Catchment Water System Modeling And Its Application Under Changing Environment

In the context of climate change mainly considered as global warming, global land surface water cycle and subsequently the spatial and temperal patterns of water resources is likely to be alterated, which is close to the land surface biogeochemical, physical processes etc. in the earth system. Meanwhile, as the development of local economy, the natural water cycle is also affected by the related human activities. Now the real water cycle is not just the natural processes of rainfall-runoff-evapotranspiration-surface water-underground water exchanges. The hydrological processes are connected with biogeochemical processes and human activities, which is an integrated system, namely as Water System, the basic unit is the Catchment Water System (CWS).Considering the problems in the previous studies on the CWS, a typical CWS model is developed based on the modification of the Distributed Time Variant Gain Model (DTVGM) and coupling with a biogeochemical model and human activities processes. Then, the coupling characteristics of water and carbon cycle in Water System are studied in two different types of ecosystems at landscape scale. The CWS model DTVGM is also used to quantify the effects of climate change and human activites and the responses of water cycle to changing environments. The major achievements are as follows:(1) A time variant CWS model coupled with multi-processes is developed.Based on the previous version of DTVGM, the one source evapotranspiration model is modified with two sources (vegetation and soil) evapotranspiration model. The original DTVGM is also improved with new modules including one-dimension soil water heat transfer model, canopy transfer model, energy balance model etc. Furthermore, the photosynthesis, stomatal conductance, carbon/nitrogen cycle and vegetation growth are also considered in the new version. Human activities including the dynamic of land use and cover change (LUCC) and harvest are also included in the new model. The model can be run from hourly to daily time steps.(2) The applicable of the CWS model in simulating land surface hydrology and carbon/nitrogen cycle at landscape scale is validated.The new DTVGM is used to simulate water and energy fluxes, carbon/nitrogen cycle at two different ecosystems in Ameriflux:Duke PP forest ecosystem and Duke OF grassland ecosystem. Water, energy and carbon balances are also analyzed, which is the basis of the follows study on the coupling characteristics in Water System. Generally speaking, the water, energy and carbon/nitrogen cycle can be simulated quite satisifactory using the CWS model with high efficiency, but in some period, there exists some errors.(3) The coupling characteristics and interaction of water-carbon cycles, which is the key processes in Water System, is further explored.On the basis of the simulation of land surface hydrology and carbon/nitrogen cycles, the characteristics of water-carbon cyles are analyzed, which shows a close relationship between photosynthesis and transpiration. The water use efficiency (WUE) is controlled differently by solar radiation, stomatal conductance, photosynthesis and transpiration at different time scales. Furthermore, the effects of CO2enrichment on water and energy are analyzed through a numerical experiment with double CO2. Results show that the interaction of water-carbon cycles is consistent with the coupling relationship of photosynthesis and transpiration.(4) The effects of changing environments on runoff changes in Water System are detected and quantified.A framework of separating the effects of climate change and human activities on runoff changes is developed and used to quantify the contributions of the two factors in the Luan River basin. The results show that the effect of human activities on the abrupt change is a litter stronger than that of climate change.(5) The responses of runoff changes to changing environment are projected.The runoff responses to different climate scenarios, CO2enrichment and LUCC are projected before2050in the Luan River basin. Based on the results of numerical experiment, the effects of climate change and LUCC is stronger than that of CO2enrichment. From the analysis using different scenarios, runoff would reduce in the future before2050which mainly due to the reduction in the wet season. Besides, runoff changes are more sensitive in the wet season than in the dry season.