Climate change confuses freshwater household

Water management in the 21st century: calculating with the unknown

The model projected changes in the average annual water outflow from ice-free land (2041-2060 vs. 1900-1970) in percent. This is based on the conditions of the scenario "SRES A1B" of the Intergovernmental Panel on Climate Change. © Science
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Climate change overrides a basic assumption of water management: today's use of freshwater resources is based on the fact that precipitation and runoff from bodies of water fluctuate within fixed limits. But the human impact on Earth's climate changes the average and extreme values ​​of these factors, so that the principle of so-called stationarity no longer applies, scientists report in the current issue of the science magazine "Science".

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In water management, water supply and demand must be balanced and risks to the lives and property of people minimized, without foreseeing natural events such as droughts or floods. So far, future conditions have been best estimated by looking back in time. "However, climate change increases the likelihood of droughts or floods in the future that have never been seen before, " says Christopher Milly of the US Geological Survey (USGS).

Serious changes in the water balance

"When investing in the infrastructure of water management, the uncertain and changing climate must be taken into account, " says Zbigniew Kundzewicz, head of the hydrology group at the Potsdam Institute for Climate Impact Research and co-author of the "Science" article. Every year around € 345 billion is spent on hydraulic engineering projects such as sewers, dams and hydroelectric power stations worldwide. When planning new infrastructure and the maintenance of old one must now adjust to non-stationary conditions. "The expected changes in the water balance will go far beyond the limits of fluctuations observed so far, " says Kundzewicz.

As the authors describe in their article, the increase in average air temperature causes more water to evaporate and enhances water transport in the atmosphere. Where water-vapor-rich air currents converge, precipitation increases and the risk of flooding increases. The meltwater of glaciers temporarily increases the water availability. But where glaciers and snow cover dwindle, less frozen fresh water is stored. In coastal regions, the deposits are endangered by the rise in sea level, the scientists report. The risk of saltwater entering increases with sea level. display

Winner and Loser

Projections of water availability provide a complex picture of winners and losers among the regions of the earth. Using data from several climate models, the researchers have created a world map resolved by country. The map shows where total runoff is likely to decrease and where it is expected to increase. The global pattern of trends already observable is unlikely to have any natural causes. It is, however, consistent with the effects of climate change simulated in models.

Water availability in the northern latitudes and in some tropical regions is likely to increase. It is likely to decline in the Mediterranean, South Africa and southwestern North America. "In these dry regions, the risk of dehydration increases, " says Milly.

"Stationarity can not be revived, " says Kundzewicz. Even if effective climate protection measures are taken, one must assume that the global climate continues to heat up. The greenhouse gas carbon dioxide, which has already been emitted, remains in the atmosphere for a long time and the earth's climate system reacts slowly to changes in the concentration of other climate-relevant gases.

Adapting water management to climate change

However, water management planning can be adapted to climate change. Climate research is making rapid progress and expanding the knowledge base. A fast and comprehensive exchange of information between climate research and water management is crucial, write the authors. New, higher-priced models would then better map the ground and surface water.

The models should also take greater account of the water management infrastructure and water use, for example in agriculture or the energy sector. Their statements could only supplement, but not replace, measurements, the authors write, suggesting that the analytical strategies should now be adapted to the new, non-stationary conditions. "The assumption that the past is the key to the future has lost much of its value to water management, " says Kundzewicz.

(idw - Potsdam Institute for Climate Impact Research, 01.02.2008 - DLO)