Water? Government Reports Likely Dry Spell for Southwest

My earliest musical memories go back to the water song by the Sons of the Pioneers. Water. Cool water.

But a recent government report warns that water may become more scarce faster than we can adjust.

Studies of tree rings suggest that North America has suffered periods of mega-droughts that have lasted more than a few decades. And that was before the prospect of global warming intensified the risks. Here are some excepts from Chapter 3.

Hydroclimatic changes are likely to affect all regions in the United States. Semi-arid regions of the Southwest are projected to dry further, and model results suggest that the transition may already be underway (Hoerling and Kumar, 2003; Seager et al., 2007d).

The drying in the Southwest is a matter of great concern because water resources in this region are already stretched, new development of resources will be extremely difficult, and the population (and thus demand for water) continues to grow rapidly (see Fig. 3.1). This situation raises the politically charged issue of whether the allocation of around 90% of the region’s water to agriculture is sustainable and consistent with the course of regional development.

Mexico is also expected to dry in the near future, turning this feature of hydroclimatic change into an international and cross-border issue with potential impacts on migration and social stability. (p. 148)

The serious hydrological changes and impacts known to have occurred in both historic and prehistoric times over North America reflect large-scale changes in the climate system that can develop in a matter of years and, in the case of the more severe past megadroughts, persist for decades. Such hydrological changes fit the definition of abrupt change because they occur faster than the time scales needed for human and natural systems to adapt, leading to substantial disruptions in those systems. (p.150)

In the Southwest, for example, the models project a permanent drying by the mid-21st century that reaches the level of aridity seen in historical droughts, and a quarter of the projections may reach this level of aridity much earlier. It is not unreasonable to think that, given the complexities involved, the strategies to deal with declining water resources in the region will take many years to develop and implement. If hardships are to be minimized, it is time to begin planning to deal with the potential hydroclimatic changes described here. (p. 151)

However significant enhanced solar forcing has been in producing past megadroughts, the level of current and future radiative forcing due to greenhouse gases is very likely to be of much greater significance. It is thus disquieting to consider the possibility that drought-inducing La Niña-like conditions may become more frequent and persistent in the future as greenhouse warming increases.

We have no firm evidence that this is happening now, even with the serious drought that has gripped the West since about 1998. Yet, a large number of climate models suggest that future subtropical drying is a virtual certainty as the world warms and, if they are correct, indicate that it may have already begun. The degree to which this is true is another pressing scientific question that must be answered if we are to know how to respond and adapt to future changes in hydroclimatic variability. (p. 210)

See the final report on “Abrupt Climate Change” issued by the U.S. Climate Change Science Program and the Subcommittee on Global Change Research.


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