Humans and our civilizations need constant access to water to sustain life. Drought can result from abnormally low precipitation, sometimes combined with abnormally high evaporation caused by warmer, drier air. It is, by definition, a temporary aberration from a historical pattern.
Drought has proven to be one of the more disruptive kinds of extreme weather. It played a role in the political instability that led to the demise of large ancient civilizations and contributed to the greatest in-country migration in American history during the dust bowl years of the Great Depression. More recently, it has at least worsened refugee crises around the world.
A drought can take weeks, months, or even years to develop and dissipate. As we navigate a changing climate, how will we recognize when hotter, drier weather is a drought that will end or when it is a transition to a permanently drier climate? And how will we prepare for the challenges it is likely to pose?
Drought in unexpected places.
Alberta is in the heartland of Canada, offering rich and diverse landscapes. Swampy, boreal forests in the north and dry prairie in the south are connected by rivers that originate from precipitation in the Canadian Rockies to the west. Alberta’s enormous stretch of land is subject to long winters and brief summers, which make it a challenging place to live. But the development of earlier-maturing varieties of wheat in the early 20th century enabled the region to transform into one of the country’s breadbaskets.
When we think of drought, Central Canada may not be the first place that comes to mind, but drought is relative to local patterns of temperature, precipitation, and soil moisture. It can happen wherever there is typically water, and it can propagate and have compounding effects. In fact, Canada is warming twice as fast as the rest of the world, and its ecosystems are struggling to adapt.
For example, abnormally low snow or rainfall can lead to dry soil conditions. If the lack of precipitation persists, river flow may dwindle, affecting cities and towns downstream. These conditions can be self-reinforcing, like when drier forests transpire less moisture for rain and snow, shaping future weather patterns.
The people and farms of Alberta get 97% of their water from surface sources such as rivers and lakes that depend on precipitation and snowmelt, both of which are likely to change in timing, location, and intensity in the future. In recent decades, the plains of Alberta have become increasingly drought-prone, sometimes with corresponding and unpredictable bouts of heavy precipitation that lead to crop failure.
Survival in a shrinking climate zone.
Just south of the Sahara Desert, stretching like a belt across the continent of Africa, is the region of the Sahel. It’s a special mix of dry semi-arid grasslands, savannas, steppes, and shrublands, and it’s one of the first landscapes in which humans flourished.
Over 300 million
Water is scarce in the Sahel, but local life has adapted to make the best use of it. Sparse precipitation falls only during a short rainy season, while the rest of the year is dry with constant, intense heat and sunshine. Annual grass species go dormant in the long dry season and return the following year when it rains. Grazing animals and larger predators like cheetahs and lions populate the land, and migratory birds visit the seasonal wetlands.
Now the Sahel is warming 1.5 times faster than the global average, pushing the region out of its delicate balance. Instead of consistent, if sparse, rain that sustains agriculture, crops go months without water as hot, dry periods are lengthening and intensifying, only to be interrupted by deluges that parched soil cannot absorb. Droughts are temporary, but these changes are unlikely to reverse. A transition to a permanently drier climate is known as aridification.
Aridification is the long-term transition of a region into drier, more arid conditions, as measured by decreasing soil moisture content. Climate change is leading to aridification around the world, notably in the Colorado River basin and other parts of the western United States, by creating hotter, drier conditions that decrease precipitation, increase evaporation, and deplete groundwater. Scientists believe any region’s aridification is likely irreversible, at least on human timescales.
Half of the Sahel’s 300 million residents already live under the strain of extreme poverty. Hotter, drier conditions are making survival even more difficult. There’s less water, less food, loss of livelihoods, and increased conflict. Rapid population growth is putting additional pressure on natural resources. As the local climate changes, those struggles intensify.
Fighting the desert.
The Gobi Desert is home to harsh climatic extremes and strong winds. For thousands of years, grasslands and semi-arid regions hemmed in this giant field of sand south of the Mongolian steppes. In 1928, around 475 million people lived in China, and few lived anywhere near these borderlands. Over the following 50 years, however, the country’s population grew by 450 million, roughly doubling the demands on land and water. People plowed the borderlands for farmland; growing cities annexed existing farms near the border and tapped groundwater for both irrigation and urban use.
