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Now showing items 1 - 16 of 20

  • Short-duration precipitation extremes over Canada in a warmer climate

    Oh, Seok-Geun   Sushama, Laxmi  

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  • Aircraft Takeoff Performance in a Changing Climate for Canadian Airports

    Zhao, Yijie   Sushama, Laxmi  

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  • Simulating Canadian Arctic Climate at Convection-Permitting Resolution

    Diro, Gulilat Tefera   Sushama, Laxmi  

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  • Urban heat island in current and future climates for the island of Montreal

    Roberge, Francois   Sushama, Laxmi  

    Urban regions with their distinct surface characteristics modify energy and water partitioning, leading to higher temperatures in comparison to the adjoining non-urban regions. This phenomenon, referred to as the Urban Heat Island (UHI), is studied for the island of Montreal situated in central-eastern Canada in the province of Quebec, for current and future climates, for the summer and fall seasons. Projected changes to the UHI for the region are studied using offline high-resolution (250 m) simulations performed with a land surface scheme, the Canadian Land Surface Scheme (CLASS), with and without the urban representation from the Town Energy Balance (TEB) model, for the RCP 8.5 scenario. Projected changes to land surface and 2m air temperature fields suggest significant increases for both urban and nonurban regions, with small increases in the UHI intensity. The small increases in UHI intensity are due to the slightly higher increase in urban surface temperatures compared with nonurban regions, associated with increase and decrease in sensible and latent heat fluxes, respectively, for the urban regions. Furthermore, analysis of the projected changes to the number of hot days suggests significant increases, with urban regions augmenting the increases by 5- 8 days in summer and 2- 5 days in fall.
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  • The role of temperature in drought projections over North America

    Sushama, Laxmi   Khaliq, M. Naveed  

    The effects of future temperature and hence evapotranspiration increases on drought risk over North America, based on ten current (1970-1999) and ten corresponding future (2040-2069) Regional Climate Model (RCM) simulations from the North American Regional Climate Change Assessment Program, are presented in this study. The ten pairs of simulations considered in this study are based on six RCMs and four driving Atmosphere Ocean Coupled Global Climate Models. The effects of temperature and evapotranspiration on drought risks are assessed by comparing characteristics of drought events identified on the basis of Standardized Precipitation Index (SPI) and Standardized Precipitation Evapotranspration Index (SPEI). The former index uses only precipitation, while the latter uses the difference (DIF) between precipitation and potential evapotranspiration (PET) as input variables. As short- and long-term droughts impact various sectors differently, multi-scale (ranging from 1- to 12-month) drought events are considered. The projected increase in mean temperature by more than 2 A degrees C in the future period compared to the current period for most parts of North America results in large increases in PET and decreases in DIF for the future period, especially for low latitude regions of North America. These changes result in large increases in future drought risks for most parts of the USA and southern Canada. Though similar results are obtained with SPI, the projected increases in the drought characteristics such as severity and duration and the spatial extent of regions susceptible to drought risks in the future are considerably larger in the case of SPEI-based analysis. Both approaches suggest that long-term and extreme drought events are affected more by the future increases in temperature and PET than short-term and moderate drought events, particularly over the high drought risk regions of North America.
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  • Projected changes to extreme ice loads for overhead transmission lines across Canada

    Jeong, Dae Il   Sushama, Laxmi   Vieira, Michael J. F.   Koenig, Kristina A.  

    Ice accretion on transmission lines can lead to serious damages from line breakage and flashover. This study investigates projected changes to design ice loads for overhead transmission lines for the 2041-2070 and 2071-2100 periods with respect to the 1976-2005 period over Canada, using transient climate change simulations of the fifth generation Canadian Regional Climate Model, for two driving Global Climate Models and two Representative Concentration Pathways. Projected changes to freezing rain characteristics are first evaluated and results suggest decreases in 50-year return levels of annual maximum daily freezing rain for the southeastern inland and coastal regions and south-western and north-eastern coastal regions of North America, but increases for other regions. Consequently, the simulations suggest statistically significant increases in 50-year return levels of annual maximum ice thickness, particularly for regions of Quebec and west of the Hudson Bay (larger than 10 mm) and some scattered increases for south-central and western Canada (mostly smaller than 3 mm). This study also helped identify regions where both wind and ice loads will increase in future climate, which can be detrimental to the electric infrastructure. Results suggest that compound event assessments would be valuable, taking into consideration larger set of simulations, to obtain more robust projections.
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  • Rain-on-snow events over North America based on two Canadian regional climate models

