger. While commercial forestry contributes only a small percentage of South Africa’s GDP, forest fires have been identified as a common occurrence in commercial forestry plantations and natural forests, which can at times spread to neighbouring grasslands or non-forest vegetation. Forest fire disasters in South Africa are well documented by the mainstream media and it is believed that proper monitoring of forest fire danger, along with grassland fire danger, may mitigate potential wildfire disasters and limit human fatalities and financial loss. The McArthur FDM also provides opportunity to model fire behaviour – a component of wildfire mitigation lacking in the Lowveld fire danger index. The study utilized the equations developed to investigate the use of the McArthur FDM in South Africa by applying the equations to historical hourly meteorological data recorded at four locations in the KwaZulu-Natal Midlands, South Africa. Modifications to the McArthur grassland fire danger index (GFDI) were needed and resulted in the development of a method to calculate vegetation curing as a function of micrometeorological variables. Datasets were analysed to investigate seasonal curing at the four locations with results indicating high monthly curing averages in all months, with the greatest range of curing averages experienced in the winter months. Frequency analysis of both the GFDI and the forest fire danger index (FFDI) indicate that lower fire danger ratings are more common than high danger ratings as one would expect. The GFDI and FFDI displayed acceptable sensitivity to changes in the microclimate as observed through conducting sensitivity analysis and by plotting diurnal variations of GFDI and FFDI during Berg wind events. The fire behaviour modelling component of the McArthur FDM does not yield realistic results on steep topography but does provide a baseline on fire characteristics on gentler slopes
Modelling the impacts of increased air temperature on maize yields in selected areas of the South African highveld using the cropsyst model.
(2014) Pasi, Jonathan M.; Savage, Michael John.
Abstract available in PDF file.
Web-based teaching, learning and research using real-time data from field-based agrometeorological measurement systems.
(2014) Savage, Michael John.; Everson, Colin Stuart.
Abstract available in PDF file.
Seasonal variation of surface energy fluxes above a mixed species and spatially homogeneous grassland.
(2011) Moyo, Nicholas C.; Savage, Michael John.
The increasing human population, industrialization, urbanisation and climate change challenges have resulted in an increased demand for already scarce water resources. This has left the agricultural sector with less water for production. Sustainable water management strategies would therefore require accurate determination of water-use. In agriculture, water-use can best be determined from total evaporation which is the loss of water from soil and vegetation to the atmosphere. Accurate quantification of total evaporation from vegetation would require a thorough understanding of water transport processes between vegetation and the atmosphere, especially in a water-scarce country like South Africa. Several methods for estimating total evaporation have been developed and are in use today. Some of the common methods used today are: the Bowen ratio energy balance, eddy covariance, scintillometry, flux variance and surface renewal. However, various methods have advantages and disadvantages. Considerations include the cost of equipment and level of skill required for use of some of the methods. A number of methods involve indirect or direct estimation of sensible heat flux then calculating latent energy flux and hence total evaporation as a residual of the shortened energy balance equation. The main objective of this study is to determine the effects of grassland management practices on the energy balance components as well as on the surface radiation balance. Eddy covariance and surface renewal methods were employed to investigate the effects of grassland management practices (mowing and burning) on the micrometeorology of naturally occurring grassland. A 4.5-ha grassland site (Ukulinga, Pietermaritzburg, South Africa) was divided into two halves: one area was initially mowed (cut-grass site) to a height of 0.1 m while the other was not mowed (tall-grass site). The tall-grass site was later treated by burning and hence referred to as the burnt-grass site. Two eddy covariance systems were deployed, one at each of the cut-grass and the tall-grass sites. The systems each comprised a three-dimensional sonic anemometer to measure high frequency sonic temperature, orthogonal wind speeds and directions and the eddy covariance sensible heat flux (W m-2). Latent energy flux, from which total evaporation was then determined, was calculated as a residual from the shortened energy balance equation from measurements of sensible heat flux, net irradiance and soil heat flux assuming closure is met. Other microclimatic measurements of soil water content, soil temperature, surface reflection coefficient and reflected solar irradiance were performed, the latter with a four-component net radiometer. An automatic weather station was also set up at the research site for continuous measurements of solar irradiance, air temperature, relative humidity, wind speed and