Doctor of Philosophy
Civil and Environmental Engineering
China experiences heavy national-wide rainfall events with distinct regional and seasonal characteristics. The tropical cyclones (TCs) originating from the Pacific ocean could cause intense rainfall along the coastal region of mainland China. Besides the severe rainfall, tropical cyclones could also cause high winds, storm surges, and large waves. Increasing direct economic loss is always caused by these tropical cyclones.
The mapping of TC wind hazard for the coastal region in mainland China could be carried out using the wind field model and empirical TC track model. The commonly used TC wind field models employed in TC wind hazard assessment are compared in this thesis. The findings of this comparison are then used to select a simple TC wind field model to be used in TC rainfall intensity modeling.
The modeling of rainfall intensity could be carried out using snapshots of the rainfall intensity field obtained from satellite data such as those from the Tropical Rainfall Measuring Mission (TRMM) satellite data. In the present study, both the precipitation radar TRMM (PR-TRMM) data and the Microwave Imager (TMI) TRMM (TMI-TRMM) data that affect onshore sites in mainland China are considered to develop rainfall intensity models. Surrogates of the snapshots are generated using an efficient simulation algorithm and applying the discrete orthogonal S-transform to augment the database. Empirical models of the rainfall intensity are developed using snapshots with or without surrogates. For the development, the TC rainfall intensity field is represented as a superposition of the axisymmetric, asymmetric, and topographic components. This consideration is guided by the parametric hurricane rain model (PHRaM) available in the literature. It is shown that the rainfall intensity inferred from the snapshots from PR-TRMM is greater than that from the snapshots from TMI-TRMM. The developed models are used in a simulation framework to map TC rain hazard (in terms of return period value of the annual maximum accumulated rain per day). A comparison of the mapped TC rain hazard with that obtained based on gauge data indicates that the developed model generally underestimates the TC rain hazard. This deficiency is caused by the underestimation of rainfall intensity inferred from PR-TRMM or TMI-TRMM data.
Similarly, a physics-based model which depends on the TC wind field is developed. This physics-based model is further adjusted by comparing the PR-TRMM data, resulting in a semi-empirical model. The use of the semi-empirical in mapping the TC rain hazard is carried out as well. The mapped TC hazard has similar spatial trends as those obtained based on empirical rainfall intensity models. A comparison of the mapped hazard to that obtained from gauge data indicates that such a model needs to be further improved for practical use.
Summary for Lay Audience
Severe tropical cyclone, known as typhoons, usually comes with intense rainfall, high winds, storm surges, and large ocean waves. An increasing significant economic loss and life threaten risk are observed from recent typhoon events. There are many researches explained various kinds of typhoon wind models to make characteristic analysis of wind. A comparison of three wind field models is introduced in this study to understand model differences. By bringing in adjustment factors, it is possible to obtain approximate results of other two wind models with outcome from any one of wind model. Wind hazard is assessed with these wind models at sites in coastal area of China.
To predict the rainfall hazard more accurate, the TC rainfall modelling and prediction are necessary. Due to the sparse of the rainfall data caused by typhoon as a benchmark, satellite rainfall data is considered in this thesis, also surrogated snapshots of rainfall intensity based on satellite rainfall data are applied to calibrate the rainfall model with mathematic method. Both statistical model (empirical model) and physical model (semi-empirical model) are then developed. The application of two rainfall model makes it possible for construction of TC rainfall hazard maps for onshore sites near the coastline in mainland China. The developed rainfall hazard mapping is valuable for the disaster prevention and decision making.
Gu, Jiyang, "Estimation of tropical cyclone rain hazard for sites in coastal region of mainland China" (2021). Electronic Thesis and Dissertation Repository. 8175.