The Importance of Ground Water Evapotranspiration in Ground Water Resources Modelling of Water-Limited Environments

Abstract 

Field experiments have already proven that many tree species in water limited environments (WLE) uptake water directly from the groundwater body or from the capillary fringe, by rooting systems that may extend to several tens of meters depth. In dry bare soil areas of WLE, groundwater can also be discharged by vapor and capillary water transport to the surface. The total loss of groundwater due to the combined action of root water uptake and evaporation from the groundwater body or from the capillary fringe is known as groundwater evapotranspiration (ET_g). In WLE typically characterized by low or very low recharge, the ET_g is usually significant, so it can substantially reduce the effective (net) recharge critical in groundwater modeling and sustainability evaluation. In practice however, the ET_g is either underestimated or disregarded, mainly because of limited knowledge about that phenomenon. This presentation will discuss the current understanding of the hydrogeological role of trees in water limited environments, the partitioning of tree transpiration into saturated and unsaturated zone contributions, the mechanism and importance of groundwater loss by evaporation and the possible integration of these processes in numerical groundwater models. Problems involved in this research will be highlighted and possible future research directions discussed.