Spatial-Temporal Variations Of Water Footprint For Grain Crop In Baojixia Irrigation Area Under Changing Environment

In recent decades,the changing environment(climate change and human activities)has imposed an important impact on both agricultural production and spatial-temporal distribution of water resources.Changing environment and consequent water shortage,water pollution,and food security issues have been the challenge of human development.Irrigation areas are the very foundation of food security and social development,which also play an important role in maintaining regional ecological environment.The water footprint theory provides a series of concepts to reveal the water shortage,water pollution,and food security problems of grain production in irrigation areas.Therefore,it’s very important to study water footprints of grain crops in irrigation area under changing environment.Based on water footprint theory,statistical methods and scenario setting,this paper has analyzed the spatial-temporal variation of water footprints of grain crops in Baojixia irrigation area(BIA)under changing environment.The main contents and conclusions are as follow:(1)Based on water footprint theory,the local meteorological data and agricultural data during 1994—2010,the water footprints of grain crops were calculated.Moreover,two derivative index of water footprint were proposed from the perspective of food security.The water footprint per unit(WF)of wheat,maize and grain supply water footprint(GSWF)were1.04 m3/kg、1.29 m3/kg and 254.79 m3/p,respectively.The regional water footprint(RWF)of wheat,maize and grain were 0.69,0.74 and 1.43 billion m3,respectively.Grain supply capacity was 5.69 million people.The WF of wheat and maize were lower than average of China,which means the water productivity in BIA was better than average level of China.(2)Spatial-temporal variation of water footprint of grain crop was detected by using Mann-Kendall test,Sen’s slop and Arc GIS.Except grey WF and grey RWF of wheat,all the water footprint index of wheat experienced a significant downward trend.The total WF and blue RWF decreased significantly,while grey WF and grey RWF increased.From 1994 to2010,the net irrigation quota(IWQ)went downward and nitrogenous fertilizer(NF)presented a gradual increment trend,which caused the structure(ratio of blue and gray components)change of WF and RWF.The spatial variation is significant,and the total WF,green WF and blue WF of wheat were increased from west to east of BIA.The similar spatial variation was found in total RWF of wheat,maize and grain.(3)Based on the calculation of WF and RWF,the driving factors which represent the changing environmental and leading to the change of WF and RWF were chose.Pearson correlation coefficient and multiple linear regression were employed to finish the qualitative analysis.A framework of attribution analysis of spatial-temporal variation of water footprints was developed based on Logarithmic mean divisia index(LMDI)model,spatial information visualization and sensitive coefficient method.Using the framework,the influences of driving factors on WF and RWF were quantitative determined.The increasing yield was the main cause of reduction of grain crops WF,and the contribution rate was from-31.5%to-41.2%.Another important driving factor was IWQ that contributed 21.6%～-32.9%of changes in grain crops WF.The increment NF caused 16.3%to 19.4%of changes,while irrigation water efficiency had very small contribution.For RWF of the grain crops,the IWQ was the most important factors for wheat and grain RWF,while green water consumption played a vital role in maize RWF.The sown area and planting ratio which leading to decline of grain crops RWF were also important.The spatial information visualization and sensitive coefficient showed that:each subarea had its own characteristic in attribution analysis.Liquan station was prone to climatic disaster which caused reduction of yield and increments of WF and RWF of grain crops.Baoji and Liquan station had problems with high NF use.Most of the driving factors were in high sensitive level,which means they can be effective ways to improve the WF and RWF.(4)Base on hydrological frequency calculation principle of inconsistent series,local hydro-meteorological data,agriculture data and references,the climate scenario and human activity plan were setted for normal year and dry year in 2030.By calculation,in 2030 the grain RWF for normal year and dry year were 1.42 and 1.25 billion m~3,respectively.Through reasonable regulation 0.23 billion m~3grey RWF,and up to 2.5 million blue RWF were saved.The regulation plan would not only mitigate the water shortage and water environment pressure,but also save money for costs of water and fertilaizer.