All coastal cities are facing sea-level rise, but some will be hit harder than others. Asian cities are in for a particularly rough ride. Part of the reason for that is that the populations of coastal cities are bulging: about four out of every five people impacted by sea-level rise by the middle of this century will live in East or South-East Asia.

Surging waters will lead to spiking food prices, growing hunger and social unrest. The conservative scientific consensus is that a 1.5°C increase in global temperature will see global sea levels rise between 1.7 and 3.2 feet by 2100. Even if governments, businesses and citizens somehow manage to keep global temperatures from rising to 2°C, by 2050 at least 570 cities and some 800 million people will be exposed to rising seas and storm surges.

It is not just people and real estate that are at risk, but roads, railways, ports, agricultural lands, sanitation and drinking water pipelines and reservoirs, as well as mass transit systems and underwater internet cables. While some coastal cities and nations will slip underwater, the rest will need to adapt - and quickly.

Few of the world’s fastest-growing coastal cities have yet to adequately prepare for rising sea levels in the 21st century. Making matters worse, a growing number of megacities such as Shanghai or Jakarta are sinking at the same time as seawaters are seeping in. This is not only because they are heavy, but due to the extraction of vast quantities of groundwater by their residents.

Chinese cities are taking action to mitigate and adapt to sea-level rise. The Chinese were motivated in part by disaster. In 1998, the country’s worst floods in half a century killed more than 4,000 people when the Yangtze River Basin overflowed. And massive cities like Beijing, which has more than doubled its total land coverage in the last decade, have also witnessed an uptick in floods. In fact, roughly 641 of China's 654 largest cities are affected by regular flooding, especially sprawling megacities on the coast.

Looking to the future, the Chinese government has responded with a combination of hard engineering, environmental and people-based strategies, together with the relocation of millions of citizens. Notably, in 2014, China launched the so-called “sponge city” initiative.

The term is not native to China, having originated in Hyderabad, in India, after city authorities started collecting storm water to offset water demand during planting season. Likewise, Vinh City in Vietnam also adopted a “city as sponge” strategy to lessen the impacts of seasonal floods on vulnerable urban areas.

In the case of China, the sponge strategy requires that 80% of all urban land is capable of absorbing or reusing 70% of storm water. The goal is to repurpose and retrofit cities – including public spaces, schools and residential areas – so that they can absorb more water. Candidate cities are investing in permeable pavement, artificial ponds and wetlands and rain gardens that store excess rainfall in underground storage tanks and tunnels. Water is only discharged into rivers after levels have receded. These kinds of projects do not come cheap, so some city authorities are entering into public-private partnerships to cover the costs. And since subsidies from the central government are due to end in 2020, local governments are scrambling to find investors – including real-estate developers – to fill the coming funding gap.

Still, at least 30 cities are part of the initiative, including Shanghai – one of the most flood-prone cities in the world. The Chinese expect that at least another 600 will join in the coming decade.

Shanghai’s authorities are putting enormous stock in adaptation strategies. And not without good reason – by 2050 the megacity is expected to experience flooding and rainfall that is 20% higher than the global average. The city is already rocked by two to three typhoons every year.

To reduce its exposure to rising seas, Shanghai has constructed 520 kilometres of protective seawalls, stretching across the Hangzhou Bay and encircling the islands of Chongming, Hengsha and Changzing. Shanghai has also installed massive mechanical gates to regulate overflowing rivers, similar to barriers established in Rotterdam.

From Asia to Europe and Africa to the Americas, sea-level rise is inevitable. Mitigation efforts must be scaled up. And adaptation is essential. At a minimum, governments, businesses and citizens need to avoid making a bad situation worse.

Upgrading zoning laws and reducing building in at-risk coastal areas and flood plains is the right place to start. Proactively developing strategies to relocate populations vulnerable to sea-level rise is no less important. Societies will need to develop new ways to share the burden of climate change, including sea-level rise. This will require innovative financing models and bold partnerships - and above all a new mindset primed to cope with too much, and too little, water.