| As the green barrier of the capital,Shelterbelt of Zhangjiakou has been degraded because of the lack of regional water conservation capacity.Water conservation capacity is an important water conservation function of the ecosystem,which is closely related to vegetation.However,the water conservation capacity of vegetation varies greatly;affected by vegetation,the processes of precipitation interception,water evapotranspiration and soil infiltration are complex and difficult to predict;existing studies mostly focus on the calculation of individual plant evapotranspiration,which is not widely applicable.In order to reasonably solve the contradiction between vegetation growth and environmental water shortage in Zhangjiakou,thesis starts from the evaluation of vegetation evapotranspiration function and soil infiltration function,we established the remote sensing estimation model of Evapotranspiration by Penman Monteith and the soil profile water infiltration model by Hydrus.The potential evapotranspiration of vegetation in each month in Zhangjiakou was estimated,and based on the evapotranspiration of different vegetation,the law of soil infiltration was studied.Finally,according to the above laws,ecological water source protection forests area,Farmland protection forest area,ecological grassland protection area were constructed.The main findings are as follows:(1)The monthly vegetation evapotranspiration of Zhangjiakou in 2019 was calculated by using penman Monteith model.The results showed that vegetation evapotranspiration has obvious temporal and spatial changes in Zhangjiakou.The spatial distribution of vegetation evapotranspiration is higher in the southeast and lower in the northwest,ranging from 0 to 0.32 cm/d.In terms of time changes,the vegetation evapotranspiration in summer and autumn is much larger than that in winter and spring.The monthly average is 0.04?0.13cm/d.(2)In order to reveal the problems and causes of water conservation in Zhangjiakou area,the paper evaluated the evapotranspiration of different land use types.The evapotranspiration rate from large to small is broad-leaved forest,evergreen coniferous forest,shrub forest,deciduous coniferous forest,Economic gardens,arable land,grassland,unused land,among which the average daily evapotranspiration rate of broad-leaved forest is 0.17cm/d,which is much higher than other vegetation types.(3)Excessive vegetation evapotranspiration can easily lead to ecological problems.For this reason,this paper examines the evapotranspiration of forest land based on districts and counties.Among them,the evapotranspiration of forest land in the four counties of Bashang is significantly higher than that of other districts and counties,and is greater than the regional average precipitation rate,and there is a water loss.The analysis of the forest stand structure in the four counties shows that it is mainly due to the excessive proportion of broad-leaved forest in the stand structure.(4)The Hydrus model was used to explore the effects of different factors on soil infiltration.The results showed that the depth of water infiltration increased with time and the range of soil water change increased with depth.The order of soil water conservation performance from strong to weak was brown soil,cinnamon soil and chestnut soil;the order of soil water conservation performance under different vegetation types was grassland,deciduous coniferous forest and broad-leaved forest.The spatial distribution of soil moisture under different conditions was investigated.Provide the basis for vegetation construction under different natural conditions.(5)According to the above rules of vegetation evapotranspiration and soil infiltration,combined with seven ecological function areas,the paper puts forward the suggestions of forest land planning and construction with 300 mm 400 mm precipitation zone and 15 ° 30 ° slope as the limit,and selects different kinds of vegetation according to the natural conditions of each function area. |
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