Preliminary Results on the Estimation of Ground Water in Africa Using GRACE and Hydrological Models

Abstract

Groundwater is a main source of fresh water in many parts of the world. Monitoring the global and regional groundwater resources is challenging nowadays because of the very scare and high cost in situ measurement networks, especially in Africa. Satellite gravimetry can be used in combination with land surface hydrological models (e.g., Global Land Data Assimilation System (GLDAS) and WaterGAP Global Hydrology Model (WGHM)) to infer groundwater storage behavior. Since 2002, the Gravity Recovery and Climate Experiment (GRACE) satellite mission provides estimation of the Earth’s dynamic gravity field with unprecedented accuracy. Differences between monthly GRACE gravity field solutions give an estimation of the Terrestrial Water Storage (TWS) changes. The groundwater storage can be obtained using the available hydrological models by subtracting the surface water, soil moisture, snow, ice and canopy water from the TWS. GRACE data are available in terms of spherical harmonics expansion. However, GLDAS and WGHM hydrological models are available in the space domain as grids of 1° and 0.5°, respectively. For consistency, both GLDAS and WGHM are approximated in terms of spherical harmonic expansions to be comparable with the used GRACE data. In this paper, the groundwater storage in Africa is studied using GRCAE data (2003–2016) as well as GLDAS and WGHM models for the same time period. Inter annual variations is investigated from monthly groundwater time series.