Farmers do not often use climate and weather information on a regular basis, as the specific infl... more Farmers do not often use climate and weather information on a regular basis, as the specific influence of weather parameters on farm-level decision making is not well-known. Agromet advisories are needed for local farming systems. Effective agrometeorological advisory systems, need tailored agricultural weather forecasts, and two-way communication. Transdisciplinary teams together with farmers can co-develop early warning Agromet advisory systems to address farmers' needs. Three examples of Agromet advisories are discussed- CAPES in Zambia, Science Field Shops in Indonesia, and the AgriCloud mobile App in South Africa. Community Agrometeorological Participatory Extension Service (CAPES) began in Monze, Zambia to communicate seasonal climate forecasts to farmers through researchers and extension interactions. Participatory groups collected spatial and temporal data about local farming systems to highlight opportunities. Communication methods used were local radio, farmers' da...
Natural disturbances play an important role in forest ecology, with effects that are highly depen... more Natural disturbances play an important role in forest ecology, with effects that are highly dependent on characteristics of the specific disturbance. Climate and weather induced risks often interfere with the productivity of forests. Excessive wind, ice, and snow regularly cause major disturbances to forests in many parts of the world. The uprooted trees are susceptible to the risk of secondary damage to the surviving trees. In the last four decades, many European countries have suffered acute forest damage.
Plant diseases have caused serious challenges in the production of food globally. This has led to... more Plant diseases have caused serious challenges in the production of food globally. This has led to hunger and food insecurity. Different solutions for crop diseases have been introduced in the recent past that include cultural control using farm management methods, chemical control, resistant cultivars, and recently, biocontrol. Each of these solutions has varied weaknesses. Faced with the changes in climate and the recurrences of crop diseases, new strategies incorporating preventive measures would be important by reducing risks to crop production from crop diseases, thus alleviating food insecurity. Strategies for the prevention of these diseases and/or forecasting favorable environmental conditions for disease development have not been fully employed as preventive measures. The use of crop modeling has been used to advise farmers on planting procedures that would bring maximum yields using different management procedures at the farm level. Little is known about the use of crop mod...
Diffuse solar radiation, which is not routinely measured at weather stations, has been estimated ... more Diffuse solar radiation, which is not routinely measured at weather stations, has been estimated empirically, from global solar radiation, around the world but not in southern Africa. We report here empirical relationships describing the components of solar radiation at eight locations throughout the subcontinent. Data on diffuse and global solar radiation were collected at weather stations, at latitudes between 22° and 34°S and at altitudes from 0 to 1725 m, representing various climate zones. A simple linear equation is proposed relating the ratio of diffuse to global solar radiation to the ratio of global to extraterrestrial solar radiation for the subcontinent, including both semi-arid / arid and warm temperate climate zones.
Physics and Chemistry of the Earth, Parts A/B/C, 2013
Reference evapotranspiration (ET) is an important parameter that needs to be estimated accurately... more Reference evapotranspiration (ET) is an important parameter that needs to be estimated accurately to enhance its utility in numerous applications. Although the widely recommended procedure for calculating this index involves using the FAO Penman-Monteith equation (ETo), the latter's effectiveness is constrained by its considerable data requirements. To overcome this constraint, alternative methods using the limited data available have to be explored. In this study the ability of the Hargreaves and Samani (ET HS) and Thornthwaite (ET T) equations to estimate ET was investigated using multi-year data (1999-2008) from eight weather stations in the semi-arid Free State Province of South Africa. Results for non-calibrated equations are closely correlated, with ET HS tending to underestimate ET for the July to December period while ET T underestimates ET for all months of the calendar year. Although estimates from calibrated equations are also closely correlated, they have smaller deviations compared to the original equations with the calibrated Hargreaves and Samani equation (ET CHS) estimating reference evapotranspiration better than its calibrated Thornthwaite (ET CT) counterpart. The former's better performance suggests that in data-scarce areas, the Hargreaves and Samani model is capable of giving results within acceptable ranges of accuracy.
... Assessment of Communication and Use of Climate Outlooks and Development of Scenarios to Promo... more ... Assessment of Communication and Use of Climate Outlooks and Development of Scenarios to Promote Food Security in the Free State ... Department of Agrometeorology, University of the Free State, PO Box 339, Bloemfontein, 9300, Republic of South Africa * Enviro Vision CC ...
