Colorado River extremes

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Events of Concern and their linkages to climate change in the Colorado River Basin.

Adapted from McCoy, A. L., Jacobs, K. L., Vano, J. A., Wilson, J. K., Martin, S., Pendergrass, A. G., & Cifelli, R. (2022). The Press and Pulse of Climate Change: Extreme Events in the Colorado River Basin. JAWRA Journal of the American Water Resources Association.

Events of Concern Noted by Water Managers Climate-Change Trend Defined Impact of Change Linkage to Climate Change Drivers Relevant Research* A Recent Example (details in text)
Intensifying heat waves Hotter periods that last longer - Air quality declines
- Water quality declines
- Increased fire danger
- Ecosystem mortality events
- Health and safety impacts, especially for outdoor workers and vulnerable populations
greenhouse gases trap more heat,
lead to warmer temperatures
US: Meehl et al., 2009; Cutting et al., 2011; Wuebbles et al.,
2017; Fahey et al., 2017; Vose et al., 2017
Global: Guo et al., 2018; Masson-Delmotte et al., 2021
In the summer of 2020 and 2021, the
Colorado River Basin experienced heat
wave conditions that exceeded multiple records
for consecutive number of days,
with temperatures surpassing historical
Diminished snowpack Less precipitation falls as snow vs. rain,
snowmelt occurs earlier
- Reduced streamflow
- Earlier peak flows
- Water shortages
- Recreation limited
more precipitation
falls as rain than as snow,
warmer temperatures cause early snowmelt
Basin specific: Reynolds et al., 2020

Western US: Barnett et al., 2005; McCabe et al., 2007; Barnhart et al., 2016; Harpold and Molotch, 2015; Li et al., 2017; Harpold and Kohler, 2017; Painter et al., 2018; Yan et al., 2018; Musselman et al., 2017, 2018, 2021; Davenport et al. 2020

US: Berghuijs et al., 2014
Snowpack monitoring stations throughout the West reveal that snowmelt is already occurring earlier in the year.
Long-duration drying (Sustained declines in runoff efficiency) Streamflow declines even when the same amount of water falls as precipitation - Reduced streamflow
- Water shortages
- Agriculture declines
warmer, thirstier atmosphere leads to more
evaporation/ transpiration/ sublimation of water, drier soils, and less water
reaching streams before returning to atmosphere
Basin specific: Vano et al. 2012, 2014; Woodhouse et al., 2016, 2021; McCabe et al. 2017; Udall and Overpeck, 2017; Hoerling et al., 2019

Western US: Das et al., 2011; Gonzalez et al., 2018

US: McCabe and Wolock, 2016
The Upper Colorado River Basin in 2020 and 2021 had unexpectly low run-off volumes.
Extensive wildfires More areas burned - Public safety threatened
- Air quality declines
- Water quality declines
- Increased erosion
increased temperatures,
increase drying and reduce snowpack
while lengthening the fire season
Western US: Abatzoglou and Kolden, 2011; Jenkins et al., 2014; Abatzoglou and Williams, 2016; Holden et al., 2018; Kean et al., 2019; Zhang et al., 2020; Brey et al., 2021

US: Wehner et al., 2017
In 2020, Colorado experienced the three largest wildfires in recorded history.
Short-duration intense wet and dry system shocks Precipitation intensity increases; each storm brings more water - Flooding
- Increased erosion
- Dam safety concerns
+ Increased groundwater recharge in some locations
+ Drought relief
a warmer atmosphere holds more
water, so when it rains or snows there a great chance that more precipitation
will fall in any given event;
additionally, storm are now developing
in warmer and more humid
environments, ocean surface temperatures drive an increase
worldwide in size and amount of storms
Basin specific: Gutmann et al., 2016; Shamir et al., 2019; Corringham et al., 2019

Western US: Zhu and Newell, 1994; Corbosiero et al., 2009; Dettinger, 2013; Rutz et al., 2015; Alexander et al., 2015; Swales et al., 2016; Demaria et al., 2019; Gershunov et al., 2019; Davenport et al., 2020; Payne et al., 2020; Rhoades et al., 2020;

US: Easterling et al., 2017; Kossin et al., 2017

Global: Trenberth, 2011; Pendergrass and Hartmann, 2014; Swann et al., 2016; Fischer and Knutti, 2016; Simpson et al., 2016; Kossin et al., 2017; Pendergrass et al., 2017; Sippel et al., 2019; Heinze-Deml et al., 2020;
In 2013, the “Front Range Flood” in Colorado resulted from record rainfall and urban runoff volumes.
Short-duration intense wet and dry system shocks Rapid onset dry year (flash drought) - Water shortages
- Agricultural losses
- Recreation limited
- Increased fire danger
large-scale atmospheric circulation changes increase temperatures, modify precipitation, reduce cloud cover, and increase wind speeds Great Plains and Eastern US: Hoell et al., 2020; Ford and Labosier, 2017

US: Otkin et al., 2018; Christian et al., 2019; Pendergrass et al., 2020

Global: Hoffmann et al., 2021
Recent example not within the Colorado River Basin.
Amplified wet and dry swings (climate whiplash) Multi-year dry spells broken by a couple of very wet years
- Dam safety concerns
- Increased erosion
- Management challenge (expecting drought and get too much rain instead)
a combination of more moisture and weakening of overall atmospheric circulation results in a drought-pluvial see-saw California/Western US: Swain et al., 2018; Wahl et al. 2020; Dettinger 2013

Global: He and Sheffield, 2020; Pendergrass et al., 2017; Pendergrass and Gerber 2016; Konapala et al. 2017; Schwarzwald et al., 2021
July 2021 was the wettest month on record in Tucson, which came after the "nonsoon" of 2020.
Dramatic decline in monsoons Timing of monsoon is later or no monsoon
Average rainfall from monsoons lessens
Change in frequency and intensity of extreme rainfall events
- Water shortages
- Agriculture loses
- Less relief from summer heat
warmer temperatures change atmospheric circulation patterns in ways that inhibit convection and cloud formation Southwest US: Cook and Seager, 2013; Pascale et al., 2017; Luong et al., 2017; Demaria et al., 2019; Carroll et al., 2020

Global: Emori and Brown et al. 2005; Wang et al., 2021
In 2020, Arizona’s monsoon was characterized as a “nonsoon” for delivering near record low precipitation.