The Puebloan Indians of the Southwest developed a mastery of irrigation that allowed them to thrive for centuries after they migrated north from present-day Mexico. Early American archaeologists termed them "the Canal Builders."

By the 13th century, however, this flourishing civilization abandoned most of its magnificent cities and ceremonial sites in parts of Arizona, New Mexico, Colorado and Utah, thanks to a 60-year drought.

California is currently experiencing its most severe sustained drought in the past 1,200 years. While rainfall amounts have fluctuated widely during past decades, rain doesn't tell the whole story. Periods between rains, and rising ambient temperatures, can influence the amount of moisture retained by the soil. That's why we're told that even the occasional torrential downpour has not broken the drought.

Heavy rains exceed the ground's capacity to absorb a lot of water in a short time. The excess runs into rivers and streams, much to be carried downstream away from the drought-stricken areas.

Higher temperatures increase evaporation from surface water and soil, depleting the reserves we count on to tide us over between rains. Exuberant irrigation contributes to evaporative losses and aquifer depletion -- until the wells and streams run dry, as they have in some parts of California. A friend in Stockton told me their well played out last summer; it is slowly recharging, but dry creek beds and a trickle of water in the Solomon aren't contributing much.

We continue to drain the Ogallala Aquifer faster than nature replenishes it. We're pumping fossil water to irrigate corn to convert into alcohol to slightly mitigate fossil fuel use. When the water is gone, we can't drink petroleum products.

Our governor and his committees, responding to special interests, are fiddling while the aquifer burns. (It's a strained metaphor, but Nero would understand.) Give us another 50 years and we'll be fully prepared to get started using our aqueous resources more rationally.

That the globe is warming, and that humans are playing a major role in the process, is not disputed by the vast majority of relevant sciences. Peruse premier multi-disciplinary peer-reviewed science journals like Science, and you'll find an abundance of studies on climate change issues. There is no longer any discussion centered on whether climate change exists; now it's all about how it will manifest, how fast, in which geographic regions, and what effects it will have on humans.

Jason Smerdon, a climate scientist at Columbia University's Lamont-Doherty Earth Observatory, is co-author of a study that shows, he says, that the 60-year Puebloan drought will look "quaint" compared to what will happen over the next century.

As solar energy builds up on our planet, it fuels chaotic events -- as we see when energy is added to a pot of water. It doesn't just warm up smoothly and evenly -- it roils and swirls, and the first bubbles can show up anywhere along the surface.

That climate extremes can manifest as increasing droughts has been supported by previous studies. Smerdon, et al, have brought a new degree of precision to drought predictions by analyzing historical drought records and extending that analysis to mesh with today's observed soil moisture measurements.

The Crystal Ball of Science is sometimes murky. In this case, the methodology has been refined to new degrees of precision, and covers many variables.

Seventeen state-of-the-art climate models' forecasts address three different measures of soil moisture over the next century, anticipating changes in rainfall and accelerated evaporation due to global warming. They also incorporate variables like wind speed and humidity.

But these are just models, right? Why should we value them?

Compiling drought histories often employs the Palmer Drought Severity Index as a proxy for soil moisture. It's widely used to assess drought, current or past, as it can be calculated from precipitation and temperature measurements alone. Its very simplicity has raised doubts over whether PDSI accurately represents the real world.

These researchers carefully examined the years between 1931 and 1990, a period for which we have very complete tree-ring records. ("Dendrochronology" allows us to identify both the dates of a tree's growth, and factors affecting its growth rate, such as available moisture.)

They used this data to predict future soil moisture changes; the predictions could be checked for accuracy by comparing them to actual, recorded soil moisture changes over the same period. They found the two data sets -- predicted and actual -- were "statistically indistinguishable." This confirms PDSI is a reliable measure of soil moisture, and can be used to predict future trends.

It also supports previous studies suggesting the thousand-year PDSI record accurately reflects past droughts. This makes it a valid benchmark for predicting the severity of future droughts.

These 17 models were all constructed differently, using varying but plausible assumptions and statistical approaches, but they all converged on the same answer.

The projected drought trends "are really quite robust and in many cases scary when you compare them to even the megadroughts" of the 12th and 13th centuries.

There's an 80 percent likelihood that at least one decades-long megadrought will hit the Midwest and Southwest between 2050 and 2100. Surface and groundwater resources will be severely strained. We might face abandonment of our modern communities, too.

This is our most sophisticated effort connecting ancient drought records with projections of future change.

Wat'cha gonna do when de well run dry?

Jon Hauxwell, MD, is a retired family

physician who grew up in Stockton and now lives outside Hays.

hauxwell@ruraltel.net