Twentieth and Twenty-First Century Water Storage Changes in the Nile River Basin from GRACE/GRACE-FO and Modeling

Emad Hasan,Pierre-Emmanuel Kirstetter,Aondover Tarhule

doi:10.3390/rs13050953

Abstract

This research assesses the changes in total water storage (TWS) during the twentieth century and future projections in the Nile River Basin (NRB) via TWSA (TWS anomalies) records from GRACE (Gravity Recovery and Climate Experiment), GRACE-FO (Follow-On), data-driven-reanalysis TWSA and a land surface model (LSM), in association with precipitation, temperature records, and standard drought indicators. The analytical approach incorporates the development of 100+ yearlong TWSA records using a probabilistic conditional distribution fitting approach by the GAMLSS (generalized additive model for location, scale, and shape) model. The model performance was tested using standard indicators including coevolution plots, the Nash–Sutcliffe coefficient, cumulative density function, standardized residuals, and uncertainty bounds. All model evaluation results are satisfactory to excellent. The drought and flooding severity/magnitude, duration, and recurrence frequencies were assessed during the studied period. The results showed, (1) The NRB between 2002 to 2020 has witnessed a substantial transition to wetter conditions. Specifically, during the wet season, the NRB received between ~50 Gt./yr. to ~300 Gt./yr. compared to ~30 Gt./yr. to ~70 Gt./yr. of water loss during the dry season. (2) The TWSA reanalysis records between 1901 to 2002 revealed that the NRB had experienced a positive increase in TWS of ~17% during the wet season. Moreover, the TWS storage had witnessed a recovery of ~28% during the dry season. (3) The projected TWSA between 2021 to 2050 unveiled a positive increase in the TWS during the rainy season. While during the dry season, the water storage showed insubstantial TWS changes. Despite these projections, the future storage suggested a reduction between 10 to 30% in TWS. The analysis of drought and flooding frequencies between 1901 to 2050 revealed that the NRB has ~64 dry-years compared to ~86 wet-years. The exceedance probabilities for the normal conditions are between 44 to 52%, relative to a 4% chance of extreme events. The recurrence interval of the normal to moderate wet or dry conditions is ~6 years. These TWSA trajectories call for further water resources planning in the region, especially during flood seasons. This research contributes to the ongoing efforts to improve the TWSA assessment and its associated dynamics for transboundary river basins.

Highlights

The Nile river basin (NRB; ~3.18 million Km2 ) is a complex transboundary hydrologic system [1,2,3,4], and one of the world’s preeminent geopolitical hotspots [5,6,7,8]
The coevolution plot shows a strong agreement between both variables with a significant p-value < 0.0001
The historical simulated TWSA records were compared to catchment land surface model (CLSM)-based TWSA estimates from 1948 to

Summary

Introduction

The Nile river basin (NRB; ~3.18 million Km2 ) is a complex transboundary hydrologic system [1,2,3,4], and one of the world’s preeminent geopolitical hotspots [5,6,7,8]. The NRB is home to more than 320 million people belonging to 11 African nations (2018 population estimation), approximately 24% of Africa’s total population [9,10]. To both upstream and downstream countries, the Nile river is crucial for development planning, food, and energy. To the 10 other countries, the Nile water is critically needed for energy generation, to assure their own food security, mitigate the disastrous effects of periodic droughts, and assure social-economic development [5,12,13]

Results

Discussion

Conclusion