The Simulation Of Hydro-regime And Key Hydro-eco-effect Analysis In Napahai Wetland, Yunnan,China

Mountains and plateaus in Southwest China contain many subalpine and alpine wetlands, with significant hydroecological functions. But ungauged or poorly gauged conditions limit the study and understanding of hydrological regimes of these wetland types. As the International Association of Hydrological Sciences (IAHS) initiated the decade on prediction in ungauged basins (PUB) during the period2003-2012, with the primary aim of reducing the degree of uncertainty in hydrological predictions, the hydrological modeling of ungauged wetland had been focused by the hydrological researchers.This study selected the Napahai Ramsar site, an ungauged subalpine wetland in northwest Yunnan, to explore operational methods in order to simulate its hydrological regime. One hundred and eleven phases of Landsat Thematic Mapper/Enhanced Thematic Mapper Plus (TM/ETM+) imageries from1987to2011were catalogued as the basic data in the Napahai wetland and NSPI (Neighborhood Similar Pixel Interpolator) method had been used to restore the Landsat ETM+(slc-off) imageries. These data were used to found the open water database which contained the areas and the spatial distribution of open water in Napahai wetland. Based on the basin lag time theory and the confirmation of the rainfall was the main driver of hydrological fluctuation, correlation coefficients between open water areas (OWAs) and correspondingly accumulated precipitation levels at different time steps were analyzed, which determined that a75-day time step was optimal to establish the simulation equation between OWAs and accumulated precipitation levels. This model could predict the OWA fluctuation when the daily precipitation data is available to acquire.A Trimble R8GNSS (Global Navigation Satellites Systems) RTK (Real-time Kinematic system) and sonar fathometer were used to survey fine-resolution elevation data and generate a digital elevation model of Napahai wetland, which helped to calculate the wetland water storage (WS) by using a conceptual model built in the study and find the inherent correlation with OWA and WS. Then, the WS could be simulate by the optimal accumulated precipitation (OAP). The multi-phase spatial distribution of open water data were used to overlap into the flood frequency spatial distribution which could calculate the most possible flooding pattern at different OWA levels. The simulation result indicated that, in the inter-annual time scale, the hydrology was stable in dry season and had a dramatic fluctuation in rainy season; and there were significant variations between rainy and dry seasons in the intra-annual time scale; it increased slowly in June and sharply in August, reached its maximum level in September, declined from October to December, and then kept slowly decreasing until next May. The sharp increase and decrease of the wetland hydrology in July and October demonstrated the wetland ecosystem was turning into terrestrial ecosystem. Fluctuation of WS had obvious time lag behind the rainfall especially in rainy season.Based on the hydrological model above, the study analyzed three key ecological responses of hydrology:flood prediction, spatial calculation of waterfowl open water habitat, and the wetland vegetation differentiation drove by hydrology.1) As accumulated75-day precipitation levels reached100-year (100a) return period, the flooding area will almost cover the whole Napahai wetland as3098.20hm2; under the scenarios of50-year (50a),20-year (20a),10-year (10a), and5-year (5a) return periods, it will occupy2812.37hm2,2427.69hm2,2126.49hm2and1807.94hm2of the Napahai wetland.2) The waterfowl habitat in Napahai wetland covered302.45hm2, which was64.80%of the max waterfowl habitat of this wetland and9.74%of the study area. The main open water habitat was in the north and the other small habitats were fragmented dispersedly. The human interference was the main threaten which should be restrained to release more space for more waterfowl population.3) There were one hundred and thirty species of plant in Napahai wetland, which belonged to eighty-eight category and thirty-six classes. Potentilla anserina and Carex muliensis were the dominant species in the wetland. The landscape would be mesophytic meadow as the flood frequency was less than2.1%; it would be marsh or wet meadow as the flood frequency was between2.1%and50%; it would be open water as the flood frequency was greater than50%. The human interference had greater influence in the low flood frequency area, where the edge effect was strong. This methodology may provide a new thought for the disputed wetland definition.