Spatiotemporal Variation Of Vegetation Cover And Its Response To Climatic Factors In Farming-pastoral Ecotone Of Gansu Province

The farming-pastoral ecotone of Gansu Province is located in inland China,with rich and diverse geographical environment and climate types.It is an important area for the study of vegetation type diversity and an ideal area for studying the response of vegetation to climate change.Based on the MODIS/NDVI remote sensing data set and the climate data of 28 meteorological stations,this paper uses Sen trend analysis method,coefficient of variation method,Hurst index,climate tendency rate and MK mutation test to analyze the vegetation coverage index NDVI and 6 types of meteorology.The spatiotemporal change characteristics of the factors,the principal component analysis method and the correlation analysis method are used to analyze the response degree of NDVI to different meteorological factors.The sustainable development of agriculture and animal husbandry in Gansu Province under climate change scenarios provides scientific guidance and theoretical basis for formulating relevant policies and maintaining a good ecological environment.The main results are as follows:(1)The vegetation coverage in the farming-pastoral ecotone of Gansu Province is showing an improvement trend,but the overall variation is small and vegetation restoration is anti-sustainable,with significant differences in spatial distribution.The growth rate of NDVI in the recent 21 a growing season was 0.64%/a,and the growth rate of VCI value was 0.35/10 a.Among them,the vegetation improvement was the best in 2011-2013 and 2017-2019;Distribution characteristics,high vegetation coverage area accounted for the largest area of the entire study area,accounting for42.67%.The regions with NDVI variation trend coefficient greater than 0 accounted for 96.36% of the entire study area,of which 55.42% were extremely significantly increased,mainly distributed in the central part of the study area,and Huan County and Huachi County in the east.The multi-year average value of NDVI variation coefficient is 0.15.The fluctuations in the southern and northwestern parts of the study area are relatively low,and the central region has strong fluctuations.The multi-year average value of the Hurst index in the growing season is 0.43,and vegetation restoration is anti-sustainable.(2)The climate change of vegetation growing season in the farming-pastoral ecotone of Gansu Province has temporal and spatial differences.The study area as a whole is in the process of increasing temperature.The minimum temperature is the most significant.The average temperature gradually rises at a rate of 0.31?/10 a.In1997,a sudden change from cold to warm occurred.The rising trend of the minimum temperature was significantly higher than the highest temperature.The mutation occurred in 1991 and 1998 respectively.The average temperature generally increases from south to north and from west to east.The heating rate in Gannan,Tianzhu,Longzhong and Longdong decreases in sequence;the highest temperature shows a trend of gradually increasing from northwest to southeast,and the trend rate decreases from southwest to northeast,and all regions show a trend of increasing temperature;the minimum temperature shows a spatial distribution pattern of high in the north,low in the south,high in the middle,and low on both sides.The inter-annual variation of precipitation fluctuates strongly,with a slight increase at a rate of 3.42mm/10 a.A sudden change occurred in 2018.The precipitation was less in the north and more in the south,and the trend rate decreased from southeast to northwest.64% of the stations showed an increasing trend.The sunshine hours show a wave-like downward trend at a rate of change of-15.2h/10 a,and the overall distribution increases from south to north.The accumulated temperature of ?10 ?showed a significant upward trend at a rate of 47.93 ?/10 a.The temperature in the central part increased rapidly,and the temperature in the border area increased relatively slowly.Both the sunshine hours and accumulated temperature had abrupt changes in 1997.(3)In the past 21 years,the most important climatic factor affecting NDVI in the growing season of vegetation in the farming-pastoral ecotone of Gansu Province is precipitation,with a determination coefficient of 0.679.The minimum temperature has a weak influence on it,with a determination coefficient of 0.295.Average temperature,highest temperature,sunshine hours,and accumulated temperature ?10 ? have a negative correlation to NDVI.Among them,the maximum temperature and sunshine hours have a strong degree of influence,with coefficients of determination of-0.547 and-0.529 respectively,followed by average temperature,which determines The coefficient is-0.037,and the coefficient of determination for accumulated temperature ?10 ? is-0.019.In most areas,the vegetation coverage is negatively correlated with the average temperature,maximum temperature,sunshine hours,and accumulated temperature ?10 ?,and positively correlated with the minimum temperature and precipitation.The influence of precipitation on NDVI is stronger than The correlation coefficients between sunshine and temperature,NDVI and different meteorological factors have significant spatial differences.The climatic factors in Longzhong,Longdong,Gannan and Tianzhu in the study area that affect the NDVI of the vegetation growth season,the most are precipitation,accumulated temperature ?10 ?,precipitation,and sunshine hours.