Intermountain Park Science
Volume 2, 2024
Drought. To many people, “drought” and “aridity” are synonymous. Dusty, parched landscapes, dry winds, cactus, yucca, sage, and tumbleweeds under an unrelenting and unforgiving sun perhaps typifies how the southwestern United States is viewed, particularly by people who do not live there. The perception is that these conditions represent drought. But drought is different than desertscapes. It is a climatic phenomenon that can occur in any biome, a persistent pattern that further desiccates even desert landscapes. In the Southwest, drought affects all environments from desert to alpine ecosystems, saguaro cactus to bristlecone pines. Regardless of the biome, its location or physiography, drought disrupts the normal, long-term conditions to which plants and animals have adapted.
The concept of soil moisture is a good way to understand drought. In practical terms, all plants respond to the actual moisture available to them in the soil. For any given biome, local plants and animals have adapted to a long-term climate pattern (both ranges and durations of exposure to specific precipitation and temperature). Topographic and edaphic properties (e.g., slope, aspect, soil type, etc.) interact with temperature and precipitation to influence the amount of water that is available (both amount and timing) to plant roots. Forests typically require higher precipitation and lower average temperatures than cactus, for instance, and thus, north-facing slopes can support some trees better than hotter and drier south-facing ones on the same mountain. In all instances, where drought occurs and persists, soil moisture is reduced long-term, and the plants and animals that rely on them, are negatively affected.
But it isn’t just plant stress that results from drought. There are other cascading consequences to ecosystems. For instance, fire can become more frequent and its effects on resources more severe. Non-native plant species may quickly invade and preclude re-establishment of native plants. Fires and higher temperatures can impact not only living plants and animals, but archeological resources, too. Streams and lakes and all the creatures that live in them are affected by thermal stress. Phenology can be disrupted. Recovery to these systems, if it occurs, is not immediate, but can take months to years depending on the severity of the drought and resources affected.
People, too, adapt to arid conditions and cycles of drought, or move to more suitable locations. Native Peoples lived on the arid lands of the Southwest for millennia. Their modifications to the landscape allowed for longer-term, persistent habitation, such as in Chaco Canyon, Bandelier, Hovenweep, Mesa Verde, and others. Those pre-settlement cultures built irrigation ditches, basins, and aqueducts to store and divert water for drinking and agriculture, making habitation possible. Only during extreme droughts does it appear that people had to abandon this arid landscape and move to locations more conducive to survival.
Early European settlement of the arid West in the 1800s also relied on the limited water supply that characterized these areas, having similar challenges to their forebearers. At first, the land and its water sources supported the small number of settlers who, like their predecessors, diverted and stored water for their needs. This small number of people exerted little pressure toward overusing the sporadic and uneven distribution of water, both spatially and temporally. Over time, as settlements grew, pressure on limited water supplies increased, and so settlers followed the cue from their predecessors, building more dams, canals, and aqueducts.
In 1902, the Roosevelt Administration created the Reclamation Service (later renamed the Bureau of Reclamation) with the mandate to “reclaim” arid lands for human use by providing a year-round supply of water for agriculture and direct consumption with a particular focus on the Southwest. Larger dams, canals, and aqueducts were constructed on a grand scale for water storage and delivery, making additional development possible, and creating Megacities in the desert such as Tucson, Phoenix, and Las Vegas. These water management measures worked well enough during the normal arid conditions, but were tested in times of drought, particularly in cases of severe or prolonged drought. This is where we find ourselves now: at the intersection of overdevelopment and drought. In the most recent drought, Lake Powell and Lake Mead have been as low as 25-26% of full capacity (although they have since recovered slightly to 35% as of 2025). Natural and cultural resources throughout the region have been greatly affected by this drought.
To recap: drought is episodic, varying in duration and intensity with wide-ranging and long-term consequences to a variety of resources. Without those (relatively) intermittent wet periods of recovery, chronic low precipitation becomes problematic even to endemic plants and animals. In this recent drought that the Southwest is experiencing, are we finally reaching or exceeding the hydrologic limits for all inhabitants? The impacts to natural and cultural resources by drought are wide ranging and some of those may be quite surprising. In this issue, authors examine the consequences of drought and their impacts to both natural and cultural resources in some interesting and often overlooked ways.
