Department of Civil and Environmental Engineering, University of Alberta, Edmonton, T6G 1H9, Canada.
Department of Meteorology, University of Reading, Berkshire, RG6 6BB, UK.
Sci Rep. 2022 May 16;12(1):8049. doi: 10.1038/s41598-022-12008-8.
Until now, driving mechanisms behind recurring droughts and hydroclimate variations that controls the Nile River Basin (NRB) remains poorly understood. Our results show significant hydroclimatic changes that contributed to recent increasing aridity of NRB since the 1970s. Besides climate warming, the influence of stronger ENSO and Indian Ocean dipole (IOD) in NRB has increased after 1980s, which have significantly contributed to NRB's drought severity at inter-annual to inter-decadal timescales. Our results demonstrate that warming, El Niño and IOD have played a crucial role on NRB's inter-decadal hydroclimate variability, but IOD has played a more important role in modulating NRB's hydroclimate at higher timescales than El Niño. Results also indicate that the impacts of positive phases of ENSO and IOD events are larger than the negative phases in the NRB hydroclimate. 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, given stream function, geopotential height and U-wind anomalies associated with El Niño shows that changes in regional atmospheric circulations during more persistent and stronger El Niño has resulted in drier NRB. After 1970s, El Niño, IOD, and drought indices shows significant anti-phase relationships, which again demonstrates that more frequent and severe El Niño and IOD in recent years has led to more severe droughts in NRB. Our results also demonstrate that IOD and and the western pole of the Indian Ocean Dipole (WIO) are better predictors of the Nile flow than El Niño, where its flow has decreased by 13.7 (upstream) and by 114.1 m/s/decade (downstream) after 1964. In summary, under the combined impact of warming and stronger IOD and El Niño, future droughts of the NRB will worsen.
迄今为止，尼罗河流域（NRB）反复出现干旱和水文气候变化的驱动机制仍未被充分理解。我们的研究结果表明，自 20 世纪 70 年代以来，NRB 出现了显著的水文气候变化，导致其近年来变得更加干燥。除了气候变暖之外，自 20 世纪 80 年代以来，ENSO 和印度洋偶极子（IOD）在 NRB 的影响也有所增强，这显著加剧了 NRB 在年际到十年际时间尺度上的干旱程度。我们的研究结果表明，变暖、厄尔尼诺和 IOD 在 NRB 的十年际水文气候变率中发挥了关键作用，但 IOD 在调节 NRB 的水文气候方面比厄尔尼诺发挥了更重要的作用。结果还表明，ENSO 和 IOD 事件的正相位的影响大于 NRB 水文气候的负相位。此外，流函数和经向（纬向）风的南（西）移导致阻塞模式增强，干燥空气的强烈反气旋波不断进入 NRB，导致 NRB 更加干燥，因为与厄尔尼诺相关的流函数、位势高度和 U 风异常表明，在更持久和更强的厄尔尼诺事件期间，区域大气环流的变化导致 NRB 更加干燥。20 世纪 70 年代以后，厄尔尼诺、IOD 和干旱指数表现出显著的反相关关系，这再次表明，近年来更频繁和更严重的厄尔尼诺和 IOD 导致 NRB 出现更严重的干旱。我们的研究结果还表明，IOD 和印度洋偶极子的西极（WIO）是尼罗河流量的更好预测因子，而厄尔尼诺的预测效果较差，自 1964 年以来，尼罗河的流量减少了 13.7（上游）和 114.1 m/s/decade（下游）。综上所述，在变暖以及更强的 IOD 和厄尔尼诺的共同影响下，NRB 的未来干旱将恶化。
