新疆气候“湿干转折”的信号和影响探讨

Signal and impact of wet-to-dry shift over Xinjiang, China

新疆是对全球变化响应最敏感地区之一,分析全球变暖背景下新疆干湿气候变化及其影响,对应对和适应未来气候变化带来的影响具有重要意义。基于气象水文观测资料,对新疆区域干湿气候变化及其影响评估进行了探讨。结果表明:①20世纪80年代中后期以来新疆气温升高,降水量增加,呈"暖湿化"特征;但1997年之后,干旱变化趋势、干旱频率、干旱发生月份等均有明显增加,导致70%以上的区域变干,新疆气候出现了从"暖湿化"向"暖干化"转折的强烈信号,即发生了"湿干转折";②新疆气候转折对区域生态和水资源造成明显的影响,归一化植被指数(Normalized Difference Vegetation Index, NDVI)经历了先增后减的变化过程,1982—1997年植被趋于"变绿",但1997年之后植被长势迟滞,土壤水分明显下降,生态逆转,生态负效应凸显;③新疆河流径流变化出现明显的区域差异,对干湿气候转折响应复杂,受冰雪融水对径流补给比例的影响,发源于天山的河流径流对区域干湿变化有正响应,但发源于昆仑山的河流径流响应不明显。研究结果表明气候"湿干转折"和极端气候事件加剧背景下新疆干旱化急剧增加,水循环系统和生态系统不稳定性加剧,相关成果可为区域干旱灾害防灾减灾和风险管理提供有价值的决策参考。

Xinjiang, a unique natural unit, is sensitive to the global warming. Studies on the spatial-temporal variation and impacts of drought and wetness in Xinjiang have a significant effect on the adaptability of future climate change. Based on observations of monthly mean temperature, monthly precipitation, and calculated standardized precipitation evapotranspiration index(SPEI), this paper analyzes the drying trend and impacts of climate change on the water resources and vegetation dynamics over Xinjiang, China. The results can be shown as follows:(1) The climate experienced a significant shift from warm-wet to warmdry over Xinjiang in 1997 based on the SPEI data, after which the frequency, trend, dry months and percentage of stations of drought increased sharply.(2) The increased meteorological drought severity had a direct effect on the normalized difference vegetation index(NDVI) and river discharge. The NDVI exhibited a significant decrease during the period 1998-2015 compared with 1982-1997, which was found to be caused by increased soil moisture loss.(3)The hydrological drought was very complicated and not entirely comparable to the SPEI droughts. Hydrological records indicate that runoff in most rivers in the Tianshan Mountains has increased, while it remained stable or even decreased slightly in the Kunlun Mountains over the past 20 years. The runoff in Xinjiang is strongly influenced by glacial melt, and it is getting worse due to global warming. The climatic shift and intensified climate extremes over Xinjiang have resulted in SPEI-drought severity. These changes also have possibly intensified the instability of water cycle system and ecosystem. The results provide valuable decisionmaking reference for the regional drought disaster prevention, reduction and emergency management over Xinjiang, China.