The concept of soil moisture is a good way to understand drought. In practical terms, all plants respond to the actual moisture available to them in the soil. For any given biome, local plants and animals have adapted to a long-term climate pattern (both ranges and durations of exposure to specific precipitation and temperature). Topographic and edaphic properties (e.g., slope, aspect, soil type, etc.) interact with temperature and precipitation to influence the amount of water that is available (both amount and timing) to plant roots. Forests typically require higher precipitation and lower average temperatures than cactus, for instance, and thus, north-facing slopes can support some trees better than hotter and drier south-facing ones on the same mountain. In all instances, where drought occurs and persists, soil moisture is reduced long-term, and the plants and animals that rely on them, are negatively affected.
But it isn’t just plant stress that results from drought. There are other cascading consequences to ecosystems. For instance, fire can become more frequent and its effects on resources more severe. Non-native plant species may quickly invade and preclude re-establishment of native plants. Fires and higher temperatures can impact not only living plants and animals, but archeological resources, too. Streams and lakes and all the creatures that live in them are affected by thermal stress. Phenology can be disrupted. Recovery to these systems, if it occurs, is not immediate, but can take months to years depending on the severity of the drought and resources affected.
People, too, adapt to arid conditions and cycles of drought, or move to more suitable locations. Native Peoples lived on the arid lands of the Southwest for millennia. Their modifications to the landscape allowed for longer-term, persistent habitation, such as in Chaco Canyon, Bandelier, Hovenweep, Mesa Verde, and others. Those pre-settlement cultures built irrigation ditches, basins, and aqueducts to store and divert water for drinking and agriculture, making habitation possible. Only during extreme droughts does it appear that people had to abandon this arid landscape and move to locations more conducive to survival.
Early European settlement of the arid West in the 1800s also relied on the limited water supply that characterized these areas, having similar challenges to their forebearers. At first, the land and its water sources supported the small number of settlers who, like their predecessors, diverted and stored water for their needs. This small number of people exerted little pressure toward overusing the sporadic and uneven distribution of water, both spatially and temporally. Over time, as settlements grew, pressure on limited water supplies increased, and so settlers followed the cue from their predecessors, building more dams, canals, and aqueducts.
In 1902, the Roosevelt Administration created the Reclamation Service (later renamed the Bureau of Reclamation) with the mandate to “reclaim” arid lands for human use by providing a year-round supply of water for agriculture and direct consumption with a particular focus on the Southwest. Larger dams, canals, and aqueducts were constructed on a grand scale for water storage and delivery, making additional development possible, and creating Megacities in the desert such as Tucson, Phoenix, and Las Vegas. These water management measures worked well enough during the normal arid conditions, but were tested in times of drought, particularly in cases of severe or prolonged drought. This is where we find ourselves now: at the intersection of overdevelopment and drought. In the most recent drought, Lake Powell and Lake Mead have been as low as 25-26% of full capacity (although they have since recovered slightly to 35% as of 2025). Natural and cultural resources throughout the region have been greatly affected by this drought.
To recap: drought is episodic, varying in duration and intensity with wide-ranging and long-term consequences to a variety of resources. Without those (relatively) intermittent wet periods of recovery, chronic low precipitation becomes problematic even to endemic plants and animals. In this recent drought that the Southwest is experiencing, are we finally reaching or exceeding the hydrologic limits for all inhabitants? The impacts to natural and cultural resources by drought are wide ranging and some of those may be quite surprising. In this issue, authors examine the consequences of drought and their impacts to both natural and cultural resources in some interesting and often overlooked ways.
Drought in the Southwest, 2024
Table of Contents-
Moving Toward Ecological ForecastsInnovative tools are being developed to nowcast and forecast the severity of drought impacts on wildfire hazard, and other conditions.
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Drought, Fire, and ArcheologyDrought is one key variable causing forest fires that result in a wide range of effects to archeological sites and historic structures.
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Phenology and Climate ChangeScientists closely monitor impacts from climate change that could impact park vegetation, wildlife, and water supply.
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Smallmouth Bass: Not a Small ThreatDecades of drought have lowered lake levels and increate the threat of invasive fish introductions.
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Developing Climate Change StrategiesLearn more about strategies to help park managers understand, adapt to, mitigate, and communicate about climate change.
Editorial Staff
Editor-in-Chief: Sallie Hejl
Editors: Michael Bozek, Nina Chambers
Last updated: January 17, 2025