Resilience Assessment Of Natural Vegetation To Drought Events

The Huaihe River Basin is located in the climate transition zone between the south and north of China,with complex topographic features and volatile climate.The special natural geographic environment has led to frequent drought disasters in the region and a long duration,which has a serious impact on the growth and development of vegetation in the region.Based on the monthly precipitation data and the Normalized Difference Vegetative Index(NDVI)provided by the China Meteorological Data Network,this paper selects typical years to analyze the drought intensity of drought events in the entire Huai River Basin.According to the analysis of land use data,the typical natural vegetation types of the Huaihe River Basin are obtained.And combined with remote sensing data and site precipitation data to calculate the recovery ability and adaptability of typical natural vegetation under drought conditions.The main conclusions obtained in this paper are as follows:(1)Based on the Standardized Precipitation Index(SPI),the characteristics of the temporal and spatial evolution of drought events in the Huaihe River Basin from 1980 to 2019 as well as the characteristics of drought frequency,drought station ratio,and drought intensity distribution were evaluated.It was found that the Huaihe River Basin as a whole showed a trend of humidification during the study period.Both the annual average SPI and the SPI of each season showed an increasing trend.The trend rate of the average annual SPI was 0.027/10 a.Most areas to the north.The basin is dominated by moderate droughts.The occurrence of moderate droughts and above is mainly concentrated in the upper and middle reaches of the Huaihe River Basin.The coverage of moderate droughts covers almost the entire region,and the high-prone areas of drought are mainly concentrated in the western and eastern Huxi area.Lake East District.The drought intensity showed a slow upward trend,while the drought coverage showed a significant decreasing trend.(2)During the growing season,based on the correlation between NDVI and SPI,NDVI is used as an index to assess the adaptability and restoration of natural vegetation in the watershed.By analyzing the average annual NDVI of the four types of natural vegetation,namely grass,shrub,coniferous forest and broad-leaved forest from 2005 to 2007 in the Huaihe River Basin,it is calculated that the four natural vegetation’s adaptability to drought are ranked as follows: shrub >broad-leaved forests>coniferous forests>grass;the order of restorative size during the dry season is: grasses>broad-leaved forests>coniferous forests>shrubs.(3)Based on the ARx model,which can be used as an indicator to quantify the recovery and adaptability of short-term vegetation in the drought period on a global scale,this paper also uses the ARx model to predict the adaptability and recovery of natural vegetation in the watershed.It is found that under moderate drought conditions,the restoration of natural vegetation is as follows:shrub> broad-leaved forest> coniferous forest> grass;vegetation adaptability is: grass> shrub>broad-leaved forest> coniferous forest;sensitivity to temperature The order of strength is grass>coniferous forest> broad-leaved forest> shrub.(4)By comparing the conclusions drawn by the NDVI and ARx prediction models,it can be seen that the ranking results obtained by the two are quite different.Compared with the NDVI evaluation indicators,the ARx model takes more factors such as vegetation evapotranspiration and temperature into account during the dry period of vegetation.The impact on it,that is,the ARx prediction model is considered more comprehensively,so this article takes the ARx prediction model as the conclusion.In this paper,two methods are used to evaluate the adaptability and restoration of vegetation in the drought period,and the two methods are compared to obtain an evaluation method that is more suitable for analyzing the natural vegetation in the Huai River Basin.At the same time,this article will get the ranking of the adaptability and restoration of the four typical natural vegetations in the Huaihe River Basin under drought stress.The ability to adapt and recover provides a scientific basis.