direction and rainfall. Water vapour pressure and grass reference evaporation were also determined online. Energy fluxes from the tall-grass site were measured from March to June 2008. Greater total evaporation rates (2.27 mm day-1) were observed at the beginning of the experiment (March). As winter approached most of the energy balance components showed a constant decreasing trend and the average total evaporation rates for May and June were 1.03 and 0.62 mm day-1, respectively. The tall-grass site had consistently lower soil temperatures that changed diurnally when compared to the cut-grass site. The soil water content at both sites showed no significant differences. Most of the energy balance components were similar between the two sites and changed diurnally. Although there were small differences observed between other energy balance components, for example, latent energy flux was slightly greater for the tall-grass site than for the cut-grass site. The tall-grass site had more basal cover and this may have contributed to the differences in temperature regimes observed between the two sites. However, the plants growing at the cut-grass site showed more vigour than the ones at the tall-grass site as spring approached. Burning of a mixed grassland surface caused significant changes to most of the optical properties and energy fluxes of the surface. Following burning, the soil temperature was elevated to noticeable levels due to removal of basal cover by burning. The surface reflection coefficient measured before and after the burn also presented a remarkable change. The surface reflection coefficient was significantly reduced after the burn but a progressive increase was observed as the burnt grass recovered after the spell of spring rains. The energy fluxes: net irradiance, latent energy flux and soil heat flux also increased following the burn but the latent energy flux was reduced as transpiration was effectively eliminated by the burning of all actively transpiring leaves. As a result, the main process that contributed towards latent energy flux was soil evaporation. An ideal surface renewal analysis model based on two air temperature structure functions was used to estimate sensible heat flux over natural grassland treated by mowing. Two air temperature lag times r (0.4 and 0.8 s) were used when computing the air temperature structure functions online. The surface renewal sensible heat fluxes were computed using an iteration process in Excel. The fluxes, obtained using an iterative procedure, were calibrated to determine the surface renewal weighting factor (a) and then validated against the eddy covariance method using different data sets for unstable conditions during 2008. The latent energy flux was computed as a residual from the shortened energy balance equation. The surface renewal weighting factor was determined for each of the two heights and two lag times for each measurement height (z) above the soil surface. The a values obtained during the surface renewal calibration period (day of year 223 to 242, 2008) ranged from 1.90 to 2.26 for measurement height 0.7 m and r = 0.4 and 0.8 s. For a measurement height of 1.2 m and r = 0.4 and 0.8 s, a values of 0.71 and 1.01 were obtained, respectively. Good agreement between surface renewal sensible heat flux and eddy covariance sensible heat flux was obtained at a height of 1.2 m using a = 0.71 and a lag time of 0.4 s. Total evaporation for the surface renewal method was compared against the eddy covariance method. The surface renewal method, for a height of 1.2 m and a lag time of 0.4 s, yielded 1.67 mm while the eddy covariance method yielded 1.57 mm for a typical cloudless day. For the same day for a measurement height of 1.2 m and a lag time of 0.8 s, eddy covariance and surface renewal methods yielded 1.57 and 1.10 mm, respectively. For a lag time of 0.4 s, the surface renewal method overestimated total evaporation by 0.10 mm while for a lag time of 0.8 s, the total evaporation was underestimated by 0.47 mm. As a result, the surface renewal method performed better for z = 1.2 m and a lag time of 0.4 s. The eddy covariance method gave reliable sensible heat fluxes throughout the experiment and this allowed a comparison of fluxes across all treatment areas to be achieved. The short-term analysis of the surface renewal method also gave reliable energy fluxes after calibration. Compared to the eddy covariance method, the surface renewal method is more attractive in the sense that it is easy to operate and use and it is relatively cheap. However, the surface renewal method requires calibration and validation against a standard method such as the eddy covariance method. This study showed that grassland management practices had a considerable effect on surface radiation and energy balance of the mowed and burnt treatment sites. Total evaporation was mainly controlled by the available energy flux, rainfall and grassland surface structure. High total evaporation values were observed during summer when net irradiance was at its highest and grass growth at its peak. Low total evaporation values were observed in winter (dry atmospheric conditions) when net irradiance was at its lowest and most vegetation was dormant.
The use of infrared thermometry for irrigation scheduling of cereal rye (Secale cereale L.) and annual ryegrass (Lolium multiflorum Lam.)
