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  • Authors: Francis Zwiers Publication Date: Apr 2016

    Our understanding of the impact of anthropogenic forcing on extremes remains limited. While we have relatively high confidence for temperature extremes and some confidence in precipitation extremes, as yet we can say relatively little about storms, droughts and floods. We are often very limited by data and, while models and methods can be improved, improving historical data is much harder. To progress, we need further methodological development and improved process understanding. Event attribution is increasingly being undertaken, but there is still much work to do to develop methods and capabilities, understand the implications of framing choices, and develop objective evaluation techniques.

  • Authors: The Pacific Climate Impacts Consortium Publication Date: Apr 2016

    The City of Vancouver is warming. Global climate models project annual average temperature to increase by 1.7°C to 4.0°C, and indicate an average increase of 2.9°C between the 1971-2000 baseline and the 2050s. This fact sheet provides specific information intended to facilitate adaptation as the climate changes. All values in the summary are for the 2050s relative to the 1971-2000 baseline. Additional variables, seasons, projections for the 2080s, and maps were also produced and provided to the City of Vancouver.

  • Authors: T. Q. Murdock, S. R. Sobie, H. D. Eckstrand, E. Jackson Publication Date: Apr 2016

    Climate change projections have been provided in this report for Metro Vancouver and the Capital Regional District from several difference sources: Global Climate Models (GCMs) directly, high resolution elevation-corrected projections from GCMs, and Regional Climate Models. Historical climate information at selected stations of interest throughout the region is also provided for comparison.
    Projected annual warming by the 2050s (compared to 1961-1990) for the two regions is similar, according to a set of 30 commonly used Global Climate Models (GCMs). Projections are given for both the 2050s and 2080s periods. For the 2050s, the range of projected change in Metro Vancouver is +1.4°C to +2.8°C in summer, +0.8°C to +2.7°C in winter, -5% to +16% in winter precipitation, and -25% to +5% in summer precipitation. For the 2050s, the range of projected change in the Capital Regional District (CRD) is +1.3°C to +2.6°C in summer, +0.8°C to +2.4°C in winter, -5% to +17% in winter precipitation, and -30% to +1% in summer precipitation. Compared to the ranges, the projected differences between regions are minor.
    Maps of high resolution projections of change are provided for several variables of interest. Projections mid-century show changes in variables related to temperature: increased growing degree days, cooling degree days, and frost free period along with decreased heating degree days and precipitation as snow. The projected 2080s maps illustrate a future climate that does not resemble the present-day for most of these variables.
    Regional Climate Models projections are used to provide projections of changes in temperature, precipitation, and indices of extremes. Extreme temperatures so warm that in the past they would be exceeded on average once every ten years (corresponding to about 32°C to 35°C) are projected to occur on average over twice as often in future in Metro Vancouver and almost four times as often in future in the CRD.
    The amount of precipitation falling during very wet days is projected to increase by 21% in Metro Vancouver and 20% in CRD, while precipitation during extremely wet days is projected to increase by 28% in Metro Vancouver and 25% in CRD. More extreme precipitation events (with 3-hour duration) so intense than in the past they would be exceeded on average only once every 10 years are projected to occur on average three times as often in future in Metro Vancouver and about three and a half times as often in future in CRD.
    The implications of these projected changes are briefly discussed for physical, social, economic, and ecological systems, and the ICLEI Canada climate adaptation planning methodology is described. This process, outlined in Changing Climate, Changing Communities: Guide and Workbook for Municipal Climate Adaptation is currently being undertaken by communities in Metro Vancouver and CRD. The information contained within this report supports Milestone Two of that process as is intended to assist with adaptation planning.

  • Source Publication: Environmental Research Letters, 11, 4, doi:10.1088/1748-9326/11/4/044011 Authors: B. Mueller, X. Zhang and F.W. Zwiers Publication Date: Apr 2016

