Effects Of Large-scale Vegetation Restoration On Evaporative Water Consumption And Eco-hydrological Process Over The Loess Plateau,China

Drought,water scarcity and soil erosion together constrain the agricultural production and ecological construction of the Loess Plateau,and vegetation plays an important role in reducing soil erosion.In order to improve the vegetation coverage of the Loess Plateau,the state has been implementing the Grain for Green project since1999,and the vegetation coverage is significantly improved.However,large-scale vegetation restoration is bound to cause changes in regional water balance,which may further exacerbate the water scarcity dynamic.How to ensure the sustainable and healthy development of the Grain for Green project has become an urgent issue to be solved.Current research on the relationship between vegetation restoration and water resources balance in the Loess Plateau mainly focused on the point scale,which is difficult to elucidate the regional water balance change over the entire Loess Plateau.Therefore,quantitative analysis based on accurate simulation of evapotranspiration?ET?on the regional scale is needed to clarify the change of evaporative water consumption caused by vegetation changes,and to further provide a scientific basis for the balance between the Grain for Green project and water resources in the Loess Plateau.In view of the above,this study constructed a calculation method of regional-scale ET through combining the PT-JPL model with remote sensing and considering the vegetation change.Based on these,the change of ET and water balance of the Loess Plateau after large-scale vegetation restoration were analyzed,particularly for the change of ET in different vegetation types.The impact of the Grain for Green project on the regional evaporative water consumption of the Loess Plateau was summarized and the main results are as follows:1.Simulation of regional ET in the Loess Plateau based on the PT-JPL modelThis study combines the PT-JPL model and remote sensing to achieve scale conversion with parameters optimized and vegetation dynamics employed.The results show that the simulation performance of the optimized PT-JPL model is greatly improved compared to that of the original model among the 12 land use types.The simulation results of the optimized PT-JPL were found reliable after evaluation of in-situ data,GLEAM ET and the method of water balance.Under three future scenarios,simulation results of PT-JPL model forced by CMIP6 data show that the increase in ET is similar to the increase in precipitation,which can provide a reference for the future research of environment-ecology-water relationship.2.Effect of revegetation on regional evaporative water consumption in the Loess PlateauVegetation restoration caused an increase in transpiration?Et?and interception evaporation?Ei?in the Loess Plateau.Large-scale vegetation restoration increased the evaporative water consumption by approximately 31×10⁸ m³/year?4.90 mm/year?,and the annual ET(386.13 mm,2.44×10¹¹ m³)is 11.2%higher than that without revegetation(342.76 mm,2.17×10¹¹ m³)during 2001-2015.The regional averaged ET of different vegetation types in the Loess Plateau are in descending order:forest>farmland>shrub>grassland.The contribution of revegetation to the increase of ET reached 59.67%from 2001 to 2015,indicating vegetation restoration is the main reason for the increase of ET in the Loess Plateau.3.Eco-hydrological effects of large-scale vegetation restoration in the Loess PlateauThe increase of ET caused by revegetation leads to a decrease in?S?changes in terrestrial water storage?and runoff,and changes is seen in the eco-hydrological process.In areas where the vegetation changes drastically,the value of?S/P is larger,and thus ignoring?S will have a greater impact on the analysis of eco-hydrological process.Taking the Budyko framework as an example,ignoring?S will cause a large bias in the runoff simulation results.The large-scale vegetation restoration has affected various hydrological elements,as well as the analysis of eco-hydrological process.In conclusion,this study simulated the regional ET on the Loess Plateau using the PT-JPL model.Based on this,the impacts of revegetation on regional evaporative water consumption and the eco-hydrological process were analyzed.The above research provided theoretical support for the simulation of regional scale ET,the analysis of the effects of revegetation on eco-hydrological process,and also the management of regional water resources in the Loess Plateau.