Developing Of A Calculation System For Regional Vegetation Carrying Capacity Of Water Resources And Its Application In Jinghe Upstream

There are severe ecological environment problems coexisting in the loess plateau of China,such as drought, water shortage, lack of vegetation and soil erosion. On the one hand, it isnecessary to recovery forest vegetation as soon as possible to alleviate soil and water erosion;On the other hand, the water yield can not excessively decreased due to vegetationreforestation. It is a challenge how to recovery and manage the forest vegetation and safeguardregional water production function at the same time in the loess plateau. Restore the forestbased on the vegetation carrying capacity of regional water resources is the key road to solvethis problem. In this thesis, the concept of the regional vegetation carrying capacity of waterresources was defined and the indicators wrer given. A calculation system for vegetationcarrying capacity of regional water resources was developed. Then it was employed to estimatethe vegetation carrying capacity of regional water resources of Jinghe upstream. We aimed atproviding technical support and scientific guidance for rational allocation of water resourcesand water-forest management in dry areas. The main results are as follows:1. Impact of forest vegetation restoration on runoffThe afforestation would result in the decrease of annual runoff and dry season runoff inthe upper reaches of Jinghe River. The maximum annual runoff reduction was10.75mm andthe maximum dry season runoff reduction was4.27mm after10%grassland of the whole areawas convered to forestland in the rocky mountain areas, meanwhile the maximum annualrunoff reduction was4.94mm and the maximum dry season runoff reduction was1.34mm.theincreasing of leaf area index would cause more annual runoff and dry season runoff reduction.But when the leaf area index exceeded2.5, the annual runoff and dry season runoff wouldreach its minimum and decreased no more.2. The concept of vegetation carrying capacity of regional water resources Based on the previous studys on water resources carrying capacity, land carrying capacity,vegetation carrying capacity of soil water, the concept of regional vegetation carrying capacityof water resources was defined as “The maximum vegetation load supported by land resourcesunder the requirements of a specific water yield for the aim of maintaining the harmoniousdevelopment of economy, society, environmental”. In this paper, the indexes of regionalvegetation carrying capacity of water resources consisted of cover ratio of different vegetationfor the region, the proportion of different vegetation for every site and the vegetation leaf areaindex.3. Developing of a calculation system for regional vegetation carrying capacity of waterresourcesUsing C#language and Access database, a calculation system was developed based on thedistributed hydrological model—Soil and Water Intergrated Model (SWIM). As visual system,it could achieve the function such as data management, hydrology simulation, statisticalanalysis of runoff and the calculation of capacity and so on. The system can count, display andstore the basic information of different vegetation restoration scenarios (different vegetationcover ratio). The SWIM model was called to simulate the hydrological process of differentvegetation restorationscenarios. Some daily scale, monthly scale, seasonal scale and yearlyscale runoff index was counted according to the different precipitation years (dry years, normalyears, wet years). The system can also help users to analyze and compare the effects ofdifferent vegetation restoration on runoff by using the graphical display way. Based on thissystem, the user can prefer vegetation restoration plan meeting different water yield demandaccording to the actual demand of basin (region).4. The vegetation carrying capacity of water resources for upper reaches of JingheWhen the water yield (annual runoff) for the upper reaches of Jinghe should be kept largerthan37.8mm (90%of current annual runoff), the grassland on the sites with slope gradient of0~15°and at the bottom of valleys in the loess area could be afforested. Forest cover ratioshould be kept less than27.23%of the basin. If the water yield (annual runoff) for the upper reaches of Jinghe should be kept larger than33.88mm (80%of current annual runoff), thegrassland on the sites with slope gradient of0~25°and at the bottom of valleys in the loss areasand at the bottom of valleys in the mountain areas could be afforested. Forest cover ratioshould be less than34.01%of the basin. when the water yield for the upper reaches of Jingheshould be kept larger than29.65mm (70%of current annual runoff). The foresr cover ratio inthe upper reaches of Jinghe can be further increased to38.8%. The sites with elevation<2300and shady slope could be further afforested. If the water yield for the upper reaches of Jingheshould be kept larger than21.8mm (50%of current annual runoff), all the suitable sites forforest in the upper reaches of Jinghe River could be restored to forest vegetation. The forestcover ratio would reach43.31%of the basin.