(2003) Mengistu, Michael Ghebrekidan.; Savage, Michael John.; Everson, Colin Stuart.
Limited water supplies are available to satisfy the increasing demands of crop production. It is therefore very important to conserve the water, which comes as rainfall, and water, which is used in irrigation. A proper irrigation water management system requires accurate, simple, automated, non-destructive method to schedule irrigations. Utilization of infrared thermometry to assess plant water stress provides a rapid, nondestructive, reliable estimate of plant water status which would be amenable to larger scale applications and would over-reach some of the sampling problems associated with point measurements. Several indices have been developed to time irrigation. The most useful is the crop water stress index (CWSI), which normalizes canopy to aIr temperature differential measurements, to atmospheric water vapour pressure deficit. A field experiment was conducted at Cedara, KwaZulu-Natal, South Africa, to determine the non-water-stressed baselines, and CWSI of cereal rye (Secale cereale L.) from 22 July to 26 September 2002, and aImual (Italian) ryegrass (Lolium multiflorum Lam.) from October 8 to December 4, 2002, when the crops completely covered the soil. An accurate measurement of canopy to air temperature differential is crucial for the determination of CWSI using the empirical (Idso et al., 1981) and theoretical (Jackson et al., 1981) methods. Calibrations of infrared thermometers, a Vaisala CS500 air temperature and relative humidity sensor and thermocouples were performed, and the reliability of the measured weather data were analysed. The Everest and Apogee infrared thermometers require correction for temperatures less than 15 QC and greater than 35 QC. Although the calibration relationships were highly linearly significant the slopes and intercepts should be corrected for greater accuracy. Since the slopes of the thermocouples and Vaisala CS500 air temperature sensor were statistically different from 1, multipliers were used to correct the readings. The relative humidity sensor needs to be calibrated for RH values less than 25 % and greater than 75 %. The integrity of weather data showed that solar irradiance, net irradiance, wind speed and vapour pressure deficit were measured accurately. Calculated soil heat flux was underestimated and the calculated surface temperature was underestimated for most of the experimental period compared to measured canopy temperature. The CWSI was determined using the empirical and theoretical methods. An investigation was made to determine if the CWSI could be used to schedule irrigation in cereal rye and annual rye grass to prevent water stress. Both the empirical and theoretical methods require an estimate or measurement of the canopy to air temperature differential, the non-waterstressed baseline, and the non-transpiring canopy to air temperature differential. The upper (stressed) and lower (non- stressed) baselines were calculated to quantify and monitor crop water stress for cereal rye and annual ryegrass. The non-water-stressed baselines were described by the linear equations Te - Ta = 2.0404 - 2.0424 * VPD for cereal rye and Te - Ta = 2.7377 - 1.2524 * VP D for annual ryegrass. The theoretical CWSI was greater than the empirical CWSI for most of the experimental days for both cereal rye and annual ryegrass. Variability of empirical (CWSI)E and theoretical (CWSI)T values followed soil water content as would be expected. The CWSI values responded predictably to rainfall and irrigation. CWSI values of 0.24 for cereal rye and 0.29 for annual ryegrass were found from this study, which can be used for timing irrigations to alleviate water stress and avoid excess irrigation water. The non-water-stressed baseline can also be used alone if the aim of the irrigator is to obtain maximum yields. However the non-water-stressed baseline determined using the empirical method cannot be applied to another location and is only valid for clear sky conditions. And the non-water-stressed baseline determined using theoretical method requires computation of aerodynamic resistance and canopy resistances, as the knowledge of canopy resistance, however the values it can assume throughout the day is still scarce. The baseline was then determined using a new method by Alves and Pereira (2000), which overcomes these problems. This method evaluated the infrared surface temperature as a wet bulb temperature for cereal rye and annual ryegrass. From this study, it is concluded that the infrared surface temperature of fully irrigated cereal rye and annual ryegrass can be regarded as a surface wet bulb temperature. The value of infrared surface temperature can be computed from measured or estimated values of net irradiance, aerodynamic resistance and air temperature. The non-water-stressed baseline is a useful concept that can effectively guide the irrigator to obtain maximum yields and to schedule irrigation. Surface temperature can be used to monitor the crop water status at any time of the day even on cloudy days, which may greatly ease the task of the irrigator.
Estimation of reference evaporation and comparison with ET-gage evaporimeter
(2003) Abezghi, Tekeste Weldegabrial.; Savage, Michael John.
