The science of drought

There’s sometimes confusion over the difference between drought and water scarcity. Drought refers to a deviation from the normal situation - where there is less water in rivers and in the soil.

Water scarcity, on the other hand, refers to an imbalance between water supply and the demand for water, where demand exceeds supply.

Lena Tallaksen, professor in hydrology at the department of Geosciences at the University of Oslo, says it is important to take human impacts like water withdrawal into account when looking at drought trends.

Professor Tallaksen, who is a member of the European Drought Centre, a portal for drought information established after the drought of 2003, warns that southern and eastern Europe is getting drier, which is a concern for the already water-scarce regions around the Mediterranean.

“Higher temperatures combined with a reduction in precipitation are driving the trend and even places which are seeing increased annual precipitation may experience a trend towards a drier spring and summer because of the reduction in seasonal rainfall combined with higher temperatures,” she says.

“A marked shift towards drying trends is observed in April, gradually spreading across Europe to reach a maximum in August. That’s not a prediction: that’s what we are seeing.”

Drought risk spreads
The effects of drought are spreading across Europe, with a northward shift of the dry Mediterranean type climate influencing climate variability in Central and Eastern Europe. It could mean that we will all experience drought and heat wave conditions more frequently, Professor Tallaksen says.

“As the soil dries out during dry weather, less energy is used for evaporation and more for heating the air. Heat waves thus frequently accompany major droughts,” she says. “This increase in variability will likely lead to more droughts in many regions in Europe in the future.”

Drought risk mitigation would be helped by the existence of an early warning system for drought, even though the continent’s complex climate system makes forecasting difficult. To that end, the European Commission’s joint research centre is helping to fund the development of a European Drought Observatory (EDO) to detect, monitor and forecast drought across Europe and elsewhere in the world.

The EDO project started last year and the EC wants to have a map server and advisory web portal up and running in 2012. Weather data, combined with soil moisture readings and vegetation status, will be used to create a “drought indicator” and probabilistic forecasts.

Problems in data sharing to build models
The longterm objective of the European Drought Centre, which collaborates with the EDO, is to help mitigate the impacts of droughts on society, the economy and environment.
But there are problems getting data from some countries, in particular in Eastern and Southern Europe. Ironically, the countries where there are barriers to data sharing - administrative, political, technical or financial - are also those predicted to be worst hit by drought in the future.

“We would like to encourage all data users and producers to engage in better databases and sharing. The data is needed urgently and will benefit everyone,” Professor Tallaksen says.

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