The latest issue of the journal Nature Climate Change included what might be viewed as a scholarly good-news/bad-news riff on future supplies of fresh water around the world. The good news, as described here by my colleague Justin Gillis, is that climate change is likely to lead to a greater number of fierce rainstorms, which could do more to recharge groundwater aquifers in some parts of the world.
The bad news is that climate change is likely to lead to smaller snowpacks in mountain ranges and even on lower ground throughout the Northern Hemisphere, from the Cascades, Rocky Mountains and Sierra Nevada in the western United States.to the Himalayas and the Urals on the other side of the globe.
The studyby Noah Diffenbaugh, a Stanford University climate scientist, suggests that within two generations’ time, these areas will be experiencing years of low snowfall far more often than they have in the past three decades.
Not all of the billion or more people in the drainage basins fed by snowfall will suffer severe consequences if this comes to pass . In India, for example, monsoon rains provide a large portion of the water. But in
places like Pakistan, Central Asia and parts of China that are more dependent on what Dr. Diffenbaugh, an assistant professor of earth system sciences, calls “hard water” — glaciers and snow
— water supplies are likely to become more irregular.
The study, which presented a variety of situations reflecting the range of predictions on the extent of warming, showed that if global temperatures rise 2 degrees Celsius (3.6
degrees Fahrenheit) beyond what they were in pre-industrial times, about 30 percent of the planet’s winters are increasingly likely to produce seasonal snowfall below the current record low levels. What now
happens once a decade or even more rarely would happen every three years or so within a couple of generations.
The worries about California’s water resources, given the state’s dependence on snow melt, have already been well chronicled, and western states that agreed in 1922 to divvy up the waters of the Colorado River have also been studying the problem as average flows have decreased. Dr. Diffenbaugh said that Pakistan, too, is making the issue a centerpiece of its reports on the potential impacts of climate change.
But all predictions based on computer projections have inherent uncertainties. What is more, a time horizon of two generations — 40 to 60 years — is short for engineers anywhere in the world, who build water-delivery systems designed to last 75 years or more. “Anywhere where the management system has been built” based on historic experience, Dr. Diffenbaugh said, “there is a potential for impact.”
“There’s a clear shift in these regions towards not only more precipitation falling as rain, but earlier melt of what does fall,” he said.