    e project that within the next two decades, half of the world's population will regularly (every second summer on average) experience regional summer mean temperatures that exceed those of the historically hottest summer, even under the moderate RCP4.5 emissions pathway. This frequency threshold for hot temperatures over land, which have adverse effects on human health, society and economy, might be broached in little more than a decade under the RCP8.5 emissions pathway. These hot summer frequency projections are based on adjusted RCP4.5 and 8.5 temperature projections, where the adjustments are performed with scaling factors determined by regularized optimal fingerprinting analyzes that compare historical model simulations with observations over the period 1950–2012. A temperature reconstruction technique is then used to simulate a multitude of possible past and future temperature evolutions, from which the probability of a hot summer is determined for each region, with a hot summer being defined as the historically warmest summer on record in that region. Probabilities with and without external forcing show that hot summers are now about ten times more likely (fraction of attributable risk 0.9) in many regions of the world than they would have been in the absence of past greenhouse gas increases. The adjusted future projections suggest that the Mediterranean, Sahara, large parts of Asia and the Western US and Canada will be among the first regions for which hot summers will become the norm (i.e. occur on average every other year), and that this will occur within the next 1–2 decades.

  • Authors: Francis Zwiers Publication Date: Apr 2016

    China’s observing system records temperatures that are broadly influenced by urban warming

    Thus the warming of the Chinese land-mass is likely overestimated. Comparison between urban and rural stations appears to lead to an underestimate of the strength of the urbanization influence. A detection and attribution formalism allows decomposition of China’s temperature record into externally forced, urbanization induced and internal variability induced components of change

    Results suggest about 1/3rd of the recorded warming is due to urbanization

    Anthropogenic and natural external forcing combined are estimated to have caused 0.93°C [0.61-1.24], consistent with the observed global land mean warming 1.09°C [0.86-1.31

  • Authors: The Pacific Climate Impacts Consortium Publication Date: Apr 2016

    This memo summarizes some of the key information required for adaptation in the Whistler area. Projected changes include: increases to the intensity and frequency of heavy rain events; longer, hotter, drier summers and milder winters with reduced snowpack at lower elevations.

  • Authors: Francis Zwiers Publication Date: Apr 2016

    The Challenge Imposed by Climate Change: observed changes, interpretation, projections, limited future warming, key messages and impacts.

  • Authors: Francis Zwiers Publication Date: Apr 2016

    Ability to attribute causes to events remains limited

    – Relatively high confidence for extreme temperature

    – Some confidence in precipitation extremes and perhaps some kinds of drought

    – Can say relatively little about frozen and freezing precipitation, storms, floods, wildfire

    Confidence is often limited by

    – Data quality and length of historical record

    – Process understanding, and ability of models to simulate events

    – Lack of supporting research on detection and attribution of long-term change related to the event type

    Findings are sensitive to framing choices

    – event definition

    – what question is asked

    – whether conditioning factors are taken into account

    Methods are still evolving, and are at least partially determined by the framing

    Need to develop objective event selection criteria

    Don’t yet have a good way to ask highly specific questions (most studies consider classes of events)

  • Authors: Faron S. Anslow Publication Date: Mar 2016

    In many respects, 2015 was a record year for British Columbia, too, both seasonally and for the year as a whole. To help us place last year’s conditions in BC into a historical and global context, PCIC Climatologist Dr. Faron Anslow offers his perspective on 2015. In brief, the warm winter saw records for daily maximum and minimum temperature broken in the southwest and this warmth continued into the spring, with the warmest minimum temperatures ever recorded in western and central BC and maximum temperature records broken in the north. While the summer and fall reverted to more typical conditions, the year overall remained exceptionally warm for the province.

  • Source Publication: Nature Climate Change 6, 706–709, doi:10.1038/NCLIMATE2956. Authors: Sun, Y., X, Zhang, G. Ren, F.W. Zwiers and T. Hu Publication Date: Mar 2016

    China has warmed rapidly over the past half century and has experienced widespread concomitant impacts on water availability, agriculture and ecosystems. Although urban areas occupy less than 1% of China’s land mass, the majority of China’s observing stations are situated in proximity to urban areas, and thus some of the recorded warming is undoubtedly the consequence of rapid urban development, particularly since the late 1970s. Here, we quantify the separate contributions of urbanization and other external forcings to the observed warming. We estimate that China’s temperature increased by 1.44 °C (90% confidence interval 1.22–1.66 °C) over the period 1961–2013 and that urban warming influences account for about a third of this observed warming, 0.49 °C (0.12–0.86 °C). Anthropogenic and natural external forcings combined explain most of the rest of the observed warming, contributing 0.93 °C (0.61–1.24 °C). This is close to the warming of 1.09 °C (0.86–1.31 °C) observed in global mean land temperatures over the period 1951–2010, which, in contrast to China’s recorded temperature change, is only weakly affected by urban warming influences. Clearly the effects of urbanization have considerably exacerbated the warming experienced by the large majority of the Chinese population in comparison with the warming that they would have experienced as a result of external forcing alone.

