The dry heart of Texas (Image: Eric Gay/AP/PA)

THEY like their beef in Texas. So when Texan ranchers started offloading their cattle at bargain prices because pastures were parched – as they did this summer – it was a clear sign that this was no ordinary drought.

While rains in October brought some relief, further drought is forecast, which will add to losses already exceeding $5 billion. The bigger question is whether the Texan rancher’s pain is a harbinger of things to come for the entire Southwest – and if so, what the broader impact on Americans living in the region will be.

Climate models indicate that the Southwest will get drier in the coming decades, threatening water supplies already under pressure from a growing population and ageing infrastructure.


Interactive graphic: “Parched future for the Southwest“

The most alarming projections come from a team led by Richard Seager of Columbia University’s Lamont-Doherty Earth Observatory in Palisades, New York. They ran 19 climate simulations, averaged out across the entire Southwest, and came to a stark conclusion: that conditions matching the 1930s Dust Bowl and the multi-year droughts of the 1950s “will become the new climatology of the American Southwest” within decades (Science, DOI: 10.1126/science.1139601).

Water infrastructure can be overhauled, and this is what some states – Texas included – are planning. But their proposals mostly do not allow for what climate change may bring. The latest draft of the Texas State Water Plan, for instance, assumes that between now and 2060 the most severe drought it will face will match the worst on record, from 1950 to 1956. Texan officials argue that climate models do not give sufficiently reliable projections, at the level of individual river basins, to warrant planning for even more severe droughts. “I really can’t adapt the planning assumptions,” says Carolyn Brittin of the Texas Water Development Board.

It is possible to “downscale” climate models to deliver local predictions, either using statistical techniques or by adjusting them to fit with regional weather models. Unfortunately, while downscaled models give fairly consistent projections for temperature, they do not for precipitation – a situation that is unlikely to change soon.

Nevertheless, some water resource managers are prepared to take climate change into account. The most ambitious such project is being run by the Bureau of Reclamation, a federal government body which manages dams and reservoirs across the region. Its Colorado River Basin Water Supply & Demand Study is considering 112 different climate “futures” for a watershed that supplies some 30 million people across seven states. On average, these scenarios suggest that total water flow into the upper Colorado basin will fall by about 9 per cent between now and 2060.

In Colorado, Denver Water, which supplies about a quarter of the state’s population, has used tree-ring records and downscaled climate models to build up a picture of possible future flows in rivers and streams in its catchment area. The tree-ring work shows that natural climate variability is likely to throw up worse droughts than those experienced since European settlement. Assuming warming of about 2.75 °C by 2050, the models also suggest there will be a water supply shortfall of 15 to 20 per cent, even if precipitation does not decline.

Denver Water is still deciding on its strategy, but given that more than half the water it supplies goes into watering lawns and other landscaping, it is likely to offer financial incentives for “xeriscaping” – replanting with native species that need less water.

In the longer term, there will be changes in store across the region. People may have to get used to the idea that water recovered from treated sewage is fit for drinking and not just for industrial use, for example.

People may have to get used to the idea that water recovered from treated sewage is fit for drinking

The cost of failing to plan for a drier future could be a replay across the Southwest of the hardship faced by Texans in 2011. But agencies that are planning for climate change say it will be possible to adapt. “It’s a manageable situation,” says Thomas Buschatzke of the Arizona Department of Water Resources. “But it’s not a situation that’s going to manage itself.”