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Byline: Bruce T. Anderson (1), Katharine Hayhoe (2), Xin-Zhong Liang (3) Abstract: Potential changes in summertime hydroclimatology over the northeastern (NE) region of the USA induced by increases in greenhouse gas (GHG) concentrations are investigated using a state-of-the-art regional climate modeling system. Results for a higher emissions scenario illustrate changes that may occur if dependence on fossil fuels continues over the coming century. Summertime precipitation is projected to decrease across much of the central NE, but increase over the southernmost and northernmost portions of the domain. Evaporation is expected to increase across the entire domain. The balance between these two results in a decrease in soil moisture content across most of the domain (by approximately 10 mm) and an increase in the summertime soil-moisture depletion rate (by approximately 10 mm/month). At the same time, an increase in both atmospheric near-surface specific and saturation specific humidity is projected, resulting in an increase in relative humidity across the southern portion of the domain, with slight decreases over the northern portion. Combined with an average increase in summer temperatures of 3.5degC, the projected increase in relative humidity results in a marked increase in the average daily maximum heat index for the region on the order of 3.9degC, as well as a 350--400% increase in the number of days with heat index values exceeding 32.2degC (90degF)--the level of 'extreme caution'. Taken together, these high-resolution, dynamically-generated projections confirm the potential for significant summertime climate change impacts on the NE over the coming century as suggested by previous studies. Author Affiliation: (1) Department of Geography and Environment, Boston University, Boston, MA, 02215, USA (2) Department of Geosciences, Texas Tech University, Lubbock, TX, 70409, USA (3) Illinois Department of Natural Resources, Illinois State Water Survey, University of Illinois, Urbana-Champaign, USA Article History: Registration Date: 05/08/2009 Received Date: 28/04/2008 Accepted Date: 19/06/2009 Online Date: 08/10/2009

Byline: Daniel R. Cayan (1,2), Edwin P. Maurer (3), Michael D. Dettinger (1,2), Mary Tyree (1), Katharine Hayhoe (4) Abstract: To investigate possible future climate changes in California, a set of climate change model simulations was selected and evaluated. From the IPCC Fourth Assessment, simulations of twenty-first century climates under a B1 (low emissions) and an A2 (a medium-high emissions) emissions scenarios were evaluated, along with occasional comparisons to the A1fi (high emissions) scenario. The climate models whose simulations were the focus of the present study were from the Parallel Climate Model (PCM1) from NCAR and DOE, and the NOAA Geophysical Fluid Dynamics Laboratory CM2.1 model (GFDL). These emission scenarios and attendant climate simulations are not 'predictions,' but rather are a purposely diverse set of examples from among the many plausible climate sequences that might affect California in the next century. Temperatures over California warm significantly during the twenty-first century in each simulation, with end-of-century temperature increases from approximately +1.5degC under the lower emissions B1 scenario in the less responsive PCM1 to +4.5degC in the higher emissions A2 scenario within the more responsive GFDL model. Three of the simulations (all except the B1 scenario in PCM1) exhibit more warming in summer than in winter. In all of the simulations, most precipitation continues to occur in winter. Relatively small (less than ~10%) changes in overall precipitation are projected. The California landscape is complex and requires that model information be parsed out onto finer scales than GCMs presently offer. When downscaled to its mountainous terrain, warming has a profound influence on California snow accumulations, with snow losses that increase with warming. Consequently, snow losses are most severe in projections by the more responsive model in response to the highest emissions. Author Affiliation: (1) Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA, USA (2) U.S. Geological Survey, La Jolla, CA, USA (3) Santa Clara University, Santa Clara, CA, USA (4) Department of Geosciences, Texas Tech University, Lubbock, TX, USA Article History: Registration Date: 23/11/2007 Received Date: 02/08/2006 Accepted Date: 05/10/2007 Online Date: 26/01/2008

