Climate Projections Used for the Assessment of the Western United States
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Climate Projections Used for the Assessment of the Western United States By Anne Wein, Todd J. Hawbaker, Richard A. Champion, Jamie L. Ratliff, Benjamin M. Sleeter, and Zhiliang Zhu Chapter 7 of Baseline and Projected Future Carbon Storage and Greenhouse-Gas Fluxes in Ecosystems of the Western United States Edited by Zhiliang Zhu and Bradley C. Reed Professional Paper 1797 U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior KEN SALAZAR, Secretary U.S. Geological Survey Marcia K. McNutt, Director U.S. Geological Survey, Reston, Virginia: 2012 For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment, visit http://www.usgs.gov or call 1–888–ASK–USGS. For an overview of USGS information products, including maps, imagery, and publications, visit http://www.usgs.gov/pubprod To order this and other USGS information products, visit http://store.usgs.gov Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted materials contained within this report. Suggested citation: Wein, Anne, Hawbaker, T.J., Champion, R.A., Ratliff, J.L., Sleeter, B.M., and Zhu, Zhiliang, 2012, Introduction to scope, methodology, and ecosystems of the assessment, chap. 7 of Zhu, Zhiliang, and Reed, B.C., eds., Climate projections used for the assessment of the Western United States: U.S. Geological Survey Professional Paper 1797, 10 p. (Also available at http://pubs.usgs/gov/pp/1797.) iii Contents 7.1. Highlights..................................................................................................................................................1 7.2. Introduction..............................................................................................................................................1 7.3. Climate Patterns .....................................................................................................................................4 7.3.1. Baseline Climate Patterns of the Western United States ....................................................4 7.3.2. Projected Climate Patterns of the Western United States ..................................................4 7.4. Summary and Discussion of Caveats Using the Climate Data ........................................................9 Figures 7.1. Maps showing the baseline (1970–1999) seasonal mean daily temperature (in degrees Celsius, °C) and total precipitation (in centimeters) by season …… 2 7.2. Chart showing the baseline summaries of mean daily temperature (in degrees Celsius, °C) and total precipitation (in centimeters) by season and grouped by both level II and level III ecoregions …………………………………………… 3 7.3. Maps showing the projected changes in mean daily temperature (in degrees Celsius, °C) and total precipitation (in centimeters) by season, calculated using the difference in mean values from 2040 to 2069 and from 1970 to 1999 ……… 5 7.4. Chart showing summaries of the projected seasonal changes in mean daily temperature (in degrees Celsius, °C) and total precipitation (in centimeters) by season and grouped by both level II and III ecoregions for all general circulation models and scenarios ………………………………………………………… 6 Tables 7.1. Projected changes in precipitation patterns derived from averaging the results from all the scenarios and general circulation models ………………… 8 This page intentionally blank Chapter 7. Climate Projections Used for the Assessment of the Western United States By Anne Wein1, Todd J. Hawbaker2, Richard A. Champion1, Jamie L. Ratliff1, Benjamin M. Sleeter1, and Zhiliang Zhu3 7.1. Highlights 7.2. Introduction • Models of projected climate change were used in this Climate-change projections are required for modeling assessment to further interpret the effects of climate future potential ecosystem properties and processes. This change on the potential for carbon sequestration chapter characterizes the baseline climate data and the projected and greenhouse-gas (GHG) emissions in terrestrial climate-change data from general circulation models (GCMs); ecosystems in the ecoregions of the Western United these data were used in this assessment for the wildland‑fire‑ States. Climate-change data were used to support two emission modeling discussed in chapter 8 and for the terrestrial modeling exercises: future potential wildland‑fire ecosystem carbon‑storage and GHG‑flux modeling discussed in emissions (chapter 8 of this report) and future potential chapter 9. The relation between this chapter and other chapters carbon storage and sequestration (chapter 9 of of this report is shown in figure 1.2 of chapter 1 of this report, this