The Three-North Shelter Forest, Northern China
These actions loosened and dried soil that had previously formed a living border to the desert. Without this natural border, the Gobi began to expand. Strong winds scoured the land, diminishing the precious remaining soil, and unprecedented dust storms began choking Northeastern China with sand.
In 1978, Chinese government leaders announced the Three-North Shelter Forest, a plan to halt and perhaps reverse the expansion of the desert and protect urban residents from sand-clogged air. It is sometimes called “The Great Green Wall” as it follows a path similar to the Great Wall of China, built millennia ago to keep out threats of Mongol invasion. The centerpiece of the policy was planting billions of trees to hold the soil and buffer the winds.
For the first 30 years of the program, officials focused on speed, favoring fast-growing poplar trees that survive harsh, cold winters in other places. But these quasi-forests rapidly faced daunting challenges, as bare, exposed saplings need tending, monoculture crops are especially vulnerable to pests and disease, and the climate was much drier than where poplars naturally grow.
In recent decades, Chinese leaders have learned from earlier difficulties. Vast commitments of labor, expertise, and money have helped move the project closer to its goals. On the edge of the Gobi, however, temperatures continue to rise while precipitation declines, compounding the challenge of holding back the encroaching desert.
Heat, drought, and fire.
A sliver of land at the southwest tip of Australia has a rare climate for the continent. While most of interior Australia is a hot, dry desert, Perth and its surrounding area form a highly productive oasis: cool and lush, with rainy winters and dry summers. This special climate is called “Mediterranean” because it’s found in the land that surrounds the Mediterranean Sea in Europe and North Africa. A similar climate can be found in pockets of land around the world, from South Africa and Chile to Northern California.
The aboriginal Noongar people inhabited this comfortable and temperate climate for tens of thousands of years before colonists arrived and began seizing attractive land, pushing out the indigenous population. Now this climate zone is shrinking as the bulging oval of the scorching interior desert at the center of Australia encroaches on what little land still feels like the Mediterranean.
Driven by climate change, drought is transforming the landscape. Long stretches without rainfall are challenging agriculture, including vineyards where the quality of wine directly correlates to precise environmental conditions. But the risks are far more dire than issues of the quality, or even viability, of viticulture.
The longer any drought goes on, the more extreme its impacts become. Eventually, drought depletes groundwater and rivers, and vegetation dies and dries out. Drought and extreme heat together create a tinder-box effect. Devastating wildfires have scarred land in and near Perth that used to be verdant and productive.
The Martian climate.
Mars is the only planet comparable to Earth in our solar system—and some people aspire to live there—yet its climate is considerably different from Earth’s. While Earth’s atmosphere traps some of the energy that radiates from our planet’s surface, the Martian atmosphere is so thin that it has a negligible greenhouse effect. The average surface air temperature on Mars is approximately -62°C (-80°F).
142 million miles from the sun
Mars is completely dry, but it is not a drought, as there is no prospect of the dry conditions ending. There is no liquid water on the planet. The planet’s north pole has an ice cap of frozen water and carbon dioxide, and scientists have detected large amounts of frozen water below the planet’s surface. Even if the surface were to warm, however, water would immediately turn to vapor due to the scant atmospheric pressure. Mars’s south pole is covered in frozen CO2 (dry ice), which falls from the sky during that region’s winter.
With frequent high winds and no plants or water to hold down surface materials, Mars is covered in dust. Some dust storms cover the entire planet. Unlike Earth, Mars has no magnetic field, so the surface of the planet is constantly exposed to harsh cosmic rays. These climate conditions appear to be too much of a challenge for life of any kind to develop.
Living well within nature’s constraints
Water is essential to life. The prospect of climates transitioning from verdant to barren brings the limits of nature into focus. But it can also put into perspective the magnificence of the climate that we inherited.
Earth is extraordinary and extraordinarily precious. Within its land, water, and atmosphere, there are myriad possibilities for humans to live well and sustainably. It will take imagination, courage, and hard work. But it is work well worth doing, as there is much that we can still preserve and enjoy.
With this in mind, we invite you to explore our maps of land and imagine new ways of living consistent with the confines of our truly unique planet.