    Jeong, Dae Il   Sushama, Laxmi  

    This study evaluates projected changes to rain-on-snow (ROS) characteristics (i.e., frequency, rainfall amount, and runoff) for the future 2041-2070 period with respect to the current 1976-2005 period over North America using six simulations, based on two Canadian RCMs, driven by two driving GCMs for RCP4.5 and 8.5 emission pathways. Prior to assessing projected changes, the two RCMs are evaluated by comparing ERA-Interim driven RCM simulations with available observations, and results indicate that both models reproduce reasonably well the observed spatial patterns of ROS event frequency and other related features. Analysis of current and future simulations suggest general increases in ROS characteristics during the November-March period for most regions of Canada and for northwestern US for the future period, due to an increase in the rainfall frequency with warmer air temperatures in future. Future ROS runoff is often projected to increase more than future ROS rainfall amounts, particularly for northeastern North America, during snowmelt months, as ROS events usually accelerate snowmelt. The simulations show that ROS event is a primary flood generating mechanism over most of Canada and north-western and -central US for the January-May period for the current period and this is projected to continue in the future period. More focused analysis over selected basins shows decreases in future spring runoff due to decreases in both snow cover and ROS runoff. The above results highlight the need to take into consideration ROS events in water resources management adaptation strategies for future climate.
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  • Improved representation of surface-groundwater interaction in the Canadian land surface scheme

    Ganji, Arman   Sushama, Laxmi  

    The improvement of surface-groundwater interactions in land surface models are necessary to determine the evolution of hydrologic variables such as surface runoff, evapotranspiration, soil moisture, and streamflows, especially during dry conditions, when streamflows are largely derived from water releases from groundwater storage. Despite its importance, investigations of the effects of surface-groundwater interactions on streamflows simulated by large-scale land surface models are lacking. In this paper, we implement a new parameterization to represent groundwater dynamics in the Canadian Land Surface Scheme (CLASS), which is used for modelling the land surface component in the Canadian regional and global climate models. We compare offline simulations performed with the original and modified versions of CLASS to find the impact of these modifications on the regional hydrology. The offline simulations are driven by ERA-Interim atmospheric forcing data from the European Centre for Medium-Range Weather Forecasts reanalysis (for the 1980-2011 period), over a northeast Canadian domain. The original and modified versions of CLASS differ in the soil bottom boundary conditions, with free (gravitational) drainage in the former, while an unconfined aquifer at the depth of bedrock is considered in the latter. Results suggest higher soil moisture levels in the simulation with modified CLASS compared to the original version, particularly for regions with shallow water table. At these locations, summer surface runoff, evapotranspiration and streamflows are also higher in the simulation with modified CLASS, and the simulated low flow values are in better agreement to those observed. This study thus demonstrates the need to account for surface-groundwater interactions in land surface models for realistic simulation of hydrological processes and streamflows.
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  • Current climate and climate change over India as simulated by the Canadian Regional Climate Model

    Alexandru, Adelina   Sushama, Laxmi  

    The performance of the fifth generation of the Canadian Regional Climate Model (CRCM5) in reproducing the main climatic characteristics over India during the southwest (SW)-, post-and pre-monsoon seasons are presented in this article. To assess the performance of CRCM5, European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40) and Interim re-analysis (ERA-Interim) driven CRCM5 simulation is compared against independent observations and reanalysis data for the 1971-2000 period. Projected changes for two future periods, 2041-2070 and 2071-2100, with respect to the 1971-2000 current period are assessed based on two transient climate change simulations of CRCM5 spanning the 1950-2100 period. These two simulations are driven by the Canadian Earth System Model version 2 (CanESM2) and the Max Planck Institute for Meteorology's Earth System Low Resolution Model (MPI-ESM-LR), respectively. The boundary forcing errors associated with errors in the driving global climate models are also studied by comparing the 1971-2000 period of the CanESM2 and MPI-ESM-LR driven simulations with that of the CRCM5 simulation driven by ERA-40/ ERA-Interim. Results show that CRCM5 driven by ERA-40/ ERA-Interim is in general able to capture well the temporal and spatial patterns of 2 m-temperature, precipitation, wind, sea level pressure, total runoff and soil moisture over India in comparison with available reanalysis and observations. However, some noticeable differences between the model and observational data were found during the SW-monsoon season within the domain of integration. CRCM5 driven by ERA-40/ERA-Interim is 1-2 degrees C colder than CRU observations and generates more precipitation over the Western Ghats and central regions of India, and not enough in the northern and north-eastern parts of India and along the Konkan west coast in comparison with the observed precipitation. The monsoon onset seems to be relatively well captured over the southwestern coast of India, while the monsoon withdrawal occurs too late in comparison with observations. Boundary forcing errors are generally of the same magnitude or larger for the SW-monsoon season and smaller for the other seasons when compared to performance errors. For the two future periods analyzed, both CanESM2 and MPI-ESM-LR driven CRCM5 simulations imply a general warming over India in the twentyfirst century, with maximum increases projected for the pre-monsoon season. However, conflicting climate change signal is noted for precipitation for both future periods with respect to the 1971-2000 current period, with CanESM2 driven simulation suggesting an increase in precipitation in future climate, which is consistent with the projected increase in evapotranspiration, while MPI-ESM-LR driven simulation suggests a decrease in precipitation and evapotranspiration. The conflicting climate change signal in precipitation is also reflected in those variables that are tightly linked with precipitation, such as total runoff, highlighting the need for multi-model ensembles to better represent the uncertainties related to future projections.
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  • Dry spell characteristics over Canada in a changing climate as simulated by the Canadian RCM

