Research On Water Conservation Function In Zhangjiakou Area Based On InVEST Seasonal Water Yield Model

The ecosystem produces a series of important products and services related to human well-being.It is generally believed that ecosystem service functions include two aspects.On the one hand,the ecosystem provides multiple materials for production and living for human beings.On the other hand,it also creates and maintains the earth and forms the necessary environmental conditions for the survival of the organism,which shows the indirect value that human beings can benefit from,and has profound implications in the aspects of climate regulation,soil and water conservation,organic matter synthesis and survival,and environmental purification,which are closely related to human survival.Among them,water conservation is one of the most important functions provided by the ecosystem.It is an important prerequisite for water resources conservation and ecological security to fully understand the water conservation capacity of the region,and it is of great significance to understand the regional water environment condition and develop reasonable district management by researching on water conservation function.Based on the In VEST seasonal water yield model,this study set 2012-2016 as the research period to obtain the simulation value of Zhangjiakou water source conservation by using meteorological,topographic,soil,land use and other process influence factors,and analyzed its temporal and spatial variation characteristics.Moreover,according to the requirements of zoning,established a comprehensive evaluation system based on 3 indices,named water supply capacity,flood reduction function and water demand.The results of the regional importance evaluation and zoning were obtained,and the results of the water conservation type area in the study area were obtained by comprehensive analysis with the support of the results of the conservation function zoning and functional importance zoning.The main conclusions of the study are as follows:(1)The results show that the total water conservation capacity is 2.81×109 m3,equaling to average water conservation capacity of 75.99 mm in 2016.The two highest average water conservation amount per year are Zhuolu and Chicheng County with 120.67 mm,115.32 mm,and the two highest total one are Chicheng and Zhuolu County with 6.14×108 m3,3.37×108 m3.Among all land types,cultivated land and grassland has the highest contribution to water conservation,which are 29.67% and 48.23%,accounting for 77.9% of the total.Grassland is the main land use types that undertake the water conservation function in Zhangjiakou city.(2)The order of water conservation capacity of different land use types is: grassland> forest land > cultivated land>construction land >unused land.Among them,the grassland shows the best water conservation function,and can conserve nearly 30% of the precipitation.The unused culvert capacity is the weakest,and 98.55% of the precipitation falling on the type of land use will be erode.Due to the strong transpiration of plants,the woodland shows low conservation function and only about 15% of the precipitation being conservered in the area.It means that increasing the area of forest land may have a negative impact on water conservation functions.When improving the environmental quality and the water conservation level of the certain region through vegetation configuration,it is necessary to comprehensively consider the characteristics of the plants to be selected.Special tree species with low water requirement,small leaf area and weak transpiration intensity should be selected,and existing tree species with large water consumption and strong transpiration during partial growth period should be removed moderately.(3)Precipitation has a positive effect on water conservation function,where evapotranspiration performe inhibitory effect.Compared with the relative influence of precipitation and evapotranspiration on water conservation,precipitation plays a leading role.The change of regional water conservation is mainly controlled by precipitation.At the same time,the change of precipitation makes the water conservation function of various land use change significantly.Under normal circumstances,The conservation capacity of different types of land use will increase with precipitation increasing.However,this correlation is not absolute,and small changes in precipitation have little effect on certain special land uses.(4)There is a significant spatial difference in the importance of water conservation functions in the study area.The overall trend is increasing from north to south,and gradually shifts from general importance to high-level importance functional areas.Among them,the importance level of Zhangjiakou urban area is extremely high,which is consistent with the characteristics of dense population,urban development and high demand for water resources.The extremely important functional areas have the dual characteristics of weak water supply capacity,poor resistance to erosion,and high demand for water conservation functions.Relative to its water conservation function,the water demand of the important important functional areas is low,and the situation is more complicated in the more important and important stages.Regional water demand varies greatly from north to south.The population in the south is concentrated and agricultural development.The overall demand for water resources is large.The northern part of the country is sparsely populated,agricultural production is infrequent,and water resources are low.At the same time,the significant difference in water demand has a significant impact on the layout of the importance of regional water conservation functions.(5)From the analysis of administrative unit scale,the distribution of regional water conservation type areas is spatially continuous.The high water source conservation functional area-the extremely important area is concentrated in the urban area of Zhangjiakou.Compared with the spatial distribution result of the Bashang plateau and the Baxia mountain and basin,although the Hebei Bashang plateau area is of strong importance,Its current water conservation function is generally insufficient.(6)The relative error value of the total simulated water production for four years is 1.71%,indicating that the parameters are better and the simulation results are credible.Comparing to the In VEST water yield model method,the seasonal water yield model can calculate the results that are more realistic in the quantitative assessment of water conservation functions.The output includes monthly runoffand annual fast flow and local recharge,as well as base flow.It can help to fully understand the processes of runoff generation and water conservating,and the results are also more interpretable.