Characterizing water storage trends and regional climate influence using GRACE observation and satellite altimetry data in the Upper Blue Nile River Basin

Abstract

Climate variability along with increase in the demand for water resources highlights the need for better understanding of the link between regional climate and terrestrial water storage. This paper examined the variation of terrestrial water storage in relation to climatic influences over the Upper Blue Nile (UBN) River Basin from GRACE Terrestrial Water Storage Anomaly (TWSA), satellite altimetry, rainfall, and Multivariate El Niño-Southern Oscillation Index (MEI) anomaly data. Although there is no statistically significant (α = 0.05) long-term trend in terrestrial water variation and rainfall in the basin (lake storage, TWSA, and rainfall, p-value = 0.45, 0.48, and 0.55, respectively), in the last decade, two visible droughts occurred between 2002 and 2004, and 2009 and 2010, which resulted in water deficit in the basin, where below average rainfall, TWSA, and lake height (storage) were observed during these periods. Extreme rainfall analysis from Standardized Precipitation Index (SPI) and strong connection between wet season rainfall, lake height, and TWSA, respectively, indicate interannual terrestrial water storage dynamics in the UBN Basin is strongly influenced by climate. Further, the El Niño-Southern Oscillation (ENSO) influences rainfall in the UBN Basin, specifically the peak rainfall season (June-September), which shows negative correlation (r = −0.62) with MEI anomaly values, which indicates that the El Niño case (positive MEI values) is linked to the dry conditions in the basin. The findings of this study, combined with studies such as socioeconomic impact of drought, will facilitate better planning and management of water resources in water stressed regions. Furthermore, this study demonstrates the application of a combination of satellite and other hydrologic data in understanding the hydro-climatic condition of a remote basin.