基于SPEI的1965-2020年中国北方农牧交错带干湿特征研究OA

[Objective]This study aims to reveal the patterns of moisture evolution in the farming-pastoral ecotone in Northern China(FPENC)to further optimize regional water resource development and utilization.[Methods]This study utilized daily meteorological records from 48 stations in the FPENC spanning 1965 to 2020.Potential evapotranspiration was determined using the Penman-Monteith equation,enabling calculation of the Standardized Precipitation Evapotranspiration Index(SPEI)in conjunction with contemporaneous precipitation measurements.Temporal and spatial characteristics of SPEI variations over the 56-year period were investigated through three statistical approaches:linear trend analysis using regression,Mann-Kendall statistical trend assessment,and wavelet transform-based analytical techniques.[Results](1)From 1965 to 2020,the annual precipitation in the farming-pastoral ecotone in Northern China showed an increasing trend(0.71 mm/a),and the annual mean temperature increased significantly(0.04℃/a);in terms of spatial change characteristics,the aggregate regional pattern of annual mean temperatures exhibited a distinct west-east gradient,with warmer conditions prevailing in western areas and cooler temperatures characterizing the eastern sector,and precipitation generally increased from north to south.(2)Except for summer,SPEI showed a significant increasing trend at the annual scale as well as in spring,autumn,and winter,with a non-significant increase in summer,and the climate exhibited a humidification trend.The first,second,and third main cycles of SPEI change were 57 a,44 a,and 9 a,respectively.(3)Droughts at all time scales were dominated by light and medium droughts,and the frequency of severe and extreme droughts was low.The spatial distribution of droughts was seasonal:spring droughts occurred in the western part of the agricultural and pastoral zone,summer droughts were concentrated in the southeastern part of the farming-pastoral ecotone,droughts frequently occurred in the central-western areas in autumn and winter,and annual droughts occurred more frequently in the eastern part of the farming-pastoral ecotone.[Conclusions]Over the study period,the FPENC exhibits a progressive moistening trajectory.This climatic shift bolsters persistent vegetation enhancement across the region.However,cautious attention merits consideration regarding potential threats posed by protracted drought episodes to these nascent greening ecosystems during specific intervals.