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  • Source Publication: Journal of Climate, 33, 4 1261-1281, doi:10.1175/JCLI-D-19-0134.1 Authors: Tan, Y., F.W. Zwiers, S. Yang, C. Li and K. Deng Publication Date: Feb 2020

    Performance in simulating atmospheric rivers (ARs) over western North America based on AR frequency and landfall latitude is evaluated for 10 models from phase 5 of the Coupled Model Intercomparison Project among which the CanESM2 model performs well. ARs are classified into southern, northern, and middle types using self-organizing maps in the ERA-Interim reanalysis and CanESM2. The southern type is associated with the development and eastward movement of anomalous lower pressure over the subtropical eastern Pacific, while the northern type is linked with the eastward movement of anomalous cyclonic circulation stimulated by warm sea surface temperatures over the subtropical western Pacific. The middle type is connected with the negative phase of North Pacific Oscillation–west Pacific teleconnection pattern. CanESM2 is further used to investigate projected AR changes at the end of the twenty-first century under the representative concentration pathway 8.5 scenario. AR definitions usually reference fixed integrated water vapor or integrated water vapor transport thresholds. AR changes under such definitions reflect both thermodynamic and dynamic influences. We therefore also use a modified AR definition that isolates change from dynamic influences only. The total AR frequency doubles compared to the historical period, with the middle AR type contributing the largest increases along the coasts of Vancouver Island and California. Atmospheric circulation (dynamic) changes decrease northern AR type frequency while increasing middle AR type frequency, indicating that future changes of circulation patterns modify the direct effect of warming on AR frequency, which would increase ARs (relative to fixed thresholds) almost everywhere along the North American coastline.

  • Authors: Sun, Q., F. Zwiers, X. Zhang and G. Li Publication Date: Jan 2020

    Trend scaling relationships between extreme precipitation and temperature are often used to represent the influence of long-term warming on the intensity of extreme precipitation. Indeed, such scaling relationships are often regarded as providing more reliable precipitation projections than direct projection, owing to higher confidence for temperature projections in model simulations. Due to limited data availability, especially for the sub-daily rainfall, so-called binning scaling relationships, which relate extreme precipitation to temperature at the time of occurrence and are estimated empirically either through a binning technique or quantile regression, have been considered as a substitute for trend scaling to project the long-term response of local extreme precipitation to temperature change (Lenderink and Van Meijgaard, 2008; Wasko and Sharma, 2014). Estimates of binning scaling rates are generally based on seasonal subdaily precipitation observations, and thus they are influenced by factors other than temperature that change systematically within a season, synchronously with the seasonal cycle (Zhang et al., 2017). In contrast to trend scaling, binning scaling often suggests faster than Clausius-Clapeyron intensification of sub-daily precipitation extremes with temperature.

    We explore this apparent contradiction between binning and trend scaling using a large ensemble of moderate resolution regional climate simulations for North America. The large amount of data that is available from this ensemble allows us to confidently estimate both trend and binning scaling rates for the climate that is simulated by that model. Specifically, we use a 35-member initial conditions ensemble of regional climate simulations produced with the Canadian CanRCM4 regional climate model for the period 1950-2100, with historical forcings for the period ending 2005 and RCP8.5 forcing subsequently. Each CanRCM4 ensemble member was driven by a corresponding member of a similar large ensemble of global simulations produced with the Canadian global Earth system model CanESM2 (Scinocca et al., 2016).

    We compare binning and trend scaling of precipitation extremes across different durations (1-hour, 3-hour, and 24-hour), considering annual and seasonal values, and both local and regional spatial scales. We provide strong evidence to clarify that binning scaling cannot project the long-term change in precipitation extreme, with substantial disagreement in the spatial pattern and magnitude of scaling rates between binning and trend scaling regardless of the duration, season, and spatial scale. Using the daily dew point temperature as scaling variable rather than dry air temperature does not eliminate the differences between binning and trend scaling rates. While shorter-duration extreme precipitation does appear to intensify faster with warming in CanRCM4, we only find super-adiabatic intensification of annual precipitation extremes in isolated regions regardless of accumulation durations. Compared with annual maximum results, winter extremes intensify more strongly over the western and southeastern North America across all timescales. A decreasing tendency of summer extremes is projected over the north and central Great Plains. The seasonal timing of the occurrences of precipitation extremes are expected to shift towards the cold season, reflecting the different changing tendencies in summer and winter extremes.


