Study On The Change Mechanism Of Water Balance Component And Water-Related Ecosystem Services Under Typical Vegetation Species In The Gully Region Of The Loess Plateau

The Loess Plateau in northwest China is well-known for its serious soil erosion and fragile ecology.In the context of global climate change and the implementation of large-scale ecological measures,it is necessary to reveal the changing mechanisms of water balance components and water-related ecosystems services,which will provide a theoretical basis for the regulation of eco-hydrological processes and vegetation adaptation management.In this study,typical forestlands(Robinia pseudoacacia,Platycladus orientalis,and Pinus tabulaeformis),grasslands(Imperata cylindrical Medicago sativa),and farmland(Lonicera japonica)in the gully area of the Loess Plateau were selected as the research subjects.Based on which,methods such as historical data analysis,field observation,and scenario simulation are combined to analyze the climate characteristics of the study area and predict its future changes;At the same time,the effect mechanism of vegetation species on water balance components were elucidated,the contribution rates of their influencing factors were analyzed,and simulation models for each element were established.On this basis,a multi factor comprehensive simulation model was constructed to evaluate the impact of climate change and vegetation conversion on various water balance components and water-related ecological services.The main research conclusions of the paper are as follows:(1)During the historical period,the annual precipitation ranged between 338.3 to 828.2 mm,and the annual average temperature ranged between 7.2 to 11.4℃.For annual precipitation,there was no significant trend,while for the annual average temperature,there was a significant upward trend with a sudden change point(1997).Under the SSP126,245,and 585 scenarios,the changes of annual precipitation showed no significant increase or decrease trend.Compared with precipitation,there is a significant increasing trend for the maximum and minimum temperatures.(2)With the increase of rainfall,the interception in forestlands would increase,while the interception rate would decrease,and all their relationships could be described as power functions(p<0.01).The average interception rates of R.pseudoacacia,P.orientalis,and P.tabulaeformis plots were 47.4%,54.3%,and 49.1%,respectively,while the stable interception rates are 16.0%,23.0%,and 20.0%,respectively.Precipitation is the most important factor affecting interception and throughfall,and it could explain 67.2%to 96.0%of the interception changes.After parameter calibration,the Wang model can effectively simulate canopy interception in all forestlands.(3)In all experimental plots,the soil evaporation generally showed strong variations in the early growth season,but a stable trend in the later stages.Except for the P.tabulaeformis plot,the leaf area index has the greatest impact on soil evaporation,with a contribution rate exceeding 30.0%in all plots.In most plots,soil moisture content would have a significant impact on soil evaporation(p<0.05).Of meteorological factors,temperature has the highest contribution rate to soil evaporation.After parameter calibration,the Shuttleworth-Wallace model can effectively simulate soil evaporation in all plots.(4)After multi-objective parameter optimization,the SWAP model can effectively simulate the changes in water balance component in all plots.The simulations under pre-set scenarios showed that future climates only had limited influence on interception.In addition,its influences on soil evaporation were similar under different vegetation species.When subjected to the future climate,responses of transpiration in forestlands could be ranked as R.pseudoacacia>P.tabulaeformis>P.orientalis,while in grasslands and farmland,it could be characterized as the M.sativa being the largest,while I.cylindrica being similar to L.japonica.Under future conditions,the soil water storage capacity in all plots will decrease,and such decreases in forestlands are greater than that in grasslands and farmland.The conversion from R.pseudoacacia to M.sativa or L.japonica would increase soil water storage by 1.4～21.6 mm and 22.7～61.7 mm,respectively.Precipitation is the main controlling factor affecting the transpiration and evaporation in all plot,and their relationships could all be expressed with linear functions(p<0.01).In forestlands,there is no precipitation conversion threshold for the transpiration-evaporation dominance;While in the grasslands and farmland,the thresholds were 172.0,136.0 and 347.6 mm,respectively.(5)The ratio of total green water to precipitation in forestlands and grasslands all exceeds 100.0%under all scenarios,while in farmland,the ratio is 91.5%～95.0%.In the R.pseudoacacia plot,the ratio of productive green water to precipitation is greater than that of non-productive green water.In other sample plots,the situation is the opposite.The conversion from R.pseudoacacia to M.sativa(or L.japonica)could reduce the total water consumption to a certain extent;However,it would also increase the ratio of non-productive green water.If the R.pseudoacacia was replaced by the M.sativa,the increase in the ratio of non-productive green water is mainly caused by the increase of interception;If the R.pseudoacacia was replaced by the L.japonica,it is mainly caused by the increase of soil evaporation.