The world's population and agriculture hotspots are particularly sensitive to changes in the capacity of mountains to store water, geological scientists say. ( dpa )
Both naturally occurring and man-made climate factors are affecting the capability of the world's mountain ranges to serve as sources for freshwater for adjacent lowlands. According to a recent study, about 7 per cent of the world's mountains are essential for providing downstream supply, said Daniel Viviroli of the University of Berne.
This number is likely to increase, as 37 per cent provide an important supply that will grow more important in years to come. The dryer the lowland climate gets, the more important the mountains become, Vivrioli said.
"If we want to know about the consequences for arid and semiarid areas, we need to be aware of the runoffs," he said, speaking on the sidelines of the annual meeting of the European Geosciences Union in Vienna.
Precipitation runoff from the world's mountain ranges are the main contributor to freshwater resources in the surrounding lowlands and are essential for agriculture or drinking water.
"Pressure on resources will increase in the subtropics, arid and semiarid regions," he said.
Current research on climate change predicts that "wet places will get wetter and dry places will get dryer," climatologist Philip Mote from the University of Washington said.
Temperature increases have triggered a string of knock-on effects, said Carmen de Jong of France's University of Savoy, who investigates mountain hydrology in the European Alps.
"Everything is being pushed higher," she said.
Snow levels were moving up ever higher in the mountains, and tourism is following.
Less water from snow and glaciers means less water in reservoirs, while ever more was needed for the tourism industry, likely to offset the fragile balance of mountain ecosystems.
"We observed a decrease of water surcharges since 1985," de Jong said.
At the same time there has been an exponential increase in water needs.
This could turn into a vicious circle, the scientists feared. Water consumption is expected to increase because of increased temperatures, while at the same time resources were dwindling because of the warmer climate, which was likely to decrease precipitation and increase evaporation.
One aspect the scientists pointed out was the shift of the timing of snowmelts, which were a major source of freshwater for lowland streams in dry summer months.
There could well be the same amount of water coming down from a mountain, but with an earlier onset of the snow melt, the timing was off for farmers, Mote said.
One group feeling the effects of water coming from the mountains' melting snow covers each summer would be farmers: up to 70 per cent of the world's freshwater use goes into food production.
The problem was less removed than people might believe, de Jong said.
"People have problems, but often they are local," she said. "People think they are alone with their problems."
Scientists had by now figured out the natural effects in a mountain's water system, but little data was available as of yet on human-generated effects.
"We don't know what is going on," de Jong said.
The question whether there would be enough water stored in the world's alpine water towers 50 years down the track could not be answered that easily, Mote said.
"It depends on where you are. South of 50 degrees latitude there will be questions about water supply," he said.
In the hotspots, the water resource balance was likely to "go the wrong way," Mote said.
The problem that needs to be tackled is global, the scientists warned.
"All mountain areas have the same problem," de Jong said.
Even in Europe's Alps, probably one of the epitomes of snow - covered slopes and lush, green hills, ground-water levels in some regions dropped by 25 per cent over the past 100 years.
"There are no water management strategies now," de Jong warned of the dry times ahead.