Actual Evapotranspiration Of Crops During Growth Period Based On Typical River Basins

With the rapid development of society,food security has attracted more and more attention.The extensive agricultural irrigation and unrestrained exploitation of groundwater resources make the regional agricultural economy unable to develop sustainably,and even cause a series of ecological problems.It is particularly urgent to rationally allocate the regional limited water resources.The Chhannur Valley in Inner Mongolia is a typical semi-arid area with low annual rainfall and much higher evaporation than rainfall.In recent years,due to the continuous expansion of cultivated land area,the increase of water-consuming crops and the continuous increase of groundwater exploitation in the basin,the groundwater level has continuously decreased,the original surface runoff into the lake has been cut off,and the lake area has shrunk substantially,resulting in frequent ecological problems.Therefore,the analysis of crop water consumption during the growth period in this basin can provide reference for agricultural water management and agricultural sustainable development in this region.In this study,the Chhannur Watershed in Inner Mongolia was designated as the study area.Firstly,the planting structure data of four major crops including sugar beet,potato,corn and wheat were obtained by using object-oriented crop recognition method based on multi-temporal Sentinel-2 image data.SEBS model was used to invert daily evapotranspiration based on the observation data of ground weather stations and landsat-8 images during the growth period of four major crops.Combined with the crop coefficient curve indorsed by the Food and Agriculture Organization of the United Nations(FAO),the crop growth state parameter curve was made,and the actual evapotranspiration of the four main crops in the growth period was interpolated by the single crop coefficient method.The key conclusions of the study are as follows:(1)Through multiple segmentation experiments,ESP segmentation scale evaluation tool was used to select the best segmentation scale parameters,and finally determine the shape parameter weight 0.6,compactness parameter weight 0.9,and segmentation scale parameter 178 suitable for the extraction of major crops in the basin.Using random forest crops on the basis of the object-oriented method in the basin four main sugar beet,potatoes,corn and wheat crops planting structure of the data,the overall accuracy of89.94%,the Kappa coefficient is 0.86,the sugar beet user accuracy and producer accuracy of more than 90%,corn,wheat,and potato classification accuracy is more close to.(2)Based on remote sensing data and SEBS model,daily Evapotranspiration at spatial scale can be accurately retrieved,with the average errors of the early and middle growth stages being 12.00% and 6.84%,respectively.From May to July,daily Evapotranspiration increased gradually,and reached the peak in July.Daily Evapotranspiration decreased gradually from August to October,and decreased significantly in September and October.Based on the Pearson correlation analysis between daily evapotranspiration and groundwater depth of shangdu,Xiaohaizi,Shibaiqing and Deshancun of four national basic hydrological monitoring stations in the basin,five meteorological factors including average atmospheric pressure,average temperature,average relative humidity,sunshine duration and average wind speed were analyzed.There was a strong positive correlation between average temperature and daily evapotranspiration(R > 0.8),while SIG values of the other four factors were all greater than 0.05,showing a weak correlation with daily evapotranspiration.There was a significant positive correlation between groundwater depth and daily evapotranspiration at four monitoring stations from May to October(P < 0.05),and the Pearson correlation coefficient was 0.79.(3)The ET of sugar beet,potato,maize and wheat in growth period increased from north to south in spatial distribution.ET varied from 479.53 to 791.46 mm,407.85 to675.32 mm,346.51 to 681.46 mm and 314.52 to 603.97 mm,respectively.There were obvious differences in ET among different crops at different growth stages: beet > potato >corn > wheat.The average annual growth period ET of sugar beet,potato,corn and wheat were 594.28 mm,549.35 mm,503.67 mm and 467.19 mm,respectively.Due to different irrigation systems,the ET of the same crop has different spatial characteristics.Specifically,the ET of irrigated potato is higher than that of dry potato.ET in growth period of common maize was higher than that of silage maize.Affected by the uneven rainfall in the north and south of the basin,ET of the four main crops showed an obvious decreasing trend from south to north.The ET of wheat near the northern lake was higher than that of other surrounding areas due to higher soil moisture content.Figure[36] Table[12] Reference[79]...