  • Authors: The Pacific Climate Impacts Consortium Publication Date: Mar 2016

    The new Science Brief covers two recent papers by Beedle et al. (2015) and Clarke et al. (2015) on changes to glaciers in western Canada. Publishing in the journal The Cryosphere, Beedle et al. use photographic methods to quantify changes to 33 glaciers in the Cariboo Mountains. They find that all of the glaciers receded over the 1952-2005 period with an average loss in surface area of about 0.19% per year. Clarke et al.’s work is published in Nature Geoscience and uses a regional glaciation model driven by global climate model output to examine possible future changes to glaciers in western Canada. Their projections show a reduction of between 70% to 95% in both glacier area and volume by the year 2100 compared to 2005.

  • Authors: The Pacific Climate Impacts Consortium Publication Date: Mar 2016

    The March 2016 edition of PCIC's Update includes stories on: The 13th International Meeting on Statistical Climatology, 2015: A Year in Review, the COP21 Paris Agreement, Faron Anslow's TV interview on CBC, PCIC at the AGU Annual Fall Meeting, an announcement for a talk by Francis Zwiers, discussion of earlier talks from the Pacific Climate Seminar Series and in UVic's Idea Fest, an announcement for new Science Briefs and a welcome to Christian Seiler, PCIC's new Research Climatologist.

  • Authors: Anslow, F.S. and Y. Wang Publication Date: Mar 2016

    This document details the exploratory efforts to create a high quality, homogenized set of monthly mean of daily minimum and maximum temperatures for the Williston Basin and Campbell River regions of British Columbia. Data from BC Hydro, the Ministry of Transportation and Infrastructure, and the Ministry of Forests Lands and Natural Resource Operation Wildfire Management Branch are used. The data records are of various lengths, from as many as 50 years to as few as a single year. A set of quality control procedures is applied to the data and then the data are subject to a two step statistical homogenization process. The quality control work revealed that the data are of high quality overall. Inconsistencies were set as missing. Homogenization efforts revealed that fewer than 50% of stations contained any discontinuities with the data in the Williston region being of greater homogeneity than that in the Campbell River region. The outlook for homogenizing daily temperature and monthly precipitation totals is also discussed. Appendices detail station metadata as well as changepoint occurrence for each station. This report will be accompanied by an archive of the results of this project including the homogenized datasets.

  • Source Publication: Wiley Interdisciplinary Reviews: Climate Change, 7, 1, pages 23–41, doi:10.1002/wcc.380. Authors: Stott, P.A., N. Christidis, F. Otto, Y. Sun, J.-P. Vanderlinden, G.J. van Oldenborgh, R. Vautard, P. Walton, P. Yiou, F.W. Zwiers Publication Date: Jan 2016

    Extreme weather and climate-related events occur in a particular place, by definition, infrequently. It is therefore challenging to detect systematic changes in their occurrence given the relative shortness of observational records. However, there is a clear interest from outside the climate science community in the extent to which recent damaging extreme events can be linked to human-induced climate change or natural climate variability. Event attribution studies seek to determine to what extent anthropogenic climate change has altered the probability or magnitude of particular events. They have shown clear evidence for human influence having increased the probability of many extremely warm seasonal temperatures and reduced the probability of extremely cold seasonal temperatures in many parts of the world. The evidence for human influence on the probability of extreme precipitation events, droughts, and storms is more mixed. Although the science of event attribution has developed rapidly in recent years, geographical coverage of events remains patchy and based on the interests and capabilities of individual research groups. The development of operational event attribution would allow a more timely and methodical production of attribution assessments than currently obtained on an ad hoc basis. For event attribution assessments to be most useful, remaining scientific uncertainties need to be robustly assessed and the results clearly communicated. This requires the continuing development of methodologies to assess the reliability of event attribution results and further work to understand the potential utility of event attribution for stakeholder groups and decision makers.

