Spatiotemporal patterns of water table fluctuations and evapotranspiration induced by riparian vegetation in a semiarid area

Groundwater evapotranspiration (ET_g) links various ecohydrological processes and is an important component in regional water budgets. In this study, an extensive monitoring network was established in a semiarid riparian area to investigate various controls on the spatiotemporal pattern of water table fluctuations (WTFs) and ET_g induced by riparian vegetation. Along a vegetation gradient (1200 m), diurnal WTFs were observed during a growing season in areas covered by woody species (Populus sect. Aigeiros and Juniperus virginiana) and wet slough vegetation (Panicum virgatum and Bromus inermis) with deeper root systems; whereas, no diurnal WTFs were found in the middle section with shallower-rooted grasses (Poa pratensis and Carex sp.). The occurrence of diurnal WTFs was related to temperature-controlled plant phenology at seasonal scales and to radiation at subdaily scales. Daily ET_g in the mid-growing season was calculated using the White method. The results revealed that depth to water table (DTWT) was the dominant control on ET_g, followed by potential evapotranspiration (ET_p). By combining the effects of DTWT and ET_p, it was found that at shallower depths, ET_g was more responsive to changes in ET_p, due to the closer linkage of land surface processes with shallower groundwater. Finally, exponential relationships between ET_g/ET_p and DTWT were obtained at the study site, although those relationships varied considerably across the sites. This study demonstrates the complex interactions of WTFs and ET_g with surrounding environmental variables and provides further insight into modeling ET_g over different time scales and riparian vegetation.