| Hetao Irrigation area is the largest large-scale plain water diversion irrigation area in China,the irrigation area is located in the arid and semi-arid area,the precipitation is seriously insufficient,the water resources are scarce,and the agricultural planting depends on irrigation area irrigation.Monitoring of irrigation water use in irrigated areas is essential.Accurate,timely,efficient and economical access to farmland irrigation information can not only improve the efficiency of agricultural water use,but also provide decision-making for agricultural water managers and improve the refined management level of modern agricultural water use.Based on the limitations of traditional methods for large-scale monitoring of irrigated areas.Remote sensing monitoring has the advantages of convenience,real-time and economy.In this paper,remote sensing was used to monitor and obtain the crop planting structure in the irrigated area,identify the irrigated area of farmland,and estimate the evapotranspiration of farmland.(1)Sentinel-2 and Landsat-8 data were used as data sources.The spatial distribution and farmland area of farmland were obtained by random forest algorithm,and then the difference of NDVI time series curve of crop normalized vegetation index was used to establish a decision tree classification model to obtain the planting structure of major crops in 2020 and 2021,including 778,150 hectares in 2020 and 791,120 hectares in 2021,and 301,000 hectares and 286,010 hectares in 2020 and 2021,respectively.The area planted with sunflower was 282,610 hectares and 296,370 hectares respectively;The area under wheat cultivation was 35,530 hectares and 44,500 hectares,respectively.After accuracy verification,the verification result is ideal and the accuracy is high.(2)Using Landsat-8 and Sentinel-2 images as data sources,the irrigation area of farmland was identified,and the improved normalized water extraction index MNDWI was used to obtain the irrigation area of spring and summer irrigation and autumn irrigation,and then the total annual irrigation area was obtained by ensembling the irrigation area of spring and summer irrigation and autumn irrigation.Among them,the irrigation area in spring and summer and autumn in 2020 was 525,270 hectares and396,230 hectares respectively,with a total annual irrigation area of 766,480 hectares,and in the spring and summer of 2021,524,360 hectares and 403,670 hectares were irrigated,with a total annual irrigation area of 777,110 hectares.(3)Using Landsat-8 as the data source,the SEBAL model was used to estimate the evapotranspiration in the irrigation area.The ET0 of the five weather stations in the study area was calculated by Penman-Monteith formula to verify the accuracy of the evapotranspiration estimated by the SEBAL model,and the R2 was greater than 0.7,which was ideal.The average evapotranspiration of farmland in the irrigation area in2020 and 2021 was 400.58 mm and 415.00 mm,respectively,and the evapotranspiration of farmland in Hetao irrigation area in 2020 was 3.1471 billion m ~3,and the evapotranspiration of farmland in 2021 was 3,323.9 million m~3.The evapotranspiration during the growth period of the main crops corn,sunflower and wheat planted in the Hetao irrigation area was estimated.Among them,the evapotranspiration in the growth period of maize was 743.5 million m~3 and 873.1 million m~3,the evapotranspiration in the growth period of sunflower was 706.2 million m~3 and 664.5 million m~3,respectively,and the evapotranspiration in the growth period of wheat was 071.6 million m ~3 and070.1 million m~3,respectively.(4)The evapotranspiration and irrigated area of the irrigated area increased year-on-year,from 3,147.1 million m~3 in 2020 to 3,323.9 million m~3 in 2021,while the irrigated area increased from 766,480 hm2 in 2020 to 77.711 hm2 in 2021.During the two years,the evapotranspiration and irrigation area remained basically unchanged,and the evapotranspiration increased with the increase of the irrigated area. |
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