Analysis of the cumulative impact of vegetation dynamics on water cycle processes in semiarid basin under climate change

The ecological environment of semiarid regions is fragile, and localized vegetation restoration is close to the sustainable development limit of regional water resources, presenting new ecological-water resource conflicts. To study the influence of vegetation dynamics on the water cycle process in semiarid regions affected by climate change, this study constructed a random forest model based on long-term field observation data, used high-resolution remote sensing images as input data, extracted the zoning of vegetation types, and analyzed the pattern of vegetation succession. The results of zoning were then introduced into BTOP (block-wise use of TOPMODEL and the Muskingum-Cunge method) to obtain continuous spatial and temporal hydrological data, and the long-term cumulative effect of vegetation dynamics on key water cycle elements in the watersheds was revealed on the basis of analyzing the changes in the state of the vegetation and the factors affecting it. It was found that the vegetation cover in the Hailar River Basin, which is located in the semiarid zone, showed a fluctuating trend in the last 5 years of the 21st century, and the growth curve began to decline, which may be related to the contradiction between the current status of the basin's water resources and the growth of vegetation; specifically, the existing vegetation cover may have exceeded the critical point of the basin's balanced development in terms of vegetation and hydrology. Under the multiyear average precipitation conditions, the evapotranspiration before and after the change in vegetation in the basin increased by 15.6%, the surface stream-flow decreased by 20.9%, and the base flow decreased by 12.3%. Additionally, the vegetation cover and the type of succession increased the water consumption of the vegetation in the basin to a certain extent and reduced the runoff in the basin. However, the current 21.9% decrease in precipitation and the 20.3% depletion of vegetation are critical. If vegetation continues to expand, water consumption in the watershed will increase without limits, reduce surface runoff and groundwater recharge, weaken soil water storage capacity, and lead to more drought in arid areas. Therefore, as an important means of regional ecological restoration, it is still necessary to carry out a comprehensive assessment of the existing water resources of the watershed and set the upper limit of water demand for vegetation in the vegetation restoration project to restore the ecological health of the watershed under the condition of normal vegetation growth and to ensure the sustainable development of the watershed's water resources.