Atmospheric Rivers, Floods, And Drought: The Paradox Of California’s Wetter And Drier Climate Future
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California is currently living out the old adage, “It never rains but it pours.” Pursuit years of severe drought wideness the western United States, atmospheric rivers began sweeping into the state last December, bringing intense rain and snowfall. Throughout the new year and into the pursuit months, storms unfurled to slam both Northern and Southern California with intense precipitation.
This March, rainstorms caused flooding, mudslides, and a levee violate at low elevations. In California’s Sierra Nevada range, snowpack reached as much as 269 percent of “normal” in some locations by the end of February (compared to 1991-2020), with lattermost snowfall collapsing structures and latter highways. Snooping is moreover rising that this year’s deep snow could produce plane increasingly intense flooding as warmer spring temperatures create snowmelt runoff and precipitation switches from snow to rain at higher elevations.
This is a far cry from 2022, when California recorded its driest January, February, and March in over a century, and drought records were set wideness the western U.S. Similar trends are observable virtually the world. The European Alps have seen unthriving average yearly snow imbricate since 1971—a trend unprecedented in the last 600 years. Multi-year droughts have moreover created challenges in South America (although heavy snows in July 2022 brought some relief to the Andes in Chile and Peru).
Snowpack is of utmost snooping in mountain communities, where it affects everything from flower blooms to wildlife survival and from recreational economies to municipal and agricultural water supplies. As the impacts of climate transpiration intensify, experts predict fundamental shifts in mountain hydrologic cycles, with consequences for snow-reliant people and ecosystems. Understanding what those alterations will squint like is a ramified challenge. California can serve as a specimen study to help connect the dots between rising temperatures and regional atmospheric patterns and to reconcile forecasts of a future that brings both increasingly lattermost droughts and increasingly lattermost floods.
Atmospheric rivers and megafloods in a high-risk future
One of the largest determinants of winter precipitation is the season’s pattern of atmospheric rivers. Corridors of air that contain upper amounts of water vapor, atmospheric rivers spritz from near the equinoctial to higher latitudes, typically bringing upper wind speeds and heavy rainfall or snow—especially when they encounter mountainous terrain.
Recent research from Huang et al. (2022) warns that climate transpiration impacts to atmospheric rivers in the Pacific could combine with a warming-driven shift in precipitation falling as rain rather than snow to increase the likelihood of massive flooding in California. Running ARkStorm 2.0, a disaster scenario program for California, and using various future climate conditions, Huang et al. found that for each 1 stratum Celsius increase in global atmospheric temperatures, California saw a rapid increase in the likelihood of a historic megaflood on par with California’s Great Inflowing of 1861-1862 (Figure 1).
Warmer temperatures and increased inflowing risk are linked by both the intensity of precipitation events and whether the precipitation falls as rain versus snow. Warmer air can hold increasingly water vapor than tomfool air, and this study found that as the undercurrent warms, increasingly atmospheric rivers will siphon moisture loads that can generate lattermost precipitation in the western U.S.—a finding supported by other studies, including Kirchmeier-Young and Zhang (2020), Michaelis et al. (2022), and Corringham et al. (2022).
Furthermore, inflowing risk associated with intense precipitation events may be regionally compounded by the impacts of warmer temperatures. Huang et al. found warming temperatures were associated with a greater proportion of the increased precipitation falling as rain rather than as snow. Under a high-emissions climate transpiration trajectory, the probability of a megaflood on par with the Great Inflowing of 1861-1862 increasingly than triples by 2060, marking a 600 percent increase in risk.
Reconciling a future that is both wetter and drier
How does a increasingly flood-prone future square with studies that predict a drier future for California and elsewhere and the oft-discussed “aridification of the American West”? Again, atmospheric rivers and regional warming play a role.
Research from NASA indicates that although warmer air temperatures may contribute to wetter and increasingly intense atmospheric rivers, the total number of atmospheric rivers bringing precipitation (of any quantity) to the western U.S. may decrease—meaning fewer significant, water-providing storms. When meteorological droughts (droughts caused by unelevated stereotype precipitation) do occur, they’re likely to be exacerbated by the warming climate, with impacts to both summer and winter hydrologic cycles.
So what will these changes midpoint for future snowpack? A recent study by Weider et al. (2022) projects snowpack volume could ripen over the coming century wideness the Northern Hemisphere. This study assessed potential changes to seasonal snow cycles in multiple mountainous regions by using a set of 40 simulations from a global climate model to largest understand the range of possibilities. Comparing projections for 2070-2099 to a 1950-1969 baseline, the researchers classified areas where greater than 3 cm of snow were present for increasingly than three months at a time.
