Articles | Volume 20, issue 9
Research article
08 Sep 2016
Research article |  | 08 Sep 2016

Shift of annual water balance in the Budyko space for catchments with groundwater-dependent evapotranspiration

Xu-Sheng Wang and Yangxiao Zhou

Abstract. The Budyko framework represents the general relationship between the evapotranspiration ratio (F) and the aridity index (φ) for the mean annual steady-state water balance at the catchment scale. It is interesting to investigate whether this standard F − φ space can also be applied to capture the shift of annual water balance in catchments with varying dryness. Previous studies have made significant progress in incorporating the storage effect into the Budyko framework for the non-steady conditions, whereas the role of groundwater-dependent evapotranspiration was not investigated. This study investigates how groundwater-dependent evapotranspiration causes the shift of the annual water balance in the standard Budyko space. A widely used monthly hydrological model, the ABCD model, is modified to incorporate groundwater-dependent evapotranspiration into the zone with a shallow water table and delayed groundwater recharge into the zone with a deep water table. This model is applied in six catchments in the Erdos Plateau, China, to estimate the actual annual evapotranspiration. Results show that the variations in the annual F value with the aridity index do not satisfy the standard Budyko formulas. The shift of the annual water balance in the standard Budyko space is a combination of the Budyko-type response in the deep groundwater zone and the quasi-energy limited condition in the shallow groundwater zone. Excess evapotranspiration (F > 1) could occur in dry years, which is contributed by the significant supply of groundwater for evapotranspiration. Use of groundwater for irrigation can increase the frequency of the F > 1 cases.

Short summary
This study reveals the effects of groundwater-dependent evapotranspiration (GDE) in the shift of annual water balance for a catchment in the Budyko space. The ABCD model is modified to incorporate GDE in simulating the monthly hydrological behaviors of a catchment, and the results are aggregated to annual data. GDE enhances the occurrence of excess evapotranspiration (E / P > 1) in dry years, which could not be captured by the traditional Budyko curves. Six catchments are analyzed with the model.