Vegetation Cover Changes In The Three Gorges Reservoir Area And Its Response To Climate Extremes

Vegetation is an integrated link between atmosphere,soil,and water,and extreme temperature events and extreme precipitation events have increased significantly in the context of global warming,leading to certain impacts on vegetation growth,so it is of great significance to study vegetation cover changes and their response to various types of climate extremes.The data selected in this paper are the normalized vegetation index data(NDVI)of the Three Gorges reservoir area from 2000 to 2019,the national vegetation type data in 2019,and the meteorological data of daily maximum temperature,daily minimum temperature,and daily precipitation at 22 meteorological stations within the Three Gorges reservoir area,and the RClim Dex model,trend analysis,Kriging spatial interpolation,Pearson correlation The spatial and temporal variability of NDVI in the Three Gorges reservoir area and its response to various extreme weather indices were analyzed.The following research results were obtained.(1)The multi-year mean value of vegetation cover in the Three Gorges reservoir area was 0.54,increasing at a rate of 0.04/10 a from 2000 to 2019.The NDVI of different vegetation ranged from high to low for broadleaf forest,coniferous forest,scrub,grass,cultivated vegetation,and urban vegetation;and the increase ranged from high to low for cultivated vegetation,grass,scrub,coniferous forest,broadleaf forest,and urban vegetation.The NDVI in the reservoir area has obvious seasonal and monthly variation characteristics,vegetation grows rapidly in March,reaches the highest value in July and then starts to decline,so the vegetation cover is the highest in summer,slightly lower in autumn,and the worst in spring and winter,and the increase of NDVI in each season is spring>autumn>winter>summer;in terms of spatial distribution,the average NDVI value basically shows a decreasing distribution pattern from east to west,and the vegetation cover in most areas of the reservoir area has been increasing in 20 years.In terms of spatial distribution,the mean NDVI values showed a decreasing distribution pattern from east to west,and the vegetation cover in most areas of the reservoir area increased in the past 20 years,and only Chongqing urban area and Yichang in Hubei Province decreased.(2)In the spatial and temporal variations of extreme temperature indices,warm indices such as TX90 p,TN90p,WSDI,and SU,which indicate extreme high temperature,show an increasing trend,while cold indices such as TX10 p,TN10p,CSDI,and FD,which indicate extreme low temperature events,show a decreasing trend,and the spatial variations are basically greater in the eastern part of the reservoir area than in the western part.In the spatial and temporal variations of extreme precipitation indices,RX1 day,RX5day,and PRCPTOT,which indicate extreme precipitation,decrease and change more significantly in the western part of the Three Gorges reservoir area;CWD decreases while CDD and R10 increase,and all three indices indicating extreme precipitation days change more significantly in the eastern part of the reservoir area.(3)In the interannual scale,NDVI was significantly correlated with TX90 p,TN10p,TN90 p,PRCPTOT,and R10(p<0.05);in the seasonal scale,the correlation coefficients of NDVI and extreme weather index were higher and mostly significant in spring and winter(p<0.05),while the correlation coefficients in summer and autumn were lower and did not show significance;in the inter-month scale,the maximum response of NDVI and TN90 p,TX10p,TX90 p,RX1day,and RX5 day was higher with the month.The maximum response of NDVI to TN90 P,TX10p,TX90 p,RX1day,and RX5 day was in the current month,and the response to TN10 p showed a higher correlation with the month,indicating that NDVI in the reservoir area only had a lagged response to TN10 p.(4)Among different vegetation types,broadleaf forests were more influenced by warm indices such as TX90 p,TN90p,WSDI,and SU;cultivated vegetation was more influenced by cold indices such as TX10 p,TN10p,CSDI,and FD;cultivated vegetation and urban vegetation were more influenced by extreme precipitation indices such as RX1 day,RX5day,PRCPTOT,R10,CWD,and CDD.