1982-2022年中国北方草地NDVI变化及其对极端气候事件的响应OA

In recent decades,the intensity and frequency of extreme global climate events have increased significantly,resulting in significant changes in the structure and function of terrestrial ecosystems.The grasslands in northern China are an ecologically fragile and important carbon sink area,and the correlation between vegetation dynamics in the grasslands and extreme climate events,patterns of spatial separation,and identification of the dominant driving factors remain key research challenges.Based on long-term global inventory modeling and mapping studies normalized difference vegetation index(GIMMS NDVI)data from 1982 to 2022 in combination with 15 extreme climate indicators,spatiotemporal evolution characteristics of the normalized difference vegetation index(NDVI)of the grasslands and their response to extreme climate events were systematically analyzed using trend,correlation,and relative importance analyses.The results were as follows:1)Grassland NDVI in northern China showed a significant upward trend as a whole(P<0.05),and the average annual change rate was 0.000 2·a-1.Significant differences were observed in the growth rates of NDVI for different grassland types.Among them,the NDVI growth rate for temperate typical grasslands was the fastest,followed by those of temperate meadow grasslands and desert grasslands.2)In terms of extreme temperature indicators,a significant positive correlation was detected between grassland NDVI and number of warm days(TX90p),number of warm nights(TN90p),and minimum temperature(TMINmean),whereas a significant negative correlation was observed with frost days(FD)(P<0.05).3)A generally positive correlation was detected between grassland NDVI and six extreme precipitation indicators,especially with significant correlations(P<0.05)with Heavy precipitation(R95p),extremely heavy precipitation(R99p),and maximum daily precipitation(RX1day)indicators.4)R95p and TN90p are the main drivers affecting the changes in grassland NDVI in northern China,dominating 17.1％and 11.6％of the regional area,respectively.With the increase in TN90p,grassland NDVI continued to increase,whereas with the increase in R95p,grassland NDVI showed a trend of increasing first and then decreasing,with a turning point at approximately 550 mm.