Future Climate: Projected Extremes summarizes the current scientific understanding about how weather and climate extremes in the Southwest are expected to change as global and regional temperatures increase, examining heat waves, cold snaps, drought, floods, and possible changes in weather related to wildland fires and to such phenomena as atmospheric “rivers” and Santa Ana winds.
Citation:
Gershunov, A., B. Rajagopalan, J. Overpeck, K. Guirguis, D. Cayan, M. Hughes, M. Dettinger, C. Castro, R. E. Schwartz, M. Anderson, A. J. Ray, J. Barsugli, T. Cavazos, and M. Alexander. 2013. “Future Climate: Projected Extremes.” In Assessment of Climate Change in the Southwest United States: A Report Prepared for the National Climate Assessment, edited by G. Garfin, A. Jardine, R. Merideth, M. Black, and S. LeRoy, 126–147. A report by the Southwest Climate Alliance. Washington, DC: Island Press.
Alexander Gershunov (Scripps Institution of Oceanography)
Balaji Rajagopalan (University of Colorado)
Jonathan Overpeck (University of Arizona)
Kristen Guirguis (Scripps Institution of Oceanography)
Dan Cayan (Scripps Institution of Oceanography)
Mimi Hughes (NOAA)
Michael Dettinger (U.S. Geological Survey)
Chris Castro (University of Arizona)
Rachel E. Schwartz (Scripps Institution of Oceanography)
Michael Anderson (California State Climate Office)
Andrea J. Ray (NOAA)
Joe Barsugli (University of Colorado/Cooperative Institute for Research in Environmental Sciences)
Tereza Cavazos (Centro de Investigación Científica y de Educación Superior de Ensenada)
Michael Alexander (NOAA)
Key Findings
Several key weather phenomena lead to extreme and flooding precipitation across the Southwest, while also contributing to water supplies.
Heat waves are projected to become more humid and therefore expressed relatively more strongly in nighttime rather than daytime temperatures.
Floods from winter storms on the western slopes of the Sierra Nevada have been projected to increase in intensity in winter.
Extreme precipitation associated with atmospheric rivers (seen here from space hitting the California coast), is projected to increase.
Projected drought, expressed in Colorado River flow, is to become more frequent and intense, and longer-lasting, resulting in water deficits.
Figure Gallery
Figure 7.1: The summertime (May– September) Heat Wave Index (HWI) for Tmax (a) and Tmin (b) for the Southwest region. Solid line is the 5-year running mean. HWI values show °C above the local 95th historical percentile. Inset shows the same data on a scale appropriate for the historical period (1950- 1999). Historical observed and modeled data as well as twenty-first century projections (according to the SRES-A2 “high-emissions” scenario) are shown from observations as well as from a GCM (CNRM-CM3) historical simulation and projection averaged over the Southwest. Adapted for the Southwest based on the work of Gershunov and Guirguis (2012) for California. Data source: Salas-Mélia et al. (2005); see also http:// www.ipcc-data.org/ar4/model-CNRM-CM3- change.html.
Figure 7.2: The wintertime (November–March) Cold Spell Index (CSI) for Tmax (a) and Tmin (b) for the Southwest region. Explanation of lines, values, and insets as in Figure 7.1. Adapted for the Southwest based on the work of Gershunov and Guirguis (2012) for California. Data source: Salas-Mélia et al. (2005); see also http://www.ipcc-data.org/ ar4/model-CNRM-CM3-change.html.
Figure 7.3: Key weather phenomena that cause extreme precipitation in the Southwest. Schematic illustration of regional patterns of the primary weather phenomena that lead to extreme precipitation and flooding, while also contributing to water supplies (Guan et al. 2010; Dettinger et al. 2011), across the western United States. Modified from Ralph et al. (2011); see http://www.westgov. org/wswc/167%20council%20meeting%20-%20id/167%20council%20mtg%20-%20oct2011.html.
Figure 7.4: Drought associated anomalies in Colorado River streamflow. Accumulated deficit in flow (10^9 m^3, or billions of cubic meters) on the Colorado River at Lees Ferry relative to the mean flow observed over the period 1906–2008 (Y axis), as a function of drought duration in years (X axis). The twenty-first-century drought is shown in red; other years are shown as black dots. For example, the red 2007 indicates an eight-year drought (2000–2007), with an accumulated deficit of around 40 billion cubic meters (around 30 million acre-feet). Grey shading indicates where, two-thirds of the time, the worst drought (accumulated streamflow deficit) of the century should fall; the blue hatched region shows where the worst drought should fall for the end of this century, estimated from downscaled climate models. The twenty-first-century drought was consistent with the expected 100-year event, given the observed climate, whereas future 100-year droughts are expected to be much more severe in terms of accumulated flow deficit.
Figure 7.5: Drought-associated anomalies in precipitation and soil moisture. Composite average of water-year precipitation (blue) and water-year soil moisture (red) anomalies associated with extreme negative soil moisture anomalies for the Southwest estimated from observations and simulated climate input from CNRM CM3 and GFDL CM2.1 GCMs SRES A2 emission scenario, for 1951–1999, 2000–2049, and 2050–2099. Modified from Cayan et al. (2010).