    Lenderink, G., and Van Meijgaard, E. 2008: Increase in hourly precipitation extremes beyond expectations from temperature changes. Nat. Geosci., 1,

    Scinocca, J. F., Kharin, V. V., Jiao, Y., Qian, M. W., Lazare, M., Solheim, L., and Flato. G. M., 2016: Coordinated Global and Regional Climate Modeling. J. Climate, 29, 17-35,

    Wasko, C., and Sharma, A. 2014: Quantile regression for investigating scaling of extreme precipitation with temperature. Water Resour. Res., 50, 3608-3614,

    Zhang, X. B., Zwiers F. W., Li, G. L., Wan, H., Cannon, A. J., 2017: Complexity in estimating past and future extreme short-duration rainfall. Nat. Geosci., 10, 255-239,

  • Authors: The Pacific Climate Impacts Consortium Publication Date: Jan 2020

    This is the Pacific Climate Impacts Consortium's 2018-2019 Corporate Report.

  • Authors: Wang, Y., C. Curry, C. Ballantyne, F. Anslow and F. Zwiers Publication Date: Dec 2019

    Analysis of extreme snow events is of great importance in many areas, including risk management and structural design. Severe natural hazards in the mountain regions, such as avalanche, are largely due to heavy snowfall events and seasonally evolving snow-pack. Moreover, guidelines for infrastructure design should include estimates of maximum snow load, not only historically but also as projected under future climate change.

    In this work, we compute annual maximum time series from daily snow depth and snow water equivalent (SWE) data at over 2000 meteorological stations across Canada from 1939- 2016. The more extensive snow depth results are converted to snow loads by applying a suitable density curve that empirically relates extreme snow depth to extreme snow load. An extreme value analysis of the latter is then conducted using the generalized extreme value (GEV) distribution, providing a description of the heavy tail behaviour of the historical snow load. Finally, return values of annual snow load are computed for a range of return periods and compared to previous estimates from the 2015 edition of the National Building Code of Canada.

  • Source Publication: Bulletin of the American Meteorological Society, doi:10.1175/BAMS-D-18-0258.1. Authors: Sun, Q., C. Miao, A. Agha Kouchak, I. Mallakpour, D. Ji, and Q Duan Publication Date: Dec 2019

    The projected occurrence of anomalous precipitation under different ENSO conditions may be changed under future climate warming, with an asymmetric response to La Niña and El Niño and an increasing frequency of ENSO-related severe dry and wet events.

    Predicting the changes in teleconnection patterns and related hydroclimate extremes can provide vital information necessary to adapt to the effects of the El Niño Southern Oscillation (ENSO). This study uses the outputs of global climate models to assess the changes in ENSO-related dry/wet patterns and the frequency of severe dry/wet events. The results show anomalous precipitation responding asymmetrically to La Niña and El Niño, indicating the teleconnections may not simply be strengthened. A “dry to drier, wet to wetter” annual anomalous precipitation pattern was projected during La Niña phases in some regions, with drier conditions over southern North America, southern South America, and southern Central Asia, and wetter conditions in Southeast Asia and Australia. These results are robust, with agreement from the 26 models and from a subset of 8 models selected for their good performance in capturing observed patterns. However, we did not observe a similar strengthening of anomalous precipitation during future El Niño phases, for which the uncertainties in the projected influences are large. Under the RCP 4.5 emissions scenario, 45 river basins under El Niño conditions and 39 river basins under La Niña conditions were predicted to experience an increase in the frequency of severe dry events; similarly, 59 river basins under El Niño conditions and 61 river basins under La Niña conditions were predicted to have an increase in the frequency of severe wet events, suggesting a likely increase in the risk of floods. Our results highlight the implications of changes in ENSO patterns for natural hazards, disaster management, and engineering infrastructure.