Water Requirement Satisfaction Index (WRSI) at three different probability levels (20%, 50%, and ... more Water Requirement Satisfaction Index (WRSI) at three different probability levels (20%, 50%, and 80%) was used to quantify drought affecting rain-fed maize production in the Free State Province of South Africa based on climate data from 227 weather stations. Results showed high spatial variability in the suitability of different areas: the southern and southwestern localities are unsuitable due to high drought incidences; the northern, central, and western regions are marginally suitable; the eastern, northerneastern areas and a few patches in the northwest are highly suitable with relatively low drought severity. Proper choice of maize varieties to suit conditions at different localities is crucial. The Mann-Kendall test and coefficient of variation were further used to determine trends and temporal variability, respectively, in the WRSI, seasonal rainfall, and seasonal maize water requirements. Results of this analysis revealed no significant positive trends in the WRSI, no significant negative trends in seasonal rainfall, and no significant positive trends in maize water requirements, contradicting previous findings of increased drought severity. Seasonal rainfall and the WRSI showed high interseasonal variability, while seasonal maize water requirements showed low variability. In view of these observations, it is apparent that realignment of management practices is an overdue prerequisite for sustainable maize production. Vasiliades 2004; National Oceanic and Atmospheric Administration NOAA 2006; Runtunuwu 2005; Wilhelmi and Wilhite 2002) The impact of drought depends on its intensity, duration, frequency, the affected area, and vulnerability of the societal resources (du Pisani 1987; Rouault and Richard 2003; Tadesse et al. 2004). Drought differs according to the way water is used and its impacts also differ depending on the economy,
ABSTRACT The climatic potential of maize under dryland farming in Lesotho, southern Africa, was i... more ABSTRACT The climatic potential of maize under dryland farming in Lesotho, southern Africa, was investigated using five suitability indices comprising probability of accumulating heat units of greater than 1,500 growing degree days, probability of a frost-free growing season, probability of seasonal rainfall of more than 500 mm, probability of drought during the flowering to grain-filling stages and the slope of an area. A geographic information system layer was prepared for each of these parameters and the layers overlaid using different weights for each of the climatic suitability indices to obtain an agroclimatic maize suitability map for Lesotho. This analysis yielded different suitability classes. This variability points to prevalence of climatic constraints that need to be acknowledged when attempting to identify management strategies that can optimize the rain-fed maize production in climatically variable environments.
Physics and Chemistry of the Earth, Parts A/B/C, 2012
ABSTRACT Low density of weather stations and high percentages of missing values of the archived c... more ABSTRACT Low density of weather stations and high percentages of missing values of the archived climate data in most places around the world makes it difficult for decision-makers to make meaningful conclusions in natural resource management. In this study, the use of NASA modelled and satellite-derived data was compared with measured minimum and maximum temperatures at selected climate stations in the Free State Province of South Africa. The NASA temperature data-fed Hargreaves evapotranspiration estimate was compared with the Penman-Monteith estimate to obtain regional coefficients for the Free State. The maize water requirement satisfaction index (WRSI) obtained using the NASA temperature data and calibrated Hargreaves equation was evaluated against the WRSI obtained using Penman-Monteith estimate. The data used is mostly from 1999 to 2008. The results of the comparison between measured minimum temperatures and NASA minimum temperatures show overestimation of the NASA values by between a monthly mean of 1.4 °C and 4.1 °C. NASA maximum temperatures seem to underestimate measured temperatures by monthly values ranging from 2.2 to 3.8 °C. NASA-fed Hargreaves equation in its original form underestimates Penman-Monteith evapotranspiration by between 20% and 40% and hence its coefficient was calibrated accordingly. The comparison of the maize WRSI simulated with NASA temperatures showed a good correlation and small deviations from WRSI calculated from measured data. Thus, the use of NASA satellite and modelled data is recommended in the Free State Province in places where there are no meteorological readings, with special consideration of the biasness of the data.
