China’s ‘sponge cities’ aim to re-use 70% of rainwater. Here’s how they do it

The Sino-Singapore Tianjin Eco-city in Tianjin Binhai New Area, China. Image: EPA.

Asian cities are struggling to accommodate rapid urban migration, and development is encroaching on flood-prone areas. Recent flooding in Mumbai was blamed in part on unregulated developmentof wetlands, while hastily built urban areas are being affected by flooding across India, Nepal, and Bangladesh.

This is not a trend only in developing countries; floods in Houston, USA, highlighted the risks of development in environmentally sensitive and low-lying areas. In 2012, a severe flood in Beijing wreaked havoc on the city’s transportation systems, and in 2016 floods overwhelmed drainage systems in Wuhan, Nanjing, and Tianjin. The challenges are clear.

Groundwater over-extraction, waterway degradation, and urban flooding are forcing China’s cities to address a vicious cycle. Sprawling urban development and use of impervious material prevent soil from absorbing rainwater, prompting further investment in infrastructures that typically impede natural processes and worsen flood impacts.

China’s “sponge city initiative” aims to arrest this cycle through the use of permeable surfaces and green infrastructures. However, the initiative faces two challenges: lack of expertise of local governments to effectively coordinate and integrate such a complex set of activities, and financial constraints.


The concept

Engineering solutions are popular interventions, but cities cannot simply pipe away flood risks. To address the issue, China’s sponge city initiative has an ambitious goal: by 2020, 80 per cent of urban areas should absorb and re-use at least 70 per cent of rainwater.

Launched in 2015 in 16 cities, the initiative seeks to reduce the intensity of rainwater runoff by enhancing and distributing absorption capacities more evenly across targeted areas. The resulting groundwater replenishment increases availability of water for various uses. This approach not only reduces flooding but also enhances water supply security.

The initiative is similar to the North American concept of low-impact development (LID), which according to the United States Environmental Protection Agency (EPA) mimics natural processes in order to protect water quality.

The case of Lingang, a planned city in Shanghai’s Pudong district, illustrates typical sponge city measures. These include rooftops covered by plants, scenic wetlands for rainwater storage, and permeable pavements that store excess runoff water and allow evaporation for temperature moderation.

With ambitions to be China’s largest sponge city project, the Lingang city government has invested $119m in retrofits and innovations that could be a model for the majority of Chinese cities lacking modern water infrastructure.

Chinese cities are making noteworthy efforts. In a pledge to expand coverage of urban greenery, Shanghai announced in early 2016 the construction of 400,000m2 of rooftop gardens. The project is a collaborative effort among city regulators, property owners, and engineers. Sponge city projects in Xiamen and Wuhan have performed effectively during heavy rainfall.

Grassy rooftops in Shanghai. Image: kafka4prez/Flickr/creative commons.

Improved policies and budgets

The sponge city initiative requires a holistic and sustained effort, including effective environmental governance. However, concerns persist about weak regulations and selective enforcement. Local officials cannot simply turn the other way when violations are discovered. The unsung tedium of tightening controls is less exciting than bold innovations, but equally crucial for managing water. Gains from sponge city programs should not be offset by poor environmental governance.

Funding is also a persistent constraint. To date, more than $12bn has been spent on all sponge city projects. The central government funds roughly 15-20 per cent of costs, with the remainder split between local governments and the private sector.

Unfortunately, the initiative coincides with a burgeoning municipal debt crisis spurred in part by restrictive financial reforms, bond ratings cuts, and nervous bond markets. China’s cities may soon find borrowing costs even higher and avenues for reducing debts narrower.

Investment in sponge city initiatives is also proving to be an increasingly difficult sell, with only tepid interest from domestic private investors. The government should improve conditions that encourage investment, including tax incentives, better project transparency, and looser credit markets.

Until this happens, sponge city initiatives will have to compete against visible and familiar infrastructure such as roads, transit, and utilities. They will also have to be attractive in a market with numerous other investment options.

Innovative water initiatives have been adopted worldwide, including wetland restoration in the American Midwest, flushing systems using collected rooftop water in Oregon USA, bioswales in Singapore, and public spaces as flexible water retention facilities in the Netherlands.

The ConversationChina has an opportunity to strengthen its emerging global leadership role in urban sustainability. However, it must first implement an effective vision for how sponge city initiatives complement broader environmental governance efforts. Improving regulatory enforcement and reviving interest in related private investment opportunities are two steps it can take.

Asit K. Biswas is a visiting professor at the Lee Kuan Yew School of Public Policy, National University of Singapore. Kris Hartley is a lecturer in city and regional planning at Cornell University.

This article was originally published on The Conversation. Read the original article.

 
 
 
 

The IPPC report on the melting ice caps makes for terrifying reading

A Greeland iceberg, 2007. Image: Getty.

