Spatio-temporal Evolution Of Runoff In China Under Climate Change

Climate change leads to the change of global hydrological cycle,which causes the variations in the spatio-temporal distribution of terrestrial water resources.It has a significant impact on the natural environment and human society.Runoff is the most important form of water resources,of which the changes show significant temporal and spatial variability.It is of great significance to study the distribution and the interannual variability in runoff,as well as the change of runoff in wet and dry years.This thesis analyzes the changes of meteorological factors during the historical?1961-2010?and the future?2011-2050?periods in China;explores the pattern of the spatial distribution of runoff trends according to 291 small catchments'restored runoff data;improves the method for estimating the runoff change under climate change based on the Budyko hypothesis;and analyzes the temporal and spatial evolution of runoff across the 208 third-level basins of China caused by climate change.Climate change shows different characteristics during different periods in China.During 1961-2010,precipitation displays a strong spatial heterogeneity,whereas the other factors exhibit a single trend in the whole country,i.e.increase in temperature and wind speed,together with decrease in solar radiation and potential evapotranspiration.During 2011-2050,precipitation,wind speed and solar radiation show a strong spatial heterogeneity,while potential evapotranspiration show an increase trend over the whole country.The runoff trend of 291 small catchments shows a DDWW pattern that“drier regions are more likely to become drier,whereas wetter regions are more likely to become wetter”,which means that the spatial distribution of runoff has become increasingly uneven.The coefficient of variation of annual runoff shows a distribution that“drier regions are larger,whereas wetter regions are smaller”,that is,the annual variability of runoff gets stronger in drier regions.The Budyko method can effectively estimate the trend and the standard deviation of runoff in the small catchments,as the coefficient of determination of the Budyko-estimated values with the measured values equal 0.72 and 0.92 respectively,and their spatial distribution is consistent with the measured one.According to the historical hydro-meteorological data,it is found that climate change is the main cause for the runoff change in the 291 catchments.Precipitation is the main meteorological factor affecting the runoff change.Across the 208 third-level basins,the runoff trend ranges from-4 to 6 mm a^-1,and the increase trend mainly appears in the Liaohe River basin,the Haihe River basin,the Yellow River basin and the Pearl River basin.The runoff trend generally exhibits the DDWW pattern across the whole country except the Inland River basin,the Huaihe River basin and the Songhua River basin.The distribution of interannual variability is consistent with that of the 291 small catchments.The precipitation change is still the dominant meteorological factor that affects the runoff change.Based on the global climate model data,the prediction of mean annual runoff shows an increase in the north and a decrease in the south,different from that during historical period,which is completely opposite to the DDWW pattern.The largest decrease,larger than 80 mm,will occur in the Pearl River basin,whereas the largest increase is less than20 mm.The interannual variability of annual runoff shows a similar spatial pattern with that found in the historical period.Additionally,the interannual variability becomes larger in regions with smaller variability,whereas that becomes smaller in regions with larger variability.Runoff in both wet and dry years increases in drier regions and reduces in wetter regions.