Li Baosheng, Zhou Lei, Qin Jianhuang, Zhou Tianjun, Chen Dake, Hou Shugui, Murtugudde Raghu
State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou, China.
Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai, China.
Nat Commun. 2023 Nov 22;14(1):7635. doi: 10.1038/s41467-023-43463-0.
The edge of a monsoon region is usually highly sensitive to climate change. Pakistan, which is located on the northern edge of the Indian monsoon, is highly vulnerable to heavy rainfall and has witnessed several debilitating floods exacerbated by global warming in recent years. However, the mechanisms for the frequent Pakistan floods are yet not fully understood. Here, we show that the Middle East is undergoing an increase in land heating during spring, which is responsible for 46% of the intensified rainfall over Pakistan and northwestern India during 1979-2022. This springtime land warming causes a decline in sea level pressure (SLP), which strengthens the meridional SLP gradient between the Middle East and the southern Arabian Sea and drives the changes of low-level jet (LLJ) subsequently. The impact persists into summer and results in a northward shift of the monsoonal LLJ, accompanied by strong positive vorticity in the atmosphere and enhanced moisture supply to Pakistan. Consequently, the transition region between the summer monsoon in South Asia and the desert climate in West Asia is shifted northwestward, posing significantly enhanced risk of floods over Pakistan and northwestern India.
季风区的边缘通常对气候变化高度敏感。位于印度季风北缘的巴基斯坦极易受到暴雨影响，近年来因全球变暖而遭受了几次破坏性极大的洪水。然而，巴基斯坦洪水频发的机制尚未完全明确。在此，我们表明中东地区春季陆地升温正在加剧，这是1979年至2022年期间巴基斯坦和印度西北部降雨增强的46%的原因。这种春季陆地变暖导致海平面气压（SLP）下降，增强了中东和阿拉伯海南部之间的经向海平面气压梯度，并随后推动低空急流（LLJ）的变化。这种影响持续到夏季，导致季风低空急流向北移动，伴随着大气中强烈的正涡度以及向巴基斯坦增加的水汽供应。因此，南亚夏季风与西亚沙漠气候之间的过渡区域向西北移动，给巴基斯坦和印度西北部带来了显著增加的洪水风险。
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