Evaluation Of Spatial Optimization Of Land And Water Resources In Northern China And Its Ecological Effects

As the country with the largest population in the world,solving the problem of food supply independently is the primary challenge facing China's economic development,social stability and national security.Due to the intensification of global climate change,the contradiction between supply and demand of resources and the growing population,it is not safe to only rely on international markets to feed China.According to the existing research results,the contribution of scientific and technological progress to food production is also approaching its limits.In this context,the proper development of reserve cultivated land resources is a feasible way for China to cope with the food problem at the peak of population.Since the reform and opening up,China's food production conditions and food demand levels have also undergone significant changes.From the production side,the continuous advancement of urbanization has gradually reduced the area of cultivated land,especially high-quality cultivated land.From the demand side,our country has passed through the period of food deprivation and satiation,and is adjusting from plant food consumption to animal food consumption,and gradually transiting to the stage of nutrition and health.However,animal food is more "water consuming" and "land consuming" than plant food,which will undoubtedly increase the pressure on China's food supply and the demand for reserve arable land resources in the future.The basis for ensuring my food safety is to have a reliable area of cultivated land,and the supply of agricultural water is a prerequisite for the function of cultivated land.Although many studies have analyzed the quantity,quality and development sequence of China's reserve cultivated land resources,the ecological impact of reserve cultivated land development has also been discussed.However,the research on existing reserve cultivated land resources is generally carried out in a small study area,while the too small research scope obviously ignores the mechanization and large-scale production requirements.In addition,the current ecological impact assessment of reserve cultivated land development generally remains in a qualitative perspective,unable to form data support for relevant policy formulation;and the existing studies rarely analyze the demand of land and water resources in China under the background of dietary structure changes,nor do they analyze the spatial optimization of land and water from a theoretical level.This paper discusses the complex ties between water resources and land resources by studying the relationship characteristics,optimization theory and technical approaches;quantitative analysis of the temporal and spatial evolution characteristics of land and water resources in China and the carrying capacity of water and land for future food safety;through the establishment of reserve cultivated land resource evaluation model,the quantity and quality of reserve cultivated land resources in northern China were analyzed;and the possible ecological impacts of reserve cultivated land development were quantitatively calculated also.The main conclusions of this paper are as follows:(1)Analysis of the complex relationship between water and land resources based on the relationship characteristicsLand and water are the most important basic resources for world's economic development and ecological security.Although water resources and land resources are closely coupled,there are still essential differences between the two.This difference is mainly reflected in two aspects:the first is that the water resources system has liquidity,while the land resources are fixed.The second is that the water resources system has the ability to renew,but the land resource system does not.Therefore,when water resources in a certain region cannot carry land resources,it is often necessary to increase the amount of regional water resources through other means.Otherwise,it is needed to control the scale of regional land resource space.This paper discusses the complex relationship between water resources and land resources from three aspects:the relationship characteristics,the spatial connotation,and the technical approaches.It is believed that the purpose of spatial optimization of water and land is to achieve the simultaneous development of economic society and environment.And this development needs to rely on the balance between economic society,ecological environment protection,industrial layout,and the natural restoration and major engineering measures.To achieve the balance of these four aspects,we must not only"download resources demand" and "load resources capacity",but also adjust the regional industrial structure according to local conditions.