Publications Library

Recently, concerns have arisen as to whether temperature-based proxy methods used to estimate potential evapotranspiration (PET) are reliable when examining future drought severity, especially in the context of a warmer climate. The objective of this study was to assess the effect of different PET approaches, focusing on proxies for radiation and humidity, on future Standardized Precipitation Evapotranspiration Index (SPEI) calculations across Canada. Using output from 22 CMIP6 global climate models (GCMs), seasonal and annual SPEI comparisons were carried out between the physically-based Penman-Monteith (PM) method and two approaches that incorporate temperature proxies to calculate radiation and/or humidity. These included the temperature-based Hargreaves (HG) approach and a PM method with derived humidity (PM-m). Results revealed that although the general patterns of SPEI projections across Canada were consistent among the methods, notable spatial and temporal differences were apparent. Specifically, both median and extreme SPEI projections based on the two temperature proxy methods revealed less annual and summer drying in much of central, eastern, and northern regions of Canada when compared to the physically based SPEI-PM. In extreme western regions (British Columbia, Yukon) these two methods, particularly HG, projected drier conditions. Differences of using temperature derived radiation and humidity were also most apparent in spring (and to a lesser degree, autumn), where the HG approach overestimated spring drying (and autumn wetting) over large regions of the country. Overall, differences tended to be more pronounced for the fully temperature-based HG approach during all periods considered. Results from this study strongly suggest that when possible, a physically-based approach be used when estimating PET to assess future drought projections. If a temperature proxy is used, the differences to a physically-based method should be understood and resultant implications be evaluated.

This Science Brief covers a paper published in Nature Climate Change that uses reanalysis data to examine extreme fire weather and the conditions that drive it over the 1979-2020 period. The paper shows that temperature and relative humidity are driving observed global trends of increased fire weather. In this Science Brief we discuss what these results tell us about changes to fire weather in our province and across Canada.

Highlights:
Improve the estimation of water temperature extremes at ungauged sites.
Incorporate non-linearities in the homogenous region delineation step using NLCCA.
Consider non-linear models in the whole estimation procedure (NLCCA + GAM).
Compare fully and partially non-linear approaches for water temperature regionalization.
The results underline the importance of considering the non-linearity of thermal processes.

One of the key uncertainties in climate model simulations has to do with the response of low-lying marine clouds to increasing temperatures. A recent paper in the journal Nature uses a mix of radar, lidar and data from atmospheric probes to test one of the mechanisms by which cloud cover is projected to be reduced under climate change. Their findings show that this mechanism is not evident in the trade wind regions, which suggests that might not occur in nature. This further suggests that the most extreme estimates of the climate's response to greenhouse gas emissions are less likely than earlier research suggests. Here we discuss what these results tell us about changes to the Earth's sensitivity to greenhouse gas emissions and what this may mean for our province.

The Climate Projections for the City of Terrace report provides projections and impacts analysis for the City of Terrace, BC and is intended to support decision making throughout the region and to help community partners better understand how their work may be affected by the changing climate

Study region:
Nechako Reservoir, British Columbia, Canada.

Study focus:
Hydrological regulation affect both hydrological and thermal conditions in the reservoir and downstream reach, subsequently disrupting fish habitats. This paper aims at developing an integrated model simulating physical processes that govern the quantity and quality of inflow, reservoir, and outflow water of the Nechako Reservoir. Such a model would help stakeholders understand the response of in-reservoir water temperature stratification and downstream water temperature to changes in inflow and reservoir operation under future climate change.

New hydrological insights for the region:
The model was calibrated against historical reservoir levels and in-reservoir and outlet water temperature field data. The integrated model simulated accurately the wide variation of reservoir levels as well as the in-reservoir water temperature at Kenney Dam and the outlet temperature. Sensitivity analysis shows that reservoir water temperature particularly the epilimnion is sensitive to changes in both meteorological and hydrological forcing. Forcing the model with different outflow scenarios shows the weak sensitivity of temperature of water released to outflow rates. Given epilimnion water releases at the spillway, the Summer Temperature Management Program could be inefficient to provide cool water in the Nechako River during the critical period of salmon migration in a warming climate. However, colder water remains available at depth at Kenney Dam to potentially mitigate and better control downstream water temperature.

