| Global warming has led to increased drought in some parts of the world,especially in arid and semi-arid regions.Most of the Yellow River Basin is an arid and semi-arid region,which is a drought-prone area in China,but also an important food base in China.Ensuring food security and ecological safety in the Yellow River Basin is a key step to achieve a beautiful China.Studying the spatial and temporal evolution characteristics of agricultural drought in the Yellow River Basin and exploring the influence of agricultural drought on soil moisture and groundwater storage are important prerequisites for ecological protection and high-quality development in the Yellow River Basin.The spatial and temporal distribution patterns of agricultural droughts in the Yellow River Basin and the relationship between soil moisture and groundwater storage and agricultural droughts need to be studied in depth.The questions that need to be addressed in this study are:What are the characteristics of the Temperature Vegetation Drought Index(TVDI)in the Yellow River Basin and how does it affect soil water and groundwater?This study calculates TVDI based on the Google Earth Engine(GEE)platform,analyzes the distribution characteristics and trends of TVDI from multiple spatial and temporal perspectives,and explores the influence of meteorological elements on TVDI;reveals the influence of TVDI on soil moisture and groundwater storage.The main conclusions are as follows:(1)The analysis of TVDI accuracy and applicability test shows that the TVDI dataset of the Yellow River Basin,calculated based on the Normalized Vegetation Index(NDVI)and Land Surface Temperature(LST)data from MODIS with the help of GEE platform in this paper,can accurately reflect the agricultural drought characteristics of the Yellow River Basin.(2)The analysis of the temporal and spatial evolution characteristics of TVDI in the Yellow River Basin,it is found that on the monthly spatio-temporal scale,the monthly average monthly TVDI in the Yellow River Basin ranges from normal to severe drought,and the proportion of severe drought is the highest from April to June.From February to April,most areas of the Yellow River Basin show a trend of drought,and other months show a wetting trend.On the seasonal spatio-temporal scale,the agricultural drought is the most serious in spring in the upper and middle reaches of the Yellow River Basin and the most serious in autumn in the lower reaches;the upstream shows a wetting trend in all four seasons,the middle reaches shows a trend of drought in winter,and the lower reaches shows a trend of wetting in autumn;there is a trend of drought in severe drought areas in spring,summer and autumn,and only in normal areas in winter.On the annual spatio-temporal scale,the annual TVDI in most areas of the Yellow River Basin belongs to mild drought,and the drought in the lower reaches is the most serious;most areas show the trend of wetting,the lower reaches show the trend of drought,and the areas of severe drought show the trend of drought.(3)The effects of air temperature and precipitation on TVDI are discussed.The results show that TVDI in the Yellow River Basin is negatively correlated with precipitation and positively correlated with air temperature.Spatially,there is a weak negative correlation between TVDI and precipitation in most areas of the Yellow River Basin,and the lag of TVDI precipitation in most regions is more than 6 months.In most regions,the negative impact of precipitation on TVDI lags more than 6 months,while the positive effect lags 3 months.There is a weak correlation between TVDI and air temperature in most areas of the Yellow River Basin,and the negative effect of air temperature on TVDI in most areas lags more than 6months,while the positive effect appears in that month.(4)The analysis of the spatial and temporal evolution of soil moisture in the Yellow River Basin found that,on the monthly spatial and temporal scales,the multi-year monthly average soil moisture distribution in the Yellow River Basin ranges from 0.05-0.17 m~3/m~3,and the lower reaches>the upper reaches>the average of the whole basin>the middle reaches;the highest percentage of the image elements shows a significant increase in soil moisture from January to May and in November and December.On the seasonal spatial and temporal scales,soil moisture in the lower reaches is highest in spring,summer,autumn and winter,and shows a decreasing trend,while soil moisture in the upper and middle reaches shows an increasing trend;soil moisture in the summer is highest in all regions;the proportion of pixels with a significant increasing trend in soil moisture in spring,summer and winter is the highest.On the annual spatial and temporal scales,soil moisture is highest in the lower reaches and shows a decreasing trend;soil moisture in most regions shows an increasing trend.To explore the influence of TVDI on soil moisture,temporally,monthly TVDI in the Yellow River Basin is negatively correlated with soil moisture.Spatially,soil moisture and TVDI are weakly negatively correlated in most regions;the negative effect of TVDI on soil moisture lags behind 4-6 months in most regions.(5)The analysis of the spatial and temporal evolution of groundwater storage in the Yellow River Basin reveals that,on the monthly spatial and temporal scales,the multi-year monthly average groundwater storage variation in the Yellow River Basin is distributed between-86.51 and 45.07 mm equivalent water height;April-August is negative,with a"funnel"shape and a deficit state,and the most serious deficit in the downstream,while the rest of the months are in a surplus state;the proportion of image elements in a surplus state is the highest in January,and the proportion of image elements in a deficit state is the highest in June;the significant downward trend is the highest proportion of image elements in September,and the significant upward trend is the highest proportion of image elements in May.On the seasonal spatial and temporal scales,the proportion of image elements in surplus is higher in autumn and winter;the proportion of image elements in deficit is higher in spring and summer;the groundwater storage in all four seasons in each region have shown a decreasing trend in the past 19 years,with the greatest decrease in winter in the middle reaches and the greatest decrease in autumn in the upper and lower reaches.On the annual spatial and temporal scales,the amount of groundwater storage change in the Yellow River Basin shows a decreasing trend,and the decreasing trend is most obvious in the downstream.To explore the influence of TVDI on groundwater storage,the correlation between TVDI and groundwater storage changes in each month in the Yellow River Basin was not significant in time series.Spatially,the changes in groundwater storage in most of the Yellow River Basin are not correlated with TVDI,and the changes in groundwater storage in most of the regions lag behind TVDI by more than 6 months. |
PDF Full Text Request