Enhanced recharge rates and a greater sensitivity to climate variations in regions with heterogeneous subsurface

Abstract:

Subsurface heterogeneity has an important control on water balance. Groundwater recharge is one of its most relevant processes feeding the world’s groundwater storages and therefore supplying fresh water to large parts of the global population for their drinking water and food production. However, large-scale hydrological models do not usually consider subsurface heterogeneity adequately to simulate groundwater recharge.

In this study we compare the model simulations of two different representations of the subsurface, one with heterogeneous and the other with homogeneous subsurface, from present day to the future (1991-2099). We look at simulated recharge rates and their inter-annual variability. In addition, we calculate the elasticity of recharge rates concerning climate variability, in terms of annual precipitation, temperature and average intensity during strong rainfall events, to quantify their controls on simulated recharge and how these controls evolve in the future.

Our model comparison shows that regions with strong subsurface heterogeneity have enhanced recharge rates with greater inter-annual variability compared to those with more homogenous subsurface properties. Furthermore, the heterogeneous representation shows stronger elasticity concerning climate variability than the homogeneous subsurface representation. This difference tends to increase towards the future.

Our results suggest that water management in regions with heterogeneous subsurface can expect a higher water availability than estimated by most of the large-scale simulations. But measures should be taken to prepare for increasingly variable groundwater recharge rates.