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The 2021 heatwave over Western North America (WNA) led to record‐breaking air temperatures and human‐perceived heat stress (humidex) values. The event was accompanied by drier conditions driven by prolonged atmospheric blocking. During the heatwave, the maximum 6‐day means of humidex and temperature (HX‐6 and TX‐6) exhibited larger anomalies (6.70 and 5.57°C) compared to the 95th percentiles (HX95 and TX95) (4.12 and 3.73°C), relative to 1981–2021 extended summer (June‐September) averages. Extreme indices of humidex show faster and larger increases than those of temperature, reflecting the nonlinear positive relationship between humidex and temperature. Future projections from a multi‐model ensemble of 19 Coupled Model Intercomparison Project Phase six (CMIP6) Global Climate Models (GCMs) clearly show an increase in humidex and temperature extremes, especially under intermediate and high emissions scenarios. Humidex indices (HX‐6 and HX95) show faster and larger increases than temperature indices (TX‐6 and TX95) for the same future years and global warming levels. Controlling for differences in GCM climate sensitivity to greenhouse gas forcing yields robust projections at various global warming levels, reducing the ranges of projected changes from the multi‐model ensemble. At 3.0°C global warming from pre‐industrial, the multi‐model ensemble projects occurrences of HX‐6, TX‐6, HX95, and TX95 over WNA that exceed 2021 levels to occur every 3.9, 1.7, 1.4, and 2.2 years, respectively, increasing to almost annually at 4.0°C. Plain Language Summary: In 2021 summer, Western North America (WNA) experienced an unprecedented heatwave, breaking air temperature and human‐perceived heat stress (humidex) records despite lower humidity due to prolonged atmospheric blocking. During the heatwave, consecutive 6‐day means of heat stress (HX‐6) and temperature (TX‐6) showed larger anomalies (6.70 and 5.57°C) compared to the 95th percentiles (HX95 and TX95) (4.12 and 3.73°C) over the region, relative to their averages over the 1981–2010 summer period (June‐September). Heat stress increased faster and more significantly than air temperature due to their nonlinear relationship. Future projections from 19 climate models reveal clear increases in heat stress and temperature, especially under intermediate and high emission scenarios. Heat stress indices show larger and faster increases than temperature indices at the same future years and global warming levels. Accounting for uncertainty related to climate model sensitivity enhances projection reliability. At 3.0°C global warming from pre‐industrial levels, 2021‐level events over WNA are projected to occur every few years, becoming an almost annual occurrence at 4.0°C. The study underscores the critical need for robust projections using multi‐model ensembles. Key Points: Unprecedented 2021 summer heatwave over Western North America resulted in record‐breaking humidex and air temperature extremesLarger increases in humidex than temperature, exceeding their 2021 levels, under intermediate and high emissions scenariosRobust projections of multi‐model ensemble, mitigating climate sensitivity uncertainty of GCMs response to greenhouse gas emissions [ABSTRACT FROM AUTHOR]

Global warming is expected to lead to increases in atmospheric moisture and intensify subhourly to hourly rainfall extremes. However, signal-to-noise ratios are low, especially at the local scale, making detection of changes in the observational record difficult. For Canada, previous studies based on short data records from 1965 to 2005 did not show conclusive evidence of increases in short-duration extreme rainfall. This study updates single-site and regional trend analyses of 5-min–24-h annual maximum rainfall in Canada using data from 1950 to 2021. Estimates of temporal trends are extended to also consider the association between rainfall intensity and dewpoint temperature, a measure of moisture availability. With longer records, evidence for increases in extreme rainfall at individual sites is stronger. Field significant increasing trends are found for the majority of durations, whereas before results were mixed and typically not statistically significant. Intensification is even more pronounced in single-site scaling of rainfall intensity with summer mean dewpoint temperature. Field significant positive scaling rates are detected for all durations. When data are pooled in space—irrespective of choice of regionalization—the results are even more clear. Notably, the strongest and most spatially homogeneous intensification of short-duration extreme rainfall is detected in subhourly to 2-h durations. When data are pooled across Canadian climate regions, field significant positive scaling is found in 72.7%–81.8% of regions for 5-min–2-h durations, with median scaling rates ranging from 5.3% to 9.4% °C−1. For durations ≥ 6 h, this falls to 27.3%–53% of regions, with scaling rates less than 4% °C−1. [ABSTRACT FROM AUTHOR]

