Water Resources Response Of Karst River Basin To Climate Change And Land Use Change

The Karst sub-streams system combined with fissures, conduits, caves, pores and other water-bearing medium widely distributes in South-West of China, it takes on some basic features, for example surface rugged, underground cave crisscross, soil layer thin, fertility low, vegetation growth difficult and soil erosion serious, karst development uneven, supplying drain is rapidly, the system's storage and regulation ability is low and the stage-discharge's seasonal variation large. The water system and ecological system in this area is very fragile, its response to changing environment is obvious, so it is the attention of global change. The extreme weather events occur repeatedly in Guizhou province, researches on restoration of ecological environment as well as comprehensive treatment of the karst region environment in southwest China have begun since 1995, which provide a unique opportunity for studying karst region in China. The land use in this area has changed since 1995, and the hydrological processes will change also. Therefore it is emergent to study the runoff variation of the karst catchment and the effect of land use change and climate change on hydrology and water resources, which provides information for developing management strategies for ecological preservation and sustainable utilization of water resources in this region.We make the Houzhai Basin as the example, which lies in the Puding country Guizhou province, which has an area of 80.6 km2, it is one of the typical areas where karstification is well developed. The study area is typical karst area of "65" and demonstration area of "95" entitled "Research on ecological environment comprehensive management and development of karst basin of Guizhou province". The human activities is strong and the ecological construction effect is obvious in the area.On the basis of analysis the research situation, this thesis builds a karst semi-distributed hydrologic mode based on sinkhole to analyze the runoff sensitivity to climate change through precipitation and evaporation two input factors. We put forward the climate change features in 2030 based on the studying the long sequence climate characteristics, then calculate the runoff in 2030 by using the hydrological model. This paper constructs three land use scenarios and then calculates the runoff under different land use scenarios, to study the runoff response to land use change. The water resources comprehensive evaluation framework was constructed under changing environment, including the supply and demand of water resources, water vulnerability, water potentiality and water resources sustainable utilization.Based on the data of temperature and precipitation observation collected from Puding meteorological station from 1960 to 2005, using the linear trend, moving average, the cumulative anomaly, and the Spearman, the seasonal mean temperature and precipitation variations during the past 45 years in Houzhai river is analysed. The mean temperature has increased in recent 45 years, the temperature increases in summer, autumn and winter while decreases a little in spring. The precipitation follow a slight declining trend in Houzhai river in recent 45 years, the precipitation is a little decreases in spring, autumn and increases in summer, winter. The land use distributions of Houzhai catchment in 1993 and 2005 were obtained from Landsat ETM, field investigations and the existing land use maps. These data were grouped into six classes according to the requirement of the study as well as the feature of the region, i.e. paddy field, dry land & barren land, forest land, open water, barren land, and dry land, the main land use types are paddy field, dry land & barren land, barren land, which accounting for over 80%of the study area. From 1993 to 2005, the most significant characteristics were decrease of dry land & barren land, and increase of barren land, forest land, and paddy field.On the basis of understanding of the karst features, we built the model based on sinkholes applied in the research of effects of land use change and climatic fluctuation. The model was calibrated against daily streamflow measurements at the three stations for the time period 1988 and 1994, and the data in 1996 were used for model validation. The goodness of fit using the Nash-Sutcliffe (1970) efficiency factor'E'was 0.82 and the standard deviation was-11%in the calibrated period, and 0.75 and-8%in the validated period, which illustrates the ability of the model to simulate the hydrological behaviour of the catchment.Based on the building hydrological model and hypothetical climate scenario, sensitivity of runoff in each subregion to climate change was analyzed. The result shows that the runoff increase with the precipitation increase while the temperature not change, the runoff decrease with the temperature increase while the precipitation not change. And results indicate that runoff in region is more sensitive to precipitation change than temperature change. Under the same condition, the runoff sensitivity followed the order of the Muzhudong>Laoheitan>the whole region. The temperature and precipitation of 2030 are forecasted by the typical scaling method. The runoff calculated by the building hydrological model decrease in 2030 under different precipitation conditions, the runoff decrease in spring and autumn, and increase in summer and winter, which can explain the phenomenon that spring drought and summer flood in recent years of Guizhou province. The frequency of flood peak when the precipitation increases 20%is larger than the precipitation decreases 20%.With the validated models, we discussed the potential effects of land use change by the simulation of "extreme land use scenarion","spatial deployment land use scenario" and "future land use scenario" with the spatial analysis function of GIS. The result show that the runoff followed the oreder of barren land> forest land>piady field under the extreme scenarios. Compared with the original landuse type, the barren land made the runoff increase, and the paidy field led runoff reduces. The runoff increase or decrease mainly concentrated in wet season, which show that the land use change mainly affect the runoff of wet season. The runoff decrease under spatial deployment land use scenario, and the runoff sensitive to land use change followed the order of the Muzhudong>laoheitan>the whole region. The land use temporal and spatial change of 2030 was simulated through the CLUE-S model based on land use of 2005 in this region, the result show that the runoff of Muzhudong and Laoheitan decreases, and the whole region decreases a little.This paper calculates the influence degree of land use change and climate change to the runoff by using the building hydrological model. The results show that the climate change is the main factor. The annual runoff reduces in 2030 under the combined action of land use change and climate change, and the runoff decrease mainly concentrated in wet season, the decrement rate is small in wet season.Preliminary analysis of supply and demand reflects that the contradiction between supply and demand is prominent in 2030, and the water deficit is more than in current condition. The natural runoff is bigger than the water demand under different precipitation condition in 2030, so the lacking water for engineering type in 2030 under different precipitation condition of Houzhai Basin. This paper analyzes the water vulnerability of Houzhai Basin under changing environment by using three methods, the two index method shows that the water vulnerability is a little large. The water sensitivity and adaptability method reflects that the water sensitivity is big and the adaptability is small, so the water sensitivity is relatively fragile. The warning lights method reveals that the reservoir storage capacity is smaller than the annual runoff, the water demand is smaller than the natural runoff, so the water sensitivity expresses medium fragile and exploitation. In conclusion, the water resources development and utilization of Houzhai Basin under changing environment is low, and is a engineering type area, the water sensitivity is medium to relatively fragile.This paper contrast analyzes the natural runoff, water availability and water potentiality under changing environment and current condition. This paper calculates the natural runoff of surface water by adopting the breakdown investigation method, and calculates the natural runoff of groundwater by using the runoff modulus method. The results reveal that the natural runoff of surface water and groundwater under changing environment are smaller than under the current condition. This paper calculates the water availability of surface water by adopting the losing deduction method, and calculates the water availability of groundwater by using the dry runoff modulus method. The results reveal that the water availability of surface water under changing environment are the same with under the current condition. The water availability of groundwater under changing environment are large different under the current condition. The water availability of changing environment is bigger than the water availability of current condition, and per capita water availability of changing environment is smaller than the per capita water availability of current condition.Based on the measurement demand of water resources sustainable utilization and previous research on the water resources sustainable utilization of karst area, this paper divide the water resources sustainable utilization index system into three level, which are garget level, rule level and index level. This paper evaluates the water resources sustainable utilization under changing environment by using fuzzy comprehensive evaluation method and support vector machine method. The results are consistent, and show that the water resources sustainable utilization under changing environment of Houzhai Basin is "general", which are decided by the water resources conditions of the study area.