  • Source Publication: Climate Dynamics, doi:10.1007/s00382-015-2807-7 Authors: Whan, K., and F.W. Zwiers Publication Date: Jan 2016

    We assess the ability of two Canadian regional climate models (RCMs), CanRCM4 and CRCM5, to simulate North American climate extremes over the period 1989–2009. Both RCMs use lateral boundary conditions derived from the ERA-Interim reanalysis and share the same dynamical core but use different nesting strategies, land-surface and physics schemes. The annual cycle and spatial patterns of extreme temperature indices are generally well reproduced in both models but the magnitude varies. In central and southern North America, maximum temperature extremes are up to 7 °C warmer in CanRCM4. There is a cool bias in minimum temperature extremes in both RCMs. The shape of the annual cycle of extreme rainfall varies between simulations. There is a wet bias in CRCM5 extreme rainfall on the west coast throughout the year and in winter rainfall elsewhere. In summer both RCMs have precipitation biases in the south-east. These rainfall and temperature biases are likely associated with differences in the physical parameterisation of rainfall. CanRCM4 simulates too little convective rainfall, while over-estimating large-scale rainfall; nevertheless, cloud cover is well simulated. CRCM5 simulates more large-scale rainfall throughout the year on the west coast and in winter in other regions. The spatial extent, intensity and location of atmospheric river (AR) landfall are well reproduced by the RCMs, as is the fraction of winter rainfall from AR days. Spectral nudging improves agreement on landfall latitude between the RCM and the driving model without greatly diminishing the intensity of the rainfall extreme.

  • Source Publication: Geophysical Research Letters, 42, 24, 10,867–10,875, doi:10.1002/2015GL066858. Authors: Kumar, S., R.P. Allan, F.W. Zwiers, D.M. Lawrence and P.A. Dirmeyer Publication Date: Dec 2015

    A theoretically expected consequence of the intensification of the hydrological cycle under global warming is that on average, wet regions get wetter and dry regions get drier (WWDD). Recent studies, however, have found significant discrepancies between the expected pattern of change and observed changes over land. We assess the WWDD theory in four climate models. We find that the reported discrepancy can be traced to two main issues: (1) unforced internal climate variability strongly affects local wetness and dryness trends and can obscure underlying agreement with WWDD, and (2) dry land regions are not constrained to become drier by enhanced moisture divergence since evaporation cannot exceed precipitation over multiannual time scales. Over land, where the available water does not limit evaporation, a “wet gets wetter” signal predominates. On seasonal time scales, where evaporation can exceed precipitation, trends in wet season becoming wetter and dry season becoming drier are also found.

  • Authors: The Pacific Climate Impacts Consortium Publication Date: Dec 2015

    Publishing in the Reviews of Geophysics, Westra et al (2014) summarize the current state of research in the analysis of future changes to the intensity, frequency and duration of extreme rainfall. Their literature review highlights the complicated relationship between short duration extreme rainfall and atmospheric temperature. In some locations, such extreme precipitation does not simply scale with the ability of the atmosphere to hold moisture (i.e. at the Clausius-Clapyron rate of 6 to 7% per °C). Instead, at these locations the general pattern is that such a relationship is found to hold up to about 12 °C, but between 12 and 24 °C extreme precipitation appears to increase more strongly with warming. This is partly due to an increase in convective rainfall. However, above about 24 °C, the pattern at these locations is one in which the response of precipitation to increasing temperature appears to be weaker, eventually reversing. This may be due to decreased moisture availability at these temperatures, though Westra et al. note that “the mechanism that causes these moisture deficits remains to be investigated.” The authors also find that anticipated changes in sub-daily precipitation associated with a warming climate will “significantly affect the magnitude and frequency of urban and rural flash floods.”

    Compared to daily rainfall, Westra et al. find that sub-daily and sub-hourly rainfall are more sensitive to local surface temperatures. They also report that while sub-daily precipitation observations are too scarce to determine regional trends, geographic location will likely affect rates of change in daily precipitation extremes. In terms of making projections of future changes in these events, the authors find that, owing to the resolution of current global climate models, they are limited in their ability to simulate such precipitation events. In particular, the models are generally not run at sufficient resolution to accurately resolve the necessary convective processes, though some very high-resolution “convection permitting” regional climate models operate at a sufficient resolution to potentially be useful in projecting such extremes. One implication of these findings is that we cannot currently make credible projections of sub-daily rainfall events.

