Observational Analysis And Numerical Simulation Of Mid-summer Precipitation And Temperature Characteristic Variations Over China In The Past 40 Years

Extreme weather and climate events often bring large disasters to human lifeand economy, so it is important to study their historical variations and forecast fu-ture changes. In this thesis, we analyzed long-term trends and decadal variationsof mid-summer precipitation and temperature characteristics with daily datafrom 740 stations over China during 1958-2000. The precipitation and tempera-ture characteristics used in this thesis means their mean and extreme indicators.Based on the results of observation, we used WCRP CMIP3 dataset to estimatethe current state-of-the-art coupled climate models'performance in simulatingpresent mid-summer precipitation and temperature characteristics and forecastfuture changes over China.The results from observation show that total precipitation variations in EastChina are mainly due to the variations of hard rain. The trend analyses showthat the amount of precipitation, the frequency of precipitation, the frequency ofextreme precipitation and the intensity of hard rain have significantly increasedalong the Yangtze River valley and evidently decreased in North China during1958-2000.The intensity of precipitation has coherently positive trend in EastChina however not statistically significant in North China. The drought in NorthChina is resulted from the decrease of the frequency for light rain, with maximumdecreasing trend as -3%/10yr. The ?ooding along the Yangtze River valley in thepast decades is resulted from the increase of all sorts precipitation frequency andintensity. The changes of precipitation characteristics along the Yangtze Rivervalley are out of phase with those over North China, as indicated by the signifi-cant negative correlations between the regional mean time series. In response tothe decadal shift of East Asian climate in late 1970s, the precipitation frequencyof North China experienced a shift starting from late 1970s. The shifts of precipi-tation intensity, extreme precipitation frequency and the maximum precipitation along the Yangtze River valley almost occurred in late 1970s.The trends in mid-summer temperature show unique cooling around theYangtze River valley and significant warming over northern China. The timeseries of regional mean temperature mainly re?ect decadal variabilities, whichdecrease in 1960s and increase in 1990s. Both indicators based on absolute valueand percentile indicate that the significant cooling region of low end tempera-ture indices locate over the mid-low Yangtze River valley, however, the high endcooling region locate to its north, i.e., regions between the Yangtze River andthe Yellow River. We applied EOF analysis on temperature characteristics, thedominant mode shows consistent variations over China and the decadal shift ofits principle component occurred in 1960s and 1990s, daily maximum temper-ature experienced its decadal shift in 1960s, and daily minimum temperature'soccurred in 1990s. The second EOF mode of temperature displays out of phasefor the Yangtze River valley and other regions over China, and the decadal shiftof its principle components occurred around late 1970s.The coupled climate models can reproduce broad spatial pattern of climatol-ogy mean precipitation and temperature characteristics, however, the majorityof models overestimate light precipitation frequency and underestimate precipi-tation amount and temperature, the largest spread among models'result locatesover the Tibetan Plateau. Generally, the high resolution models have better per-formance than medium and low resolution models over China. Although largediscrepancy exists among models, the multi-model ensemble and the majoritymodels'results indicate that the climate would be warmer,there would be moreextreme temperature events when CO2 doubled, and there would be more mid-summer total and extreme precipitation under a warmer climate over China.