黄河上游暖湿化的多时间尺度特征及对生态植被的影响

The Multi-Time Scale Characteristics and Impacts on Ecological Vegetation of Warming and Humidification in the Upper Yellow River

黄河上游地处青藏高原、黄土高原、蒙古高原交汇区,气候变化敏感,生态环境脆弱,是黄河流域主要的产流区和水源涵养区,生态区位对于黄河流域水资源和生态安全非常重要。21世纪初以来黄河上游呈现出了显著的暖湿化特征,但暖湿化的多时间尺度特征、成因及对生态植被的影响并不清楚。为此,本文基于观测、再分析、卫星遥感以及未来情景预估等多源数据,利用EOF、EEMD等多种统计方法,对半个多世纪以来黄河上游的增暖与干湿特征进行了系统分析,并就当前暖湿化的成因及对生态植被的影响进行了探讨。研究表明:1961年以来黄河上游平均温度以0.37℃·(10a)^(-1)的速率增加,较全球、全国乃至西北地区同期的增温更为显著;降水表现出了明显的年代际变化,其中1997年以来以32 mm·(10a)^(-1)速率显著增加,因此,1997年以来黄河上游呈显著的暖湿化趋势。从空间异常分布特征来看,平均温度与降水主要以区域一致的模态变化为主。从多时间尺度变化来看,平均温度主要以长期趋势变化为主,年际变化次之,而降水主要以年际变化为主,多年代际变化次之,1961年以来黄河上游之所以持续增暖,主要是平均温度趋势项分量增加的结果,而1997年以来的显著湿化主要是由降水30 a以上多年代际尺度分量增加所致。从空间动态变化来看,黄河上游1961-2010年期间每个气候态时段区域整体呈暖干化,但干化趋势逐气候态时段减缓,而1991-2020年区域呈一致的暖湿化。黄河上游降水变化主要受西风、东亚夏季风和南亚夏季风环流系统的共同影响,但在不同时间尺度上影响的环流因子差异较大,年际尺度上主要受南亚夏季风单一环流因子影响,年代际尺度上主要受西风和南亚夏季风共同影响,多年代际尺度上主要受西风和东亚夏季风环流共同影响,1997年以来的湿化趋势主要是西风和东亚夏季风环流协同增强的结果。预计未来80年黄河上游继续呈暖湿化趋势,增暖趋势同当前基本相当,而湿化趋势明显弱于当前。黄河上游水热条件不足,生态植被对近3个月以来的平均温度与降水具有一定的依赖性,相比较对同期降水的依赖性更强,此外平均温度对生态植被的滞后效应较降水更长。从温度和降水的协同作用看,暖湿匹配的气候类型最有利于植被生长,冷干匹配的气候类型则相反。近20年来的气候暖湿化使得黄河上游生态植被整体呈向好态势,未来80年的暖湿化可能使得生态植被继续向好。

The upper Yellow River are located at the intersection of the Qinghai-Xizang Plateau,the Loess Plateau,and the Mongolian Plateau,it is sensitive to climate change and the ecological environment is fragile,it is the main flow-producing area and water conservation area in the Yellow River Basin,the ecological location is very important for the water resources and ecological security of the Yellow River Basin.The upper Yellow River have shown significant warming and humidification characteristics since the beginning of this century,but they are unclear that the multi-time scale characteristics,causes and effects on ecological vegetation of warming and humidification.So,based on various data such as observation,reanalysis,satellite remote sensing and future scenario prediction,using EOF,EEMD and other statistical methods,this paper systematically analyzed the warming and dry-wet characteristics of the upper Yellow River for more than half a century,and discussed the causes of current warming and humidification and its impact on ecological vegetation.It is found that the upper reaches of the Yellow River average temperature have increased at a rate of 0.37°C·(10a)-1 since 1961,which is more obvious than that of the whole world,the whole country and even the whole northwest.Precipitation shows obvious interdecadal changes,which has increased significantly at a rate of 32 mm·(10a)-1 since 1997.Therefore,the upper reaches of the Yellow River have shown an obvious warming-wetting trend since 1997.From the perspective of spatial anomaly distribution characteristics,temperature and precipitation are mainly dominated by regional consistent modal changes.From the point of view of multi-time scale changes,the average temperature is mainly dominated by long-term trend changes,followed by inter-annual changes,and precipitation is mainly dominated by inter-annual changes,followed by multi-decadal changes.The reason for the continuous warming since 1961 is mainly the result of an increase of the average temperature trend component.The obvious humidification trend since 1997 is mainly due to the humidifying channel at the multi-decadal weight of precipitation over 30 years.From the perspective of spatial dynamic changes,the upper reaches of the Yellow River in each climatic period from 1961 to 2010 showed overall warming and drying,but the drying trend slowed down by climatic period,and the region showed consistent warming and drying from 1991 to 2020.The variation of precipitation in the upper reaches of the Yellow River is mainly affected by the westerly,East Asian summer monsoon and South Asian summer monsoon.However,the circulation factors affected are quite different at multi time scales.The interannual scale is mainly affected by the single circulation factor of the South Asian summer monsoon,the interdecadal scale is mainly affected by the westerly and South Asian summer monsoon,and the multi-decadal scale is mainly affected by the westerly and South Asian summer monsoon circulation.The wetting trend since 1997 is mainly the result of the enhancement of the westerly and South Asian summer monsoon circulation.It is expected that the upper reaches of the Yellow River will continue to show a warming and wetting trend in the next 80 years,and the warming trend is basically the same as that at present,while the wetting trend is significantly weaker than that at present.Water and heat conditions is insufficient in the upper reaches of the Yellow River,and ecological vegetation has a certain dependence on the average temperature and precipitation in the past three months,and the stronger dependence on precipitation in the same period.In addition,the average temperature has a longer lag effect on ecological vegetation than precipitation,Average temperature and precipitation have a synergistic effect on ecological vegetation.A warm and wet climate is the most conducive to vegetation growth,while a cold and dry climate is not.The warming and wetting climate makes the ecological vegetation in the upper reaches of the Yellow River tend to be good in the recent 20 years,and warming and wetting trend may make ecological vegetation continue to improve in the next years.