Study On Global Crop Water Demand And Water Shortage In Major Agricultural Production Countries

The shortage of water resources worldwide is becoming increasingly serious and has become a global crisis.In recent years,climate change,socio-economic development and population growth have not only affected the supply of water resources,but also greatly affected the demand for water resources.More than 70%of the world’s water was used for agricultural production,and 90%of the water footprint of human consumption comes from agricultural products.Agriculture has become the industry that consumes the most water.About 80%of the world’s rain-fed agricultural areas produced about 60%of the world’s food,while irrigated agricultural areas,which account for 20%of arable land,produced about 40%of the world’s food.The uneven distribution of water resources in time and space,coupled with the high water consumption characteristics of agriculture,and the irrational use of water resources,have brought tremendous pressure on agricultural water supply.At the same time,climate change and changes in the scale of crop planting will inevitably affect the water demand pattern of regional agriculture,and then affect regional water balance.Therefore,a comprehensive understanding of the pattern of crop water demand and the degree of water scarcity in typical river basins under the background of climatic factors and changes in planting scale is of great significance to reveal the contradiction between the supply and demand of agricultural water resources,scientific and reasonable water resource management,agricultural planting scale adjustment and the formulation of regional irrigation schemes.In order to evaluate the impact of climatic factors and planting scale on the water demand of major global crops,the crop coefficient method was used to calculate the water demand intensity of major crops in the world after correction of daily-scale crop coefficients.Then,we quantitatively analyzed the influencing factors of crop water demand in major agricultural countries by combining the characteristics of crop planting scale and climatic factors.Finally,through the analysis of the rainfall deficits in the major basins of the major agricultural producing countries,the characteristics of the spatial and temporal changes of the agricultural water shortages in the major basins were clarified,The the following conclusions were mainly drawn:1.From the characteristics of water demand intensity of major crops in the world,the water demand intensity of wheat was mostly between 350mm-700mm.The water demand intensity of winter wheat was relatively high,generally greater than 450mm,while that of spring wheat was relatively low,generally less than 450mm.The water demand intensity of maize was between 350mm-650mm.Soybean water demand intensity ranged from 350mm to 550mm,but Brazil and Argentina had higher water demand intensity,which was generally more than450mm.2.The spatial and temporal distribution of water demand for crops had changed greatly since 1980.In the main wheat producing countries,the water demand of wheat in China and the United States decreased significantly,the water demand of wheat in the United States decreased by 46%.China’s fluctuations were not significant before 1997,but decreased rapidly after 1997,a total of 23%.India’s wheat region saw a bigger increase in water demand,of about40%.Among the main maize producing countries,except France and the United States,the maize water demand of other countries showed a significant rising trend.China’s maize water demand increased the most with an increase of 91%,followed by Brazil and India with an increase of 40%.Among the major soybean producing countries,except China,the soybean water demand of other countries increased significantly,among which the increase of soybean water demand in India was up to 15.8 times,followed by the increase of 8 times in Argentina and 2.7 times in Brazil,and the decrease of 32%in China.3.Changes in planting scale and climatic factors were the main influencing factors for changes in crop water demand.Among the major wheat-producing countries,the change in planting scale was the dominant factor affecting wheat water demand in various countries.Under the same climatic conditions,the scale of wheat cultivation in the United States decreased by 13.57 million hectares from 1980 to 2017,resulting in a reduction in wheat water requirements of 63.7 billion m~3.Among the main maize producing countries,the change of climatic factors was the main influencing factor of maize water demand in France,while the planting scale was the main influencing factor of maize water demand in other countries.Among them,the maize planting scale in China increased by 22 million hectares from 1980 to2017,Leading to an increase of 81.6 billion m~3 in water demand for maize.Among the main soybean producing countries,all countries except China were greatly affected by the planting scale.The soybean planting scale in Brazil,Argentina,and India had increased by 2516 hectares,1531 hectares,and 9.99 million hectares respectively,resulting in an increase of 115 billion m~3and 795 Billion m~3 and 37.2 billion m~3.4.From the analysis of the changes in the precipitation deficit of crops in four typical basins,it was found that the water shortage of crops in all basins was at a relatively high level and shows an increasing trend.The most serious water shortage was the Indus River Basin.The rainfall deficit of the three crops was between 0.5 and 0.8,which was significantly higher than that of other river basins.The soybean season had the most serious water shortage and the highest rainfall deficit is up to 0.79.The second was the Yellow River Basin,where the average precipitation deficit of all crops was above 0.5;the Haihe River Basin had the highest degree of water shortage in the wheat season,with an average precipitation deficit of up to 0.51.The water shortage in the maize and soybean seasons fluctuates greatly,but the precipitation deficit Relatively low.The overall crop water shortage in the Mississippi River Basin is relatively light,and the precipitation deficit is basically between 0.2-0.5,but the wheat season fluctuates greatly.In the past 40 years,the degree of water shortage of crops in each watershed shown an increasing trend.It can be seen that the contradiction between global agricultural water supply and demand was still intensifying,and water shortage was threatening global food security.Reasonable and appropriate planting scale and species structure adjustment and water-saving agriculture were important measures to achieve sustainable use of global agricultural water resources and guarantee food security.