    Sushama, Laxmi   Khaliq, Naveed   Laprise, Rene  

    Dry spells defined as extended periods of dry days can serve as indicators of drought conditions and are often used in the management of water resource systems particularly for agriculture In this study the Canadian RCM (CRCM) projected changes to dry spell characteristics over Canada for the April-September period and their validation in current climate are presented Two CRCM integrations are considered one validation integration for the 1961-2000 period and a transient climate change integration for the 19612100 period corresponding to the SRES A2 scenario The ability of the model to simulate dry spell characteristics i e mean number of dry days mean number of dry spells and selected return levels of maximum dry spell durations and associated errors are assessed through comparison of integrations for the current 1971-2000 April-September period with those observed derived from the observed precipitation records Results suggest an underestimation of the mean number of dry days and 10 and 30 year return levels while the model slightly overestimates the mean number of dry spells at the grid cell scale Analysis of projected changes to dry spell characteristics for the future 2041-2070 and 2071-2100 periods with respect to 1971-2000 period suggests significant changes particularly for the southern Prairies where both mean number of dry days and return levels of maximum dry spell durations are projected to increase Furthermore combined analysis of changes to the amount of precipitation and mean number of dry days also suggests potential increase in drought conditions in future climates in this already drought-prone region for the Apnl-September period In addition to southern Prairies this study also suggests significant changes to dry spell characteristics for other regions of Canada (C) 2010 Elsevier BV All rights reserved
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  • Canadian RCM projected changes to short- and long-term drought characteristics over the Canadian Prairies

    PaiMazumder, Debasish   Sushama, Laxmi   Laprise, Rene   Khaliq, M. Naveed   Sauchyn, Dave  

    The Canadian Prairies have experienced severe and extended droughts that have had significant impacts on agriculture, energy and other socio-economic sectors; it is therefore desirable to assess future changes to drought characteristics in this drought prone region, in the context of a changing climate. This study addresses validation and projected changes to short- and long-term drought characteristics, i.e. severity, frequency and duration, over the Canadian Prairies, using an ensemble of ten Canadian RCM (CRCM) simulations, of which five correspond to the current 19712000 period and the other five are the matching simulations for the future 20412070 period. These five pairs of current and future CRCM simulations were driven by five different members of a Canadian Global Climate Model ensemble. Validation of CRCM simulated precipitation suggests that the model reproduces the observed precipitation distribution for all seasons, except summer, across a large portion of the Canadian Prairies. However, comparison of CRCM simulated drought characteristics with those observed suggests that the model has difficulties in reproducing observed severity, frequency and duration of drought events, particularly those associated with longer events, possibly due to the overestimation of summer precipitation by the model. Analysis of projected changes to precipitation and drought characteristics between the 19712000 and 20412070 periods suggests a decrease in mean precipitation in summer and an increase for the other seasons, while the severity, frequency and maximum duration of both short- and long-term droughts are projected to increase over the southern Prairies, with the largest projected changes associated with longer drought events. Classification of the watersheds spanning the southern Prairies based on changes to both severity and frequency further reveal the vulnerability of this region in a changing climate. Copyright (c) 2012 Royal Meteorological Society
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  • Climate projections over CORDEX Africa domain using the fifth-generation Canadian Regional Climate Model (CRCM5)