report). where climate data is featured in the “input data” and “climate projections” boxes of the diagram. • Climate-change data were represented in three general The term “climate change” refers to the changes in daily circulation models (GCMs) for each of three scenarios and weekly weather over months, seasons, centuries, and (A1B, A2, B1). The models of wildland fires and millennia. The climate affects the carbon cycle in terrestrial the biogeochemical modeling of carbon and GHGs and aquatic systems through biogeochemical processes and used different sources of downscaling for the same natural disturbances (such as wildland fires), and also influences GCMs because of the tasks’ unique requirements. The where land-use and land-cover (LULC) changes occur. This projected patterns of precipitation differed between the assessment sought to answer two questions related to the effects two sources, particularly in mountainous areas. of climate change on carbon sequestration and GHG fluxes: • The models indicated a projected seasonal increase (1) What are the projected potential changes to the critical in mean temperature throughout the Western United climate variables within the ecoregions of the Western United States. Warming was projected to be most prevalent in States, and (2) What are the uncertainties for the climate-change summer and fall and in the eastern part of the Western projections in each of the ecoregions? United States. The climate-change data described here, along with the projected LULC scenarios (chapter 6) were aligned with the • The projected warming was greater in scenarios A1B Intergovernmental Panel on Climate Change’s Special Report and A2; the MIROC 3.2-medres model projected on Emission Scenarios (IPCC–SRES; Nakicenovic and others, the most warming and the CSIRO–Mk3.0 model 2000). Although multiple scenarios (A1B, A2, and B1) provided projected the least. The projected increases in seasonal the emission projections, the assessment used outputs from temperature extremes (minimums and maximums) the GCMs, which were forced by the scenarios to capture the generally followed patterns of projected increases in uncertainties of the analyses. The three GCMs used in this mean temperature. study are The Third Generation Coupled Global Climate Model • The projected precipitation patterns were highly of the Canadian Centre for Climate Modelling and Analysis variable among the GCMs, scenarios, seasons, and (CCCma CGCM 3.1), Australia’s Commonwealth Scientific and within the level II ecoregions, which necessitated the Industrial Research Organisation Mark 3.0 (CSIRO–Mk3.0) analyses of variabilities within each ecoregion. model, and the Model for Interdisciplinary Research on Climate version 3.2, medium resolution (MIROC 3.2-medres). The • The variability in temperature and precipitation selection of GCMs represents a range of projected climate changes of the GCMs made the ranges of climate change that was constrained by the availability of suitably change for each scenario less distinct. downscaled versions and resources to simulate multiple effects 1U.S. Geological Survey, Menlo Park, Calif. of climate change. 2 U.S. Geological Survey, Denver, Colo. 3U.S. Geological Survey, Reston, Va. 2 Baseline and Projected Future Carbon Storage and Greenhouse-Gas Fluxes in Ecosystems of the Western United States The GCMs are mathematical representations of the most common variables used in this assessment when the atmospheric, oceanic, cryospheric, and land-surface processes influence of climate change on carbon cycling was simulated. that express how those processes interact and respond to Other climate-related variables, such as humidity, were then changes in GHG concentrations (Randall and others, 2007; U.S. derived from temperature and precipitation. Therefore, the Climate Change Science Program (CCSP), 2008). The GCMs discussion of potential climate change focuses on temperature subdivide the world into volumetric pixels (voxels) representing and precipitation variables. the layers of the atmosphere, land, and ocean at regularly spaced Climate and weather input data were required in locations. The GCM outputs may include hourly, daily, and order to model both wildland fires (chapters 3 and 8) and monthly estimates of temperature, precipitation, air pressure, biogeochemical processes of carbon and GHG fluxes (chapters 5 wind, cloud cover, soil moisture, snow, humidity, or short- and and 9); however, two sources of downscaled climate and long‑wave fluxes of solar radiation. According to McAvaney and weather data were used for the same GCMs because of the others (2001), projected surface-air temperatures generally