  • Source Publication: Climatic Change, doi:10.1007/s10584-019-02591-7. Authors: Ben Alaya, M.A., F.W. Zwiers and X. Zhang Publication Date: Dec 2019

    In the context of climate change and projected increase in global temperature, the atmosphere’s water holding capacity is expected to increase at the Clausius-Clapeyron (C-C) rate by about 7% per 1 °C warming. Such an increase may lead to more intense extreme precipitation events and thus directly affect the probable maximum precipitation (PMP), a parameter that is often used for dam safety and civil engineering purposes. We therefore use a statistically motivated approach that quantifies uncertainty and accounts for nonstationarity, which allows us to determine the rate of change of PMP per 1 °C warming. This approach, which is based on a bivariate extreme value model of precipitable water (PW) and precipitation efficiency (PE), provides interpretation of how PW and PE may evolve in a warming climate. Nonstationarity is accounted for in this approach by including temperature as a covariate in the bivariate extreme value model. The approach is demonstrated by evaluating and comparing projected changes to 6-hourly PMP from two Canadian regional climate models (RCMs), CanRCM4 and CRCM5, over North America. The main results suggest that, on the continental scale, PMP increases in these models at a rate of approximately 4% per 1 °C warming, which is somewhat lower than the C-C rate. At the continental scale, PW extremes increase on average at the rate of 5% per 1 °C near surface warming for both RCMs. Most of the PMP increase is caused by the increase in PW extremes with only a minor contribution from changes in PE extremes. Nevertheless, substantial deviations from the average rate of change in PMP rates occur in some areas, and these are mostly caused by sensitivity of PE extremes to near surface warming in these regions.

  • Source Publication: Environmental Health, 18, 116, doi:10.1186/s12940-019-0550-y Authors: Chhetri, B.K, Galanis, E., Sobie, S., Brubacher, J., Balshaw, R., Otterstatter, M., Mak, S., Lem, M., Lysyshyn, M., Murdock, T., Fleury, M., Zickfeld, K., Zubel, M., Clarkson, L. and T.K. Takaro Publication Date: Dec 2019

    Climate change is increasing the number and intensity of extreme weather events in many parts of the world. Precipitation extremes have been linked to both outbreaks and sporadic cases of waterborne illness. We have previously shown a link between heavy rain and turbidity to population-level risk of sporadic cryptosporidiosis and giardiasis in a major Canadian urban population. The risk increased with 30 or more dry days in the 60 days preceding the week of extreme rain. The goal of this study was to investigate the change in cryptosporidiosis and giardiasis risk due to climate change, primarily change in extreme precipitation.

    Cases of cryptosporidiosis and giardiasis were extracted from a reportable disease system (1997–2009). We used distributed lag non-linear Poisson regression models and projections of the exposure-outcome relationship to estimate future illness (2020–2099). The climate projections are derived from twelve statistically downscaled regional climate models. Relative Concentration Pathway 8.5 was used to project precipitation derived from daily gridded weather observation data (~ 6 × 10 km resolution) covering the central of three adjacent watersheds serving metropolitan Vancouver for the 2020s, 2040s, 2060s and 2080s.

    Precipitation is predicted to steadily increase in these watersheds during the wet season (Oct. -Mar.) and decrease in other parts of the year up through the 2080s. More weeks with extreme rain (>90th percentile) are expected. These weeks are predicted to increase the annual rates of cryptosporidiosis and giardiasis by approximately 16% by the 2080s corresponding to an increase of 55–136 additional cases per year depending upon the climate model used. The predicted increase in the number of waterborne illness cases are during the wet months. The range in future projections compared to historical monthly case counts typically differed by 10–20% across climate models but the direction of change was consistent for all models.

    If new water filtration measures had not been implemented in our study area in 2010–2015, the risk of cryptosporidiosis and giardiasis would have been expected to increase with climate change, particularly precipitation changes. In addition to the predicted increase in the frequency and intensity of extreme precipitation events, the frequency and length of wet and dry spells could also affect the risk of waterborne diseases as we observed in the historical period. These findings add to the growing evidence regarding the need to prepare water systems to manage and become resilient to climate change-related health risks.

