Explore The Interactions Between Vegetation And Hydrology Under A Changing Environment In Chinese Typical Basins

One of the core issues in ecohydrology is to study the complex interaction between atmosphere,vegetation and hydrology system,which is not only related to the available water resources but also significate to the environment quality.Recently,the catchment ecological and hydrological processes and available water resources are profoundly influenced by global climate change and intense human activities.Rational utilization of water resources and effective protection of ecosystem under changing environment should be based on the deep understanding of the interaction between ecological and hydrological processes.In this research,typical Chinses basins with different climate and underlying surface conditions are selected as study areas.Based on coupled water-energy balance principle and ecological optimality principle,we aim to explore the interactions between vegetation and hydrology under a changing environment.Firstly,this research explores the relationship between Budyko landscape parameter and vegetation?represented by LAI,leaf area index?in 52 Chinese catchments where the landscape changes are mainly contributed by vegetation changes.The ratios of parameter change to LAI change are found to be significantly related to catchment aridity index?the ratio of potential evapotranspiration to precipitation?,and thus,an empirical equation between them is fitted.Combining with the relationship between Budyko parameter change and mean annual runoff change,we obtain the empirical equation for the vegetation elasticity of runoff,which means relative change in runoff caused by unit change in LAI.Secondly,through the combination of Budyko framework,Porporato's stochastic soil moisture model and Guswa's plant rooting depth model,an analytical expression for Budyko parameter is derived.Based on this analytical expression,we obtain the analytical relationship between Budyko parameter change and LAI change which also shows significant positive correlation with the aridity index.Furthermore,an analytical expression for the vegetation?LAI?elasticity of runoff is derived.From both the empirical and analytical perspective,our results demonstrate how the interaction between ecological and hydrological processes is controlled by climatic conditions.Based on the analytical expressions for the climate?i.e.,precipitation and potential evapotranspiration?and vegetation?i.e.,LAI?elasticity of runoff,we quantify the impacts of precipitation,potential evapotranspiration and LAI changes on the hydrological partitioning during 1982-2010 in China and predict the future hydrological influence of these changes for the 21^st century using climate model projections.Results show that LAI change exhibits an increasing importance on altering hydrological partitioning as climate becomes drier.In semi-arid and arid China,increased LAI has led to substantial runoff reductions over the past three decades,and this negative contribution to runoff change is projected to continue towards the end of this century due to predicted LAI increases.In a typical region,the Loess Plateau,we verify and apply the Eagleson's eco-hydrological model and his ecological optimality principle to explore the equilibrium and change of ecohydrological interaction.Results show that the current vegetation cover has already exceeded the climate-defined equilibrium vegetation cover in many parts of the Loess Plateau,especially in the middle-to-east regions.This indicates a widespread over-planting,which is found to primarily responsible for soil drying in the area.We also find that planting trees would roughly double the reduction of soil wetness in comparison with planting grasses with the same magnitude of coverage.Additionally,both the equilibrium vegetation cover and soil moisture tend to decrease under future climate scenarios?i.e.,2011-2050?due to declined atmospheric water supply and increased atmospheric water demand.This research is potentially useful for quantitative evaluation and prediction of the regional ecohydrological response to vegetation and climate change and provides valuable information to promote a sustainable ecohydrological environment.