April 11, 2005

Relative Yield Anomaly Map Overlaid with the 2005 Crop Tour Route

The above relative-yield image is derived from the Water Requirement Satisfaction Index (WRSI).  WRSI is a water-balance model originally developed by the Food and Agricultural Organization (FAO) in the 1970s that serves as indicator of crop performance based on the availability of rainfall to the crop during the growing season.  More recently the WRSI relative-yield model has been adapted and extended for geospatial applications to monitor crop water requirements in Africa .  The main inputs to the WRSI relative-yield model are precipitation, potential evapotranspiration, soil water-holding capacity, start-of-season, and average length of growing period.   The main output is a relative crop yield estimate based on seasonal rainfall received during the current year and compared to average crop water availability for the region. Ten-day relative yield products for Africa are available at the Africa Data Dissemination Service web site.

For more information, contact Curt Reynolds
with the Production Estimates and Crop Assessment Division, at Curt.Reynolds@fas.usda.gov or (202) 690-0134.