Estimating actual evapotranspiration from irrigated fields using a simplified surface energy balance approach

Food security assessment in many developing countries, such as Afghanistan, is vital because the early identification of populations at risk can enable the timely and appropriate actions needed to avert widespread hunger, destitution, or even famine. The assessment is complex, requiring the simultaneous consideration of multiple socioeconomic and environmental variables. Since large and widely dispersed

populations depend on rain-fed and irrigated agriculture and pastoralism, large-area weather monitoring and forecasting are important inputs to food security assessments. The Famine Early Warning Systems Network (FEWS NET), an activity funded by the United States Agency for International Development (USAID), employs a crop water balance model (based on the water demand and supply at a given location) to monitor the performance of rain-fed agriculture and forecast relative production before the end of the crop-growing season. While a crop water balance approach appears to be effective in rain-fed agriculture [1,2], irrigated agriculture is best monitored by other methods, since the supply (water used for irrigation) is usually generated from upstream areas, farther away from the demand location.