Water Footprint And Benchmark Of Wheat Production In China Under Different Irrigation Techniques

There is no food security without water security around the fact that irrigation is an important guarantee for increasing grain production.Water resource scarcity have led to the variable grain production,which was adjudged to be the cause of the existing food crisis.China,as in most parts of the world,inter-sector competition for water intensifies has severely restricted the water usage for irrigation.The water footprint（WF）is an indicator to consider the impact of human activities on the quantity and quality of water resources comprehensively.The WF can reflect the water consumption and water type,respectively,in each stage of crop growth compared with the current crop production water consumption evaluation indicator（ET）.Moreover,the WF per ton of cereal has broken through the limitations of water efficiency indicators for dry farming and irrigation farming and provides a new perspective for integrated water resources management.The objective of this study is to explicitly address the effect of the popularization of water-saving irrigation techniques on large-scale WF accounting,through the case for wheat in China over 2000～2014.The green and blue WFs of both rain-fed and irrigated wheat are estimated using the Aqua Crop model at a 5?×?5 arc-minute resolution for each year.For irrigated wheat,we distinguish three irrigation technologies（furrow,sprinkler and micro-irrigation）.The WF benchmark levels for each irrigation technology are further estimated for arid and humid zones,respectively.In addition,three typical reference years in the Yellow River Basin are taken as the research object for regional application.Mainly conclusions are as following:（1）Overall,the WF（m3）related to China’s wheat production decreases by 4.4%during the study period,while the share of WF for different irrigation methods changed significantly to the total WF over the years.In particular,there is a 7-fold increase of WF of micro irrigation after a 15 years development,though it accounted for a small proportion at the beginning of the study.（2）The total green-blue WF(m3t^-1)of wheat in China continue to decline.Both productive water consumption T and non-productive water consumption E are kept at a fixed ratio under different irrigation methods,but the total evapotranspiration and the ineffective blue water evaporation are the highest in sprinkler,followed by furrow and micro irrigation.From the national average,the yield decreases by only 2.8%while the blue water consumption is reduced by 4.7%when switching from furrow to micro irrigation.（3）The benchmarks for WF of wheat in China are strongly affected by climate and the spatial differences in yield levels.We conclude that WF benchmarks differ greatly under both the scenarios of different irrigation methods in arid regions and different climate regions with the same irrigation method.Therefore,the benchmarks for WF of wheat must be set by distinguishing the irrigation methods and climate zones.（4）The average annual WF of wheat in the Yellow River Basin was 1216 m3t^-1,of which the blue water footprint accounted for 65%,and the spatial distribution showed a decreasing trend from the upper reaches to the middle and lower reaches.In typical years,the WF(m3t^-1)was the highest in dry years,followed by wet years and normal years.Under different irrigation techniques,the blue WF and green WF（m3）of wheat were dominated by traditional surface irrigation,which were 92%and 50%,respectively.In the upstream region with the largest proportion of water-saving irrigation area,the WF(m3t^-1)of wheat under micro irrigation was the smallest,followed by furrow irrigation and sprinkler irrigation.This study aims to overcome the shortcoming of considering only natural factors and separating from actual production conditions in the water footprint calculation of regional high-spatial resolution crop production,and to provide a scientific basis for improving regional agricultural water use efficiency and field water productivity,alleviating water contradiction and realizing sustainable water management.