Title: Shift of annual water balance in the Budyko space for a catchment with groundwater dependent evapotranspiration
Abstract:Abstract. Empirical equations have been formulated for the general relationship between the evapotranspiration ratio (F) and the aridity index (φ) in the Budyko framework. Though it is normally applie...Abstract. Empirical equations have been formulated for the general relationship between the evapotranspiration ratio (F) and the aridity index (φ) in the Budyko framework. Though it is normally applied for mean annual behaviors, the Budyko hypothesis has been directly adopted to analyze the interannual change in water balance. However, there are reported cases where the annual evapotranspiration ratio is larger than 1.0 (F > 1). This study reveals the effects of groundwater dependent evapotranspiration in triggering such abnormal shift of annual water balance in the Budyko space. A widely used monthly hydrological model, the ABCD model, is modified to incorporate the groundwater dependent evapotranspiration in the zone with shallow water table and delayed groundwater recharge in the zone with deep water table. This model is applied in the Hailiutu River catchment in China. Results show that the variations in the annual evapotranspiration ratio with aridity index do not satisfy the traditional Budyko hypothesis. The shift of the annual water balance in the Budyko space depends on the proportion of shallow water table area, intensity of groundwater dependent evapotranspiration, and the normal Budyko-type trend of F in the deep groundwater zone. Excess evapotranspiration (F > 1) could occur in extreme dry years, which is enhanced by groundwater-dependent evapotranspiration. Use of groundwater for irrigation may increase the frequency of occurrence of the F > 1 cases.Read More