Cyclone Michaung points to a looming urban crisis

Surge in urban floods represents a complex challenge stemming from the interplay of urbanisation, inadequate planning and the climate crisis

Climatologically, two or three tropical cyclones (TC) form over the northern Indian Ocean during the post-monsoon season (October-December). TC Michaung, which devastated the coastal areas of northern Tamil Nadu (TN) and southern Andhra Pradesh (AP), was the fifth this season. Extremely heavy rains and strong winds accompanied Michaung; Chennai reported in excess of 500 mm of rain within 36 hours. While this is not unprecedented, it is a rare event. Although the death toll was limited to around 20, the damage is estimated to be at least ₹11,000 crore. Crop damage and losses due to flooding of fields were also reported in AP. The India Meteorological Department (IMD) had predicted the track and landfall very accurately. IMD’s predictions for rainfall associated with the storm were also quite good. While the TN and AP governments were able to save many lives, the damage caused by rising water levels could not be averted. The last time Chennai was hit by such a flood was in 2015 when heavy rains occurred in conjunction with a strong northeast monsoon.

Cyclone Michaung hit Chennai. (PTI)

Is this due to the climate crisis? It could be. The next question might be whether this type of event can be expected in the future. The answer is yes and with increasing frequency.

The warming of oceans due to the human-induced climate crisis will probably lead to stronger TCs. The destructive power of individual TCs through flooding will be exacerbated by rising sea levels. In addition, heavy rainfall associated with TCs will continue to grow due to increased atmospheric moisture associated with global warming. Climate models predict that global warming will lead to a slowdown in the forward motion of TCs in the coming decades. It is important to note that Michaung moved very slowly around the Chennai coast before making landfall near Bapatla in AP, causing extremely heavy rainfall. It is widely believed that the current trend of global warming will lead to a further increase in extreme rainfall events, which, in turn, will increase the risk of flooding in many cities. In fact, the combined effects of the observed climate crisis and urbanisation have led to a significant increase in urban flooding in recent decades.

A major catalyst for increasing urban flooding is the transformation of natural landscapes through rapid urbanisation. Their mutation into impervious surfaces reduces the infiltration of water into the soil and increases surface runoff and flooding. The increase in runoff can be significant, as even a 10% to 20% increase in impervious surfaces can double runoff. The higher runoff and peak stream discharges in heavily built-up urban areas lead to higher flood damage. Coastal cities such as Chennai are particularly vulnerable as rising sea levels amplify the impact of storm surges by breaching flood defences and inundating low-lying areas. According to reports, at least 300 tanks, canals and lakes that existed 20 years ago have disappeared in Chennai. Much of the city’s infrastructure and technological facilities are built on marshlands, water bodies and watercourses.

Inadequate stormwater management systems, outdated drainage networks and the neglect of natural waterways exacerbate the vulnerability of urban areas to flooding. Even large cities with complex drainage networks are facing growing challenges due to increasing flood volumes. The design standard of current urban drainage systems is often based on historical rainfall events without considering the potential changes in rainfall for the intended rainfall return period. Therefore, current infrastructure (drainage systems and the capacity of dams) may be increasingly affected by the additional flooding caused by the climate crisis in the future.

Although flooding cannot be completely avoided, its consequences can be minimised through appropriate mitigation measures. Traditional methods of flood management by improving drainage capacity may be difficult to implement in highly developed cities, which are also not flexible enough to cope with the effects of the climate crisis. Recent studies have shown that the concept of Low Impact Development (LID) practices in urban areas is effective in adapting to the potential impacts of the climate crisis on urban flooding.

In conclusion, the surge in urban floods represents a complex challenge stemming from the interplay of urbanisation, the climate crisis, and inadequate urban planning. Tackling this crisis demands collaborative efforts from governments, urban planners, and communities to implement sustainable solutions that safeguard our cities against the growing threat of inundation.

While the COP28 meeting in Dubai is underway, there is little hope that we can limit global warming to the desirable level of 1.5 degrees Celsius. Rather, we should now hope to stay below 2 degrees Celsius. However, the Intergovernmental Panel on Climate Change report suggests that the devastating effects of 2 degrees Celsius warming could be many times greater than the effects of 1.5 Celsius warming. As greenhouse gas emissions reach new highs, the UN’s Emissions Gap Report 2023 finds that the world is heading for a temperature rise that far exceeds the targets of the Paris Agreement unless countries do more than they have promised. The year 2023 will likely be the warmest ever recorded in instrumental records.

The UN report calls on all nations to accelerate the transition of the entire economy to low-carbon development. Countries with greater capacity and responsibility for emissions must take more ambitious action and support developing countries in their low-carbon development growth. However, no breakthrough in terms of commitment from industrialised countries can be expected from COP28. Apparently, they do not want to discuss fossil fuel divestment at these meetings as they believe it could ultimately hinder development and take us back to the old days when humans lived in caves.

In the meantime, cities like Chennai will continue to drown underwater.

M Rajeevan, former secretary, ministry of earth sciences, is vice-chancellor, Atria University, Bengaluru. The views expressed are personal