Abstract：
In the context of global warming, the occurrence and severity of extreme events like atmospheric drought (AD) and warm spell duration index (WSDI) have increased, causing significant impacts on terrestrial ecosystems in Central Asia\'s arid regions. Previous research has focused on single extreme events such as AD and WSDI, but the effect of compound hot and dry events (CHWE) on grassland phenology in the arid regions of Central Asia remains unclear. This study utilized structural equation modeling (SEM) and the Pettitt breakpoint test to quantify the direct and indirect responses of grassland phenology (start of season - SOS, length of season - LOS, and end of season - EOS) to AD, WSDI, and CHWE. Furthermore, this research investigated the threshold of grassland phenology response to compound hot and dry events. The research findings indicate a significant increasing trend in AD, WSDI, and CHWE in the arid regions of Central Asia from 1982 to 2022 (0.51 day/year, P < 0.01; 0.25 day/year, P < 0.01; 0.26 day/year, P < 0.01). SOS in the arid regions of Central Asia showed a significant advancement trend, while EOS exhibited a significant advance. LOS demonstrated an increasing trend (-0.23 day/year, P < 0.01; -0.12 day/year, P < 0.01; 0.56 day/year). The temperature primarily governs the variation in SOS. While higher temperatures promote an earlier SOS, they also offset the delaying effect of CHWE on SOS. AD, temperature, and CHWE have negative impacts on EOS, whereas WSDI has a positive effect on EOS. AD exhibits the strongest negative effect on EOS, with an increase in AD leading to an earlier EOS. Temperature and WSDI are positively correlated with LOS, indicating that higher temperatures and increased WSDI contribute to a longer LOS. The threshold values for the response of SOS, EOS, and LOS to CHWE are 16.14, 18.49, and 16.61 days, respectively. When CHWE exceeds these critical thresholds, there are significant changes in the response of SOS, EOS, and LOS to CHWE. These findings deepen our understanding of the mechanisms by which extreme climate events influence grassland phenology dynamics in Central Asia. They can contribute to better protection and management of grassland ecosystems and help in addressing the impacts of global warming and climate change in practice.
摘要：
在全球变暖的背景下,大气干旱(AD)、暖期持续指数(WSDI)等极端事件的发生和严重程度有所增加，对中亚干旱地区的陆地生态系统造成重大影响。以前的研究集中在单一极端事件，如AD和WSDI，但是，复合干热事件（CHWE）对中亚干旱地区草地物候的影响尚不清楚。本研究利用结构方程模型（SEM）和Pettitt断点检验来量化草地物候的直接和间接响应（季节开始-SOS，季节长度-LOS，和赛季末-EOS）到AD，WSDI,和CHWE。此外，这项研究调查了草地物候对复合干热事件的响应阈值。研究结果表明，AD呈显著上升趋势，WSDI,和CHWE在中亚干旱地区从1982年到2022年(0.51天/年，P<0.01；0.25天/年，P<0.01；0.26天/年，P<0.01)。中亚干旱地区的SOS表现出明显的上升趋势,而EOS表现出显著的进步。LOS表现出增加的趋势(-0.23天/年，P<0.01;-0.12天/年,P<0.01；0.56天/年）。温度主要控制SOS的变化。虽然较高的温度会促进较早的SOS，它们还抵消了CHWE对SOS的延迟作用。AD,温度,CHWE对EOS有负面影响，而WSDI对EOS有积极影响。AD对EOS的负面影响最强，随着AD的增加导致了较早的EOS。温度和WSDI与LOS呈正相关，这表明较高的温度和增加的WSDI有助于较长的LOS。SOS响应的阈值，EOS,和LOS到CHWE分别为16.14、18.49和16.61天，分别。当CHWE超过这些临界阈值时，SOS的反应发生了重大变化，EOS,和LOS给CHWE。这些发现加深了我们对极端气候事件影响中亚草地物候动态的机制的理解。它们有助于更好地保护和管理草地生态系统，并有助于在实践中解决全球变暖和气候变化的影响。
