Spatial Variance Analysis Of Water Footprint Of Grain Crop In Northwestern Semi-arid And Arid Area In China

Northwest Arid Areas are important basis for grain production in China, but this area is short of water resource and its water use efficiency during grain production is lower than other parts of China. Therefore, it‘s significant to evaluate the water use condition of grain production correctly to make sure that the agricultural water use efficiency can be improved and agricultural water can be used sustainably. As an indicator of water use efficiency, water footprint can evaluate both green and blue water‘s use efficiency. Meanwhile, water footprint includes water consumption both at field scale and city scale, achieving the unification of evaluating water use efficiency for irrigated farming and rainfed farming with one indicator. Based on grain production data, agricultural irrigation data of 56 cities in Northwest Arid Areas 2010, according to the principle of ?water distribution among crops on their demand‘, this research calculated the water footprint and its component for wheat, maize, other grain crops and integrated grain crops, respectively. Then using spatial autocorrelation analysis, we analyzed the spatial distribution of crop water footprint and its component; last, we analyzed the influence of the chosen meteorological factors and agricultural inputs having on crop water footprint. The main conclusions were as following:(1) There was difference for crop water footprint among crops as well as among cities: water footprint of maize and its spatial difference were relative small, while water footprint of other grain crops and its spatial difference were large; in general, water footprint of grain crops became larger from south to north and from east to west.The water footprint of wheat, maize, other grain crops and integrated grain crops were 0.919 m3/kg、0.589m3/kg、1.374m3/kg and 0.841m3/kg, respectively. And the percentage of blue water footprint for those crops were 64.4%、48.6%、44.2% and 53.1%, respectively. Water footprint and the percentage of blue water footprint for maize were both small, but the difference of the above two indicators between maize and the other two kinds of grain crops was not so obvious in the area(like Xinjiang) where there was little rainfall and a lot of irrigation was needed to make sure maize grow well. Generally, the water footprint of other was large and wheat depended on blue water most heavily.The variance of water footprint for wheat, maize, other grain crops and integrated grain crops were 0.262、0.070、0.971 and 0.199, respectively, showing that the spatial difference of water footprint of maize was smallest while the spatial difference of water footprint of other grain crops was largest. Besides, the variance of blue water footprint for the above crops were 0.233、0.141、1.224 and 0.217, respectively. Except wheat, the variance of blue water footprint was smaller than that of water footprint for the other three crops, which showed that the spatial difference of water footprint was smaller than that of blue water footprint. The spatial distribution of water footprint, blue water footprint and the percentage of blue water footprint for crops were all contrast to the spatial distribution of their green water footprint. Water footprint, blue water footprint and its percentage became larger both from south to north and from east to west, meaning that for areas including Xinjiang, Hetao Irrigation District and Hexi Corridor Irrigation District, water footprint and percentage of blue water footprint were higher generally; while in areas including Guanzhong Plain, Longnan, Eastern of Neimeng and Eastern of Qinghai, those two indicators were relatively low.Water footprint of integrated grain crops for each province in ascending order were as following: 0.644m3/kg(Shaanxi)、0.765m3/kg(Neimenggu)、0.802m3/kg(Gansu)、0.932m3/kg(Qinghai)、0.998m3/kg(Xinjiang) and 1.015m3/kg(Ningxia). Meanwhile the percentage of blue water footprint for those provinces were 25.7%、47.8%、34.9%、43.2%、82.1% and 59.9%, respectively。In addition to that, the water footprint of each grain crop was largest in Agriculture-Forest Area, while in industry-mining area and dry farming area where irrigation rate was lower, the water footprint of integrated grain crops was relative small.(2) The global correlation of water footprint for grain crops was weak. In contrast to that, the global correlation both for blue water footprint and its percentage were strong. For local correlation, water footprint and its component of crops mainly showed HH and LL and the local correlation for percentage of blue water footprint was strongest.The global correlation of water footprint for wheat, maize and integrated grain crops were weak, however the global correlation of blue water footprint and its percentage for those crops were obvious. The global correlation of water footprint and its component for other grain crops was strong.The LISA map of water footprints for each crop showed that the local correlation of water footprint were mainly as HH and LL, especially for blue water footprint and its percentage, the local correlation was very likely with each other. The distribution of areas with local correlation of water footprint, blue water footprint and its percentage showed as HH or LL were mainly contrast to those of green water footprint. Xinjiang, Hetao Irrigation District and Hexi Corridor were the mainly HH areas for blue water footprint and its percentage and Shaanxi, Longnan, Qinghai and Eastern of Neimenggu were their mainly LL areas.(3) Generally, the blue water footprints in field scale calculated by the method of ―crop water requirement‖ based on Cropwat were larger than that calculated based on the amount of real irrigation water. Especially for the areas where irrigation could not be met and dry farming was the mainly style, the gap of water footprint calculated by those two methods was much larger.(4) Measures and suggestions for decreasing water footpirntsSince local meteorological factors had influence on crop water footprints and there were difference for water footprints among crops, it was significant to adjust grain crops structure to improve crop water use efficiency. Second taking precise irrigation and deficit irrigation to control the amount of irrigation water so that improving grain yield and achieving the largest marginal benefit of irrigation water could be got at the same time. Both the utilization coefficient of irrigation water and the utilization of fertilizer for unit land could restrain the increasing of crop water footprint, therefore lining the channel and increasing the utilization of fertilizer at unit land could be used to control the crop water footprint.