Accurate estimation of reference evaporation is necessary for the estimation of actual evaporation for irrigation and water resource management purposes. Estimation of reference evaporati~n using the Penman-Monteith method using automatic weather station (AWS)measurements requires the available energy to be accurately estimated. The available energy of short grass of 0.12 m was measured using a component net radiometer and soil heat flux plate measurements at the Faculty of Sciences and Agricultural (Agrometeorological station, University of Natal, Pietermaritzburg, latitude ~29.79 oS, longitude ~ 30.95 °E, altitude ~ 650 m). In an attempt to evaluate the accuracy of commonly used procedures of estimating available energy, estimates of net irradiance (from net long wave irradiance and reflection coefficient estimate) and soil heat flux density were compared to the actual measurements. The linear approximation of atmosphere minus crop surface emittance based on air temperature was compared with measured net long wave irradiance and similar empirical formulations. The underestimation of the measured net long wave irradiance was observed using the linear approach. Furthermore, a plot of measured clear sky net long wave irradiance and air temperature showed a logarithmic relation. The estimated reflected solar irradiance was overestimated for the reference crop. The measured soil heat flux density was observed to vary not only with net irradiance but also with cloudiness, wind speed and soil water content. The soil heat flux density measured with plates was noticed to follow the measured net irradiance. The sensitivity of Penman-Monteith latent heat estimate was investigated for the use of estimated reflection coefficient and soil heat flux density as well as ignored soil heat flux density. Results showed the latent heat estimate to be greater when soil heat flux density was ignored. Reduced set assumptions of Penman-Monteith were assessed usmg the microclimatic measurements. The grass reference evaporation estimate using estimated water vapour pressure from the pervious day minimum air temperature and approximated wind speed were found to be seasonal and procedure dependent. The hourly-reduced set estimate of reference evaporation was in good agreement with the grass Penman-Monteith estimate. The estimated daily water vapour pressure underestimated the daily grass Penman-Monteith estimate. The sensitivity of the reduced set reference evaporation estimate was compared for the two values of approximated wind speeds. The assumption of 2 m S-1 wind speed gave a relatively better result. The sensitivity of the surface temperature energy balance (STEB) estimate of reference evaporation was investigated using two different atmospheric stability procedures. The evaporation estimate agreement and performance of the technique were found to vary depending on the stability correction procedure. The Monteith (1973) correction procedure was observed to be more sensitive to a higher surface-air temperature difference. The Monteith (1973) procedure was found to underestimate the reference evaporation and this resulted in a lower correlation coefficient. The uncorrected and Campbell and Norman (1998) stability corrected procedure of STEB estimate overestimated the reference evaporation but resulted in good agreement with actual reference evaporation. The use of estimated available energy using the STEB method resulted in a 7 % overestimate of measured available energy. Different designs of atmometers have been used to measure evaporation. The less expensive and simple ET_gageR (Model A and E) atmometer for daily evaporation measures were compared to grass-based and alfalfa-based Penman-Monteith and STEB estimate of reference evaporation. Two different evaporation surface covers used with the device allowed for the comparison to be made. Measurements using the canvas 30 ET-gage cover for grass reference evaporation were compared to grass based Penman-Monteith and STEB reference evaporation estimates. Correlation between the canvas 30 measures and Penman-Monteith estimates were good compared to the STEB estimate. The ET-gage canvas 54 measures were in a good agreement with alfalfa based Penman-Monteith reference evaporation estimate. There was, however, a slight time lag in ET-gage evaporation with ET-gage evaporation continuing accumulation when the reference evaporation was zero. The sensitivity of the ET-gage for microclimate variation was tested using the measurements made for two levels and three different microclimates. A shade measurement of reference evaporation was overestimated. The response of the ET-gage to one and two meter microclimate measures was similar to the short grass measurement. Furthermore, the ET-gage surface evaporation estimate using the STEB method showed equal response to the ET-gage surface for the microclimate measure and explained the possible cause of the lag of the ET-gage response. Accurate microclimate measurements is a requirement for the performance of the PenmanMonteith approach for the estimation of reference evaporation. The investment cost required for an AWS set up is high. Alternative options for gathering information of the microc1imate measurements required for calculating