Worsening Drought of Nile Basin under shift in Atmospheric Circulation, Stronger ENSO and Indian Ocean Dipole

Abstract

Until now, driving mechanisms behind recurring droughts and hydroclimate variations that controls the Nile River Basin (NRB) remain not well understood. In this study, we demonstrate that recent increasing aridity of NRB is attributed to the growing influence of stronger ENSO and Indian Ocean dipole (IOD), and SST gradient over the Arabian Sea (WTIO) in NRB after 1980s, which have significantly contributed to NRB’s drought severity at inter-annual to inter-decadal timescales. Further, the southward (westward) shift in stream functions and meridional (zonal) winds caused an enhancement in the blocking pattern, with strong anticyclonic waves of dry air that keeps moving into NRB, has resulted in drier NRB, where its streamflow at gauging stations have decreased from 137 to 114.1 m3/s/decade. Contrary to past findings, we show that IOD and WTIO are better predictors of the Nile streamflow than El Niño. Under the combined impact of warming and stronger WTIO and El Niño, future droughts of the NRB will worsen.