"Many studies have already shown that the developing world is particularly vulnerable to the impacts of climate change," Philip Ward of the VU University Amsterdam in the Netherlands told environmentalresearchweb. "In this study we show that the costs of adaptation to climate change in the industrial and municipal water supply sector are also greater for developing countries than for developed countries, both in absolute terms and as a percentage of GDP."

The highest climate adaptation costs were for sub-Saharan Africa, where western Central Africa is projected to dry, followed by Latin America, which is likely to see increased seasonal and interannual rainfall variability in eastern Brazil.

To come up with the figures, the team first analysed the cost of meeting existing and future demand for water by 2050 without the effects of climate change, in what they called the baseline scenario. "Since present-day demand is not yet met, baseline costs cover both the elimination of any development deficit, and the consequences of socioeconomic development without climate change," explained Ward.

The researchers then analysed the effect of adaptation to climate change over and above this baseline, using one emissions scenario and two global climate models to project the effects of climate on water supply.

"We found that in most regions the baseline costs far exceed adaptation costs," said Ward. "This supports the notion of mainstreaming climate-change adaptation, and current and future climate vulnerability, into broader policy aims. It raises the question of 'how much climate change adaptation should be factored into the current design of water supply systems?' "

On a global scale, the baseline costs for water supply were $73 billion per year, compared with $12 billion per year for adaptation to climate change.

The researchers assumed that increased demand for water was met by building additional surface reservoirs, unless this would cost more than $0.30/cubic metre of water, or take up more than 80% of run-off. In those cases, the demand was met by other techniques, such as desalination, recycling, rainwater harvesting, at an assumed cost of $0.30/cubic meter.

The building of reservoirs is controversial as it can cause heavy environmental and social impacts. The team's projections indicate that under these assumptions, global reservoir storage capacity would need to increase by around 34–36% by 2050 to cope with water demand.

According to Ward, the lack of research on the costs of climate change was highlighted in the IPCC's Fourth Assessment Report. "Such information is of key importance in international negotiations such as the CoP [Conference of the Parties] events of UNFCCC," he said. "The results of our work can assist in such negotiations."

Now the researchers hope to use their method with a larger number of climate models and more emissions scenarios, which will give an insight into the size of the uncertainty in costs resulting from the uncertainty in climate projections. The VU University Amsterdam is developing a global flood risk model to improve global estimates of adaptation costs related to flood risk management. And the MIT Joint Program for the Science and Policy of Global Change is incorporating the work into their Integrated Global System Model framework for assessing global climate change impacts and adaptation.

The researchers reported their findings in Environmental Research Letters (ERL).