reference evaporation were assessed in terms of cost saving, accuracy and other advantages. A weather station system using a Hobo H8 logger (internal relative humidity and air temperature sensor and two external channels, one which was used for solar irradiance measurements) was found to be a cost-effective method for calculating the necessary microclimatic information for calculating reference evaporation. With this system reference evaporation was estimated with reasonable accuracy, at 16 % of the cost of normal AWS system. The use of an Event Hobo logger and an ET-gage was found to provide a reasonable estimate of reference evaporation. The use of the reduced set evaporation weather station was found to be unreasonable in terms of cost and accuracy. Air temperature and relative humidity were measured from different design of radiation shields and Stevenson screens. The use of home-made seven-plate plastic radiation shields provided a similar shield to radiation and ventilation compared to manufactured shields. At a low solar angle when wind speed was very low, all the radiation shields including the small Stevenson screens showed a higher air temperature difference relative to the standard Stevenson screen. The highest average difference of air temperature measurement was measured within the small Stevenson screen and metal-radiation shield. The home-made plastic radiation shield showed similar averages of air temperature and water vapour pressure difference compared to the six- and twelve-plate Gill radiation shields. The home-made metal radiation shield showed relatively higher deviation from the mean being cold at night time and hot during the day. More research is needed to explore the efficiency of the ET-gage evaporation from variety of microclimates to establish the cause of the overestimate under shade, to develop better relation of clear day net long wave irradiance and air temperature and the use of a wind speed sensor with Hobo H8 weather station system.
Comparative evaporation measurements above commercial forestry and sugarcane canopies in the KwaZulu-Natal Midlands.
(1999) Burger, Caren.; Savage, Michael John.
An understanding of the water use of different crops commonly grown in an area is essential for the implementation of integrated catchment management in South Africa. With increasing pressure on water resources, mainly due to the recent changes in the Water Act, it has become important to determine the actual water demands of agricultural and other crops. Policy makers require knowledge of whether forestry canopies use more water than grassland and other agricultural crops. The Bowen ratio and Penman-Monteith methods were used in a comparative study of the evaporation from Saccharum, Acacia and Eucalyptus. All of the research was conducted at marginal sites located in the KwaZulu-Natal Midlands of South Africa over a period of two years. The Bowen ratio energy balance (BREB) technique combines the Bowen ratio (J3) (the ratio between the sensible, H and latent heat flux density, XE), with the net irradiance (Rn) and soil heat flux densities (G) to calculate evaporation. A comparative study of the sitespecific energy balance components (Rn, G, H and AE), general climatic conditions (rainfall, solar irradiance and air temperature) and other site-specific parameters (leaf area index and average canopy height) was conducted on Saccharum and young commercial forests consisting of Acacia and Eucalyptus. The energy balance highlighted important differences in the energy balance components between the different canopies. The differences between the reflection coefficients at the three sites contributed mainly to the differences in the evaporation rates. The low reflection coefficients of the forest canopies (Acacia and Eucalyptus) (0.1 and 0.08 respectively) were smaller than of the sugarcane canopy (0.2). This resulted in more energy available (« 6 %) for partitioning between the sensible and latent heat flux densities and higher evaporation rates for the forestry canopies. Where low leaf area indices existed (Acacia and Eucalyptus sites) (LAI < 2), the soil heat flux density contributed up to 40 % of the net irradiance (G = 0.4 Rn). The evaporation rates for Saccharum, Acacia and Eucalyptus averaged 2 mm day"1 in winter and 5 mm day"1 in summer. The slightly higher summer evaporation rate for Eucalyptus (5.6 mm day"1), compared to Acacia (4.9 mm day"1), resulted from the lower reflection coefficients and canopy resistance (rc) for Eucalyptus (ocs = 0.08, rc = 35 s m"1) compared to Acacia (ocs = 0.1, rc = 45 s m"1). Automatic weather station data (solar irradiance, air temperature, water vapour pressure and windspeed) were applied to site-specific Penman-Monteith equations to predict evaporation for all three sites. Statistically significant relationships (slope, m « 1, r2 > 0.8) were found between the measured (Bowen ratio) and simulated (site-specific Penman-Monteith) evaporation estimates. The current study has demonstrated the effectiveness of applying the Penman-Monteith equation to forest and sugarcane canopies to predict evaporation, provided accurate net irradiance, soil heat flux densities and canopy resistances are used.

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