Tag Archives: flash floods

Is it Climate Change?

Everyone wants to talk about the flash floods. The rains have always been fairly torrential. The water has always come on pretty quickly. But these were different.

In March of 2013, 11 people were killed in a flash flood in the capital city of Port Louis when 152 mm (6.1in) of rain fell in less than an hour. When the rain started, offices closed. People went to parking garages to retrieve vehicles and, tragically, found themselves stuck. Others left their offices and were trapped in flooded underground tunnels. Many went to the bus terminal, though no buses were running. The radio stations had no information. No one seemed to have information.

Nearly everyone that I have spoke to about climate change in Mauritius mentions the floods. Rightly so. It is a huge, climatic disaster. It is something tangible and terrible to point to and say “that is climate change.” But it is more than that. It is what happens when the changing climate meets our development choices.

Port Louis is a coastal city surrounded by largely deforested mountains. When it rains, the water drains along the quickest path toward the sea. In Mauritius, like many places, new development means impervious surfaces. To develop that new, modern look while cutting down on costs, you don’t plant trees, you don’t landscape, you create a huge slab of asphalt and top it with a huge boxy concrete building. With these conditions, drainage is going to be a problem.

Water always finds the path of least resistance. In a natural setting, flash floods occur when the soil is too dry to absorb water or over-saturated. The runoff collects in gullies and streams and joins to form a fast flowing front of water and debris. In urban areas, this path is usually pavement, and instead of gullies and streams, the water is funneled by walls and buildings. There is so little soil and permeable surfaces that nearly all of the precipitation is swept into the quickly overburdened stormwater and sewage systems. The high intensity rainfall that is frequently experienced in Mauritius causes flooding when the city sewage system and drainage canals do not have the necessary capacity to drain away the amounts of rain that are falling. The results are tragic.

Another impact of the type of development occurring in Port Louis is the urban heat island effect. This is an impact of urban development that is felt in the increased temperatures in major cities around the world and is simplistically explained in our material choices. The concrete and asphalt that make up our cities store heat energy much more effectively than the surrounding natural environment. The temperature increase that is expected in Mauritius will be more dramatic in these areas without green spaces and shade.

Climate change is a broad, complicated, all-encompassing issue. You can talk about everything from agriculture to tidal patterns under the auspices of climate change. But lets simplify the conversation. We can talk about real, doable solutions to some of the problems we are seeing. We have choices.

The interventions do not need to be huge. They do need to be handled with long-term plans. Here is what I propose: requirements for permeable surfaces and plant coverage with new developments; green roofs and/or reflective roofs and the building codes and incentives to replace and create them; replacing as much non-porous surfaces with green space as possible; expanding areas of parkland where the flooding occurs for the purpose of water diversion; gutters, canals, and drainage that can handle the water flow; no-build areas along sensitive coastal areas and natural flood plains; and more trees.

The results of these actions would be less stormwater runoff, leading to less flooding. The same actions that create permeable surfaces and reduce the urban heat island effect could also create amazing green spaces in vacant areas, along streets, and on rooftops. Even the drainage areas could be something of an attraction. Think of canals, perhaps with public artwork, shady spaces, and pathways to enjoy the area when the weather is more promising.

I am slowly realizing that all of the climate change adaptation actions are actions that we should be taking whether you frame it as climate change or not. Nature-based solutions, like planting mangroves, forests, and coral restoration projects, create a more sustainable environment and ecosystem. Development-based solutions create a more pleasant living environment with less pollution.

We do not seem to be able to get mitigation under control. We can barely wrap our heads around sea level rise, drought, or a myriad of other lurking impacts. But planning our cities and developments for a future with more pleasant surroundings and fewer disasters may be something that we can do.