Water Requirement Satisfaction Index

The spatially explicit water requirement satisfaction index (WRSI) is an indicator of crop performance based on the availability of water to the crop during a growing season.

WRSI is the ratio of seasonal actual crop evapotranspiration (AETc) to the seasonal crop water requirement, which is the same as the potential crop evapotranspiration (PETc). PETc denotes crop specific potential evapotranspiration after an adjustment is made to the reference crop potential evapotranspiration (PET) by the use of appropriate crop coefficients (Kc). Kc values define the water use pattern of a crop. Published values (FAO, 1998) are available for critical points in a crop phenology and intervening values are linearly interpolated. For example, maize Kc values are given as 0.3, 0.3, 1.20, 1.20, and 0.35 for the times corresponding to 0%, 16%, 44%, 76%, and 100% of LGP, respectively.