What Is Ecological Drought?
Droughts and other natural hazards have been part of Earth’s natural processes since the beginning of time. Plants, animals, and ecological systems have adapted and evolved with these hazards. When driven beyond their capacity to adapt, ecosystems may cross critical thresholds, resulting in temporary or permanent alteration in their composition, structure, and/or functioning at local or landscape scales. The vulnerability of natural systems to withstand or adapt to drought disturbances depends on the sensitivity of the system, its exposure to the hazard, and its capacity to adapt and recover from drought.
Ecological drought is an “episodic deficit in water availability that drives ecosystems beyond thresholds of vulnerability, impacts ecosystem services, and triggers feedbacks in natural and/or human systems” (Crausbay et al. 2017). Examples of drought impacts to ecological systems may include:
- Reduced plant growth over a season or permanently
- Local species reduction or extinction
- Landscape-level transitions, such as forest conversion to non-forested vegetation, which may in turn reduce water retention in soils
- Freshwater ecosystems may change flow regimes, increase water temperature, and deteriorate water quality, which may result in fish kills, reduced opportunities for recreation, and decreased hydropower production.
Ecological drought may be driven by natural phenomena, such as lack of rainfall or warming temperatures, and it may result in or be exacerbated by multiple competing demands on existing limited water supplies. Thus, land use and water allocation decisions may drive or exacerbate ecological drought; for example, modification of hydrological processes to store water prior to drought may reduce water available to ecosystems.
According to recent research, major large-scale ecological changes “are becoming more commonplace as anthropogenic climate change drives more extreme high temperatures, greater evaporative demand (a ‘thirstier’ atmosphere), faster onset, longer duration, and altered timing of drought conditions that cross ecological thresholds, e.g., Smith [2011a, 2011b] and Allen et al.,” creating “novel forms of drought ... globally, challenging our ability to anticipate and manage drought impacts” (Crausbay et al. 2020).