Planning for Sustained Hydrological Anomalies in a Warming Climate: An Australian Perspective

Most fields of engineering have significantly advanced since the Industrial Revolution, making life safer and easier for all of us. Floods are a prominent exception with millions of people affected and several thousand killed each year. As cities expand with more surfaces sealed and as rainfall events become more unpredictable with climate change, flooding events from storm water remain a big challenge. Floods have a profound impact on an area’s economic output and indirectly on government support for poor communities, disease outbreaks, and the transport of necessary goods, and thus pose a huge problem for people in both flooded and flood-prone areas.

In recent years, weather events around the globe are changing. Some attempts to predict the change in weather patterns—and storm events in particular—have been made, but they do not reach conclusions similar to those of the models predicting temperature changes, and, depending on the assumptions made, point in very different directions. This lack of clarity regarding future storm types makes it hard to prepare for storm water flood events. Ashish Sharma and his team have been working on a simpler and more universal model to predict storms in a warming climate using only the assumption that temperatures will increase. They have successfully identified a couple of patterns that hold true for all of the most severe storm events in Australia:

• If temperatures rise, rainfall becomes more extreme and less evenly distributed over time. Quick peak rainfall, as we know it from typical summer-storms, will be observed more often, though the extremes will not be as pronounced in regions closer to the poles. Areas closer to the equator will suffer the most dramatic changes in storm patterns. They will experience more severe storms and will have higher costs to prepare for these changes than regions in more moderate climates.
• Not only the temporal, but also the spatial pattern of storms will be change. While the total amount of rain used to be spread out over larger land areas, in the future it will be confined to smaller regions. Thus the entire “rain load” of a cloud will be deposited faster over a smaller area.
• The total rain volume of extreme storms generally does not increase. The development of total rain volume varied significantly in different regions of Australia. While some regions showed the anticipated rise in the total rain amount, others experienced less rain per storm event.

Climate changes at the global and local levels have and will continue to have a significant effect on the incidence of storm-induced flood events. Current infrastructure was not designed to handle storms with the intensity and typical patterns observed in recent years and expected for the future. The “design flood” that urban planners and civil engineers prepare their projects for poorly describes the actual and expected storms, and therefore even new infrastructure projects are and will be unable to cope with the amount of water suddenly hitting the ground.

In rural areas, much of the extra rainfall can be absorbed by soils that are drier from the higher evaporation rates in a warmer climate. But in urbanized regions, more intense rainfalls pose many problems. The many sealed surfaces prevent rainwater’s rapid reabsorption into the ground, and in an urbanized area many more people are affected by a flood event.

To prepare for these changing weather patterns, city planners must check whether their city’s drains, bridges and sewer systems are equipped to handle higher amounts of water in a shorter timespan, and update them if necessary. Future projects need to work with updated “design floods” or rather use continuous simulation of rainfall that considers storms’ temporal and spatial extension. Cities need to incorporate more permeable infrastructures (from green areas to water tanks) that are able to absorb part of the increased rainfall and support the drain system.

The world’s poorest areas will be those most affected by extreme storm events. How to implement low-cost, effective and simple structures to avoid damages or floods altogether, is an open question left for policy makers to resolve.