Physics and Chemistry of the Earth, Parts A/B/C, 2004
A number of studies have been conducted to determine species specific transpiration efficiency co... more A number of studies have been conducted to determine species specific transpiration efficiency coefficient. Although the value is available for some C3 legumes, no value has been determined for common beans within the semi-arid tropics. The coefficient is useful in modelling crop water use as it has been found to be conservative over a range of climates when differences in vapour pressure deficits are accounted for. The objective of the experiment was to determine the transpiration efficiency coefficient for common beans for use in modelling within the semi-arid region of South Africa. Common bean (Phaseoulus vulgaris L.) was grown on a weighing lysimeter during the 2000/2001 and 2001/2002 seasons. Transpiration was measured on hourly basis using the weighing lysimeter and the data integrated over the growing season to determine the seasonal transpiration for the crop. At the same time hourly measurement of canopy vapour pressure deficit was made using wet and dry bulb resistance thermometers housed in mini-shelters at 200-400 mm height. Wet and dry bulb temperature data was also collected at the nearby standard automatic weather station and used to normalize the transpiration efficiency. Transpiration efficiency for the common bean was 1.33 and 1.93 g kg À1 which when normalized and root adjusted, gave a transpiration efficiency coefficient of 3.02 and 3.51 g kPa kg À1 for the 2000/2001 and 2001/2002 seasons respectively. A mean transpiration efficiency coefficient of 3.26 ± 0.25 g kPa kg À1 was adopted for the two seasons. This value is fairly consistent with those obtained for other C3 legumes species, confirming the conservativeness of the coefficient and therefore its usefulness as modelling parameter.
Physics and Chemistry of the Earth, Parts A/B/C, 2004
Given an improved understanding of Eritrean climate, numerous benefits could be expected in many ... more Given an improved understanding of Eritrean climate, numerous benefits could be expected in many related activities: better management of agriculture and water resources stemming from more reliable seasonal predictions. In this study the Indian Ocean sea surface temperature was identified out of 11 predictors to be the most influential predictor for the July and August rainfall in the highlands of Eritrea. A statistical model was developed for peak rainy months (July-August, JA) of the study area. The model jackknife skill test gave the correlation of 0.89 and 0.85 for Asmara and Mendefera stations, which is very high for rainfall prediction. Thus, validation of the model shows that the model can reproduce the measured monthly sum for JA rainfall totals with confidence.
Farmers do not often use climate and weather information on a regular basis, as the specific infl... more Farmers do not often use climate and weather information on a regular basis, as the specific influence of weather parameters on farm-level decision making is not well-known. Agromet advisories are needed for local farming systems. Effective agrometeorological advisory systems, need tailored agricultural weather forecasts, and two-way communication. Transdisciplinary teams together with farmers can co-develop early warning Agromet advisory systems to address farmers' needs. Three examples of Agromet advisories are discussed- CAPES in Zambia, Science Field Shops in Indonesia, and the AgriCloud mobile App in South Africa. Community Agrometeorological Participatory Extension Service (CAPES) began in Monze, Zambia to communicate seasonal climate forecasts to farmers through researchers and extension interactions. Participatory groups collected spatial and temporal data about local farming systems to highlight opportunities. Communication methods used were local radio, farmers' da...
Natural disturbances play an important role in forest ecology, with effects that are highly depen... more Natural disturbances play an important role in forest ecology, with effects that are highly dependent on characteristics of the specific disturbance. Climate and weather induced risks often interfere with the productivity of forests. Excessive wind, ice, and snow regularly cause major disturbances to forests in many parts of the world. The uprooted trees are susceptible to the risk of secondary damage to the surviving trees. In the last four decades, many European countries have suffered acute forest damage.
Plant diseases have caused serious challenges in the production of food globally. This has led to... more Plant diseases have caused serious challenges in the production of food globally. This has led to hunger and food insecurity. Different solutions for crop diseases have been introduced in the recent past that include cultural control using farm management methods, chemical control, resistant cultivars, and recently, biocontrol. Each of these solutions has varied weaknesses. Faced with the changes in climate and the recurrences of crop diseases, new strategies incorporating preventive measures would be important by reducing risks to crop production from crop diseases, thus alleviating food insecurity. Strategies for the prevention of these diseases and/or forecasting favorable environmental conditions for disease development have not been fully employed as preventive measures. The use of crop modeling has been used to advise farmers on planting procedures that would bring maximum yields using different management procedures at the farm level. Little is known about the use of crop mod...