Spring barley (Hordeum vulgare L.), being a cold‐tolerant crop, may not benefit as much from a warmer climate and a lengthening of the growing season due to climate change though its suitable production area could expand further north. The objectives of this study were to assess the impact of climate change on barley yields across Canada for both current production regions and potential northern crop expansion regions in the future. Three crop models (DeNitrification and DeComposition, Decision Support System for Agrotechnology Transfer, and Simulateur mulTIdisciplinaire pour les Cultures Standard) and 18 climate scenarios (1981–2100) were used to simulate the effect of climate change on potential (non‐water and non‐nitrogen limited) and rainfed (non‐nitrogen limited) spring barley yields for 32 locations across Canada. For the currently planted spring barley regions characterized by a humid summer in Eastern Canada (growing season precipitation >500 mm), potential and rainfed yields were projected to slightly increase in the future (<+0.2 t ha−1). In western regions where precipitation amount is lower (growing season precipitation <500 mm), changes in the potential yield varied slightly (−0.1 to +0.2 t ha−1), while the rainfed yield was projected to increase (0.2–1.0 t ha−1) mainly due to a reduction in water stress under elevated CO2. Finally, in northern regions where future expansion may occur, projected yield increases were generally large (up to 2.8 t ha−1 for potential yield), but the risk of crop failure usually remained high. Our findings suggest that future climate change will present both opportunities and regionalized risks for spring barley producers with the potential to further expand barley production northward. Core Ideas: Three crop models have been used to project the effect of climate change on spring barley yield in Canada.In the currently grown spring barley regions, small yield increases are projected in humid regions of eastern Canada.Larger yield increases are projected in the drier regions of western Canada where spring barley is currently grown.In northern regions where future expansion may occur, projected yield increases were generally large.Risk of crop failure usually remained high in northern regions where future expansion may occur. [ABSTRACT FROM AUTHOR]

The unprecedented 2021 June‐July heatwave in Western North America resulted in record‐breaking human‐perceived heat stress across the region, measured by the humidex considering both air temperature and humidity. During extended summer (June‐September), both 95th percentiles of daily maximum humidex (HX95) and air temperature (TX95) have increased over the 1940–2022 period, with even faster intensification in the last two decades (2001–2022). HX95 has increased more than TX95 because of the positive monotonic nonlinear relationship between humidex and air temperature at a given level of relative humidity. The Canadian Earth System Model version 5 (CanESM5) projects a larger increase in human‐perceived heat stress than air temperature across the region under low to high emission scenarios (HX95 increases 4.40–7.04°C and TX95 increases 2.92–4.65°C between 1981–2010 and 2041–2060). Moreover, CanESM5 projects significant increases in the frequency of HX and TX conditions that exceed the levels reached in 2021 under intermediate and high emission scenarios. Plain Language Summary: Using humidex, a measure that combines air temperature and humidity, we assessed the human‐perceived heat stress during the record‐breaking 2021 summer heatwave in Western North America. The 2021 heatwave broke records for both air temperature and humidex, and these two measures have been increasing in the past decades. The heatwave was drier than usual due to high pressure in the atmosphere, clear skies, and more heat warming up the air instead of evaporating water. Humidex will rise more than air temperature under various emission scenarios, making people feel even hotter in the region. The climate model used suggests that humidex values and temperatures that exceed