Monthly and annual changes in precipitation in South China during 1990-2011 are examined in this study. As located in the sub-tropical climate zone, the annual rainfall in South China is concentrated in the summer. During the same period of time, an average of 9 tropical cyclones approaching South China each year which also contribute ample of rainfall to South China during the tropical cyclone season (June-September). Since the climatic system is interconnected, so this study attempts to examine the combined effect on inter annual rainfall variations in South China due to El Nino Southern Oscillation (ENSO), tropical cyclones affecting South China and the Asian Monsoon. It is generally agreed that during the El Nino onset years, South China would be more wetter, but with less than average tropical cyclones affecting South China. As such, effects on precipitation in South China caused by these two factors offsetting each other and data indicate there is no consistent trend of either more or less rainfall recorded for the El Nino onset years during 1990-2011. On the other hand, the first half of the year right after the El Nino years are in general more wetter than normal. This can be due to the lagging effect of El Nino events normally happened in the winter time, plus the fact that the strength of winter monsoon during the El Nino years is weak, resulting in more rainfall in the following year. Furthermore, annual changes in precipitation in South China directly affect the surface runoff of the Pearl River and a strong positive correlation between the two variables exists for the period 2000-2011. The +/- 25% annual variations and the seasonal variations of rainfall in South China post a challenge to the water resource management in the Pearl River Delta Region. Therefore dams and reservoirs built along the Pearl River are necessary to store surplus rainwater in order to supply sufficient fresh water to the Pearl River Delta Region during the dry seasons or years. On the other hand, further studies and monitoring programs are recommended to continue assessing and evaluating impacts of dam constructions to the environment and the ecosystem of the Pearl River Delta Region. / published_or_final_version / Applied Geosciences / Master / Master of Science

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published_or_final_version / Electrical Engineering / Doctoral / Doctor of Philosophy

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Project Completion Report / OWRT Project No. A-027-ARIZ / Development of a mathematical model of infiltration which includes the effects of raindrop impact / Agreement No. 14-31-0001-3503 / Project Dates: July 1971-December 1972. / The purpose of this investigation was to use an existing mathematical model of infiltration to assist in determining which factors, including raindrop impaction, were responsible for infiltration characteristics of a bare semiarid watershed. The infiltration model developed by Roger Smith was selected as best suited for this investigation. Several laboratory and field rainfall simulator runs were modeled. Good correlation was found between the modeled and experimental results for both the infiltration data and the saturation profiles, for both bare and grass covered plots. For the lab and field experiments a realistic rotating disk rainfall simulator was used. In the field tests bare and grass covered plots were tested. In the lab specially constructed soil boxes were used that permitted measurement of infiltration and saturation profiles with time. Gross changes in saturated hydraulic conductivities due to crusting effects were also measured. Gamma ray attenuation techniques were used to obtain density and soil moisture profiles for the laboratory experiments. It was found that the Smith model can be used to simulate infiltration from different surface conditions as long as there is some method to calibrate the model. Carefully obtained saturated and unsaturated hydraulic properties for the soil types present in the watershed are needed in addition to infiltration data from a realistic rainfall simulator or through hydrograph analysis from unit subwatersheds.

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Distributions of amount of rain with rainfall rate and of duration with rate are determined for all rain of 1963 and for the heavy rain of 1958 to 1962. The rainfall rates are obtained from the rain chart records of the McGill Cbservatory tipping-bucket recording rain gauge. Separate distributions for winter and summer rain are evaluated. The distributions of amount with rate for both winter and summer rain are log-normal; they have logarithmic means of 2.5 mm hr⁻¹ and 12.6 mm hr⁻¹ respectively and logarithmic standard deviations of 0.4 and 0.7 respectively. A comparison of the distributions of amount with rate for winter rain and for snow shows that the two distributions are similar in form. [...]