(2)Analysis of future food security capabilities based on current status of land andwater useBy comparing the water and land development situation of various cities in China in 2005,2010 and 2015,it can be seen that the situation of "water shortage in the north"has intensified in recent years.North China,Hexi corridor and the west side of Tarim basin are the three concentration areas of water resources development.In 2015,the water resources utilization rates in North China,Hexi Corridor and the Western Tarim Basin were 185%,313%and 128%respectively.The Northeast Plain,the North China Plain,the Guanzhong Plain,the Sichuan Basin,and the coastal areas of Guangdong are the regions with the highest level of land resource utilization in China.The first four regions are China's main grain producing areas,and the land use types are mainly cultivated land;while the land types in Guangdong coastal areas are mainly construction land.From the matching pattern of water and land,the areas where water and land are very well matched and concentrated are the Northeast Plain,Jianghan Plain,the central Sichuan Basin and the southern Yunnan-Guizhou Plateau;The most unmatched areas of water and land are distributed in Inner Mongolia,Hexi Corridor,Western Xinjiang,Yangtze River Estuary,Pearl River Estuary and Linzhi City.The first three region of water and land mismatches are caused by a serious shortage of water resources,however,the latter three caused by a serious shortage of land.Based on the prediction of the future diet structure and population size,under the current climatic conditions and production capacity,the area of cultivated land needed to meet China's food safety in 2020 and 2032 is 139-149 million hectares and 146-157 million hectares,respectively.This number has exceeded the area of actually cultivated land in China in 2017(13.492 million hectares);the range of irrigation water required to meet food safety in 2020 and 2032 is 1870-2004 billion m3 and 1970-210.8 billion m3,respectively.(3)Analysis of the quantity and quality of reserve cultivated land resources in northern China based on an evaluation modelBased on the characters of topography,heat,precipitation and soil,this paper constructs an evaluation model of reserve cultivated land resources in the north China,and uses entropy weight method and fuzzy mathematics theory to evaluate the development potential of reserve cultivated land in study area.The calculation results show that the total reserve cultivated land area in northern China is 2.01 million km2,of which the high-quality area is 279,000 km2,accounting for only 14%of the total cultivated land area of the entire study area.Xinjiang,Inner Mongolia and Gansu are the provinces with the largest reserve of cultivated land in the northern region,accounting for 61.35%,21.50%and 10.18%of the study area,respectively.The quantity and quality of reserve arable land in northern China does not match spatially.The quality of reserve arable land in the eastern region is generally high,but the area is small.The quality of reserve arable land in the western region is generally low,but the area is large.In general,the western part of Gansu,the western part of Inner Mongolia,and the border area of Inner Mongolia and Shaanxi are the concentrated areas of high-quality reserve cultivated land resources in northern China.Although have relatively good farming conditions,these areas are also having many problems,such as water shortages,poor soil condition and large winds and sands.Therefore,these reserves arable land must be cultivated after large-scale water and soil improvement.(4)Assessment of eco-environmental effects of reserve arable land developmentDue to the uncertain development scale and development method of reserve farmland resources in the north,the ecological model based on this context cannot be tested for reliability.Considering that the Loess Plateau began to implement a large-scale ecological restoration project at the end of 1999,the impact of this project on the ecological environment of the Loess Plateau is likely to be a rehearsal of reserve cultivated land development in the northwest region.Therefore,this paper analyzes the changes of regional land surface processes by afforestation in the Loess Plateau.The results show that the large-scale vegetation restoration will cause the surface albedo gradually to decrease in the vegetation growing season.The returning farmland to forest process may reduce the surface albedo,with an average reduction of-0.013.Conversely,the process of returning farmland to grassland may Increase the surface albedo of the area.Vegetation recovery also brings about changes in land surface temperature.Based on the research in the Jing River Basin,the land surface temperature in the summer decreased by 4.3 ? from 2000 to 2013,while the land surface temperature at night increased by 1.4 ?,of which the contribution of vegetation restoration was 58%and 60%,respectively.In this study,the contribution of vegetation restoration on the evapotranspiration in the Loess Plateau was calculated by partial prediction of the Choudhury-Yang formula.The results show that precipitation is the dominant factor in the progress of evapotranspiration change during the whole study period,with an average contribution rate of 85.6%;however,the contribution rate of vegetation change on evapotranspiration in the Loess Plateau is only 12.1%.In addition,large-scale irrigation in the northern region may lead to increased precipitation,which may futher lead to changes in potential vegetation pattern in the region.According to the classification index of northern vegetation and meteorological factors established in this study by Bydyko system,and the influence of farmland irrigation on precipitation in the previous literature,this study suggests that the potential vegetation in the western Gansu,western Inner Mongolia,and Inner Mongolia-Shaanxi border areas may be more advanced.