Intensive Storm/Rainfall

With the progress of climate change, more and more extreme weather conditions including extreme intensive storms/rainfall events were reported. The flood in ZhenZhou China on July 20, is one of the examples [2].

Extreme large amount of surface runoff

The intensive storm/rainfall combined with low ratio of grass coverage and high ratio of impervious surfaces built-up areas (like concrete, asphalt and large roofs) and by the overall concentration of development [1] often generates high amount of fast-moving surface runoff that turned streets into killer rivers.

Under designed or not well-maintained stormwater drainage systems

Urban flooding is often caused by intensive rain that falls on impervious surfaces and overwhelms local stormwater drainage capacity. Each of these components—heavy precipitation (which is expected to become more frequent due to climate change), increased urbanization that increased impervious areas, and insufficient or outdated stormwater infrastructure that reduced drainage capacity—presents a challenge in and of itself[5].

Fast-Moving Water

Excess amount of surface runoff accumulated in low areas often runs down streets and enters subsurface infrastructures like subways, storm sewers, etc. that results to massive destruction and fatalities.

Electric Shocks

Live wires contacting extended surface water accumulated in low areas are often causes of electric shocks to people crossing the water covered streets.

Wounds and Infection

Wounds are common during urban flooding events. The wounds could be cuts by sharp edges or falling objects. Such wounds can be easily infected when contacting with contaminated water.

Contamination

Chemical spilling from gas stations and vehicles or other types of chemical containers is a common phenomenon during urban flooding. Potential risks include contaminated drinking water induced sickness, allergy to toxic mold growing in wetted houses. Contamination control and remediation is always a big challenge during and after an urban flooding.

Stress and Diseases

The shock of urban flooding is often powerful on the victims of floods. Stress, lack of rest, contaminated drinking water and diseases passed by dead animals are often cause people sick during especially when medicines are lack.

Drainage Network Models

A type of models mainly focus on the processes of urban drainage and surface runoff and are based on hydrological methods.

Models Based on Shallow-water Equations

A group of computer and remote sensing aided models that can be 2D shallow-water models or drainage network coupled with urban surface models or a hydrological model supported by hydrodynamic urban flood model.

Hydrogeomorphic Approaches

An approach to delineate approximate inundation areas based on terra analysis.

Alternative Methods (Cellular Automata and Neural Networks)

The development and application of cellular automata and neural networks models are a new trend in urban flooding modeling with a great potential. It is foreseen that machine learning will play a big role in urban flooding prediction in the future.

Urban flooding early warning systems

Storm induced urban flooding sometime is hard to predict due to the randomness of extreme weather conditions resulted from climate change and the short time window available to develop an emergency response plan to cope a flooding event. Therefore, municipalities should develop an early warning system with triggers to automatically activate the emergency response plan. The early warning systems should include the forecasted amount of rain and duration, the delineation of low areas and their ponding water depth thresholds, identification of vulnerable facilities, infrastructures, sources of contamination, live electric wires, and neighborhoods, etc.

Municipal infostructure upgrade

Most municipalities have infrastructures built several decades or centuries ago and were not well maintained. Their capacities were well underestimated. As a result, when extreme weather brings a great amount of water that surpasses the capacity of the infrastructures, a localized urban flooding event occurs. With the increase of storm induced urban floods, municipalities should check their existing infrastructures and make necessary upgrades to prevent flooding.

Better design of new municipal infrastructures

Municipal storm management systems are often designed based on the 100 year return precipitation events, and most urban areas are often over developed with low grass coverage rates. With the on-going climate change, the design criteria such as the designed rain event have to be updated properly to reflect the changes of weather and land surface conditions to prevent potential urban flooding.

Well-designed emergency reaction plans

A well-designed emergency reaction plan is essential for all municipalities. The plan could dramatically reduce casualties and property damages. The plan should be developed with the help of urban flooding prevention specialists and municipal operation representatives, and all other stakeholders. The reaction plan should also have an education/training program for residents living in urban areas especially in those vulnerable areas to help residents get prepared for flooding events such as the locations of high ground areas to retrieve, the escape routes, the emergency supplies including rain coats, flash lights, safety jackets, ropes, knives, fire starters, foods, water and medicines, boats, communication tools such as fully charged cell phones and chargers, radios, etc.