Simulation Of Crop Soil Water Availability And Drought Assessment In The Northen Songnen Plain

Drought is the most important meteorological disaster in China's agriculture.It is of great significance to accurately evaluate the temporal and spatial distribution and severity of crop drought for the improvement of crop growth and grain yield.At present,domestic and foreign scholars have put forward a variety of drought indexes for the evaluation of agricultural drought,which can be divided into two categories: drought index based on meteorological data and drought index based on remote sensing monitoring data.However,the current agricultural drought index is still limited to the station precipitation,vegetation index,or single soil moisture data.In view of this,this study systematically analyzed the threshold range of soil water availability under different crop types,different growth periods,different soil texture,precipitation,and climate conditions in the northern Songnen Plain which was the main grain-producing area of China and one of three black soil regions of the world.On this basis,combined with the surface and different depth of soil moisture data,the agricultural drought index which was called the Crop Loss and Surplus Water(CLSW)was put forward,the severity of crop drought in the study area was quantitatively analyzed in the spatial and temporal distribution,and the quantitative evaluation model of regional crop drought was established.The main research contents and conclusions are as follows:(1)Study on scaling method of surface soil moisture data.Based on the Random Forest(RF)regression algorithm and MODIS optical remote sensing data,the SMAP microwave remote sensing data were converted to scale.The scale conversion process and method for microwave remote sensing surface soil moisture data were constructed,and the surface soil moisture data with high spatial and temporal resolution were obtained.The results show that this method can not only obtained high spatial-temporal resolution surface soil moisture data but also improved the accuracy of surface soil moisture data.(2)Research on crop classification method based on multi feature parameter set.Based on the traditional time series vegetation index and the parameter set of crop phenological characteristics,a new parameter set of crop classification characteristics was constructed by adding time series surface soil moisture data.Based on Random Forest(RF)classification algorithm,the traditional and new feature parameter sets were used as input parameters of the model,the crop planting areas were extracted.The results show that the new set of characteristic parameters of crop classification can improve the classification accuracy of crops,especially,the precision of rice planting area extraction was improved.(3)Retrieval method of deep soil moisture based on data assimilation.According to the land surface data assimilation framework,a data assimilation system based on Ensemble Kalman filter(En KF)and community land model(CLM)was constructed.The surface soil moisture data and soil moisture data at different depths were assimilated to obtaining the soil moisture data of 0 ? 200 cm.The results show that assimilating highprecision surface soil moisture data and actual site data can further improve the accuracy of soil moisture data at different depths.(4)Research on crop drought assessment method based on soil water movement.Based on Hydrus-1D model,the root absorption rate and soil water movement of maize and soybean in the whole growth cycle were simulated,and the soil water availability thresholds of maize and soybean in different growth stages were obtained.Combined with the soil moisture data of 0 ? 200 cm depth,a new agricultural drought index which is called the Crop Loss and Surplus Water(CLSW),was proposed,and the spatial and temporal distribution and drought degree of maize and soybean in the study area were analyzed.The results show that the Crop Loss and Surplus Water(CLSW)has good correlation and high precision,which can meet the needs of regional crop drought assessment.In conclusion,based on the model and method of data scale conversion of surface soil moisture,crop planting area extraction,soil moisture assimilation and soil moisture migration in different depth,the paper has made a study on the basis of the model and method,The agricultural drought index combined with crop growth cycle,soil texture,precipitation and other climatic conditions which was called “the Crop Loss and Surplus Water(CLSW)” was put forward.Based on the above content,this paper constructs the drought assessment model of regional crop growth stage.This paper has a certain guiding role for regional crop growth and agricultural water use,and ensures food production and food security.At the same time,it also promotes the interdisciplinary application of geography research theory and method with hydrology and meteorology.