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- Author or Editor: A. G. Barr x
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Abstract
Drought on the Canadian prairies is the single most limiting factor to crop yield. Several indices have been developed that indicate the onset, severity, and persistence of drought. This study was conducted to assess the validity of the Palmer Drought index for characterizing drought on the Canadian prairies. When the empirical relationship used by Palmer for calculating the weighting factor K was applied to historical weather data, the relationship appeared inappropriate. There was only a weak relationship between K and the moisture balance variables from which it is usually calculated. The regional correction factor was calculated to be 14.2, which is lower than the generally accepted value of 17.67. A soil water model, the Versatile Soil Moisture Budget (VMB), was coupled with the Palmer model to improve the modeling of soil water. The drought index obtained with the VMB explained 49% of the variation in wheat yield, while the original Palmer index explained 33%. In addition, a new drought index, which does not rely on the weighting factor K explained 57% of the variation in wheat yield, which is almost twice the variation explained by the original Palmer index.
Abstract
Drought on the Canadian prairies is the single most limiting factor to crop yield. Several indices have been developed that indicate the onset, severity, and persistence of drought. This study was conducted to assess the validity of the Palmer Drought index for characterizing drought on the Canadian prairies. When the empirical relationship used by Palmer for calculating the weighting factor K was applied to historical weather data, the relationship appeared inappropriate. There was only a weak relationship between K and the moisture balance variables from which it is usually calculated. The regional correction factor was calculated to be 14.2, which is lower than the generally accepted value of 17.67. A soil water model, the Versatile Soil Moisture Budget (VMB), was coupled with the Palmer model to improve the modeling of soil water. The drought index obtained with the VMB explained 49% of the variation in wheat yield, while the original Palmer index explained 33%. In addition, a new drought index, which does not rely on the weighting factor K explained 57% of the variation in wheat yield, which is almost twice the variation explained by the original Palmer index.
Abstract
Humidity of air is a key environmental variable in controlling the stomatal conductance (g) of plant leaves. The stomatal conductance–humidity relationships employed in the Ball–Woodrow–Berry (BWB) model and the Leuning model have been widely used in the last decade. Results of independent evaluations of the two models vary greatly. In this study, the authors develop a new diagnostic parameter that is based on canopy water vapor and CO2 fluxes to assess the response of canopy g to humidity. Using eddy-covariance flux measurements at three boreal forest sites in Canada, they critically examine the performance of the BWB and the Leuning models. The results show that the BWB model, which employs a linear relationship between g and relative humidity (hs ), leads to large underestimates of g when the air is wet. The Leuning model, which employs a nonlinear function of water vapor pressure deficit (Ds ), reduced this bias, but it still could not adequately capture the significant increase of g under the wet conditions. New models are proposed to improve the prediction of canopy g to humidity. The best performance was obtained by the model that employs a power function of Ds , followed by the model that employs a power function of relative humidity deficit (1 − hs ). The results also indicate that models based on water vapor pressure deficit generally performed better than those based on relative humidity. This is consistent with the hypothesis that the stomatal aperture responds to leaf water loss because water vapor pressure deficit rather than relative humidity directly affects the transpiration rate of canopy leaves.
Abstract
Humidity of air is a key environmental variable in controlling the stomatal conductance (g) of plant leaves. The stomatal conductance–humidity relationships employed in the Ball–Woodrow–Berry (BWB) model and the Leuning model have been widely used in the last decade. Results of independent evaluations of the two models vary greatly. In this study, the authors develop a new diagnostic parameter that is based on canopy water vapor and CO2 fluxes to assess the response of canopy g to humidity. Using eddy-covariance flux measurements at three boreal forest sites in Canada, they critically examine the performance of the BWB and the Leuning models. The results show that the BWB model, which employs a linear relationship between g and relative humidity (hs ), leads to large underestimates of g when the air is wet. The Leuning model, which employs a nonlinear function of water vapor pressure deficit (Ds ), reduced this bias, but it still could not adequately capture the significant increase of g under the wet conditions. New models are proposed to improve the prediction of canopy g to humidity. The best performance was obtained by the model that employs a power function of Ds , followed by the model that employs a power function of relative humidity deficit (1 − hs ). The results also indicate that models based on water vapor pressure deficit generally performed better than those based on relative humidity. This is consistent with the hypothesis that the stomatal aperture responds to leaf water loss because water vapor pressure deficit rather than relative humidity directly affects the transpiration rate of canopy leaves.
Abstract
Winter roads play a vital role in linking communities and building economies in the northern high latitudes. With these regions warming 2–3 times faster than the global average, climate change threatens the long-term viability of these important seasonal transport routes. We examine how climate change will impact the world’s busiest heavy-haul winter road—the Tibbitt to Contwoyto Winter Road (TCWR) in northern Canada. The FLake freshwater lake model is used to project ice thickness for a lake at the start of the TCWR—first using observational climate data, and second using modeled future climate scenarios corresponding to varying rates of warming ranging from 1.5° to 4°C above preindustrial temperatures. Our results suggest that 2°C warming could be a tipping point for the viability of the TCWR, requiring at best costly adaptation and at worst alternative forms of transportation. Containing warming to the more ambitious temperature target of 1.5°C pledged at the 2016 Paris Agreement may be the only way to keep the TCWR viable—albeit with a shortened annual operational season relative to present. More widely, we show that higher regional winter warming across much of the rest of Arctic North America threatens the long-term viability of winter roads at a continental scale. This underlines the importance of continued global efforts to curb greenhouse gas emissions to avoid many long-term and irreversible impacts of climate change.
Abstract
Winter roads play a vital role in linking communities and building economies in the northern high latitudes. With these regions warming 2–3 times faster than the global average, climate change threatens the long-term viability of these important seasonal transport routes. We examine how climate change will impact the world’s busiest heavy-haul winter road—the Tibbitt to Contwoyto Winter Road (TCWR) in northern Canada. The FLake freshwater lake model is used to project ice thickness for a lake at the start of the TCWR—first using observational climate data, and second using modeled future climate scenarios corresponding to varying rates of warming ranging from 1.5° to 4°C above preindustrial temperatures. Our results suggest that 2°C warming could be a tipping point for the viability of the TCWR, requiring at best costly adaptation and at worst alternative forms of transportation. Containing warming to the more ambitious temperature target of 1.5°C pledged at the 2016 Paris Agreement may be the only way to keep the TCWR viable—albeit with a shortened annual operational season relative to present. More widely, we show that higher regional winter warming across much of the rest of Arctic North America threatens the long-term viability of winter roads at a continental scale. This underlines the importance of continued global efforts to curb greenhouse gas emissions to avoid many long-term and irreversible impacts of climate change.
