Rapid Urbanization and Its Impact on Flooding: A Case Study in the Pearl River Delta Area

Urbanization is a world trend in the past century, the urbanization process in the developed countries is still going on, while the urbanization in developing countries is much more rapid in recent decades. For example, China’s urban population reached 50% in 2011 from 19.39% in 1980, and the projected urban population will be over 65% in 2050. Urbanization has caused big changes in many aspects, such as the flow of population from the rural villages to the urbanized cities, more concentrated economic and commercial activities in urbanized area. One of the direct changes induced by urbanization is the land use/cover changes(LUCC), which causes much more impervious surfaces, including the residential areas, factories and commercial facilities. Increased impervious surfaces causes less infiltration and rapid runoff routing, thus increasing flooding and flood vulnerability to the urban areas, but how to quantify the impact of rapid urbanized on flood is not well studied yet.

The Pearl River Delta Area is China’s biggest economic zone, which has observed the rapidest urbanization in China in the past 3 decades. In this study, the urbanization processes of Guangzhou City, the hub of South China’s politics, economy and culture, is studied first by using satellite remote sensing imageries. The Landsat satellite imageries is used to estimate the Land use/cover change from 1987 to 2015 at a three year interval by employing the SVM algorithm. Results shows that the Guangzhou City’s LUCC is significant, the unique change is the high urbanization rates among the creeks draining to the city which pose great threat to the city’s flood security.

Based on the above results, the impact of LUCC on flood is studied, and three creeks draining to the city are selected as the study cases. As the creeks in the Pearl River Delta Area only have precipitation observation, no river discharge measures, so the model that could determines model parameters physically from the terrain properties is needed for this study. The Liuxihe Model, a physically based, distributed watershed hydrological model proposed for watershed flood forecasting is employed to simulate the hydrological processes. Liuxihe Model derives model parameters from the terrain properties physically, including the DEM, soil maps and Land use/cover maps, so it is the ideal hydrological model for this study. The Liuxihe Model are set up in the three creeks, and a few flood events with precipitation observations in recent years are simulated, and the results are reasonable good. 

Based on the simulation results, the hydrological changes have been analyzed. From the simulated results, it could be found that the hydrological changes is significant, but with different precipitation patterns, the changes are different, and even for different creeks, the changes are also different. Finally the reasons for hydrological changes are studied and the adaptation policies and actions are proposed to mitigate the negative impact of urbanization on flooding.