Diffuse solar radiation, which is not routinely measured at weather stations, has been estimated ... more Diffuse solar radiation, which is not routinely measured at weather stations, has been estimated empirically, from global solar radiation, around the world but not in southern Africa. We report here empirical relationships describing the components of solar radiation at eight locations throughout the subcontinent. Data on diffuse and global solar radiation were collected at weather stations, at latitudes between 22° and 34°S and at altitudes from 0 to 1725 m, representing various climate zones. A simple linear equation is proposed relating the ratio of diffuse to global solar radiation to the ratio of global to extraterrestrial solar radiation for the subcontinent, including both semi-arid / arid and warm temperate climate zones.
Physics and Chemistry of the Earth, Parts A/B/C, 2013
Reference evapotranspiration (ET) is an important parameter that needs to be estimated accurately... more Reference evapotranspiration (ET) is an important parameter that needs to be estimated accurately to enhance its utility in numerous applications. Although the widely recommended procedure for calculating this index involves using the FAO Penman-Monteith equation (ETo), the latter's effectiveness is constrained by its considerable data requirements. To overcome this constraint, alternative methods using the limited data available have to be explored. In this study the ability of the Hargreaves and Samani (ET HS) and Thornthwaite (ET T) equations to estimate ET was investigated using multi-year data (1999-2008) from eight weather stations in the semi-arid Free State Province of South Africa. Results for non-calibrated equations are closely correlated, with ET HS tending to underestimate ET for the July to December period while ET T underestimates ET for all months of the calendar year. Although estimates from calibrated equations are also closely correlated, they have smaller deviations compared to the original equations with the calibrated Hargreaves and Samani equation (ET CHS) estimating reference evapotranspiration better than its calibrated Thornthwaite (ET CT) counterpart. The former's better performance suggests that in data-scarce areas, the Hargreaves and Samani model is capable of giving results within acceptable ranges of accuracy.
... Assessment of Communication and Use of Climate Outlooks and Development of Scenarios to Promo... more ... Assessment of Communication and Use of Climate Outlooks and Development of Scenarios to Promote Food Security in the Free State ... Department of Agrometeorology, University of the Free State, PO Box 339, Bloemfontein, 9300, Republic of South Africa * Enviro Vision CC ...
Water Requirement Satisfaction Index (WRSI) at three different probability levels (20%, 50%, and ... more Water Requirement Satisfaction Index (WRSI) at three different probability levels (20%, 50%, and 80%) was used to quantify drought affecting rain-fed maize production in the Free State Province of South Africa based on climate data from 227 weather stations. Results showed high spatial variability in the suitability of different areas: the southern and southwestern localities are unsuitable due to high drought incidences; the northern, central, and western regions are marginally suitable; the eastern, northerneastern areas and a few patches in the northwest are highly suitable with relatively low drought severity. Proper choice of maize varieties to suit conditions at different localities is crucial. The Mann-Kendall test and coefficient of variation were further used to determine trends and temporal variability, respectively, in the WRSI, seasonal rainfall, and seasonal maize water requirements. Results of this analysis revealed no significant positive trends in the WRSI, no significant negative trends in seasonal rainfall, and no significant positive trends in maize water requirements, contradicting previous findings of increased drought severity. Seasonal rainfall and the WRSI showed high interseasonal variability, while seasonal maize water requirements showed low variability. In view of these observations, it is apparent that realignment of management practices is an overdue prerequisite for sustainable maize production. Vasiliades 2004; National Oceanic and Atmospheric Administration NOAA 2006; Runtunuwu 2005; Wilhelmi and Wilhite 2002) The impact of drought depends on its intensity, duration, frequency, the affected area, and vulnerability of the societal resources (du Pisani 1987; Rouault and Richard 2003; Tadesse et al. 2004). Drought differs according to the way water is used and its impacts also differ depending on the economy,
ABSTRACT The climatic potential of maize under dryland farming in Lesotho, southern Africa, was i... more ABSTRACT The climatic potential of maize under dryland farming in Lesotho, southern Africa, was investigated using five suitability indices comprising probability of accumulating heat units of greater than 1,500 growing degree days, probability of a frost-free growing season, probability of seasonal rainfall of more than 500 mm, probability of drought during the flowering to grain-filling stages and the slope of an area. A geographic information system layer was prepared for each of these parameters and the layers overlaid using different weights for each of the climatic suitability indices to obtain an agroclimatic maize suitability map for Lesotho. This analysis yielded different suitability classes. This variability points to prevalence of climatic constraints that need to be acknowledged when attempting to identify management strategies that can optimize the rain-fed maize production in climatically variable environments.