As glaciers across the world continue to recede, there is a concern that their loss as a fresh water reservoir within mountainous basins will have a negative impact on stream temperatures and downstream water resources. Currently, there are relatively few glacio-hydrological models (GHMs) appropriate to study such phenomena and studies that have used GHMs generally acknowledge the high uncertainty associated with their simulations. Calibration techniques present a particular issue in GHMs as available glacier observations are limited and errors in the glacierized portion of a basin can be compensated by errors in the non-glacierized portion. Using as a study site the Cheakamus Basin in British Columbia, Canada, we 1) present a new, fully-coupled GHM, 2) analyze the effects different calibration techniques have on the model’s summer streamflow projections, and 3) compare the fully-coupled GHM results to projections using a one-way GHM. The calibration techniques studied vary in terms of glacier representation (dynamic/static), and glacier constraint (mass balance/thinning rates/thinning rates and area change). We find projected future climate forcings are sufficiently strong in the Cheakamus Basin so as to generally make the sign and significance of changes to the basin’s hydrology insensitive to the calibration and projection procedures studied. However, the variation among these procedures produces significant changes in the projected magnitude of future hydrological changes and therefore should be carefully considered in studies where precision beyond the sign and significance of change is required. Based on analysis of the variation within each procedure’s set of model outputs, we conclude 1) the two-way GHM has benefits over the one-way model, 2) calibration using dynamic glaciers and a thinning rate constraint is preferable for the new GHM, and 3) there is a need for additional studies on the uncertainties associated with the calibration of glacio-hydrological models.

Observations show that summer precipitation in China has undergone pronounced changes, resulting in an enigmatic “north-south drying-wetting” pattern in eastern China that is of great concern for socio-economic development. Scientific consensus on the mechanisms that are responsible for this pattern of change has not yet been achieved. We show that this complex pattern of summer total precipitation trends observed in China since the 1960s is overwhelmingly the result of changes in daily precipitation frequency, rather than being the result of changes in precipitation intensity or the frequency of synoptic circulation patterns favorable to precipitation. Changes in precipitation intensity, which are very likely due to anthropogenic greenhouse gas forcing, contribute a relatively homogeneous wetting tendency across the country while changes due to synoptic circulation change are weak. The changes in daily precipitation frequency that drive the observed patterns of change may be due to aerosols, but improved process understanding will be required to resolve that question and enable reliable projections of regional scale precipitation change in China and elsewhere.

Towards the end of June 2021, temperature records were broken by several degrees Celsius in several cities in the Pacific Northwest areas of the US and Canada, leading to spikes in sudden deaths and sharp increases in emergency calls and hospital visits for heat-related illnesses. Here we present a multi-model, multi-method attribution analysis to investigate the extent to which human-induced climate change has influenced the probability and intensity of extreme heat waves in this region. Based on observations, modelling and a classical statistical approach, the occurrence of a heat wave defined as the maximum daily temperature (TXx) observed in the area 45–52∘ N, 119–123∘ W, was found to be virtually impossible without human-caused climate change. The observed temperatures were so extreme that they lay far outside the range of historical temperature observations. This makes it hard to state with confidence how rare the event was. Using a statistical analysis that assumes that the heat wave is part of the same distribution as previous heat waves in this region led to a first-order estimation of the event frequency of the order of once in 1000 years under current climate conditions. Using this assumption and combining the results from the analysis of climate models and weather observations, we found that such a heat wave event would be at least 150 times less common without human-induced climate change. Also, this heat wave was about 2 ∘C hotter than a 1-in-1000-year heat wave would have been in 1850–1900, when global mean temperatures were 1.2 ∘C cooler than today. Looking into the future, in a world with 2 ∘C of global warming (0.8 ∘C warmer than today), a 1000-year event would be another degree hotter. Our results provide a strong warning: our rapidly warming climate is bringing us into uncharted territory with significant consequences for health, well-being and livelihoods. Adaptation and mitigation are urgently needed to prepare societies for a very different future.