Temporal And Spatial Variation Of Extreme Climate Indices And Its Impact On NDVI In Southwestern China

This paper used the daily temperature and precipitation sequence data of 477 ground meteorological stations in southwestern China from 1971 to 2013 to calculate 27 extreme climate indices,the temporal and spatial variation characteristics of extreme climate indices in Southwest China were analyzed.Combined with GIMMS NDVI data,the influence of extreme climate indices on NDVI in southwestern China were explored.The results were as follows:(1)Extreme high temperature events in the study area increased from 1971 to 2013,while extreme low temperature events decreased significantly.The jump point of the extreme temperature indices occurred mainly in the 1990s.Warming trends were more obvious in southern Yunnan,southwestern Guangxi,and eastern Sichuan.TX90 in coniferous mixed forest increased significantly,and the rate was 8.93d/10a(p<0.05).TXn,TNn and TNx in grassland were the most significant,and the rates were 0.38?/10a,0.75?/10a and 0.33?/10a(p<0.05).Therefore,the trend of warming in coniferous mixed forest and grassland were even more serious.(2)From 1971 to 2013,drought was severe in southwestern China.R1mm,R10mm,and SDII decreased significantly(p<0.05),CDD increased significantly(p<0.05).The jump point of the extreme precipitation indices mainly occurred in the 1990s to 2000s.The precipitation situation at the junction of Yunnan,Guangxi and Guizhou provinces has deteriorated year by year,and the drought is more serious.The extreme precipitation in eastern Guangxi and southwestern Yunnan increased significantly.Changes of extreme precipitation indices under different vegetation types were different.Rlmm and SDII of shrub,cultivated vegetation and coniferous mixed forest were significantly lower(p<0.05).(3)On the interannual scale,the high temperature frequency indices and the temperature intensity indices were positively correlated with NDVI,while the low temperature frequency indices were negatively correlated with NDVI.The effects of extreme precipitation indices on NDVI were less than that of temperature indices.Only CWD showed a significant negative correlation with NDVI,and the correlation coefficient was-0.498(p<0.05).For different vegetation types,the extreme temperature indices of shrub and coniferous and coniferous mixed forest had a great influence on the growth of vegetation.The extreme precipitation indices had a great influence on the growth of vegetation(4)The seasonal correlation between extreme climate indices and NDVI is roughly the same as the interannual correlation.For different vegetation types,the response of NDVI to the extreme temperature indices was more obvious in shrub,grassland and coniferous mixed forest,and NDVI in evergreen broad-leaved forest had obvious response to the extreme precipitation indices.(5)In the case of a one-quarter lag,the lag correlation between spring NDVI and temperature indices was strong,and the lag correlation between summer,autumn and winter was weak,while the lag correlation between NDVI and precipitation indices in the study area was poor.For different vegetation types,NDVI in evergreen broad-leaved forest,shrub and coniferous mixed forest had obvious response to extreme temperature indices in spring and summer,NDVI in grassland had obvious response to extreme temperature indices in autumn,NDVI in grassland had obvious response to extreme precipitation indices in summer.(6)In typical years,extreme high temperature weather has a positive effect on NDVI,while extreme precipitation weather has a negative inhibitory effect on NDVI,which is consistent with the response characteristics of NDVI to extreme climate on annual and seasonal scales.