  • Source Publication: Environment International, 128, 125-136, doi:10.1016/j.envint.2019.04.025 Authors: Sun, Q., C. Miao, M. Hanel, A.G.L. Borthwick, Q. Duan, D. Jid and H. Li Publication Date: Dec 2019

    The effects of heat stress are spatially heterogeneous owing to local variations in climate response, population density, and social conditions. Using global climate and impact models from the Inter-Sectoral Impact Model Intercomparison Project, our analysis shows that the frequency and intensity of heat events increase, especially in tropical regions (geographic perspective) and developing countries (national perspective), even with global warming held to the 1.5 °C target. An additional 0.5 °C increase to the 2 °C warming target leads to >15% of global land area becoming exposed to levels of heat stress that affect human health; almost all countries in Europe will be subject to increased fire danger, with the duration of the fire season lasting 3.3 days longer; 106 countries are projected to experience an increase in the wheat production-damage index. Globally, about 38%, 50%, 46%, 36%, and 48% of the increases in exposure to health threats, wildfire, crop heat stress for soybeans, wheat, and maize could be avoided by constraining global warming to 1.5 °C rather than 2 °C. With high emissions, these impacts will continue to intensify over time, extending to almost all countries by the end of the 21st century: >95% of countries will face exposure to health-related heat stress, with India and Brazil ranked highest for integrated heat-stress exposure. The magnitude of the changes in fire season length and wildfire frequency are projected to increase substantially over 74% global land, with particularly strong effects in the United States, Canada, Brazil, China, Australia, and Russia. Our study should help facilitate climate policies that account for international variations in the heat-related threats posed by climate change.

  • Authors: The Pacific Climate Impacts Consortium Publication Date: Nov 2019

    Understanding how human influences are affecting different parts of the climate system allows us to improve future climate projections. Due to the relative sparsity of precipitation data and the large amount of internal variability that it exhibits, detecting and attributing the human influence on precipitation is difficult. This Science Brief covers recent research that uses information about the physical processes responsible for precipitation in order to detect the anthropogenic influence on winter precipitation over North America and Eurasia over the 1920-2015 period.

    Publishing in Geophysical Research Letters, Guo et al. (2019) use a technique known as "dynamical adjustment," to estimate the atmospheric circulation and thermodynamic contributions to observed precipitation over Eastern North America and Northern Eurasia over the 1920-2015 period. They find that the thermodynamic component, due to anthropogenic emissions, contributes to increases in precipitation in both regions. They then compare the spatial pattern and magnitude of these components to those obtained from global climate models driven with anthropogenic forcings. They find strong agreement between the thermodynamic components of precipitation obtained from the observational data and those obtained from climate model output.

  • Source Publication: Journal of Hydrometeorology, 20, 10, 2069-2089, doi:10.1175/JHM-D-18-0233.1 Authors: Ben Alaya, M.A.., F. Zwiers, and X. Zhang Publication Date: Oct 2019

    Recently dam managers have begun to use data produced by regional climate models to estimate how probable maximum precipitation (PMP) might evolve in the future. Before accomplishing such a task, it is essential to assess PMP estimates derived from regional climate models (RCMs). In the current study PMP over North America estimated from two Canadian RCMs, CanRCM4 and CRCM5, is compared with estimates derived from three reanalysis products: ERA-Interim, NARR, and CFSR. An additional hybrid dataset (MSWEP-ERA) produced by combining precipitation from the Multi-Source Weighted-Ensemble Precipitation (MSWEP) dataset and precipitable water (PW) from ERA-Interim is also considered to derive PMP estimates that can serve as a reference. A recently developed approach using a statistical bivariate extreme values distribution is used to provide a probabilistic description of the PMP estimates using the moisture maximization method. Such a probabilistic description naturally allows an assessment of PMP estimates that includes quantification of their uncertainty. While PMP estimates based on the two RCMs exhibit spatial patterns similar to those of MSWEP-ERA and the three sets of reanalyses on the continental scale over North America, CanRCM4 has a tendency for overestimation while CRCM5 has a tendency for modest underestimation. Generally, CRCM5 shows good agreement with ERA-Interim, while CanRCM4 is more comparable to CFSR. Overall, the good ability of the two RCMs to reproduce the major characteristics of the different components involved in the estimation of PMP suggests that they may be useful tools for PMP estimation that could serve as a basis for flood studies at the basin scale.

