The Human Costs of Droughts Then and Now

The archaeological record suggests that the extended periods of drought in the Medieval era caused severe hardship for both coastal and inland peoples— particularly the ancestral Pueblo communities—as dwindling resources increased disease, malnutrition, and warfare. Long inhabited sites were abandoned as the desperate populations wandered in search of new water sources.

Ancient pueblo cliff dwelling at Mesa Verde, southwestern Colorado. (Photo taken by B. Lynn Ingram)

Much of what archaeologists know about the ancestral Pueblo comes from pueblo and cliff dwellings from the four corners region, including Chaco Canyon in northwestern New Mexico, Mesa Verde in southwestern Colorado, and Canyon de Chelly in northeastern Arizona.

Chaco Canyon in New Mexico was the site of one of the most extensive of the ancestral Pueblo settlements. At its peak, during the 11th and early 12th centuries CE, Chaco Canyon had great pueblos the size of apartment blocks housing hundreds of residents in large, high-ceilinged rooms.

These settlements were supported by agriculture, allowing people to settle in one place year-round. Most of the farming depended on annual rains, supplemented by water from nearby streams and groundwater.

But over time, the climate became increasingly arid and unpredictable. The ancestral Pueblo farmers were forced to build an extensive system of diversion dams and canals, directing rainwater from the mesa tops to fields on the canyon floor, allowing them to expand the area of arable land.

The population in the four corners region swelled throughout the 11th and 12th centuries CE—but then collapsed.

Another ancient society, the Hohokam, lived in central Arizona near the confluence of Arizona’s only three rivers, the Gila, Verde, and Salt. The Hohokam civilization thrived in central Arizona for a thousand years, building an extensive network of integrated canal systems, capable of transporting large volumes of water long distances.

At their peak, an estimated 40,000 Hohokam lived in Arizona, but they suddenly vanished in the mid-15th century.

Montezuma’s Castle, a cliff dwelling occupied by the Sinagua, located just north of Camp Verde in central Arizona. (Photo by B. Lynn Ingram.)

In northern Arizona, between Phoenix and Flagstaff, the Sinagua culture also thrived during this period. As the climate turned drier, they built cliff dwellings in central Arizona, suggesting that resources became scarce, forcing them to build fortified dwellings with hidden food storage areas. The Sinagua also disappeared about the same time as the Hohokam.

All of these societies were flourishing prior to a rather abrupt collapse. The archaeological record of the last decades of the ancestral Pueblo in Chaco Canyon abounds with signs of suffering.

Skeletal remains show signs of malnutrition, starvation and disease; life spans declined and infant mortality rates increased. Evidence of violence, possibly warfare, was found in mass graves containing bones penetrated with arrowheads and teeth marks, and skulls bearing the scars of scalping.

Piles of belongings were found, apparently left behind as the people abandoned their settlements and fled, some to live in fortified hideouts carved in the cliff faces, protecting their hoarded food from enemies.

The unusually dry climate of the Medieval period also appeared to have tested the endurance and coping strategies of even the well-adapted native populations in California.

The skeletal remains show that life in the interior of California was particularly difficult, as the drought severely reduced sources of food (nuts, plants, deer, and other game). Settlements along rivers were abandoned, and trade between inland and coastal groups broke down. As water supplies dried up, conflicts – even battles – between groups arose over territory and food and water resources.

The Watery Lessons of the Past

The “Medieval Drought” serves as a model for what can happen in the West. It also provides an important impetus for water sustainability planning. And the hardships suffered by the first human inhabitants in the West provide important lessons.

For instance, during extended periods of abundant moisture, some societies experienced rapid population growth, leaving them vulnerable to collapse when the climate inevitably turned dry again.

Modern societies in the West have followed a similar path over the past century— after a century of fairly abundant moisture, the population in this region has exploded (and become more urbanized).

Modern engineering has allowed the exploitation of all available water sources for human use, and western water policy has favored water development for power, cities, and farms over sustainability of the environment and ecosystems.

These policies have allowed populations to grow to the limit that this region can support, leaving us vulnerable during extended drier conditions.

The longest six-year droughts experienced by the West over the past century are meager by comparison, despite the extreme hardship they brought to the region.

In fact, in the context of the longer-term climate history, the 20th century actually stands out as one of the wettest over the past 1,300 years, yet the droughts of the mid-1920s, 1977 and the late 1980s caused immense hardship for our society, based as it is upon heavy water usage.

In addition, future changes in the global climate will interact with the natural cycles of drought in California and the West in ways that are difficult to predict. Climate models predict that warming will likely make the extreme events, particularly floods and droughts, even larger and more frequent.

Some of these impacts have already begun. Over the past two decades, warming and an earlier start of the spring season have caused forest fires to become more frequent and intense.

A warmer climate will also bring less precipitation that falls as snow. The American West depends on snow-bearing winter storms for a natural water reservoir. This snow begins melting in the late spring, and continues into the summer, filling streams, lakes, and reservoirs that sustain natural ecosystems throughout the dry summer months.

The snow pack supports cities and irrigated agriculture, providing up to 80 percent of the year’s water supply across the West. As the region warms, the snow that does fall will melt faster and earlier in the spring, rather than melting during the late spring and summer, when it is so critically needed.

The message of past climates is that the range of “normal” climate is enormous—and we have experienced only a relatively benign portion of it in recent history. The region’s climate over the past decade has been dry when compared to the 20th century average, suggesting a return to a drier period.

This past year was also the warmest on record in the American West, and the ten hottest years on record occurred since 1997. The position of inhabitants of the West is precarious now and growing more so.

As we continue with an unsustainable pattern of water use, we become more vulnerable each year to a future we cannot control. It is time for policy makers in the West to begin taking action toward preparing for drier conditions and decreased water availability.


Read more from B. Lynn Ingram: 

The West without Water: What Past Floods, Droughts, and Other Climatic Clues Tell Us about Tomorrow 

by B. Lynn Ingram and Frances Malamud-Roam (University of California Press, 2013)