Byline: Daniel R. Cayan (1,2), Peter D. Bromirski (1), Katharine Hayhoe (3), Mary Tyree (1), Michael D. Dettinger (2,1), Reinhard E. Flick (4,1) Abstract: California's coastal observations and global model projections indicate that California's open coast and estuaries will experience rising sea levels over the next century. During the last several decades, the upward historical trends, quantified from a small set of California tide gages, have been approximately 20 cm/century, quite similar to that estimated for global mean sea level. In the next several decades, warming produced by climate model simulations indicates that sea level rise (SLR) could substantially exceed the rate experienced during modern human development along the California coast and estuaries. A range of future SLR is estimated from a set of climate simulations governed by lower (B1), middle--upper (A2), and higher (A1fi) GHG emission scenarios. Projecting SLR from the ocean warming in GCMs, observational evidence of SLR, and separate calculations using a simple climate model yields a range of potential sea level increases, from 11 to 72 cm, by the 2070--2099 period. The combination of predicted astronomical tides with projected weather forcing, El Nino related variability, and secular SLR, gives a series of hourly sea level projections for 2005--2100. Gradual sea level rise progressively worsens the impacts of high tides, surge and waves resulting from storms, and also freshwater floods from Sierra and coastal mountain catchments. The occurrence of extreme sea levels is pronounced when these factors coincide. The frequency and magnitude of extreme events, relative to current levels, follows a sharply escalating pattern as the magnitude of future sea level rise increases. Author Affiliation: (1) Scripps Institution of Oceanography, University of California, La Jolla, CA, USA (2) Water Resources Division, U. S. Geological Survey, La Jolla, CA, USA (3) Department of Geosciences, Texas Tech University, Lubbock, TX, USA (4) California Department of Boating and Waterways, La Jolla, CA, USA Article History: Registration Date: 23/11/2007 Received Date: 02/08/2006 Accepted Date: 05/10/2007 Online Date: 26/01/2008

Byline: Jeremy S. Fried (1), J. Keith Gilless (2), William J. Riley (3), Tadashi J. Moody (4), Clara Simon de Blas (5), Katharine Hayhoe (6), Max Moritz (4), Scott Stephens (4), Margaret Torn (3) Abstract: This study focused on how climate change-induced effects on weather will translate into changes in wildland fire severity and outcomes in California, particularly on the effectiveness of initial attack at limiting the number of fires that escape initial attack. The results indicate that subtle shifts in fire behavior of the sort that might be induced by the climate changes anticipated for the next century are of sufficient magnitude to generate an appreciable increase in the number of fires that escape initial attack. Such escapes are of considerable importance in wildland fire protection planning, given the high cost to society of a catastrophic escape like those experienced in recent decades in the Berkeley-Oakland, Santa Barbara, San Diego, or Los Angeles areas. However, at least for the three study areas considered, it would appear that relatively modest augmentations to existing firefighting resources might be sufficient to compensate for change-induced changes in wildland fire outcomes. Author Affiliation: (1) USDA Forest Service Pacific Northwest Research Station, Forest Inventory and Analysis, Portland, OR, USA (2) Berkeley, Agricultural and Resource Economics, University of California, Berkeley, CA, 94720-3100, USA (3) Lawrence Berkeley National Laboratory Center for Isotope Geochemistry, Berkeley, CA, USA (4) Berkeley Environmental Science, Policy, and Management, University of California, Berkeley, CA, USA (5) Universidad Rey Juan Carlos, Madrid, Spain (6) ATMOS Research and Consulting, Lubbock, TX, USA Article History: Registration Date: 29/10/2007 Received Date: 02/08/2006 Accepted Date: 05/10/2007 Online Date: 19/12/2007

