Seasonal and Decadal Groundwater Changes in African Sedimentary Aquifers Estimated Using GRACE Products and LSMs

H Bonsor,B Marchant,R Taylor,M Shamsudduha,A Macdonald

doi:10.3390/rs10060904

H Bonsor, B Marchant + Show 3 more

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https://doi.org/10.3390/rs10060904

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Abstract

Increased groundwater abstraction is important to the economic development of Africa and to achieving many of the Sustainable Development Goals. However, there is little information on long-term or seasonal groundwater trends due to a lack of in situ monitoring. Here, we used GRACE data from three products (the Centre for Space Research land solution (CSR), the Jet Propulsion Laboratory’s Global Mascon solution (JPL-MSCN), and the Centre National D’etudes Spatiales / Groupe de Recherches de Géodésie Spatiale solution (GRGS)), to examine terrestrial water storage (TWS) changes in 12 African sedimentary aquifers, to examine relationships between TWS and rainfall , and estimate groundwater storage (GWS) changes using four Land Surface Models (LSMs) (Community Land Model (CLM2.0), the Variable Infiltration Capacity model (VIC), the Mosaic model (MOSAIC) and the Noah model (NOAH)). We find that there are no substantial continuous long-term decreasing trends in groundwater storage from 2002 to 2016 in any of the African basins, however, consistent rising groundwater trends amounting to ~1 km3/year and 1.5 km3/year are identified in the Iullemmeden and Senegal basins, respectively, and longer term variations in ΔTWS in several basins associated with rainfall patterns. Discrete seasonal ΔTWS responses of ±1–5 cm/year are indicated by GRACE for each of the basins, with the exception of the Congo, North Kalahari, and Senegal basins, which display larger seasonal ΔTWS equivalent to approx. ±11–20 cm/year. The different seasonal responses in ΔTWS provide useful information about groundwater, including the identification of 5 to 9 month accumulation periods of rainfall in many semi-arid and arid basins as well as differences in ΔTWS responses between Sahelian and southern African aquifers to similar rainfall, likely reflecting differences in landcover. Seasonal ΔGWS estimated by combining GRACE ΔTWS with LSM outputs compare inconsistently to available in situ measurements of groundwater recharge from different basins, highlighting the need to further develop the representation of the recharge process in LSMs and the need for more in situ observations from piezometry.

Highlights

Groundwater supplies an estimated 36% of all global domestic water and 42% of agricultural water [1] and its use is forecast to continue to rise in response to economic and population growth [2,3]
This study demonstrates the value of using Gravity Recovery and Climate Experiment (GRACE) products to characterise terrestrial water storage (TWS) and groundwater storage (GWS) variation across large African sedimentary aquifer basins where in situ data are scarce
The three GRACE products considered (CRC, JPL-MSCN, and Groupe de Recherches de Géodésie Spatiale (GRGS)) provide similar long-term behaviour for each aquifer which were interpreted as GWS changes through the use of the Land Surface Models (LSMs) CLM2.0, Variable Infiltration Capacity model (VIC), MOSAIC, and Noah model (NOAH)

Summary

Introduction

Groundwater supplies an estimated 36% of all global domestic water and 42% of agricultural water [1] and its use is forecast to continue to rise in response to economic and population growth [2,3]. Already it is estimated that globally, groundwater storage is being mined at a rate of approximately 150–200 km per year [6,7], which a small proportion of the estimated global groundwater reserves [8], can lead to several unwanted impacts These can include: falling water tables [9,10], which are associated with the failure of shallow wells and springs [11], the ingress of poor quality water into aquifers [12,13], and the deterioration of aquatic ecosystems [14,15]. Groundwater depletion contributes to sea-level rise through the net transfer of water from long-term terrestrial storage to the ocean [3], which may contribute 0.4 to 0. 6 mm per year to sea level rise [6,7]

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