Why Water is the Sharp End of the Climate Change Stick

Earlier this year, the city government of Bangkok reported its greenhouse gas emissions and other climate change-related information to the Carbon Disclosure Project. Its analysis of the risks that the city faces from climate change is proving prescient:

"The tide from the Gulf of Thailand affects the water level in the Chao Phraya River and can rise to 2.1 meters (mean sea level). At the same time, because the city is close to the sea, the direction of flow of the Chao Phraya River at high tide can be reversed and in the process the river can over flow its banks when tidal surges meet the heavy runoff from other parts of the country."

The recent heavy rains in Thailand have very nearly made this risk a reality. On Tuesday, the water level in the Chao Phraya River -- the main waterway through Bangkok -- reached 2.44 meters at high tide, with widespread flooding in some parts of Bangkok and in its surrounding areas. According to the city government, annual rainfall as of October 21 was more than 40 percent above average.

Water is the sharp end of the climate change stick. Too much and a city floods; too little and a city dries up. Our organization, CDP, has traditionally focused on climate change data, such as greenhouse gas emissions, fuel use, risks and opportunities. But we are increasingly attuned to the links between climate change and water.

In 2009, we launched CDP Water Disclosure, which provides a platform for the world's largest corporations to report on their water use and their water-related risks and opportunities. And this year, inspired by the response from Bangkok and other cities, we are adding a number of water-related questions to CDP Cities, our reporting platform for municipal governments.

Bangkok is far from the only city with a serious water risk story to tell. A recent study by the Natural Resources Defense Council, "Thirsty for Answers," found that all 12 of the U.S. communities they surveyed faced "significant water-related vulnerabilities because of climate change." Our own data tells a similar story. Of the 48 cities that reported their climate change data to CDP last year, more than two-thirds mentioned water as a risk.

The ways in which water can present risks to cities are myriad. Flash precipitation events can damage city infrastructure and lead to loss of life. In 2010, Rio de Janeiro experienced one of the worst natural disasters in Brazil's history when an intense rainfall led to landslides and flooding that affected more than 800 people.

But many cities are also simultaneously likely to face droughts and water shortages. In Johannesburg, more frequent droughts cause a " 'disruption to water security' with effects on sanitation and human health," according to the city's 2011 CDP Cities response.

Water supply issues also present significant risks for businesses. The current flooding in Thailand, for example, has caused the closure of more than 10,000 factories -- affecting companies including Honda and Western Digital -- and the central bank has recently reduced its estimates of GDP growth for Thailand by 40 percent. In Rotterdam, which hosts the Netherlands' main port, drought could limit the flow of goods that travels from Rotterdam to the interior via the country's river system. Water is also a key component for energy production.

In its 2011 CDP Cities response, Seattle reported that reduced average annual rainfall is "leading to changes in the amount of water available for electricity generation and community water supply (energy and water supply)."

Despite the severity of the water impacts we've mentioned here, cities like Bangkok, Rio, Seattle and Rotterdam are leaders in addressing these risks. The first step to managing risks is to identify them.

Cities that identify the risks their city will face and make plans for the future are those that will best be able to guarantee water and energy security. By including water-related questions in our annual CDP Cities platform this year, we hope to catalyze more cities to measure and manage water-related risks.