Spatiotemporal Variations Of Vegetation On The Qinghai-Tibet Plateau And Its Response To Extreme Climate Events

Under the general trend of global warming,the frequent occurrence of extreme climate events has gradually attracted great attention from governments and academic organizations around the world.Because of its fragile ecological environment,the Qinghai-Tibet Plateau is even more sensitive to climate change.Extreme climate change has become an important factor affecting the growth and coverage of local vegetation,and it will also affect the climate and vegetation growth of the whole country and even Asia.Therefore,studying the temporal and spatial changes of the vegetation on the Qinghai-Tibet Plateau and its response to extreme climate events is not only conducive to promoting the protection of the vegetation ecological environment of the Qinghai-Tibet Plateau,but also provides an effective scientific basis for the relevant emergency work to deal with the adverse effects of extreme climate events.This article focuses on the research theme of the spatial and temporal changes of vegetation on the Tibetan Plateau and its response to extreme climate events.First,based on the long-term GIMMS NDVI 3g data,the temporal and spatial changes of vegetation on the Tibetan Plateau during 1982-2015 were analyzed from two different time scales: year and season.Secondly,based on the daily maximum temperature,minimum temperature and precipitation data of 134 surface meteorological observation stations in the study area,14 extreme temperature indicators and 10 extreme precipitation indicators were calculated.After that,the spatial and temporal changes of extreme climatic events in the Qinghai-Tibet Plateau were analyzed from the perspectives of intensity,frequency and duration.Finally,the correlation analysis,multicollinearity analysis and geographic weighted regression model were used to study the response of NDVI to three extreme climate events such as the number of FD,R95 p and CDD at different time and space scales.First,this study describes the temporal and spatial changes of vegetation in the Tibetan Plateau.On the interannual scale,from 1982 to 2015,the NDVI of theQinghai-Tibet Plateau showed a significant upward trend of fluctuations,with an interannual change rate of 0.0016 /10 a.On the seasonal scale,NDVI in spring,summer,Qiu and winter all showed upward trends,but only spring and autumn passed the significance test.The rising speeds of NDVI of the two are 0.0023 / 10 a and0.0016 / 10 a,respectively,and the change trend in spring(P <0.05)is more significant than in autumn(P <0.1).In addition,the four types of vegetation of desert,steppe,meadow and forest all show an increasing trend of fluctuations,but the specific changes of different types of vegetation are also different.In terms of spatial pattern,the area of NDVI growth in the Qinghai-Tibet Plateau was significantly higher than the degraded area during 1982-2015.The area of NDVI showing an upward trend accounted for 67.66% of the total area of the plateau,of which the proportion of significant increase was 37.74%.There is a small-scale reduction trend in the northwestern edge and southern edge of the plateau.In addition,the vegetation changes in different seasons also show significant spatial heterogeneity.Secondly,this study describes the temporal and spatial variation of extreme climate events in the Tibetan Plateau.From 1982 to 2015,extreme warming occurred in the Qinghai-Tibet Plateau region.The intensity,frequency and duration index of extreme warming indicators all increased significantly,and several extreme temperature indicators maintained a rise rate of 0.4 ~ 0.6?/10 a.The frequency and duration index of the extreme cold index are significantly reduced.Taking FD as an example,its rate of decline can reach 5.98 days / 10 a.During 1982-2015,most of the extreme precipitation indicators on the Tibetan Plateau showed an increasing trend.The increase rate of SDII was about 0.10 mm/day/10a(P <0.01),and Rx1 day changed by 0.67 mm/10 a,and none of the remaining indicators have changed significantly.The rainfall on the Qinghai-Tibet Plateau mainly comes from extreme rainfall,which just explains the unevenness of rainfall in the area.In addition,the extreme precipitation index values in the 34-year period almost showed a decreasing trend in the forest zone in the southern Tibetan Plateau.Finally,this study also explored the relationship between the vegetation of the Qinghai-Tibet Plateau and extreme climate events.Overall,the vegetation on theQinghai-Tibet Plateau is more sensitive to extreme low temperature events,which may significantly inhibit the growth and development of local vegetation.The proportion of sites with a negative correlation between NDVI and FD was 95.52%,of which 80.60%reached a significant level of P <0.05.The impact of extreme precipitation events on NDVI is much more obvious than that of extreme temperature events,and they are basically positive promoting effects.NDVI and R95 p all have a positive response relationship in the Tibetan Plateau,and the proportion of sites that pass the P <0.05 significance test is 79.85%.The proportion of sites with negative regression coefficients between NDVI and CDD was 91.79%,of which 73.88% passed the significance test.It is worth noting that the impact of extreme climatic events on vegetation growth and development in the 34 years has become stronger and more obvious.In terms of spatial pattern,the inhibitory effect of extreme low temperature events on vegetation growth gradually weakened from the south to the north of the plateau.The promoting effect of extreme rainfall on vegetation growth gradually increased from the south to the north of the plateau,and it was the strongest in the grassland of the northeast of the plateau.The suppression of extreme drought generally showed a gradual weakening trend from the southwest of the plateau to the northeast.In addition,some vegetation in the east of the plateau also showed a significant negative correlation response to extreme arid climate.