Evaluating MODIS data to estimate irrigated crop production in Afghanistan using a thermal-based ET fraction approach

Abstract

Accurate crop performance monitoring and production estimation is critical for timely assessment of the food balance of several countries in the world. Recently, the Famine Early Warning System Network (FEWS NET) has been monitoring crop performance and to some extent relative production using satellite derived data and simulation models in Africa, Central America and Afghanistan where ground based monitoring is limited due to the scarcity of weather stations. The commonly used crop monitoring models use a crop water balance algorithm with inputs from satellite-derived rainfall. While these models provide useful monitoring for rain-fed agriculture, they are ineffective for irrigated areas. Over 80% of the agricultural production in Afghanistan is from irrigated agriculture. In this study, we implemented a thermal-based ET fraction approach to monitor and assess the performance of irrigated agriculture in Afghanistan using the combination of 250-m NDVI and 1-km Land Surface Temperature (LST) data from MODIS. Six images per year were used to estimate seasonal evapotranspiration (ET) from irrigated lands in a given growing season between 2000 and 2004. Seasonal ET estimates from the different years were used as relative indicators of year-to-year production magnitude differences. The results were comparable to field reports and crop water balance based estimates for irrigated watersheds in that 2003 was a good year for crop production in Afghanistan. The advantage of this method over crop water balance method is that it helps identify irrigated areas directly and thus helps estimate total irrigated area and its spatial distribution in a given region.