| Quantitative analysis of the change rule of water requirement of agricultural net irrigation in irrigated area,and clear the main environmental factors that affected the change of water demand of agricultural net irrigation was of great significance for ensuring the safety of agricultural and food and improving the carrying capacity of regional water resources.According to the characteristics of crop distribution in the People's Victory Canal,the shape,spatial and topological characteristics of crops,a rule set was established to extract crop related information.Based on the meteorological data,soil data and the extracted crop data,the agricultural net irrigation water demand model based on the soil water dynamic stochastic simulation was built,and the net irrigation water requirement of the research area in recent ten years was calculated.On this basis,using the spatial analysis from the past agricultural net irrigation variation of crop planting area,the water space,the sensitivity index analysis of precipitation,potential evapotranspiration and crop planting area of influence agricultural net irrigation water requirement,effectively reveal the change trend of agricultural irrigation water net area,to provide technical support for the irrigation area structural adjustment and management of water resources.The main results were as follows.(1)The spatial distribution information of main crops of winter wheat,summer corn and rice in the People's Victory Canal was extracted with the object-oriented classification method and the algorithm of multi scale segmentation and fuzzy rule classification.The results showed that the vegetation normalized area index(NDVI)in the irrigation area was much larger than that in the non vegetation area under the condition of 50 segmentation.Under the condition of the segmentation scale of 10,with 2015 as an example,NDVI greater than 0.71 was winter wheat,the normalized water index(NDWI)was greater than 0.52 was rice,and the gray level co-occurrence matrix(GLCM)was less than 12.8 for summer corn.There was a difference in the range of the selected index in different years.According to the method accuracy evaluation of the comparison sample category in eCognition,the accuracy of the classification results was high,which meet the needs of the research.(2)In this study,a model of net irrigation water demand based on stochastic model of soil water dynamics was improved.Based on the dynamic stochastic model of soil water,on the basis of calculating the water requirement of net irrigation at point scale,considering the difference of soil texture and crop planting area and the requirement of precision,the regional soil parameters and crop parameters were perfected,and the calculation model of regional net irrigation water demand was built.The results showed that the net irrigation water demand in 2007 and 2011 was relatively high,and the net irrigation water demand in Fengqiu,Huaxian,Huojia and Yuanyang County was relatively high in the same year and rainy season.(3)A sensitivity analysis method was used to analyze the crop and meteorological factors that caused the spatial and temporal variations of net irrigation demand in the study area.Statistical results showed that the daily average precipitation,mean temperature and precipitation frequency fluctuated more significantly in the dry season,and the daily average precipitation and precipitation frequency fluctuated more significantly in the rainy season.The degree of sensitivity change showed that the rainfall frequency caused a greater change in net irrigation water demand in the study area,and the net irrigation water demand decreased by about percent 4.17 in the range of percent 5 of the precipitation frequency.The precipitation frequency was a strong sensitive parameter,followed by daily average precipitation,while wind speed,sunshine hours,summer corn and rice planting area are weak sensitive parameters. |
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