Response And Scaling On Eco-hydrologhy To Land Use/forest Vegetation Change In Typical Watersheds Of Loess Plateau

Loess Plateau with heavily soil erosion is limited in water resources and sensitive to hydrological environment, especially, this fragile ecological environment has a deep affect on the harmonious development of social economy, natural resources and eco-environment. At Present, many of massive ecological constructions aimed at soil and water conservation have been executed. Research on typical watershed eco-hydrological process and its synergistic changes based on land cover/ land change (LUCC) has an important theoretical significance of land use planning and management and environmental constructions in Loess Plateau.This thesis was carried out in multi-scale coupling watersheds in Loess Plateau. Based on the methods of GIS&RS technical, landscape ecology, systemic hydrological observation, and the information data of land use, soil classification, hydrology and meteorology, this thesis analyzed the land use/ forest vegetation change and its driving force system, the different heterogeneities of precipitation distribution, and deeply studied the mechanism of reducing runoff and sediment yield on land use/ forest vegetation change, response of land use change to hydrological dynamics in typical watershed in multi-scale coupling watersheds. Besides, runoff and sediment discharge of typical sub-watersheds were simulated by WEPP model; the coupling relationship between runoff and sediment discharge and topographic form was established based on the watersheds' topographic fractal information dimension; according to self-similarity theory, scale transfer model was made, which based on the relationship between sediment delivery ratio (SDR) and watershed area, considering the different heterogeneities of distribution of precipitation; combining the data of topographic fractal information dimension, land use pattern, precipitation distribution, the spatial and temporal heterogeneities coupling hydrological model was established; the transformation method based on different spatial and temporal scale of runoff and sediment discharge was discussed. The main conclusions of this thesis were listed as following:Single rainfall event and rainfall intensity distribution were uneven in study watershed. The probability of becoming rainstorm center is under 25%, whether in middle or outlet, any point in watershed. The correlation domain of single rainfall event is 7 kilometers. Therefore, the spatial different heterogeneities of precipitation is exist in study watersheds.Based on the spatial and temporal changes of land resources amount, land use degree and the transition of land use types, this thesis deeply analyzed the dynamic of land use/ forest vegetation pattern of testing watersheds. According to the indexes of landscape pattern, the landscape pattern dynamic process was studied.The reducing tendency of yearly runoff and sediment yield had scale rules after increasing vegetation cover and improved land use pattern in watershed. With yearly precipitation variation, the rules of runoff reducing ratio with different area have three types, which are linear type, single-peaked concave para-curve type, and keeping an relative state value; that of sediment reducing ratio just have one single type, which is single-peaked concave para-curve. The lowest point value and its corresponding rainfall amount were different with different watershed areas. Sediment modulus could reduce each 20%, as long as vegetation cover increases each 5%.The relationship between different types of rainstorm event and flood runoff and sediment discharge was analyzed. Besides, many researches were deeply studied including of scale laws of rainfall, flood peak and sediment discharge process under different types of rainstorm, covariance rule of flood peak and sediment yield under different scale and the relationship of time lag between flood peak and sediment peak.The applicability and popularized usage tips of WEPP model in Loess Plateau were discussed embedded from the aspects of the accuracy of simulated weather data, calibration and validation of the simulation of runoff and sediment yield, and the mechanism of slope-rill erosion equation. Many typical sub-catchments were delineated and simulated hydrological process based on WEPP model. The simulation results showed that runoff amount from slope took up to 98% of outlet amount; sediment deposit amount in slopeland was under 3% of sediment yield from slope erosion; sediment deposit amount in channel was up to 74% of sediment delivery amount; the source of outlet sediment discharge was from slope soil loss.Topographic fractal information dimension and sediment erosion coupling model was established based on the simulated data of 25 typical sub-catchments. According to self-similarity theory, the fractal feature of SDR was analyzed and scale transfer model was established on the basis of SDR. This model applicability area was under 500 km~2. Combining the features of precipitation, land use/ forest vegetation pattern and landform, different scales of coupling hydrological model was set up. The condition of scale transfer was discussed either.