Study On The Ecohydrological Processes In Changchuan Catchment Based On SWAT Model

Changchuan catchment,a typical area of Farming-pastoral Zone of North China, is located in a soft sand-rock area at the middle reach of Yellow River.This area experienced several ecological problems,such as soil erosion,water deficiency and so on.It is important to explore the coo-hydrological characteristics and provide theoretical foundation for eco-environment restoration.SWAT model is used in this study to simulate eco-hydrological processes.The result showed that SWAT was an useful tool to explore the eco-hydrological characteristics.On the basis of datasets included climate data,spatial data and hydrological data, SWAT was calibrated and validated for period 1986-1989 and 1990-1997 respectively. In order to evaluate the applicability of SWAT about modeling soil water dynamic, transpiration and leaf area index(LAI),the field experiments results about water balance and community characters for main vegetation types in Changchuan catchment during growing season,2006～2007 were used for parameters adjustment and simulation results comparison.With the validated model,we simulated and analyzed the water balance for main vegetation types,the eco-hydrological processes at catchment scale,and the eco-hydrological response to different precipitation years.The result shows that SWAT model,which can simulate the runoff well,is applicable in Changchuan catchment.After adjusting some correlated parameters,it can also simulate soil water content,leaf area index(LAI) and transpiration well. Analyses of water balance components in different HRU(hydrologic response unit) shows that water balance of different landuse and soil combination is influenced by vegetation status and soil characters.Forest and farmland have more evapotranspiration,transpiration,T/E ratio(transpiration/vapotranspiratio) and soil water increase,but less surface runoff and infiltration than shrub-land and grassland. Sandy soil have less surface runoff than lands with other soil types.Long-term ecohydrological process indicates that evapotranspiration is the main process consuming precipitation.Annual average of evapotranspiration is 75.43%of precipitation.Proportion of infiltration is 18.40%,and surface runoff is 5.13%of precipitation.Lateral flow is little,which is only 1.15%of precipitation.Annual soil water change reduces slightly(0.4 mm per year in 600 mm soil profile). Eco-hydrological processes in different hydrological years are different.Soil moisture, evapotranspiration,runoff are bigger in high-flow year,while the ones in normal-flow year and low-flow year are smaller.Comparative analysis shows that evapotranspiration is correlated with not only precipitation but also vegetation status and soil water content.If plants grow well and initial soil water content is abundant, plants can maintain high transpiration by consuming soil water.So evapotranspiration in low-flow years is probably considerable,which caused soil water deficition.