Changes Of Vegetation And Its Response To Extreme Climate In The Loess Plateau

Vegetation is the link connecting soil,water and atmosphere,and plays an important role in global climate change.As global warming,extreme climate occurs frequently and intensifies,which will have an important impact on the growth of vegetation and leading to the change of vegetation cover.Based on the GIMMS NDVI data from 1982 to 1999,and MODIS NDVI data from 2000 to 2017 of the loess plateau,and the daily rainfall,daily maximum temperature and daily minimum temperature data of 87 meteorological stations,the study used Mann-Kendall trend test and correlation analysis method to analyze temporal and spatial changes of vegetation in Loess Plateau and its response to extreme climate.To study the dynamics changes of vegetation on the Loess Plateau and its response to extreme climate.Research indicates the following:(1)The results showed that NDVI exhibited a significant increase trend in the loess plateau.From 1982 to 2017,NDVI on the Loess Plateau increased by an annual rate of 0.37%(p<0.01).In the loess plateau,the seasonal variation of monthly NDVI was obvious.It started to grow in April and reaches a peak in August.After August,the NDVI value generally declines.Spatially,the vegetation in this region presented an increasing spatial distribution pattern from northwest to southeast on the Loess Plateau.Compared with 1982,the vegetation cover in the northwest of the loess plateau in 2017 has significantly improved,and the vegetation cover in the southeast of the high-value region also shows an increasing trend.(2)As for the change of extreme climate index,the extreme temperature index has a significant changetrend,while the significance test of extreme precipitation index was not obvious.The variation trend of extreme temperature index was relatively consistent and the extreme temperature index(SU25,TMAXmean,TMINmean,TN90p,TXx,TNn)represented extreme high temperature events showed a significant increase trend,and the index represented extreme low temperature events(FD0,TN10p)showed an extremely significant downward trend.However,the extreme precipitation index did not change significantly.The spatial distribution of extreme precipitation index(RX1day,RX5 day,R50 mm,CDD)was relatively consistent,and they all showed the spatial distribution pattern increasing from northwest to southeast.The central and southeastern parts of the loess plateau have more precipitation,which is mainly distributed in ziwuling forest area,huanglongshan forest area,luliang of Shanxi Province and taihang mountain area.Compared with the precipitation index,the temperature index of each station has a significant change trend.(3)The correlation between NDVI and extreme climate index at different time scales was different.In the correlation analysis between extreme climate index and NDVI,the interannual variation of NDVI was significantly correlated with extreme temperature index(TMAXmean,TMINmean,TN90p,TXx,TNn)(p<0.01).On the monthly scale,NDVI was significantly correlated with extreme precipitation index(RX1day,RX5day)and extreme temperature index(TMAXmean,TMINmean,TN90p,TXx,TNn)(p < 0.01).The correlation between NDVI and extreme temperature index TMAXmean,TN10p,TN90p,TNx and TXx a lag of one month is greater than that current month,a lag of two months and a lag of three mouth,indicating that the response of vegetation change to extreme climate has a certain lag.As the seasonal scale,there was no significant correlation between NDVI changes and extreme precipitation index in all seasons.However,NDVI presented a significant correlation with extreme temperature index,moreover,the correlation of spring and summer was higher than that autumn and winter.