Higher temperatures caused by anthropogenic climate change have exacerbated drought conditions in the American West from 2020-2022, turning an ordinary drought into an exceptional one. A study by UCLA and National Oceanic and Atmospheric Administration (NOAA) scientists found that evaporation accounted for 61% of the drought’s severity, while reduced precipitation only accounted for 39%. This research suggests that evaporative demand has played a more significant role in drought severity since 2000, indicating that droughts will become increasingly severe as the climate continues to warm.
Traditionally, drought in the West has been primarily attributed to a lack of precipitation, with evaporative demand playing a minor role. However, climate change resulting from the burning of fossil fuels has led to higher average temperatures, exacerbating drought conditions. With increased heat, more moisture is extracted from bodies of water, plants, and soil, leading to more severe droughts. The study’s findings highlight the shift towards rising temperatures as the primary driver of intense droughts, with precipitation now playing a secondary role.
As the atmosphere warms, it can hold more water vapor before reaching saturation, inhibiting the condensation necessary for precipitation to occur. This phenomenon creates a cycle where higher temperatures lead to increased evaporation into the atmosphere, but a smaller fraction of this moisture returns as precipitation. Consequently, droughts are lasting longer, covering wider areas, and becoming drier with each incremental rise in global temperatures.
The study utilized observational data over a 70-year period to distinguish between “natural” droughts caused by changing weather patterns and those exacerbated by human-caused climate change. Surprisingly, climate change was found to account for 80% of the increase in evaporative demand since 2000, with this figure rising to over 90% during drought periods. This highlights climate change as the primary driver of increased drought severity and expansion of drought areas since 2000.
Comparing the 1948-1999 period to the years 2000-2022, there was a 17% increase in average drought area in the American West due to rising evaporative demand. Around 66% of historical and emerging drought-prone regions now experience droughts due to high evaporative demand alone, even in the absence of a precipitation deficit. This marks a significant shift from pre-2000 conditions, where only 26% of the area experienced droughts solely due to evaporative demand.
Climate model simulations based on these findings suggest that greenhouse gas emissions from fossil fuel combustion will escalate the frequency and severity of droughts. Droughts similar to the exceptional conditions witnessed from 2020-2022, previously considered rare events occurring every thousand years, may become more common, happening every 60 years by the mid-21st century and every six years by the late 21st century. The study underscores the urgent need to mitigate greenhouse gas emissions to prevent further exacerbation of drought conditions.