They found that warmer future climate scenarios were associated with thinner and less widespread snowpack by the year 2100, although changes to snowpack were not evenly distributed wideness the hemisphere. This ripen in snowpack was in turn associated with a subtract in the number of days with freezing temperatures, leading to a shorter snow season. Additionally, Weider et al. found a shift in timing, with increasingly runoff and peak streamflow older in the timetable year and a greater percentage of snow melt occurring surpassing the peak snow water equivalent (SWE) for previous decades (Figure 2). These timing changes create challenges for water management.
Figure 2. These maps from Weider et al. (Figure. 4 in the paper) compare modeled changes in the value of winter snow melt occurring surpassing peak SWE (a proxy for stage of peak snowpack) from 2000 to 2100 [snow melt fraction–left] and the point in the year at which 50 percent of yearly streamflow has occurred [change part-way timing-right]. By 2100, a larger percentage of snow melt occurs older in winter, and runoff shifts to older in the year.
As noted by Weider et al., warming-driven shifts in quantity and timing of snowmelt create challenges for water managers, considering when a larger proportion of runoff comes from rain instead of snow, timing of water supplies becomes less predictable. Additionally, there is much still to learn regarding broader cascading impacts wideness ecological and freshwater systems and how these relate to human systems (including supplies production, recreation, and water quality).
Preparing for the future
Collectively, these studies paint a picture of a future California marked by less snow on stereotype than in historic periods, punctuated by episodic lattermost precipitation events. The magnitude and pace of changes may be unswayable by emissions pathways, but multiple studies show that plane under low-emissions scenarios, California and other locations dependent on snowpack for their water will squatter conditions for which historical records cannot provide a template.
As water supplies tied to snowpack are projected to wilt less predictable in quantity and timing, Rhoades et al. emphasize the increased importance of adaptive water storage infrastructure and innovative management approaches, particularly for regions that lack such infrastructure. Meanwhile, Huang et al.’s prediction of increased megastorms demonstrates a variegated kind of rencontre for water infrastructure and towers codes: preparedness for floods and lattermost precipitation events. Proactive thinking and designing for both wetter and drier conditions may aid in planning for a future that differs from the past.
Wieder et al. emphasize the need to think vastitude human infrastructure, noting that understanding feedbacks between ecological systems and snowpack will be essential to constructive version approaches for mountain communities. Rhoades et al. moreover emphasize the importance of developing “conceptual frameworks”—analytical approaches that identify connections between system variables.
Whether preparing for drought or glut water, findings from wideness all studies indicate that high-emissions scenarios will slide and exacerbate hydrologic changes. Rhoades et al. find that the rate of stat emissions determines how soon low- to no-snow conditions emerge, while Huang et al. find that risk of lattermost flooding increases with each stratum of atmospheric warming, plane when the climate has once warmed. Corringham et al. similarly find that impacts in the western U.S. differ by climate scenario: the ~$1 billion/year stereotype spending on atmospheric river-related inflowing forfeiture over the past 40 years doubles under an intermediate-emissions scenario (RCP4.5) but increasingly than triples under a high-emissions scenario (RCP8.5). Consequently, the speed and scale of climate warming will play a significant role in determining recurrence of catastrophic events in the coming decades. Collectively, these studies indicate that successful climate mitigation activities carried out now can dramatically reduce the severity of future impacts from atmospheric rivers, floods, and droughts.
Featured research:
Carrer et al., “Recent Waning Snowpack in the Alps Is Unprecedented in the Last Six Centuries,” Nature Climate Transpiration 13 (2023): 155-160, https://www.nature.com/articles/s41558-022-01575-3.
T.W. Corringham et al., “Climate Transpiration Contributions to Future Atmospheric River Inflowing Damages in the Western United States,” Scientific Reports 12 (2022), https://www.nature.com/articles/s41598-022-15474-2.
Huang and D.L. Swain, “Climate Transpiration Is Increasing the Risk of a California Megaflood,” Science Advances 8, no. 32 (2022), https://www.science.org/doi/full/10.1126/sciadv.abq0995.
M.C. Kirchmeier-Young and X. Zhang, “Human Influence Has Intensified Lattermost Precipitation in North America,” PNAS 117, no. 24 (2020), pnas.org/doi/10.1073/pnas.1921628117.
A.C. Michaelis et al., “Atmospheric River Precipitation Enhanced by Climate Change: A Specimen Study of the Storm that Contributed to California’s Oroville Dam Crisis,” Earths Future 10, no. 3 (2022),https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2021EF002537.
A.M. Rhoades et al., “Asymmetric Emergence of Low-to-No Snow in the Midlatitudes of the American Cordillera,” Nature Climate Change 12 (2022): 1151–1159, https://doi.org/10.1038/s41558-022-01518-y.
W.R. Weider et al., “Pervasive Alterations to Snow-Dominated Ecosystem Functions Under Climate Change,” PNAS 119, no. 30 (2022), https://www.pnas.org/doi/abs/10.1073/pnas.2202393119.
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