  • Authors: The Pacific Climate Impacts Consortium Publication Date: Oct 2019

    The October 2019 edition of the PCIC Update newsletter contains stories on: new adaptation reports for the Kootenay and Boundary, and Bulkley Nechako and Fraser-Fort George regions; work on PCIC's online tools; a co-produced report on the Cowichan Valley which was featured in the media; the new Gridded Hydrologic Model Output Data Portal page; the new video series on climate change and BC agriculture; going live and PCIC research to support salmon conservation. The newsletter also has a staff profile on Kari Tyler and covers the Pacific Climate Seminar Series, staff changes at PCIC and recent PCIC publications.

  • Source Publication: Journal of Hydrometeorology, 20, 9, 1757-1778, doi:10.1175/JHM-D-18-0262.1. Authors: Shrestha, R.R., A.J. Cannon, M. Schnorbus and H. Alford Publication Date: Sep 2019

    We describe a state-of-the-art framework for projecting hydrologic impacts due to enhanced warming and amplified moisture fluxes in the subarctic environment under anthropogenic climate change. We projected future hydrologic changes based on phase 5 of the Coupled Model Intercomparison Project global climate model simulations using the Variable Infiltration Capacity hydrologic model and a multivariate bias correction/downscaling method for the Liard basin in subarctic northwestern Canada. Subsequently, the variable importance of key climatic controls on a set of hydrologic indicators was analyzed using the random forests statistical model. Results indicate that enhanced warming and wetness by the end of century would lead to pronounced declines in annual and monthly snow water equivalent (SWE) and earlier maximum SWE. Prominent changes in the streamflow regime include increased annual mean and minimum flows, earlier maximum flows, and either increased or decreased maximum flows depending on interactions between temperature, precipitation, and snow. Using the variable importance analysis, we find that precipitation exerts the primary control on maximum SWE and annual mean and maximum flows, and temperature has the main influence on timings of maximum SWE and flow, and minimum flow. Given these climatic controls, the changes in the hydrologic indicators become progressively larger under the scenarios of 1.5°, 2.0°, and 3.0°C global mean temperature increases above the preindustrial period. Hence, the framework presented in this study provides a detailed diagnosis of the hydrologic changes as well as controls and interactions of the climatic variables, which could be generalized for understanding regional scale changes in subarctic/nival basins.

  • Authors: The BC Agriculture & Food Climate Action Initiative Publication Date: Aug 2019

    Bulkley-Nechako & Fraser-Fort George Adaptation Strategies plan is the eighth regional plan developed as part of the Regional Adaptation Program delivered by the BC Agriculture & Food Climate Action Initiative. The report contains a distinctive set of local sector impacts and priorities, as well as a series of strategies and actions for adapting and strengthening resilience. The plans are intended to offer clear actions suited to the specifics of the local context, both with respect to anticipated changes and local capacity and assets.

  • Authors: The Fraser Basin Council Publication Date: Aug 2019

    Climate change is challenging industry and communities across the Northeast region of the province. Wildfires, hail storms, and floods have already challenged local infrastructure and posed health risks to communities. Projected climate change for the region includes increases in frequency and intensity of extremes. Ensuring the region is as prepared as possible for future climate events is critical to maintaining a thriving community, robust natural environment, and vibrant economy. As prepared as possible means the region understands how the climate is changing, and is working together to increase resiliency, and to improve natural and physical infrastructure. Early efforts will reduce the reliance on emergency management and support the ability to thrive over time. Local governments in the region are taking a proactive approach to understanding how climate change will pose risks to Northeast communities and are planning together to build resiliency across the region.

    This document is intended to offer science-based information on how the Northeast’s climate is changing and expected to change over the 21st century. Designing to current and future climate parameters is anticipated to be markedly more cost effective than reacting to climate shocks and stresses over time. In the report, climate projections for the 2020s are offered to represent current climate conditions; projections for the 2050s illustrate the trajectory of change regardless of global emissions reductions; and projections for the 2080s illustrate our likely “business as usual” future climate scenario by late century. The 2020s projections are useful as they more accurately depict the current state of climate than historical observed baseline data. The 2050s projections are useful for medium-term planning and infrastructure purposes, while the 2080s provide guidance for long-term infrastructure decisions.

