Application of the Regional Water Mass Variations from GRACE Satellite Gravimetry to Large-Scale Water Management in Africa

Abstract

Time series of regional 2° × 2° Gravity Recovery and Climate Experiment (GRACE) solutions of surface water mass change have been computed over Africa from 2003 to 2012 with a 10-day resolution by using a new regional approach. These regional maps are used to describe and quantify water mass change. The contribution of African hydrology to actual sea level rise is negative and small in magnitude (i.e., −0.1 mm/y of equivalent sea level (ESL)) mainly explained by the water retained in the Zambezi River basin. Analysis of the regional water mass maps is used to distinguish different zones of important water mass variations, with the exception of the dominant seasonal cycle of the African monsoon in the Sahel and Central Africa. The analysis of the regional solutions reveals the accumulation in the Okavango swamp and South Niger. It confirms the continuous depletion of water in the North Sahara aquifer at the rate of −2.3 km 3 /y, with a decrease in early 2008. Synergistic use of altimetry-based lake water volume with total water storage (TWS) from GRACE permits a continuous monitoring of sub-surface water storage for large lake drainage areas. These different applications demonstrate the potential of the GRACE mission for the management of water resources at the regional scale.

Assessing Global Water Storage Variability from GRACE: Trends, Seasonal Cycle, Subseasonal Anomalies and Extremes

“…Significant positive trends can also be found in southern Africa, near the Upper Zambezi and Okavango river basins as well as in the Sahel and the Niger basin, and these trends have already been well documented (Ramillien et al 2014). In a comparison with rainfall observations from different sources, Ahmed et al (2014) have found that the increasing trend in the Niger basin could be related to an increase in precipitation; however, this was not the case for the Upper Zambezi and the Okavango basins.…”

“…So far, little attention has been devoted to GRACE variability in this region as most of the signal is contaminated by noise. Nevertheless, these drying trends have been partly documented (Ahmed et al 2014;Ramillien et al 2014) and to some extent attributed to groundwater extraction from fossil aquifers in the Sahara region.…”

A Comparative Study of GRACE with Continental Evapotranspiration Estimates in Australian Semi-Arid and Arid Basins: Sensitivity to Climate Variability and Extremes

“…Usually, arid and semi-arid basins have poor rainfall monitoring networks. In our case, MDB has much denser monitoring networks than LEB does; the latter has a large unpopulated region without rainfall stations [63]. At basin scales, the RMSE calculated between BoM and TRMM 3B43 rainfall datasets are 3.0 and 27.4 mm/month for MDB and LEB, respectively.…”

“…At basin scales, the RMSE calculated between BoM and TRMM 3B43 rainfall datasets are 3.0 and 27.4 mm/month for MDB and LEB, respectively. By blending gauge records with ancillary rainfall data, such as radar and satellite measurements or an ensemble method, may improve the accuracy of rainfall input data [63,64].…”

“…Several studies over different continents-South America [61], Australia [62], and Africa [63]-demonstrated that this regional approach offers a reduction of both north-south striping due to the distribution of GRACE satellite tracks and temporal aliasing of correcting models that are present in the global GRACE solutions. GRACE regional solutions were available at a spatial resolution of 2 • × 2 • from 4 July 2003 to 3 December 2010 at intervals of 10 days [62].…”