  • Source Publication: Hydrological Processes, 28, 4294–4310, doi: 10.1002/hyp.9997 Authors: Shrestha, R.R., D.L. Peters and M.A. Schnorbus Publication Date: Nov 2015

    It is a common practice to employ hydrologic models for assessing alterations to streamflow as a result of anthropogenically driven changes, such as riverine, land use, and climate change. However, the ability of the models to replicate different components of the hydrograph simultaneously is not clear. Hence, this study evaluates the ability of a standard hydrologic model set-up: Variable Infiltration Capacity (VIC) hydrologic model for two headwater sub-basins in the Fraser River (Salmon and Willow), British Columbia, Canada, with climate inputs derived from observations and statistically downscaled global climate models (GCMs); to simulate six general water resource indicators (WRIs) and 32 ecologically relevant indicators of hydrologic alterations (IHA). The results show a generally good skill of the observation-driven VIC model in replicating most of the WRIs and IHAs. Although the WRIs, including annual volume, centre of timing, and seasonal flows, and the IHAs, including maximum and minimum flows, were reasonably well replicated, statistically significant differences in some of the monthly flows, number and duration of flow pulses, rise and fall rates, and reversals were noted. In the case of GCM-driven results, additional monthly, maximum, and minimum flow indicators produced statistically significant differences. A number of issues with the model input/output data, hydrologic model parametrization and structure as well as downscaling methods were identified, which lead to such discrepancies. Therefore, there is a need to exercise caution in the use of model-simulated indicators. Overall, the WRIs and IHAs can be useful tools for evaluating changes in an altered hydrologic system, provided the skill and limitations of the model in replicating these indicators are understood.

  • Source Publication: Weather and Climate Extremes, 9, 57-67, doi:10.1016/j.wace.2015.05.001 Authors: Whan, K., J. Zscheischler, R., Orth, M. Shongwe, M., Rahimi, E.O. Asare and S.I. Seneviratne Publication Date: Nov 2015

    Land-atmosphere interactions play an important role for hot temperature extremes in Europe. Dry soils may amplify such extremes through feedbacks with evapotranspiration. While previous observational studies generally focused on the relationship between precipitation deficits and the number of hot days, we investigate here the influence of soil moisture (SM) on summer monthly maximum temperatures (TXx) using water balance model-based SM estimates (driven with observations) and temperature observations. Generalized extreme value distributions are fitted to TXx using SM as a covariate. We identify a negative relationship between SM and TXx, whereby a 100 mm decrease in model-based SM is associated with a 1.6 °C increase in TXx in Southern-Central and Southeastern Europe. Dry SM conditions result in a 2–4 °C increase in the 20-year return value of TXx compared to wet conditions in these two regions. In contrast with SM impacts on the number of hot days (NHD), where low and high surface-moisture conditions lead to different variability, we find a mostly linear dependency of the 20-year return value on surface-moisture conditions. We attribute this difference to the non-linear relationship between TXx and NHD that stems from the threshold-based calculation of NHD. Furthermore the employed SM data and the Standardized Precipitation Index (SPI) are only weakly correlated in the investigated regions, highlighting the importance of evapotranspiration and runoff for resulting SM. Finally, in a case study for the hot 2003 summer we illustrate that if 2003 spring conditions in Southern-Central Europe had been as dry as in the more recent 2011 event, temperature extremes in summer would have been higher by about 1 °C, further enhancing the already extreme conditions which prevailed in that year.

  • Source Publication: Earth’s Future, 2, 3, 152‐160, doi: 10.1002/2013EF000159 Authors: Kumar, S., D. Lawrence, P. Dirmeyer and J. Sheffield Publication Date: Nov 2015

    The temporal variability of river and soil water affects society at time scales ranging from hourly to decadal. The available water (AW), i.e., precipitation minus evapotranspiration, represents the total water available for runoff, soil water storage change, and ground water recharge. The reliability of AW is defined as the annual range of AW between local wet and dry seasons. A smaller annual range represents greater reliability and a larger range denotes less reliability. Here we assess the reliability of AW in the 21st century climate projections by 20 climate models from phase 5 of the Coupled Model Intercomparison Project (CMIP5). The multimodel consensus suggests less reliable AW in the 21st century than in the 20th century with generally decreasing AW in local dry seasons and increasing AW in local wet seasons. In addition to the canonical perspective from climate models that wet regions will get wetter, this study suggests greater dryness during dry seasons even in regions where the mean climate becomes wetter. Lower emission scenarios show significant advantages in terms of minimizing impacts on AW but do not eliminate these impacts altogether.

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