基于分类效率识别的水资源承载能力三层次评价方法

Improved three-level water resources carrying capacity method based on classification of water use efficiency

针对现有的水资源承载能力三层次评价方法以万元GDP产业用水量表达综合用水效率对农业用水影响考虑不足的问题,提出以二、三产业单位增加值综合用水量分析可承载经济规模,改进计算流程,推导直接计算可承载人口数量的公式,避免原有试算过程,更准确地反映产业结构变化对用水效率的影响,适应“四水四定”(以水定城、以水定地、以水定人、以水定产)新要求,提高评价结果的合理性。以宁夏为例开展应用分析,按照农业用水保持现状不变,在全面小康水平下改进方法计算的可承载人口数量为903.7万人,相对现有方法可多承载140.2万人,在基本现代化水平下可承载人口数量降低至681.5万人,相对现有方法少承载90万人。结合宁夏实际情况设定不同情景,分析农业用水量、人均GDP、产业用水效率三者变化对结果的影响。按“四水四定”目标大幅压减水稻面积使农业用水量降低22%后,可承载人口提高118%,表明农业用水管控目标对承载能力影响显著。改进方法揭示农业用水量、非农用水效率、发展水平和承载能力的量化关系和作用机制,可为提高区域水资源承载能力决策提供依据。

Current three-level water resources carrying capacity analysis method is not accurate enough to calculate the comprehensive water use efficiency,which is greatly affected by agriculture due to its high-proportion of water use and low water use efficiency.It is difficult to truly reflect the water use efficiency changes of other high-efficiency industries.Under such mode of analysis,It is highly possible that water for agriculture is occupied by other industries,which is not in line with the principle of"water dominates land"and relevant policies for food safety.Therefore,in order to guarantee agricultural water demand and more accurately describe the water use efficiency changes in light of the characteristics of regional industries,agricultural water demand is analyzed separately,thus the bearable economic scale is figured out by water consumption per unit added value of secondary and tertiary industries and the available water resources with deduction of agricultural water demand.Further derivation of the calculation formula simplifies the calculation process,eliminates the need for checking and iterative calculation,and improves the accuracy of results.Through the formula and adjustment of parameters,the influence of regional industrial characteristics on carrying capacity can be reflected more accurately.In the case study of Ningxia Hui Autonomous Region,which has a high proportion of agricultural water consumption,the water use efficiency and industrial proportion were confirmed for calculation of water carrying capacity by two carrying levels of comprehensive well-off society and basic modernization.The population and economic scale that regional water resources can support in different carrying levels were calculated by the original method and improved method respectively.The results showed that the bearable population decreased by the improved method,while basically remained unchanged by the original method.The reason was that the agricultural water demand did not change in the calculation of the improved method,while the original method reduced the agricultural water consumption with the improvement of comprehensive efficiency,transferred it to other industries with higher added value,and improved the carrying economic scale and population.However,it brought about the problem of whether the agricultural water could be effectively guaranteed.The results showed that the agricultural water use efficiency changed with the overall economic levels and lacked of mechanism of decision-making conditions in the original three-level analysis method.The improved method could take the impact of the change of agricultural water use into account,adapt to the analysis and calculation under the rigid constraints of water resources and the principle of"water dominates development".It proved that the impact of agricultural water on bearing capacity was more accurate and the result was more reasonable,through the comparison of different boundary of agricultural water demand.The formula for directly solving the regional bearable population was deduced to avoid the iteration calculation.Effect of the major factors on water carrying capacity of this method was figured out by adjusting the three variables of agricultural water consumption,GDP per capita and industrial water efficiency.When the agricultural water withholding was gradually reduced,the carrying population and GDP showed a straight increasing trend.When GDP per capita increased gradually,the regional carrying population decreased,while the carrying GDP increased.When the comprehensive water efficiency of the secondary and tertiary industries was gradually improved,the regional carrying population and GDP showed an exponential upward trend.The analysis shows that in order to achieve the planned population target and living standard,it is necessary to reduce agricultural water consumption and improve the water efficiency of secondary and tertiary industries under the condition of rapid growth of per capita GDP.If agricultural water consumption and water efficiency of secondary and tertiary industries are limited,economic development speed should be limited.