The Multiple Perspective Response Of Vegetation Greeness To Drought On The Qinghai-Tibetan Plateau

In the context of global warming,the increasing frequency and intensity of drought will have a further negative impact on ecosystems,especially in areas with extremely fragile ecosystems such as the Qinghai-Tibet Plateau.In order to prevent and mitigate drought,it is necessary to quantitatively analyze the characteristics of drought events and to analyze the characteristics of vegetation response to drought from multiple perspectives.Therefore,the normalized vegetation difference index(NDVI)and standardized precipitation evapotranspiration Index(SPEI)were used in this study to quantitatively analyze the characteristics of drought events over the QTP during 2000-2019,the temporal effect of vegetation greeness response to drought and the stability of vegetation response to drought on the QTP from 2000 to 2018.The characteristics of vegetation response to drought were analyzed from multiple perspectives and the differences among vegetation types were further understood.The main research conclusions are as follows:(1)The interannual temperature change over the QTP showed a fluctuating upward trend from 2000 to 2019,with a break in 2000 and a slowing down trend after 2012.There was significant warming in south central and eastern parts of the Plateau.The annual total precipitation fluctuated and decreased continuously from 2012 to 2015.The annual total precipitation in the southwest of the QTP decreased significantly.The potential evapotranspiration showed a fluctuating upward trend,and the upward trend slowed down after 2009.The southwest part showed a significant rise in banded areas.When compared to the east monsoon region,most of the western regions have higher frequency and lower intensity of drought events,especially the zonal distribution in the western boundary region of the QTP.The characteristics of drought events have obvious differences with the increase of altitude.Drought events occurred more frequently in the higher elevations above 5000 m,the drought duration was shorter and the drought intensity was weaker,but the drought intensity varied significantly with different elevations.The drought characteristics of ecological zones in different temperature zones were significantly different.(2)In most areas of the QTP,vegetation were sensitive to annual drought,and the most responsive SPEI time scale was 24 months.Steppe and meadow were sensitive to longer time scale.There was a positive correlation between vegetation and SPEI at different time scales during the growing season,and there were some differences in the response of vegetation to drought at different growth stages.In the growing season,vegetation was most sensitive to SPEI12 in all regions of QTP except May.The steppe and meadow were more sensitive to drought response and had significant spatiotemporal differences with the growth season.(3)The time-lag response of vegetation to annual SPEI over the QTP from 2000 to 2018 was not significant,and the optimum time-lag time scale was 12 months in most regions.Drought has time-lag effect on vegetation on the QTP during the growing season,there has significant time-lag effect on vegetation in grassland areas of the QTP,the optimum time-lag time scale of grasslad was relatively short.The overall correlation coefficient of annual scale cumulative effects was higher than time-lag effects.And the optimal cumulative time scale in most areas was 24 months.There was a cumulative response of vegetation to drought in the growing season,and the optimal accumulated time scale was 3 months.The cumulative response of vegetation to drought was significant in the steppe and meadow areas,and the proportion of the area with significant cumulative response reached the peak in July and August.The temporal effect of vegetation drought response and its corresponding time scale showed significant spatio-temporal differences in the growing season.(4)The resistance and resilience of the QTP showed significant spatial differences from 2000 and 2018,with resistance less than 75 and resilience less than 3 in most areas of the plateau.The forest showed high resistance and resilience,followed by crop and steppe.There were significant differences in the resistance of the same type of vegetation in each ecological zone,but no significant differences in the resilience of shrub and steppe in different ecological zones.