Earlier this year, the Intergovernmental Panel on Climate Change (IPCC) – the UN body responsible for communicating the science of climate breakdown – released its long-awaited Special Report on the Ocean and Cryosphere in a Changing Climate.

Based on almost 7,000 peer-reviewed research articles, the report is a cutting-edge crash course in how human-caused climate breakdown is changing our ice and oceans and what it means for humanity and the living planet. In a nutshell, the news isn’t good.

Cryosphere in decline

Most of us rarely come into contact with the cryosphere, but it is a critical part of our climate system. The term refers to the frozen parts of our planet – the great ice sheets of Greenland and Antarctica, the icebergs that break off and drift in the oceans, the glaciers on our high mountain ranges, our winter snow, the ice on lakes and the polar oceans, and the frozen ground in much of the Arctic landscape called permafrost.

The cryosphere is shrinking. Snow cover is reducing, glaciers and ice sheets are melting and permafrost is thawing. We’ve known this for most of my 25-year career, but the report highlights that melting is accelerating, with potentially disastrous consequences for humanity and marine and high mountain ecosystems.

At the moment, we’re on track to lose more than half of all the permafrost by the end of the century. Thousands of roads and buildings sit on this frozen soil – and their foundations are slowly transitioning to mud. Permafrost also stores almost twice the amount of carbon as is present in the atmosphere. While increased plant growth may be able to offset some of the release of carbon from newly thawed soils, much will be released to the atmosphere, significantly accelerating the pace of global heating.

Sea ice is declining rapidly, and an ice-free Arctic ocean will become a regular summer occurrence as things stand. Indigenous peoples who live in the Arctic are already having to change how they hunt and travel, and some coastal communities are already planning for relocation. Populations of seals, walruses, polar bears, whales and other mammals and sea birds who depend on the ice may crash if sea ice is regularly absent. And as water in its bright-white solid form is much more effective at reflecting heat from the sun, its rapid loss is also accelerating global heating.

Glaciers are also melting. If emissions continue on their current trajectory, smaller glaciers will shrink by more than 80 per cent by the end of the century. This retreat will place increasing strain on the hundreds of millions of people globally who rely on glaciers for water, agriculture, and power. Dangerous landslides, avalanches, rockfalls and floods will become increasingly normal in mountain areas.


Rising oceans, rising problems

All this melting ice means that sea levels are rising. While seas rose globally by around 15cm during the 20th century, they’re now rising more than twice as fast –- and this rate is accelerating.

Thanks to research from myself and others, we now better understand how Antarctica and Greenland’s ice sheets interact with the oceans. As a result, the latest report has upgraded its long-term estimates for how much sea level is expected to rise. Uncertainties still remain, but we’re headed for a rise of between 60 and 110cm by 2100.

Of course, sea level isn’t static. Intense rainfall and cyclones – themselves exacerbated by climate breakdown – can cause water to surge metres above the normal level. The IPCC’s report is very clear: these extreme storm surges we used to expect once per century will now be expected every year by mid-century. In addition to rapidly curbing emissions, we must invest millions to protect at-risk coastal and low-lying areas from flooding and loss of life.

Ocean ecosystems

Up to now, the ocean has taken up more than 90 per cent of the excess heat in the global climate system. Warming to date has already reduced the mixing between water layers and, as a consequence, has reduced the supply of oxygen and nutrients for marine life. By 2100 the ocean will take up five to seven times more heat than it has done in the past 50 years if we don’t change our emissions trajectory. Marine heatwaves are also projected to be more intense, last longer and occur 50 times more often. To top it off, the ocean is becoming more acidic as it continues to absorb a proportion of the carbon dioxide we emit.

Collectively, these pressures place marine life across the globe under unprecedented threat. Some species may move to new waters, but others less able to adapt will decline or even die out. This could cause major problems for communities that depend on local seafood. As it stands, coral reefs – beautiful ecosystems that support thousands of species – will be nearly totally wiped out by the end of the century.

Between the lines

While the document makes some striking statements, it is actually relatively conservative with its conclusions – perhaps because it had to be approved by the 195 nations that ratify the IPCC’s reports. Right now, I would expect that sea level rise and ice melt will occur faster than the report predicts. Ten years ago, I might have said the opposite. But the latest science is painting an increasingly grave picture for the future of our oceans and cryosphere – particularly if we carry on with “business as usual”.

The difference between 1.5°C and 2°C of heating is especially important for the icy poles, which warm much faster than the global average. At 1.5°C of warming, the probability of an ice-free September in the Arctic ocean is one in 100. But at 2°C, we’d expect to see this happening about one-third of the time. Rising sea levels, ocean warming and acidification, melting glaciers, and permafrost also will also happen faster – and with it, the risks to humanity and the living planet increase. It’s up to us and the leaders we choose to stem the rising tide of climate and ecological breakdown.

Mark Brandon, Professor of Polar Oceanography, The Open University.

This article is republished from The Conversation under a Creative Commons license. Read the original article.