Projections of changes in climate extremes are critical to assessing the potential impacts of climate change on human and natural systems. Modeling advances now provide the opportunity of utilizing global general circulation models (GCMs) for projections of extreme temperature and precipitation indicators. We analyze historical and future simulations of ten such indicators as derived from an ensemble of 9 GCMs contributing to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC-AR4), under a range of emissions scenarios. Our focus is on the consensus from the GCM ensemble, in terms of direction and significance of the changes, at the global average and geographical scale. The climate extremes described by the ten indices range from heat-wave frequency to frost-day occurrence, from dry-spell length to heavy rainfall amounts. Historical trends generally agree with previous observational studies, providing a basic sense of reliability for the GCM simulations. Individual model projections for the 21st century across the three scenarios examined are in agreement in showing greater temperature extremes consistent with a warmer climate. For any specific temperature index, minor differences appear in the spatial distribution of the changes across models and across scenarios, while substantial differences appear in the relative magnitude of the trends under different emissions rates. Depictions of a wetter world and greater precipitation intensity emerge unequivocally in the global averages of most of the precipitation indices. However, consensus and significance are less strong when regional patterns are considered. This analysis provides a first overview of projected changes in climate extremes from the 1PCC-AR4 model ensemble, and has significant implications with regard to climate projections for impact assessments.

Byline: Claudia Tebaldi (1), Katharine Hayhoe (2,3), Julie M. Arblaster (4,5), Gerald A. Meehl (4) Author Affiliation: (1) Institute for the Study of Society and Environment, National Center for Atmospheric Research (NCAR), PO BOX 3000, Boulder, CO, 80301, USA (2) Department of Atmospheric Sciences, University of Illinois at Urbana-Champaign, Urbana, IL, USA (3) Department of Geosciences, Texas Tech University, Lubbock, TX, USA (4) Climate and Global Dynamics Division, NCAR, Boulder, CO, USA (5) Bureau of Meteorology Research Centre, Melbourne, Australia Article History: Registration Date: 19/02/2007 Online Date: 15/03/2007 Article note: The online version of the original article can be found at: doi: 10.1007/s10584-006-9051-4.

Past heavy precipitation events in the Chicago metropolitan area have caused significant flood-related economic and environmental damages. A key component in flood management policies and actions is determining flood magnitudes for specified return periods. This is a particularly difficult task in areas with a complex and changing climate and land-use, such as the Chicago metropolitan area. The standard design storm methodology based on the NOAA Atlas 14 and ISWS Bulletin 70 has been used in the past to estimate flood hydrographs with variable return periods in this region. In a changing climate, however, these publications may not be accurate. This study presents and illustrates a methodology for diagnostic analysis of future climate scenarios in the framework of urban flooding, and assesses the corresponding uncertainties. First, the design storms are calculated using data downscaled by a regional climate model (RCM) at 30-km spacing for the present and 2050s under the IPCC A1Fi (high) and B1 (low) emissions scenarios. Next, the corresponding flood discharges at six watersheds in suburban Chicago are estimated using a hydrologic event model. The resulting scenarios in flood frequency were first assessed through a set of diagnostic tests for precipitation timing and frequency. The study did not reveal any significant changes in the 2050s in the average timing of heavy storms, but their regularity decreased. The average timing did not exhibit any significant spatial variability throughout the region. The precipitation frequency analysis revealed distinct differences between the northern and southeastern subregions of the Chicago metropolitan area. The quantiles in the northern subregion averaged for 2-year, 5-year, and 10-year return periods exhibited a 20% and 16% increase in daily precipitation for scenarios B1 and A1Fi, respectively. The southeastern subregion, however, exhibited a decrease of 12% for scenario B1 and a minor increase of 3% for scenario A1Fi. The hydrologic effects of changing precipitation on the flood quantiles were illustrated using six small watersheds in the region. The relative increases or decreases in precipitation translated into even larger relative increases or decreases in flood peaks, due to the nonlinear nature of the rainfall-runoff process. Simulations using multiple climate models, for longer periods, finer spatio-temporal resolution, and larger areal coverage could be used to more accurately account for numerous uncertainties in the precipitation and flood projections. [ABSTRACT FROM AUTHOR]

The article presents a correction to the article "Going to the extremes: An intercomparison of model-simulated historical and future changes in extreme events," which was published in the 15 March 2007 issue.