  • Source Publication: npj Climate and Atmospheric Science, 2, 24, doi:10.1038/s41612-019-0079-3 Authors: Sillmann, J., C. Weum Stjern, G. Myhre, B. Samset, Ø. Hodnebrog, O. Boucher, P. Forster, A. Kirkevåg, J.F. Lamarque, D. Olivié, D. Shindell, A. Voulgarakis, F. Zwiers, T. Andrews, G. Faluvegi, M. Kasoar, T. Richardson, T. Takemura, and V. Kharin Publication Date: Jul 2019

    Global warming due to greenhouse gases and atmospheric aerosols alter precipitation rates, but the influence on extreme precipitation by aerosols relative to greenhouse gases is still not well known. Here we use the simulations from the Precipitation Driver and Response Model Intercomparison Project that enable us to compare changes in mean and extreme precipitation due to greenhouse gases with those due to black carbon and sulfate aerosols, using indicators for dry extremes as well as for moderate and very extreme precipitation. Generally, we find that the more extreme a precipitation event is, the more pronounced is its response relative to global mean surface temperature change, both for aerosol and greenhouse gas changes. Black carbon (BC) stands out with distinct behavior and large differences between individual models. Dry days become more frequent with BC-induced warming compared to greenhouse gases, but so does the intensity and frequency of extreme precipitation. An increase in sulfate aerosols cools the surface and thereby the atmosphere, and thus induces a reduction in precipitation with a stronger effect on extreme than on mean precipitation. A better understanding and representation of these processes in models will provide knowledge for developing strategies for both climate change and air pollution mitigation.

  • Authors: The BC Agriculture & Food Climate Action Initiative Publication Date: Jul 2019

    The Kootenay & Boundary Regional Adaptation Strategies plan is the seventh regional plan developed as part of the Regional Adaptation Program delivered by the BC Agriculture & Food Climate Action Initiative. The report contains a distinctive set of local sector impacts and priorities, as well as a series of strategies and actions for adapting and strengthening resilience. The plans are intended to offer clear actions suited to the specifics of the local context, both with respect to anticipated changes and local capacity and assets.

  • Authors: BC Housing, BC Hydro, the City of Vancouver, the City of New Westminster and the Province of BC Publication Date: Jun 2019

    The Design Guide Supplement on Overheating and Air Quality was published by BC Housing in collaboration with BC Hydro, the City of Vancouver, the City of New Westminster, and the Province of BC. It provides information on the key strategies and approaches necessary to reduce the impacts of a warmer climate on mid- and high-rise wood-frame and noncombustible residential buildings within British Columbia. Specifically, it is intended to provide building industry actors, including local governments, public sector organizations, architects, and developers, with an accessible source of information on the key means of addressing issues of overheating and indoor air quality.

  • Authors: Murdock, T. Publication Date: Jun 2019

    Presentation for the Private Forest Landowners Association Annual Conference.

  • Source Publication: Kootenay & Boundary Adaptation Strategies, The BC Agriculture & Food Climate Action Initiative, 64 pp. Authors: The BC Agriculture & Food Climate Action Initiative Publication Date: Jun 2019
  • Source Publication: Geophysical Research Letters, doi:10.1029/2019GL082908. Authors: Li, C., F. Zwiers, X. Zhang, G. Chen, J. Lu, G. Li, J. Norris, Y. Tan, Y. Sun and M. Liu Publication Date: Jun 2019

    Climate models project that extreme precipitation events will intensify in proportion to their intensity during the 21st century at large spatial scales. The identification of the causes of this phenomenon nevertheless remains tenuous. Using a large ensemble of North American regional climate simulations, we show that the more rapid intensification of more extreme events also appears as a robust feature at finer regional scales. The larger increases in more extreme events than in less extreme events are found to be primarily due to atmospheric circulation changes. Thermodynamically induced changes have relatively uniform effects across extreme events and regions. In contrast, circulation changes weaken moderate events over western interior regions of North America, and enhance them elsewhere. The weakening effect decreases and even reverses for more extreme events, whereas there is further intensification over other parts of North America, creating an “intense gets intenser” pattern over most of the continent.