For many years, scientists have considered unpredictable and extreme rainfall patterns as a likely long-term effect of climate change. While this has yet to be written as evidential truth, the devastating effects of increased rainfall are already forcing cities and communities to act on what they do know: short-term torrents and flash floods are becoming a common occurrence, and it is causing devastating effects to the human population and the global economy.

In their sixth assessment report, the Intergovernmental Panel on Climate Change (IPCC) highlights that the water cycle is indeed becoming more intense because of climate change. In fact, high latitudinal areas are expected to experience increased precipitation, while large parts of the subtropics may see less rain. 

As recently as September 2021, Hurricane Ida brought in 3.15 inches of water to New York within a single hour, making it one of the largest floods the city had ever seen.

Earlier in July in Europe, the flash floods in Germany and Belgium left more than 200 dead and have left researchers thinking about when the next extreme rainfall event would hit. The World Weather Attribution network found that heavy downpours in Western Europe will be 1.2-9 times more likely and 3-19% heavier than before. It used to be that only one such extreme rainfall event in Europe could be experienced in 400 years.

Cities Are Most At Risk

Other recent flooding events in China and India are redirecting attention to urban areas, where even larger populations are threatened. In this study on hourly rainfall extremes, researchers demonstrated that the urban development in the city centre of Kuala Lumpur, Malaysia has caused more intense and extreme rainfall events to occur in the city than in surrounding rural areas. Using observations and modelling experiments, results showed a significant increase of hourly precipitation rates over the last thirty years. Compared to suburban Kuala Lumpur, the city centre experienced the urban heat island effect, which creates a more unstable atmosphere, increased vertical uplift, and moisture convergence, in turn leading to intense rainfall over the city.

To improve flood management and risk-reduction policies, researchers in Turkey conducted a study to analyse the relationship between urbanisation and floods. The analysis used images over a 30 year period to determine how large an area was affected by flooding in different years. Using these results as inputs for multi-criteria decision-making models, researchers created maps of basins that could be at high risk under various conditions such as variations in precipitation levels or changes due to human development.

Mohana Basu, a special correspondent for ThePrint’s PureScience podcast series, discussed how rising global temperatures are affecting several cities across the world with unprecedented levels of short-term rainfall. 

“You look at the annual rainfall levels, you will perhaps not see a huge departure from the long-term average, but more water falls over a short span of time, which is what our cities are absolutely not prepared for. On the other hand, the same mechanism also increases the odds of worsening drought in many parts of the world, warmer temperatures, and enhanced evaporation from soil,” she said.

A global perspective on this phenomenon reveals a whole new world of problems. Chennai, the capital of Tamil Nadu, for example, has no way to cope with its historic monsoon flooding that occurs every year from July through November. A rise in rainfall during these months will only increase the city’s vulnerability to storms and other unpredictable weather patterns.

As rainfall events continue to plague cities everywhere, smart city planners may have no choice but to alter their infrastructure for an unpredictable future.

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How Some Cities Have Adapted to Rising Rainfall

This question is now being asked in major cities around the world. To date, no single effective solution has emerged as a victor for combating this growing environmental issue. Despite this, many lessons can be learned from local governments embarking on paradigm shifts and innovations aimed at making cities more responsive to climate change.

Researchers in the coastal cities of Shenzhen and Hong Kong conducted a study to further inform flood management and risk-reduction policies. They proposed an equivalent drainage method, calibrated with a physically-based drainage model which considers varying rainfall intensities and sea levels to simulate the capacity of a network’s infiltration system.

In a joint project between Fukui and Toyama cities, scientists developed an integrated system that combines urban area rainfall radar and short-term rainfall prediction model technology with real-time runoff analysis. The system proved effective at helping governments prepare cities to manage water during heavy rainfall or flooding, giving residents enough lead time to set up sandbags around their homes and move cars away from flood zones ahead of a storm.

From an even wider perspective, Portland, Seoul, and Tokyo participated in a study on using the integrated social-ecological-technological systems (SETS) lens as a framework for flood risk management. According to this study, the three cities are integrating the SETS in their flood risk management plans since they realise that human-natural systems are closely linked. As a result of lessons learned from previous flooding events, all three cities have started to use green infrastructure, public education, and floodplain restoration as effective ways of mitigating urban floods. The new urban SETS flood vulnerability framework helps to engage stakeholders and co-produce multi-disciplinary knowledge that leads to sustainable infrastructure investments for resilient ecosystems.

Smart Cities are Key to Climate-Responsiveness

While no single method has proven entirely effective in combating rainfall’s effects on urban development, perhaps examining these case studies may give some insight into what needs to be done across the world. 

As scientists work towards finding more ways to mitigate flood risk in cities, local governments will need to prepare for disruptions in infrastructure while also encouraging citizens to embrace flood resilient strategies. In the next few years, it will be up to city planners and everyday citizens alike to take notice of global warming indicators, so that we can adapt accordingly. 

If we want to mitigate the impacts of flooding on our cities, then we will have to work together with the environment around us. The true challenge for smart city initiatives lies in transforming our current strategies into effective, citizen-driven, long-term policies that foster sustainable infrastructures that can withstand future environmental crises.

Featured image by: Pixahive