Less snowfall, less water

That's the conclusion reached by a Columbia University project which examined 421 mountain drainage basins on four continents. They reviewed current climate-change models and analyzed present demographics and water-use patterns to identify ninety-seven drainage basins in which people run at least a two-thirds chance of experiencing serious water shortages in the future. 

Snow-covered mountains supply a lot of our water as they store enormous amounts of precipitation in the winter and then release it gradually as meltwater in the spring and summer, precisely when people at lower altitudes need it for irrigating crops. But snowfall levels are expected to decrease in many parts of the world as a result of climate change. What happens then? 

The scientists conclude that two billion people live in regions that are likely to experience much drier springs and summers by the end of this century as a result of nearby mountain ranges accumulating less snow in winter months. The regions likely to be affected include Northern and Central California; a large swath of the American Southwest and northern Mexico; and vast stretches of Iran, Syria, and Iraq. Also likely to be affected are parts of Portugal, Spain, and France; a section of Northern Africa; and parts of Italy, the Balkans, and Central Asia. The lead scientist says, “Mountains in these areas are likely to receive more of their winter precipitation as rain, which will wash away. The snow that does fall will melt earlier in the year."