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Shiyang River Watershed is one of the most difficult in-land watersheds in China due to its arid climate,limited water resources and inappropriate water-related human activities.The water resource crisis of the Shiyang River seriously affects regional economic development and also endangers the sustainability of its ecosystem.The water resources in this region are very vulnerable to climate changes.It is therefore extremely important to assess the trend of precipitation,temperature and PET in order to adapt to the changing climate and mitigate the adverse effects.The Mann–Kendall trend test and Regression Method are two widely used methods to detect significant trends in time series and therefore was employed in this study.The observed precipitation and temperature data for the three basins of Shiyang River watershed were used to investigate the trends in the annual and monthly scales.The projected future climate conditions were obtained from one general circulation model (GCMs),CGCM 3.1for the year of 2000 to 2100.A strong increase in annual mean temperature (0.06-0.07oC/Y) was identified throughout the study area (by using historical data only),which is much higher than the projected global mean temperature increase (0.015oC to 0.045 oC /Y) according to IPCC (2007).The investigation of temperature in the monthly scale has revealed a strong seasonal variability in the trend.The increase in annual precipitation was only identified in Wushaoling basin,which implies that the increase in precipitation is due to accelerated glacier melt from the Qilian Mountain as a result of the increase of winter and spring temperatures.Therefore,the increase of precipitation is not sustainable,and it may result in a more severe drought conditions and worsen the water crisis in the future.A more effective integrated water management and conservation plan is urgently needed for the Shiyang River Watershed.