华北平原小麦、玉米作物生产水足迹的研究

水足迹概念将水问题拓展到了社会经济领域,是当前测度人类活动对水资源系统影响的理想指标。本文借助水足迹的概念,计算了华北平原地区(河北、北京、天津)小麦、玉米的虚拟水含量及其生长生产水足迹,并就绿水的重要性和灰水对环境的不利影响进行了相关分析。结果显示:2007年华北平原主要地区小麦虚拟水含量为1.054m3/㎏,生长用水以蓝水为主;玉米虚拟水含量为0.808m3/㎏,生长用水以绿水为主;小麦生产水足迹为172×108m3,其中绿水足迹30.85×108m3,蓝水足迹102.5×108m3,灰水足迹38.65×108m3;玉米生产水足迹为173.07×108m3,其中绿水足迹101.06×108m3,蓝水足迹26.92×108m3,灰水足迹45.09×108m3。通过分析表明:绿水在当地农作物生产中占有重要的地位,绿水的使用与作物的生长特点及作物生长周期有关;小麦、玉米总水足迹约为当地水资源总量的2.2倍,减少小麦、玉米作物生产水足迹对华北平原具有重要的意义。

A Study on Production Water Footprint of Winter-Wheat and Maize in the North China Plain

Water footprint is an indicator of freshwater use that accounts for not only the direct water consumption of a consumer or producer, but also the indirect water consumption. In general, water footprint can be regarded as a comprehensive indicator of freshwater resources appropriation, close to the traditional and restricted measure of water withdrawal. Based on the concept and calculation methods of water footprint, this paper estimates virtual water and water footprint of the production of major crops (i.e., winter wheat and summer maize) of the North China Plain, Hebei Province, Beijing and Tianjin Municipalities, in year 2007. Furthermore, the study clarifies three types of impacts, i.e., evaporation of infiltrated rainwater for crop growth (green water use), withdrawal of ground- or surface water for irrigation or processing (blue water use), and water pollution during growth. The latter impact was quantified in terms of the dilution volume necessary to abate pollution. Results showed that the total crop production water footprint was roughly 345.07 billion m³ per year, 2.2 times of the total local water resources, from which it is clear that reduction in wheat and maize crop production water footprint seemed to be significant over the North China Plain. Of the total crop production water footprint, wheat accounted for 172 billion m³, and that of maize took up 173.07 billion m³. As for the wheat production water footprint, 30.85 billion m³ was considered green water footprint, 102.5 billion m³ was blue water footprint, and 38.65 billion m³ was grey water footprint. Concerning maize production water footprint, about 101.06 billion m³ was green water footprint, 26.92 billion m³ was blue water footprint, and 45.09 billion m³ was grey water footprint. The major volume of water to sustain wheat plant growth was from blue water, and the major volume of water to sustain maize plant came from green water (rainwater). In general, utilization of blue water can affect the environment more than does the green water use. Furthermore, green water use shows relatively few negative environmental impacts in that there is only a slight difference between the evapotranspiration from the crop field and the evapotranspiration that would take place in presence of natural vegetated cover. Therefore, the green water footprint seems to be of more importance in water resources management and environmental protection. The portion of the water footprint mitigating water requirements deserves attention as well.