Rapidly intensifying global land drought poses severe threats to human societies, economies, and ecosystems. While previous studies have primarily investigated long-term drought trends, the frequency and concurrence of trend turnings have been largely neglected. In this study, we address this gap by employing the Running Slope Difference (RSD)-t-test to quantify trend turning frequency in Afro-Eurasian drought severity. Based on Palmer Drought Severity Index (PDSI), our analysis indicates that the PDSI trend in most parts of the Afro-Eurasian continent has experienced two turnings since 1950, although, the types of trend turnings vary regionally. The concurrence of these PDSI trending turnings is further investigated. Around 1985, a dipole pattern emerged - Eastern Europe experiences a drying trend turning, accompanied by decreased P-E and intensified drought, while Sahel exhibits a wetting trend turning, with increased P-E and mitigated drought. Around 2000, a tripole pattern is observed in Eastern Eurasia: The Russian Far East and South Asia experienced a drying trend turning, with reduced P-E and intensified drought, while Northeast Asia exhibited a further wetting trend, characterized by increased P-E and mitigated drought. We further investigate the influence of large-scale circulation changes. The enhanced Northern Hemisphere warming trend before and after 1985 contributes to increased land surface high pressure and an amplified meridional temperature gradient, favoring cross-equatorial water vapor transport. This mechanism potentially drives the dipole pattern of trend turning observed around 1985. Additionally, the North Pacific Ocean Sea Surface Temperature (SST) exhibited an enhanced North Pacific Gyre Oscillation (NPGO) pattern around 2000, which induced a tripole atmospheric circulation pattern over East Asia, corresponding to the observed tripole pattern of PDSI trend turnings. The identified dipole and tripole patterns of drought trend turnings, and their potential links to large-scale atmospheric circulation changes, provide insights into the complex dynamics of land drought variability across Afro-Eurasian.

中文翻译：

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自 1950 年以来，非洲-欧亚大陆干旱严重程度的并发趋势转变


迅速加剧的全球土地干旱对人类社会、经济和生态系统构成严重威胁。虽然以前的研究主要调查了长期干旱趋势，但趋势转变的频率和同时性在很大程度上被忽视了。在这项研究中，我们通过使用运行斜率差 （RSD）-t 检验来量化非洲-欧亚干旱严重程度的趋势转向频率来解决这一差距。基于帕尔默干旱严重程度指数 （PDSI），我们的分析表明，自 1950 年以来，非洲-欧亚大陆大部分地区的 PDSI 趋势经历了两次转变，尽管趋势转变的类型因地区而异。进一步研究了这些 PDSI 趋势转向的并发性。1985 年左右，出现了一种偶极子模式——东欧经历了干旱趋势的转变，伴随着 P-E 的减少和加剧的干旱，而萨赫勒地区则表现出湿润趋势的转变，P-E 增加并缓解了干旱。2000 年左右，在欧亚大陆东部观察到三极模式：俄罗斯远东和南亚经历了干旱趋势转变，P-E 减少和干旱加剧，而东北亚则表现出进一步的湿润趋势，其特征是 P-E 增加和干旱缓解。我们进一步研究了大规模环流变化的影响。1985 年前后北半球变暖趋势增强导致地表高压增加和经向温度梯度放大，有利于跨赤道水汽输送。这种机制可能推动了 1985 年左右观察到的趋势转向偶极子模式。 此外，北太平洋海表温度 （SST） 在 2000 年左右表现出增强的北太平洋环流振荡 （NPGO） 模式，这在东亚引起了三极大气环流模式，对应于观察到的 PDSI 趋势转向的三极模式。已确定的干旱趋势转向的偶极子和三极子模式，以及它们与大尺度大气环流变化的潜在联系，为了解非洲-欧亚大陆土地干旱变化的复杂动态提供了见解。