| The contradictions between water resources supply and demand have being shown a significant day-by-day rise in Yellow River Basin, resulting of climate change and human socio-economic activities. A series of national policies were carried out, for water distribution in the entire basin, so that Hetao Irrigation District, as a key area, was limited to sell water rights. The local agricultural water resources security is facing serious challenges. However, as a new concept, the definition of water resources security is being perfected, and its measurement methods are also being explored.Based on the above background, first of all, the concept of agricultural water resources security was defined, and the connotation and extension of this concept were ascertained; Second, the background of climate changes was analyzed in Hetao Irrigation District of Yellow River basin; Third, the applicability was tested, which the WOFOST model was applied to crop simulating in Hetao Irrigation District; Fourth, based on the framework of the definition of agricultural water resources security, and taking into account the main challenges of water resources safe use, in Hetao Irrigation District, the model of relative security degree of agricultural water resources was found; Fifth, the model of relative security degree of agricultural water resources, as a tool, the security situation of agricultural water resources was evaluated in Hetao Irrigation District, in the future(2015).The objectives of this study are two ones, one is the model of relative security degree of agricultural water resources was found, under the framework of the definition of agricultural water resources security; another is that as a water resources security measurement method, the model was applied to evaluate the future of the regional agricultural water resources supply and demand situation, and the degree of agricultural water resources security of the future in relation to the present. In detail, the evaluation was based on, that climate has being change, agricultural water was limited, water conservation projects have implemented, expected agricultural production in a fairly long period of time can not be reduced.The main conclusions in this study are as follows:(1) Agricultural water resources security is the provision of water resources that ensures protection of agriculture against threat, hazards, destruction, and loss. The connotation of the definition has natural attributes, socioeconomic attributes, and cultural attributes. The extension of agricultural water resources security include both broad and narrow ones, as well as,food security, agroenvironmental security, agroecnomiv security, rural society security, etc.(2) In Hetao Irrigation District, temperature continued to rise; sunshine duration decreased or increased which there was spatial differences; average wind speed decreased in most sites; average vapor pressure increased as a nonlinear; there was no a significant trend in precipitation data.(3) WOFOST model is reliable and the crop parameters are reasonable. The outputs of model, by appropriately corrected as a linear model, can be applied to simulating biomass of maize in Linhe, at the potential level or the water limited level. (4) In Hetao Irrigation District, resulting of the increase in irrigated area, and the decrease in water volume, the gross ration was shown a significantly downward trend. The contradictions between water resources supply and demand have aggravated. There is a great potential of saving water, resulting of low use efficiency of channel water.(5) There is a downward trend in crop water requirement in a certain threshold, resulting of climate change.(6) There is a significant quantitative relationship between the simulated the weight of storage organ and the theoretical yield.(7) Agricultural production can be predicted, based on the simulated theoretical yield, and the function of time model of the social productive forces coefficient.(8) The model of relative security degree of agricultural water resources can interpret the main attributes of agricultural water resources security.(9) Based on climate change scenarios in the future, the target of planning for agriculture water use, and expected yield increase in an "S-curve", 2000 as the reference year, in 2015 the relative security degree of agricultural water resources will depend on the specific ratios of water use in irrigation channel systems in Hetao Irrigation District.
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