Physics and Chemistry of the Earth, Parts A/B/C, 2012
ABSTRACT Low density of weather stations and high percentages of missing values of the archived c... more ABSTRACT Low density of weather stations and high percentages of missing values of the archived climate data in most places around the world makes it difficult for decision-makers to make meaningful conclusions in natural resource management. In this study, the use of NASA modelled and satellite-derived data was compared with measured minimum and maximum temperatures at selected climate stations in the Free State Province of South Africa. The NASA temperature data-fed Hargreaves evapotranspiration estimate was compared with the Penman-Monteith estimate to obtain regional coefficients for the Free State. The maize water requirement satisfaction index (WRSI) obtained using the NASA temperature data and calibrated Hargreaves equation was evaluated against the WRSI obtained using Penman-Monteith estimate. The data used is mostly from 1999 to 2008. The results of the comparison between measured minimum temperatures and NASA minimum temperatures show overestimation of the NASA values by between a monthly mean of 1.4 °C and 4.1 °C. NASA maximum temperatures seem to underestimate measured temperatures by monthly values ranging from 2.2 to 3.8 °C. NASA-fed Hargreaves equation in its original form underestimates Penman-Monteith evapotranspiration by between 20% and 40% and hence its coefficient was calibrated accordingly. The comparison of the maize WRSI simulated with NASA temperatures showed a good correlation and small deviations from WRSI calculated from measured data. Thus, the use of NASA satellite and modelled data is recommended in the Free State Province in places where there are no meteorological readings, with special consideration of the biasness of the data.
Physics and Chemistry of the Earth, Parts A/B/C, 2004
A number of studies have been conducted to determine species specific transpiration efficiency co... more A number of studies have been conducted to determine species specific transpiration efficiency coefficient. Although the value is available for some C3 legumes, no value has been determined for common beans within the semi-arid tropics. The coefficient is useful in modelling crop water use as it has been found to be conservative over a range of climates when differences in vapour pressure deficits are accounted for. The objective of the experiment was to determine the transpiration efficiency coefficient for common beans for use in modelling within the semi-arid region of South Africa. Common bean (Phaseoulus vulgaris L.) was grown on a weighing lysimeter during the 2000/2001 and 2001/2002 seasons. Transpiration was measured on hourly basis using the weighing lysimeter and the data integrated over the growing season to determine the seasonal transpiration for the crop. At the same time hourly measurement of canopy vapour pressure deficit was made using wet and dry bulb resistance thermometers housed in mini-shelters at 200-400 mm height. Wet and dry bulb temperature data was also collected at the nearby standard automatic weather station and used to normalize the transpiration efficiency. Transpiration efficiency for the common bean was 1.33 and 1.93 g kg À1 which when normalized and root adjusted, gave a transpiration efficiency coefficient of 3.02 and 3.51 g kPa kg À1 for the 2000/2001 and 2001/2002 seasons respectively. A mean transpiration efficiency coefficient of 3.26 ± 0.25 g kPa kg À1 was adopted for the two seasons. This value is fairly consistent with those obtained for other C3 legumes species, confirming the conservativeness of the coefficient and therefore its usefulness as modelling parameter.
Physics and Chemistry of the Earth, Parts A/B/C, 2004
Given an improved understanding of Eritrean climate, numerous benefits could be expected in many ... more Given an improved understanding of Eritrean climate, numerous benefits could be expected in many related activities: better management of agriculture and water resources stemming from more reliable seasonal predictions. In this study the Indian Ocean sea surface temperature was identified out of 11 predictors to be the most influential predictor for the July and August rainfall in the highlands of Eritrea. A statistical model was developed for peak rainy months (July-August, JA) of the study area. The model jackknife skill test gave the correlation of 0.89 and 0.85 for Asmara and Mendefera stations, which is very high for rainfall prediction. Thus, validation of the model shows that the model can reproduce the measured monthly sum for JA rainfall totals with confidence.
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