Urban flood risk warning under rapid urbanization.

In the past decades, China has observed rapid urbanization, the nation's urban population reached 50% in 2000, and is still in steady increase. Rapid urbanization in China has an adverse impact on urban hydrological processes, particularly in increasing the urban flood risks and causing serious urban flooding losses. Urban flooding also increases health risks such as causing epidemic disease break out, polluting drinking water and damaging the living environment. In the highly urbanized area, non-engineering measurement is the main way for managing urban flood risk, such as flood risk warning. There is no mature method and pilot study for urban flood risk warning, the purpose of this study is to propose the urban flood risk warning method for the rapidly urbanized Chinese cities. This paper first presented an urban flood forecasting model, which produces urban flood inundation index for urban flood risk warning. The model has 5 modules. The drainage system and grid dividing module divides the whole city terrain into drainage systems according to its first-order river system, and delineates the drainage system into grids based on the spatial structure with irregular gridding technique; the precipitation assimilation module assimilates precipitation for every grids which is used as the model input, which could either be the radar based precipitation estimation or interpolated one from rain gauges; runoff production module classifies the surface into pervious and impervious surface, and employs different methods to calculate the runoff respectively; surface runoff routing module routes the surface runoff and determines the inundation index. The routing on surface grid is calculated according to the two dimensional shallow water unsteady flow algorithm, the routing on land channel and special channel is calculated according to the one dimensional unsteady flow algorithm. This paper then proposed the urban flood risk warning method that is called DPSIR model based multiple index fuzzy evaluation warning method, and referred to as DMFEW method. DMFEW first selects 5 evaluation indexes based on the DPSIR model for flood risk warning evaluation, including driving force index, pressure index, state index, impact index and response index. Based on the values of all evaluation indexes, one evaluation index for the whole system evaluation result is determined by using the fuzzy comprehensive evaluation method. The flood risk level is divided into 4 levels, having Level 1 the most serious. Every evaluation index is also categorized as 4 levels, and a linear fuzzy subjection function is proposed to do the fuzzy comprehensive evaluation. Dongguan City is used as the study case to validate the proposed method. The urban flood forecasting model is set up with the topographic data, the city map, the underground pipelines and land cover types, and two flood events are simulated with observed precipitation, one is interpolated from the rain gauges data, and another is estimated by digital weather radar. The simulated results are compared with the investigated water depth, and the results show the model has very good performances. The results are further used for the flood risk warning simulation, and are very reasonable.

Chen Y ，Zhou H ，Zhang H ，Du G ，Zhou J ... -  《-》

Exploring the Linkage between Urban Flood Risk and Spatial Patterns in Small Urbanized Catchments of Beijing, China.

Yao L ，Chen L ，Wei W 《-》

Uncertainties of urban flood modeling: Influence of parameters for different underlying surfaces.

Rapid urbanization has dramatically increased the impermeable surface in urban area, which led to urban severe flooding and waterlogging in the world, especially in China and southeast Asia. There are more than 100 cities that suffered from urban flood every year since 2006, and more than 100 million citizens are involved in China. Urban flood mitigation is one of the most critical issues for both water administration and city management agency, in which urban flood modeling is vital and necessary. Whereas, there are relatively few data of waterlogging and runoff in urban area during flooding episodes to calibrate and validate the models, for there are usually few observation facilities installed in the cities. This paper used a combination of experiment and modelling to overcome the lack of reliable discharge data and be able to characterize the urban flooding problems in Xiamen Island, China. This paper simulated the urban flooding in Xiamen Island based on a hydrodynamic model coupled with hydrological model. The datasets of underlying surfaces were input to the model, including the terrain data, building plan, land use, etc. The uncertainty of the urban flood model was analyzed based on the generalized likelihood uncertainty estimation (GLUE) method with shuffled complex evolution Metropolis (SCEM-UA) sampling algorithm. The key parameters were evaluated by on-site experiment to reduce the uncertainties of the model, which could improve the accuracy of the model. If using the recommended parameter value range, the average relative error of flood depth was less than 27.2% at 90% confidence level. A typical rain pattern of 50 years return event was used for flood simulation. The results show that the main inundated areas (flooded depth more than 40 cm) are located in three groups: southeast to the Yundang Lake, around the Hubian Reservoir, along the Exhibition Road. The other inundated areas that less than 40 cm deep are scattered in some low-lying land of Xiamen Island. The main inundated areas simulated are consistent with the point survey of urban flooding, which verifies that the suggested model and the on-site experiment is effective and reliable for urban flood prediction.

Liu J ，Shao W ，Xiang C ，Mei C ，Li Z ... -  《-》

Assessing options for the development of surface water flood warning in England and Wales.

This paper explores the technical options for warning of surface water flooding in England and Wales and presents the results of an Environment Agency funded project. Following the extensive surface water flooding experienced in summer 2007 a rainfall threshold-based Extreme Rainfall Alert (ERA) was piloted by the Met Office and Environment Agency providing initial steps towards the establishment of a warning for some types of surface water flooding. The findings of this paper are based primarily on feedback on technical options from a range of professionals involved in flood forecasting and warning and flood risk management, about the current alerts and about the potential options for developing a more targeted surface water flood warning service. Providing surface water flooding warnings presents a set of technical, forecasting and warning challenges related to the rapid onset of flooding, the localised nature of the flooding, and the linking of rainfall and flood forecasts to flood likelihood and impact on the ground. Some examples of rainfall alerting and surface water flood warning services from other countries are evaluated, as well as a small number of recently implemented local services in England and Wales. Various potential options for implementation of a service are then explored and assessed. The paper concludes that development of a surface water flood warning service for England and Wales is feasible and is likely to be useful to emergency responders and operational agencies, although developing such a service for the pluvial components of this type of flooding is likely to be feasible sooner than for other components of surface water flooding such as that caused by sewers. A targeted surface water flood warning service could be developed for professional emergency responders in the first instance rather than for the public for whom such a service without further operational testing and piloting would be premature.

Priest SJ ，Parker DJ ，Hurford AP ，Walker J ，Evans K ... -  《-》

Adaptation to urbanization impacts on drainage in the city of Hohhot, China.

Zhou Q ，Ren Y ，Xu M ，Han N ，Wang H ... -  《WATER SCIENCE AND TECHNOLOGY》