| Drought is a frequent natural disaster,which has a long-term impact on agricultural production,ecological environment and economic development.Timely and accurate monitoring of agricultural drought is of great significance for reducing agricultural production losses and ensuring food security.Therefore,this paper uses AMSR-E and AMSR-2 passive microwave radiometer brightness temperature data as the main data source to invert and downscale the soil water content of the Luan River Basin,and build agricultural drought index SSI based on the downscaling soil water content data set.Based on this index,the change regularity and characteristics of agricultural drought in Luanhe River basin were analyzed.The main research contents and conclusions are as follows:(1)Inversion and evaluation of soil water content.Based on AMSR-E and AMSR-2 brightness temperature data,LPRM algorithm was used to invert soil water content.From the perspective of time,the soil water content obtained by the algorithm conforms to the seasonal variation of soil water content in the Luanhe River Basin.From the perspective of spatial pattern,the soil water content in the Luanhe River Basin is generally low in the upper reaches and high in the middle and lower reaches.The inversion results were verified by site data,which shows the correlation coefficient between the inversion soil water content data and the measured soil water content data of each site ranged from 0.487-0.665,the average correlation coefficient was 0.521,the RMSE was 0.015-0.024,and the average RMSE was 0.02.It can be concluded that the correlation between inversion soil moisture content and measured soil moisture content is high and stable.AMSR series soil moisture data can basically accurately reflect the actual soil moisture content of the Luanhe River Basin.According to the correlation between soil water content inversion and measured site soil water content in each season,it can be concluded that the inversion accuracy of soil water content in autumn is the highest.(2)Downscaling and evaluation of soil water content.After downscaling the inversion results,the mean correlation coefficient between soil moisture content and soil moisture content measured at the site was 0.588,and the mean root mean square error was 0.021.Statistical increment was used to express the variation of soil moisture content data set error before and after scaling down the statistical increment of correlation coefficient with measured data after downscaling is 0.08,and the statistical increment of root mean square error is 0.064(m3/m3),indicating that the soil water content data obtained by this method has maintained the accuracy of low-resolution passive microwave soil water content data.At the same time,it can reflect more accurate and rich spatial details.Therefore,this downscaling method can obtain a high spatial resolution soil moisture data set with relatively reliable accuracy in the Luanhe River Basin.(3)Establishment of SSI and evaluation of agricultural drought.Nine commonly used probability distributions are tested,and the optimal distribution function of each grid unit in the Luan River Basin is selected.The standardized soil moisture index(SSI)of each grid unit was calculated based on the downscaling soil moisture content,which could reflect the historical drought situation of the Luanhe River Basin more comprehensively.The spatial and temporal distribution characteristics of agricultural drought in the Luanhe River Basin were analyzed by using this index.The results showed that the spatial distribution of agricultural drought in the Luanhe River Basin had a good consistency,and showed a significant decreasing trend from 2002 to 2019,especially in summer and autumn.The spatial and temporal distribution characteristics of agricultural drought in the Luanhe River Basin from 2002 to 2019 were analyzed by using SSI index.The results showed that the occurrence frequency of drought in different regions of the Basin was not different,mainly light and moderate drought.The frequency of drought is relatively high in the southeast of the basin,and the severe drought is more serious in the southeast of the basin.In addition,the changes of agricultural drought characteristics in the Luanhe River Basin from 2002 to 2019 were basically the same,with a slight decreasing trend on the whole.Spatially,the central and southeastern regions are more prone to long-term and severe agricultural drought events,which have a greater impact on crops in the basin and easily lead to crop reduction. |
PDF Full Text Request