Abstract
Abstract. In climate models, lateral terrestrial water fluxes are usually neglected. We estimated the contribution of vertical and lateral groundwater fluxes to the land surface water budget at a subcontinental scale, by modeling convergence of groundwater and surfacewater fluxes. We present a hydrological model of the entire Danube Basin at 5 km resolution, and use it to show the importance of groundwater for the surface climate. Results show that the contribution of groundwater to evaporation is significant, and can locally be higher than 30 % in summer. We demonstrate through the same model that this contribution also has important temporal characteristics. A wet episode can influence groundwater contribution to summer evaporation for several years afterwards. This indicates that modeling groundwater flow has the potential to augment the multi-year memory of climate models. We also show that the groundwater contribution to evaporation is local by presenting the groundwater travel times and the magnitude of groundwater convergence. Throughout the Danube Basin the lateral fluxes of groundwater are negligible when modeling at this scale and resolution. This suggests that groundwater can be adequately added in land surface models by including a lower closed groundwater reservoir of sufficient size with two-way interaction with surface water and the overlying soil layers.
Highlights
In the last decades, the importance of land-surface – atmosphere feedbacks in climate has been more and more recognized
There are Land Surface Models (LSMs) in Global Climate Models (GCMs) and Regional Climate Models (RCMs) with soils deeper than 2 m that still show a continental bias as result of the “memory loss” (Hirschi et al, 2007), of which HTESSEL (Balsamo et al, 2009) is one example
We show that groundwater is important as a source for dry season evaporation and we show that, at the scale of GCMs or RCMs and in flat terrain, horizontal redistribution and convergence of groundwater is not important as a source for evaporation
Summary
The importance of land-surface – atmosphere feedbacks in climate has been more and more recognized. Precipitation recycling, the process from local evaporation to local precipitation, is one of the important land – atmosphere interactions in the climate system (e.g., Trenberth, 1999; Brubaker et al, 1993; Koster et al, 2004; Bisselink and Dolman, 2009). In absence of topography-related gradients, groundwater is free to engage in lateral movements in any direction within aquifers, as gradients are dominated by gradients in aquifer downward (recharge) and upward (seepage, extraction, capillary rise) fluxes.
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