Study Of Estimation Of Main Crops Evapotranspiration And Water Footprint In The North China Plain

The North China Plain(NCP) is a vital granary of China, with an area of 140 000km2 of arable land which produces about 20% of the nation’s grain. As local precipitation is not enough to meet crop water requirements in the NCP, irrigation is widely used to increase yields and to gurantee food supply. Agriculture water accounts for about 70% of total water consumption in the NCP, over 75% of which is from groundwater. Groundwater resource has steadily been depleted due to persistent over-pumping, posing tremendous challenges for sustainability. Meanwhile, excessive use of groundwater has resulted in serious environmental problems in the region.Thus, in order to achieve sustainable agricultural water management in the NCP, it is extremely important to explicitly estimate crop evapotranspiration in recent decades.In this paper, a model based on crop coefficient and vegetation remote sensing data was developed to estimate crop evapotranspiration in the NCP. The model not only estimated crop evapotranspiration, but also reflected the spatial distribution of crops and soil moisture in the region. With the model, winter wheat and summer maize evapotranspiration was estimated for 2000-2013 in the the NCP. The results of the model were consistent with those of ETWatch(2000-2009) and autual evapotranspiration(2008-2013) which was measured based on Eddy covariance method at Luancheng station. The results were as follows: 1) Winter wheat evapotranspiration was higher in the southern than in the northern region of the NCP.Winter wheat evapotranspiration was in excess of 400 mm in the piedmont region of Taihang Mountains and in the irrigation region of Henan-Shandong Yellow River.While summer maize evapotranspiration was in excess of 300 mm in these regions.Winter wheat evapotranspiration was less than 350 mm in the middle plains and even less than 200 mm in coastal areas. While summer maize evapotranspiration was more than 250 mm in the north of Hebei Plain and less than 150 mm in coastal areas.2) Irrigation water consumption for winter wheat was higher in the southern than in the northern region of the NCP. Irrigation was in excess of 250 mm in the piedmont region of Taihang Mountains and in the irrigation region ofHenan-Shandong Yellow River while it was less than 100 mm in northern Hebei Plain.Water surplus of summer maize in its growing seasons varied between 100 mm and300 mm. 3) There was a significant declining trend in cultivated area and irrigation water consumption of winter wheat in northern Hebei Plain in recent 14 years.Declining of irrigation water consumption slowed effectively downward trend of regional groundwater level.On the other hand, water footprint of main crops was estimated in the NCP. The results were as follows:1) Blue water footprint of winter wheat during growing seasons was more than its green water footprint, and the proportion of blue water footprint accounted for water footprint varied from 57.4% to 61.3% in different parts of the NCP; 2) Blue water footprint of summer maize during growing seasons was less than its green water footprint, and the proportion of blue water footprint accounted for water footprint varied from 17.8% to 26.1% in different parts of the NCP.At last, sustainable utilization of agricultural water resources was analyzed in the typical regions which were the piedmont region of Taihang Mountains and ground water funnel region. The results showed that total grain yield was 117 million ton and total groundwater net consumption was 26.3km3,groundwater table depth declined9.4m from 2000 to 2010 in the piedmont region of Taihang Mountains. In order to alleviate the shortage of water resources and ensure high yield, suggestions were as follows:(1) it should develop agriculture of water saving irrigation and improve the efficiency of irrigation, thus reducing the blue water footprint;(2) it should adjust planting pattern appropriately and curtail the sowing area of winter wheat so as to reduce consumption of blue water resources. For ground water funnel region, it should consider utilizing surface water resources. Storage potential of surface water resources of Cangzhou was estimated and reached to 570 million m3. 24.6% of blue water footprint for winter wheat can be replaced by storage potential of surface water resources. Otherwise, it should make full use of rainwater, wastewater and brackish water to ensure sustainable utilization of groundwater resources. These measures will play an important role on easing the drawdown and have an important and long-termsignificance for groundwater resource protection.