New perspective about application of extended Budyko formula in arid irrigation district with shallow groundwater

Budyko's treatment of the long-term water balance of watersheds was based on the competition between water availability and energy supply. It assumes, in the long-term, that precipitation is the only source of water availability for evapotranspiration while the changes in soil water storage are negligible. For arid irrigation areas with shallow water tables, however, groundwater also can supply crop water demand in addition to irrigation and precipitation. In this study, we present a new Budyko formula considering seasonal groundwater uptake and soil water storage changes estimated by Aver'yanov's equation and abed model, respectively. The use of groundwater depths rather than the variation of groundwater levels makes it more reasonable to estimate seasonal groundwater consumption. For the application of the Budyko equation in unsteady state areas, equivalent precipitation was designed to take the place of precipitation as water availability. With the newly defined water availability, the relationship between evapotranspiration ratio and aridity index was described successfully by Budyko curves, otherwise the points exceeded Budyko domain with only precipitation and irrigation considered. Furthermore, for agricultural irrigation areas, the variation of seasonal to is supposed to be affected by vegetation coverage (denoted by NDVI). Overall, it is possible to estimate regional actual seasonal and annual evapotranspiration for irrigation areas with shallow groundwater using the extended Budyko models. This new method can play significant role in water management in arid and semiarid agricultural regions.