| Against the background of climate change, the process of water supply and demand in the water resource system changes and the contradiction between water supply and demand exacerbates. In Heihe River Basin, the imbalance of water resources allocation has not been solved, and the ecological environment deterioration has not been curbed, while water dervison has been implemented for14years. Under climate change, the imbalance between water supply and demand has been aggravated, and the ecological water demand has not been met, which have a threat to the social-economical-environmental sustainable development of the basin.Based on the technology of geographic information system, digital simulation and fileld observation, from the perspective of water resources system, the interaction mechanism of climate change on water resources system is analyzed. On the basis of phenology, water demand and its process are predicted. The impact of climate change on the process of water supply is evaluated from the amount of water resources, available water resources and water supply.This study extends the theory and methods of evaluating the impact of climate change on water resources system. Furthermore, the difference from the traditional method is as follows: First, from the perspective of water resources system, the water supply and demand is evaluated. The paper emphases on the resource amount, time rhythm and spatial distribution of water supply and water demand in the water resource systems. Based on the SWAT model and the techonology of water resource assessment, the evolutionary characterisitics of water cycle, water resouces, available water resouces, water supply, water demand and water defict are analysed gradually. The phenological observations and accumulated temperature threshold method are used to determine the phenological variation of typical crops and vegetation. The water deficit ratio, time and regions are considered to support the adjustment of water diversion scheme under climate change.Collective strategy coping to climate change is conducted on the basis of both respecting the nature laws and satisfying the demands of social and economic development. The combination of normal and emergency management is used. The regulation goal is to control water availability. Specifically, the collective strategies are to make the time-space distribution of water resources rational through optimizing the hydraulic projects groups and dispatching water, without effecting the natural balance. Furthermore, the collective strategies are to meet the requirements of the social and economic development with rational allocation of water resources among different water consumers, through adjusting socio-economic development patterns.In the support of above basic theory and key technology, the conclusions about the impacts of climate change on water resources system in Heihe River Basin can be described below:(1) Evolutionary characteristics of water cycle elements and drought and flood in the changing environmentThe mean annual precipitation and daily maximum precipitation in Heihe river Basin increased. For the water-rich region in the upstream, the precipitation takes an increasing trend, while the precipitation takes a decreasing trend for the water-poor region in the downstream. The date of daily maximum precipitation moves from July to August and September. The intensity of precipitation increased. There is an increase in daily mean temperature, maximum temperature, minimum temperature and accumulated temperature. The lowest temperature happened in late January and the highest temperature happened in late July.The runoff has an upward trend, and it rises from15.61×108m3during1945-1991to16.80×108m3during1992～2010. In the flood season from June to September, the proportion of total annual runoff decreases from68%to66%, while the runoff from August to November increases from44%to47%.Due to the water diversion project, the water table in middle reaches of Heihe river Basin becomes falling, while rising in lower reaches. After the water diversion, the groundwater level in middle reaches declined by2.96m and water depth in lower reaches reduced by0.2m. The groundwater depth is gradually decreased due to the gradual decrease in water quantity from the upstream to downstream. The change of water table is dependent on the distance from the river, and the closer to the river, the shallower the depth is.The drought frequency, drought coverage, and the shift of dought and flood increase. For the drought duration, the area in the downstream tends to be longer than that in the upstream. The precipitation intensity after the drought in the midstream is greater than that in the downstream. For the middle and upper reaches, the precipitation intensity after drought is greater than that on the normal condition.The temperature after drought tends to be higher and the water vapor pressure after drought tends to be lower than the normal value. The temperature increases with the continuous dry days and the actual water vapor pressure decreases with the continuous dry days. The average temperature and actual vapour pressure varies with the degree of drought with the most change in June and followed by July and August. In June, the variation of temperature and vapor pressure in drought decrease from upstream to downstream.(2) The impact of climate change on water resources system in Heihe River BasinDue to climate warming, water demand in Heihe River Basin increases. Water demand is18.65×108m3in the baseline period and21.23×108m3in the control period with an increase of13.8%. The maximum of water demand is in June, July and May. The water demand presents obvious spatial differences. In the upstream, the water demand increases with the maximum in May. In the midstream, water demand increase by0.519×108m3,0.819×108m3and0.637×108m3in April, May and August, respectively. Furthermore, the time rhythm of water demand has changed, with an increase in the ratio from November to May of the following year. In the downstream, the ratio of water demand in June increase from22.84%to23.26%. For the whole basin, under guaranteeing rate of25%, the maximum water demand happens in September and May; under guarantee rate of50%, the maximum water demand occurs in August and July; under guarantee rate of90%, the maximum water demand happens in June, May and July.Under guarantee rate of90%, the quantity of available water resources decrease by0.91x108m3during the dry year in the control period compared to the baseline period. The quantity of available water resources in drought period are less with a decrease between June and December due to climate change. Under guarantee rate of50%, the available water resources decreases by1.21x108m3during the normal year in the control period when compared to the baseline period. The water resources are less with a decrease from September to April in the following year and an increase from May to August. Under guarantee rate of25%, the quantity of available water resources decreases by15.7%with an increase between April and August. The water resource increases in flood season and decreases in dry season due to climate change.The water shortage in wet year is concentrated in April and May, and the rate of water shortage in April increases weakly. The time of water shortage in normal year is from April to May, and the water shortage increases significantly in June. The water shortage in drought year is from April to June, and the maximum water shortage is in June. Under climate change, the rate of water shortage increases in the middle reaches. The time of water shortage goes forward gradually. For the upstream, the impacts of climate change are not obvious currently, and water supply can meet the basic water demand. For the downstream, due to continuous wet years, its rate of water shortage drops by21.96%to15.90%, and the rate of water shortage in wet year and normal year are declining. The rate of water shortage in drought is increasing. The time of water demand is earlier to March, April and June, and the maximum amplification is from March to April.(3) General framework concerning integrated strategies for coping with climate changeThe management framework of collective strategies should be formed on both the levels of planning and implementation. For the planning level, the management mode should shift from crisis management mode to collective management mode, unifying normal and emergent management. For the planning level, the goals are to revise the traditional method of drought and flood risk zoning, to implement the combined risk zoning of drought and flood, and to optimize the regulation ability of the hydraulic projects groups. For the level of implementation, based on the collective water resource management oriented at the normal and extreme values, the goals proposed to combat the rapid shifting of drought and flood are to implement rational water resources allocation oriented at normal and extreme value process, to dispatch hydraulic projects group at the extreme value process, to dynamically control the flood limit water level of reservoir, and to maximize the utilization efficiency of water resources. |
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