The East Asian monsoon is one of the most complex monsoon systems on the earth, profoundly affecting the livelihoods of more than one-fifth of the global population. The monsoon characteristics, including monsoon onset, precipitation, and its future changes in a warm climate, are closely related to agricultural activities, water resources management, and flood control now and in the future. Hence, the principal objective of this thesis research is to diagnose the spatiotemporal characteristics of the East Asian monsoon now and in the future and provide potential predictability.

My research begins with identifying the summer monsoon rainfall patterns over Southeast China. Three distinct rain belts over the Huai River basin, the Lower Yangtze River basin, and the South Coast region are...[ Read more ]

The East Asian monsoon is one of the most complex monsoon systems on the earth, profoundly affecting the livelihoods of more than one-fifth of the global population. The monsoon characteristics, including monsoon onset, precipitation, and its future changes in a warm climate, are closely related to agricultural activities, water resources management, and flood control now and in the future. Hence, the principal objective of this thesis research is to diagnose the spatiotemporal characteristics of the East Asian monsoon now and in the future and provide potential predictability.

My research begins with identifying the summer monsoon rainfall patterns over Southeast China. Three distinct rain belts over the Huai River basin, the Lower Yangtze River basin, and the South Coast region are found. Their subseasonal variability strongly agrees with the northward progression of the East Asian Summer Monsoon front in a stepwise fashion. Promising predictability of average daily rainfall over these three regions is obtained, with about 39% to 50% of the total variance explained by the circulation informed regression models. Findings may offer insights into the source of bias for numerical simulations of daily summer monsoon rainfall in the region.

The analysis is extended from summer to the whole year. Instead of using the ad hoc and diverse criteria methods to define the East Asian monsoon, a simple and coherent approach based on the self-organizing map to systematically is established to derive the monsoon annual cycle. In addition, potential predictability of the Meiyu and Fall onset is obtained from the analysis in the subseasonal to seasonal timescale. Besides, the Aleutian Low, the western North Pacific subtropical high, and the upper-level westerlies play important roles in the Spring, Pre-Meiyu, and Meiyu onsets. Heavy rain belt events form right after the monsoonal wind onsets in the warm season are observed as expected. The proposed approach to deriving monsoon stages and onsets would be useful for monsoon climate studies and operational monsoon diagnosis and forecasting.

Based on the annual cycle analysis, the last objective focuses on the response of the East Asian monsoon annual cycle to anthropogenic warming. Hence, the future changes in eight intraseasonal monsoon stages are holistically assessed under two climate scenarios. A skewed monsoon annual cycle with a stretched rainy season due to prolonged Mid-summer at the expense of delayed and shortened winter stages may be expected. More significant and earlier flood risk in all land regions is anticipated during the rainy season in the late-21st century under a business-as-usual scenario. The distressing hydrological risks will be considerably attenuated under substantial mitigations to reduce carbon emissions.

Overall, the main contribution of this thesis study is to extend the knowledge of the spatiotemporal characteristics, provide a new index for the annual cycle, and give a novel analysis of the future changes of the East Asian Monson.