蓝水和绿水视角下划定“中国农业用水红线”探索

水是制约中国粮食生产的最重要因素。实现中国粮食安全和口粮安全的战略目标必然要求粮食的持续增产,而粮食增产对水资源需求的增长又是刚性的、不可减少的。在多部门用水需求加大的情况下,如何保证农业用水量是亟待解决的科学和决策问题。文章首先回顾了国内外水资源管理领域的最新进展,总结了以蓝水(耕地灌溉)和绿水(耕地降水)理念为核心的农业水管理分析范式的转变。在基于蓝水和绿水视角下的广义农业可用水资源的概念和计算基础上,分析了1998—2012年中国农业(种植业中四大主要粮食作物)用水、耗水和水分生产力,并基于此提出了农业用水红线。根据研究时段内15年的中国粮食水分生产力的变化趋势,推导出2020年生产5.5×108 t粮食所需要的农业用水红线的蓝水分量的高、中、低值。并根据近15年来广义农业可用水资源量中的绿水分量,推导出农业用水红线中绿水分量的高、中、低值。结果显示,到2020年,中国保证粮食安全的灌溉水需求总体平均在3 800×108 m3左右,而农业用水红线中绿水分量平均在4 500×108 m3左右。本研究最后提出了划定和实施农业用水红线的相关政策建议:从保护农业用水红线的角度,严格保护和实施18亿亩耕地红线;建立、健全完整、完善的蓝水和绿水测量和监督体系;加强以耕地土壤水为中心的农业用水和耗水管理;利用各地水热资源特点,调整种植结构;继续提高灌溉的保证程度;加强耕地基础设施建设,提高高标准农田和旱涝保收耕地面积和比例。本研究对回答农业部提出的治理农村环境污染一控两减三基本的基本方针中的一控中的控水的底线(即农业用水红线)是什么?具有重要的理论和实践参考价值。

Defining the Baselines for China Agricultural Water Use in Green and Blue Water Approach

Water is the prime limiting factor in grain production in China. Agricultural water withdrawal has been under ever growing pressures in the context of population growth, economic development, urbanization process, diet change, and ecosystem preservation. However, to realize the national strategic goal of food security requires more grains to be produced, and consequently, does demand more water to be consumed. Hence, how to resolve the competing claims for water by various sectors while retaining adequate water for grain production will be the major challenge presenting to both researchers and decision makers. The paper firstly reviewed the state-of-the-arts ideas, concepts, and mindsets that had been emerged and developed in global water communities in the last 20 years, from which a paradigm shift in which green water and blue water lie at the center was identified and presented. Then, based on the “Broadly-defined Available Water for Agriculture (BAWA)” incorporating both green (i.e. cropland irrigation) and blue water (i.e. cropland precipitation) components, agricultural water use, consumption, and productivity were analyzed over a 15-year period from 1998 to 2012. Next the “Baselines for Agricultural Water Use” was proposed and proactively defined, in which blue water component was derived by projecting historical crop water productivity onto 2020. The green water component was likewise determined by using projection of last 15-year BAWA. The results showed that the redlines for blue water withdrawal in terms of assuring 550 million tons of grains to the year 2020 was 380 km³, while the green water component of the redlines was 450 km³. The paper proposed a set of policies in implementing the redlines, including conserving arable land and improving arable land infrastructure, building a sound-developed system for measuring and monitoring blue and green water, developing a water-adapted farming system, improving crop water productivity, and adopting basin- and region-scale water saving practices. The conclusion of the paper will also have implications for recent policy directives issued by China Ministry of Agriculture to combat agriculture-derived pollution in rural areas, “one control, two abatements, and three basic requirements”, of which one control means the definition of baseline agricultural water withdrawals and water use efficiency.