Study On The Characteristics Of Major Extreme Climate Change And Its Impact On NDVI In Qinghai Province From 1961 To 2020

Within the context of climate change,extreme climate events have accurred frequently.Extreme climate events have more significant and stronger impact than average state on social-economic development and ecological environment evolution.Qinghai province is an area with high ecological vulnerability and is extremely sensitive to climate change.Extreme climatic events such as cold wave,high temperature,sandstorm,drought,hail and rainstorm occur frequently in this area,causing serious consequences such as river water level drop,disaster in pastoral areas,agricultural production reduction and human health damage.affect the regional socio-economic sustainable development directly,which poses a huge challenge and a serious threat to the ecological and environment protection and people’s living conditions.Vegetation coverage plays a very important role in ecological services in Qinghai Province.In recent years,the changes of extreme climatic events such as high temperature,cold wave and drought have a certain degree of impact on vegetation coverage in Qinghai Province,resulting in the changes of regional primary productivity,soil and water conservation,atmospheric regulation,climate maintenance and even the whole ecosystem.In view of this,study the time variation of the extreme climate events in Qinghai province,the difference of space characteristics,and further explore the extreme climate events impact on vegetation,not only conducive to promoting regional ecological environment protection and ecological construction results,and can provide strong support for the sustainable economic development of Qinghai province decision-making.Based on the daily mean temperature,daily maximum(low)temperature and daily precipitation data of surface meteorological stations in Qinghai Province during 1961-2020,27 extreme temperature and extreme precipitation indices are calculated,and 15 indices with large weights are screened out by principal component analysis.The trend of extreme climate events in Qinghai province,its persistence,abrupt change and spatial pattern were analyzed comprehensively and deeply.Meanwhile,based on MODISNDVI3 G data,the temporal variation trend,mutation characteristics,spatial distribution characteristics and future change trend of NDVI in Qinghai Province and its sub-regions from 2000 to 2020 were analyzed.Finally,correlation analysis and hysteresis analysis were used to explore the impact characteristics of extreme climate events on NDVI in Qinghai Province.The main conclusions of this paper are as follows:(1)Among the interannual changes of five extreme temperature indexes,the warming trend of Qinghai province is obvious.The trends of warm days(TX90p),warm nights(TN90p),extremely high daily minimum temperature(TNx)and extremely high daily maximum temperature(TXx)in extreme temperature indexes passed the SIGNIFICANCE test of P<0.01,and showed a significant increasing trend.In terms of the spatial variation trend,the extreme temperature index showed an upward trend in northwest China and a downward trend in southeast China,and the extreme temperature index showed the most obvious change in the eastern agricultural region.(2)Under the background that the total precipitation in the study area showed a slight increase trend from 1961 to 2020,the number of continuous wet days(CWD)showed a decreasing trend.Six extreme precipitation indices(RX1day,RX5 day,R95p,R99 p,PRCPTOT,SDII)and three extreme precipitation indices(R10,R20,R25)represented by total annual mean precipitation Day(PRCPTOT)showed an increasing trend,and the abrupt changes of extreme precipitation indices mainly occurred in 2018.Over the years,the extreme precipitation index showed a declining trend in the province,and the decline was more obvious in the eastern and southern regions.(3)From 2000 to 2020,the mean VALUE of NDVI in Qinghai province was 0.187,with a change rate of 0.015/10 a,with a slight improvement trend.The mean value of NDVI in eastern agricultural areas was the highest,and that in Qaidam Basin was the lowest.In the NDVI of the year,the NDVI values showed an upward trend in all months,and the upward trend was most obvious in May,June and July.The vegetation fluctuation in the northwest of Qinghai province is relatively stable,and the fluctuation in the southeast is strong,and the vegetation change trend in some areas will change from improvement to degradation in the future.(4)Among the extreme climate indices,the correlation between NDVI and extreme precipitation indices in eastern China is obvious,and the correlation between NDVI and extreme temperature indices in western China is obvious,and the correlation between NDVI and extreme temperature indices in night is higher than that in day.The spatial correlation between monthly extreme climate index and NDVI was consistent with the inter-annual characteristics.Meanwhile,NDVI was significantly affected by extreme temperature index from January to June,while NDVI was significantly affected by extreme precipitation index from April to August.(5)The response of NDVI to climate extremes in Qinghai province was 1,3,5 and7 months.When the lag periods were 1,3 and 7 months,both extreme temperature and extreme precipitation had a significant positive driving effect on vegetation growth.The lag response of vegetation in eastern China to extreme climate was higher than that in western China,and the lag response of NDVI to extreme daily minimum temperature(TNx)was the most significant.