the levels observed in 2021 will happen much more often and be much more intense across the region in the future, with estimates of three to ten times for humidex and two to seven times for air temperature more frequent under intermediate to high emission scenarios by the end of the century. However, the likelihood of extreme humidex in dry conditions, as observed in 2021, will remain low, like historical levels. Key Points: Unprecedented 2021 heatwave in Western North America resulted in record‐breaking human‐perceived heat stress, considering both air temperature and humidityExtreme human‐perceived heat stress increased at a faster rate than extreme air temperature, both showing rapid increases in recent decadesFor events exceeding 2021 level, a larger future increase in extreme human‐perceived heat stress is projected compared to air temperature [ABSTRACT FROM AUTHOR]

Rainfall extreme value estimates in Canada have historically been based on fitting the Gumbel distribution to annual maxima at individual sites by the method of moments (MOM). Studies have, however, shown that regional frequency analyses (RFA) may perform better than at-site methods. Also, the Frechet rather than Gumbel form of the generalized extreme value (GEV) distribution may better describe the distribution of annual extremes. In this study, at-site Gumbel MOM and GEV extreme value analyses based on L-moment, maximum likelihood (MLE), and generalized maximum likelihood (GML) estimators are compared against RFA with L- moment methods at stations in southern British Columbia, Canada via cross-validation and Monte Carlo simulations. While GEV shape parameter estimates are predominately negative, qualitatively showing weak evidence for the Frechet form of the GEV distribution, field significant differences from the Gumbel distribution in the region are not found. Regional frequency analysis leads to substantial reductions in error relative to at-site methods, especially for the GEV distribution and small samples. While Gumbel estimators exhibit lower variance than GEV estimators, they are also more biased, underestimating 100 year return levels. Of the at-site GEV estimators, GML tended to perform better than the L-moment estimator, in some cases nearing performance of RFA. Maximum likelihood performed worst, especially for small samples sizes. Key words: extreme value analysis, regionalization, precipitation, floods. Au Canada, on a toujours estime les valeurs extremes de precipitation en appliquant la distribution de Gumbel aux maxima enregistres a des emplacements particuliers a l'aide de la methode des moments (MOM). Cependant, des etudes ont montre que les analyses frequentielles regionales (AFR) pouvaient s'averer plus fiables que les methodes sur le terrain. De plus, il semble que la distribution generalisee des valeurs extremes (GEV) de type Frechet decrit mieux la distribution des extremes annuels que celle de type Gumbel. Dans la presente etude, la MOM de Gumbel et les analyses de la GEV sur le terrain, basees sur le moment L et sur les estimateurs de probabilite maximale (EPM) et de probabilite maximale generalisee (EPMG), sont comparees aux methodes des AFR basees sur le moment L, dans des stations du sud de la Colombie-Britannique, au Canada, par validation croisee et a l'aide de simulations de Monte Carlo. Les parametres de forme de la GEV sont principalement negatifs et font peu apparaitre, sur le plan qualitatif, la GEV de type Frechet et l'on n'observe pas sur le terrain de differences importantes avec la distribution de Gumbel dans la region consideree. Les AFR entrainent une nette reduction des erreurs, comparativement aux methodes sur le terrain, en particulierement dans le cas de la GEV et des petits echantillons. Bien que les estimateurs de Gumbel presentent une variance plus faible que ceux de la GEV, ils sont egalement plus biaises et sous-estiment les niveaux de retour centennaux. Parmi les estimateurs de la GEV sur le terrain, les EPMG semblent etre plus efficaces que l'estimateur base sur le moment L, s'approchant parfois de l'efficacite des AFR. Les EPM sont quant a eux les estimateurs les plus inefficaces, notamment dans le cas des echantillons de petite taille. [Traduit par la Redaction] Mots-cles: analyse des valeurs extremes, regionalisation, precipitation, inondations., 1. Introduction Annual rainfall extreme value analyses are used to set design criteria for water management infrastructure in Canada (CSA 2012). Nationally, Environment Canada estimates return values for different rainfall [...]