Spatial And Temporal Characteristics Of Dry And Wet Changes And Its Influence On Vegetation In The Yunnan-Guizhou Region Of The Southwest China Based On Multiple Drought Index

Climate change is a key issue in global change research,especially drought disasters,which is the most serious natural disaster in China.Estimates of dry and wet changes are highly dependent on indicators such as precipitation and drought indices.Related studies have shown that different drought indices have different adaptability in the design process,so how to obtain deterministic dry and wet changes generally needs to confirm the common changes of different indices.To this end,this paper chooses the Yungui area as the study area,although the area is relatively humid,but experienced a rare drought event in 2009-2012.This paper intends to select precipitation,physical drought index PDSI(and its deformation scPDSI),statistical drought index SPEI,and soil moisture quantile(VCPCT)based on hydrological model simulation.From the perspective of multi-index,comprehensive analysis of the study area in 1961-2012 The spatial and temporal characteristics of interannual dry and wet changes during the year,especially the multi-index consistency law,to clarify the definite trend of long-term dry and wet changes in the region.The growth of vegetation is mainly affected by meteorological conditions such as temperature,light and moisture,especially the drought events are thought to have a huge impact on vegetation.Vegetation(including natural vegetation and farmland)is also an important disaster victim in drought events.Therefore,this paper selects the normalized vegetation index(NDVI)as an indicator,and studies its correlation with precipitation and multiple drought indices,and determines the main factors affecting the vegetation variability in the region.Furthermore,the characteristics of drought degree in the study area,including the intensity,area and duration of the drought,were analyzed in the southwestern drought(2009-2012),and the drought data was collected by collating agricultural data sets in national statistics.The impact on agriculture was assessed.The main findings and conclusions of this study are as follows:(1)During the same period of rain and heat in Yungui area,precipitation is mainly concentrated in June-August,and it is also the highest temperature.In terms of spatial distribution,the annual average temperature change in Yunnan-Guizhou area is basically increased with the increase of latitude.The average annual temperature is the lowest in northwestern Yunnan due to topography.The average annual precipitation decreases from low latitude to high latitude,northwest Yunnan.The Ministry has the least amount of precipitation due to terrain.Based on the analysis of drought index,Yunnan was generally wet during the period from 1961 to 2012.Guizhou was generally dry,and the western part of Yunnan and the central part of the country were generally wet.However,due to the plateau topography,the northwestern Yunnan was dry,and the eastern part of Yunnan was dry for some reasons.The wet range in central Yunnan may decrease in spring and summer due to insufficient precipitation and elevated temperature.(2)In 1961-2012,the temperature in Yungui area showed an upward trend with an interannual variability of 0.015 °C/a.The rising trend of the whole year and the four seasons was significant(P < 0.1),and the upward trend in autumn and winter was relatively large.The half-year heating rate is higher than the summer half.The precipitation in the study area showed a downward trend,and the annual average and the interannual time series of the four seasons showed a downward trend,and the annual average and the summer and autumn seasons showed a significant downward trend(P < 0.1).The five drought indices showed a downward trend as a whole,that is,the study area showed a tendency to dry out from 1961 to 2012.Due to the consistent trend of multiple indexes,the determination of this change can be considered to be higher.The drying trend of summer,autumn and winter is more obvious than that of spring,and the downward trend in winter is larger than that in summer.Therefore,the overall trend of the Yunnan-Guizhou region is developing.(3)In the trend of dry and wet space,Yunnan and Guizhou showed a trend of increasing temperature and decreasing rainfall.Among them,Yunnan's warming is more obvious than that of Guizhou,and the inter-annual changes of precipitation in the two provinces are more consistent.From the seasonal point of view,the spring precipitation in Yunnan increased significantly,while the precipitation in Guizhou decreased during the same period,resulting in a strong inconsistency in the two provinces during this period.From the spatial morphology of the five drought index changes,the morphology is more consistent.Compared with Yunnan,Guizhou is more obvious,and the most significant area is the junction of the two provinces.(4)The seasonal pattern of NDVI between 1982 and 2012 was consistent with temperature and precipitation.The interannual variation of NDVI in the study area showed a significant upward trend during the 31 years,and the green color was 0.8*10-3/a(P < 0.1).That is to say,NDVI did not decline due to the drought trend,but instead rose.NDVI showed a significant upward trend in the whole year,spring,autumn,May and November.The highest rate of increase in April was 0.0024/a,of which spring contributed the most to the annual trend.By comparing the correlation between NDVI and precipitation,temperature and index,it is found that the vegetation in the study area has the highest sensitivity to temperature and is positively correlated.The correlation between NDVI and temperature is high and significant in the whole year,spring and winter,and the vegetation and precipitation are negative overall.Relevant,and vegetation is not sensitive to the drought index.Temperature is the main factor affecting the variability of vegetation in the area.However,during the extreme drought period,drought has a significant impact on plant growth and food production.During the drought in Southwest China during 2009-2012,Yunnan experienced a significant reduction in grain harvests in the summer of 2010,while Guizhou's summer harvest in 2010 and autumn grain production in 2011 showed significant reductions.