There are many reasons to worry about the connections between climate change and drought. As temperatures increase, they change precipitation patterns for several reasons. These include changing the rate of evaporation from rivers and lakes, altering the composition of ecosystems, and other impacts. Forests, in particular, play important roles in the hydrological cycle. Some, like Kenya’s Mau forest, are hydrologically critical for large regions. If climate change makes forests change composition, dry out, and burn, it could have big effects on downstream agriculture.
Another major danger is loss of glaciers and summer snowpack. Both play a moderating role when it comes to river levels: accumulating snow in winter and releasing it as meltwater in summer. When rivers lose this buffer, they expand in wet times and shrivel in dry ones. This is dangerous not only for agriculture, but for electrical generation as well. The Colorado River, host to a slew of dams, may encounter serious problems of this sort in coming decades. Lake Mead, located on the Colorado and serving Las Vegas, is drying up dramatically. So will many others. Himalayan glaciers are especially concerning, given how important they are to the flow patterns of major rivers that serve densely populated areas.
Desalination, as an alternative to fresh water use, has major problems of its own – foremost among them that it uses a lot of energy. If that energy is coming from fossil fuels, the use of desalination may well worsen water problems in the long term, by contributing ever more to the stock of greenhouse gasses in the atmosphere.
Responding to all of this requires more than just climate change mitigation. It also requires more intelligent water policies, such as discouraging the overuse of non-renewable aquifers and ensuring that farmers and industrial users of water pay for it at a level that encourages responsible use. People who argue that ‘water is a human right’ and should therefore be free are ignoring the fundamental problem of scarcity. If we allow heavy users unlimited license to take what they want for next to nothing, we risk depriving other people of the more basic right to the quantities required for basic consumption and sanitation. The alternative is to effectively subsidize drought. States should also be thinking about ways in which they can import ’embedded water’ in the form of crops from wetter regions. Growing wheat in deserts is a folly some states have indulged in so far, but may do well to abandon in a more water-constrained (and riverflow-variable) future.