    Laprise, Rene   Hernandez-Diaz, Leticia   Tete, Kossivi   Sushama, Laxmi   Separovic, Leo   Martynov, Andrey   Winger, Katja   Valin, Michel  

    Following the CORDEX experimental protocol, climate simulations and climate-change projections for Africa were made with the new fifth-generation Canadian Regional Climate Model (CRCM5). The model was driven by two Global Climate Models (GCMs), one developed by the Max-Planck-Institut fur Meteorologie and the other by the Canadian Centre for Climate Modelling and Analysis, for the period 1950-2100 under the RCP4.5 emission scenario. The performance of the CRCM5 simulations for current climate is discussed first and compared also with a reanalysis-driven CRCM5 simulation. It is shown that errors in lateral boundary conditions and sea-surface temperature from the GCMs have deleterious consequences on the skill of the CRCM5 at reproducing specific regional climate features such as the West African Monsoon and the annual cycle of precipitation. For other aspects of the African climate however the regional model is able to add value compared to the simulations of the driving GCMs. Climate-change projections for periods until the end of this century are also analysed. All models project a warming throughout the twenty-first century, although the details of the climate changes differ notably between model projections, especially for precipitation changes. It is shown that the climate changes projected by CRCM5 often differ noticeably from those of the driving GCMs.
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  • Tropical cyclone activity enhanced by Sahara greening and reduced dust emissions during the African Humid Period

    Pausata, Francesco S. R.   Emanuel, Kerry A.   Chiacchio, Marc   Diro, Gulilat T.   Zhang, Qiong   Sushama, Laxmi   Stager, J. Curt   Donnelly, Jeffrey P.  

    Tropical cyclones (TCs) can have devastating socioeconomic impacts. Understanding the nature and causes of their variability is of paramount importance for society. However, historical records of TCs are too short to fully characterize such changes and paleosediment archives of Holocene TC activity are temporally and geographically sparse. Thus, it is of interest to apply physical modeling to understanding TC variability under different climate conditions. Here we investigate global TC activity during a warm climate state (mid-Holocene, 6,000 yBP) characterized by increased boreal summer insolation, a vegetated Sahara, and reduced dust emissions. We analyze a set of sensitivity experiments in which not only solar insolation changes are varied but also vegetation and dust concentrations. Our results show that the greening of the Sahara and reduced dust loadings lead to more favorable conditions for tropical cyclone development compared with the orbital forcing alone. In particular, the strengthening of the West African Monsoon induced by the Sahara greening triggers a change in atmospheric circulation that affects the entire tropics. Furthermore, whereas previous studies suggest lower TC activity despite stronger summer insolation and warmer sea surface temperature in the Northern Hemisphere, accounting for the Sahara greening and reduced dust concentrations leads instead to an increase of TC activity in both hemispheres, particularly over the Caribbean basin and East Coast of North America. Our study highlights the importance of regional changes in land cover and dust concentrations in affecting the potential intensity and genesis of past TCs and suggests that both factors may have appreciable influence on TC activity in a future warmer climate.
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  • Biophysical Impacts of Land Use Change over North America as Simulated by the Canadian Regional Climate Model

    Chacón, Arlette   Sushama, Laxmi   Beltrami, Hugo  

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  • The impact of lateral boundary data errors on the simulated climate of a nested regional climate model

    Diaconescu, Emilia Paula   Laprise, Rene   Sushama, Laxmi  

    In this study, we investigate the response of a Regional Climate Model (RCM) to errors in the atmospheric data used as lateral boundary conditions (LBCs) using a perfect-model framework nick-named the "Big-Brother Experiment" (BBE). The BBE has been designed to evaluate the errors due to the nesting process excluding other model errors. First, a high-resolution (45 km) RCM simulation is made over a large domain. This simulation, called the Perfect Big Brother (PBB), is driven by the National Centres for Environmental Prediction (NCEP) reanalyses; it serves as reference virtual-reality climate to which other RCM runs will be compared. Next, errors of adjustable magnitude are introduced by performing RCM simulations with increasingly larger domains at lower horizontal resolution (90 km mesh). Such simulations with errors typical of today's Coupled General Circulation Models (CGCM) are called the Imperfect Big-Brother (IBB) simulations. After removing small scales in order to achieve low-resolution typical of today's CGCMs, they are used as LBCs for driving smaller domain high-resolution RCM runs; these small-domain high-resolution simulations are called Little-Brother (LB) simulations. The difference between the climate statistics of the IBB and those of PBB simulations mimic errors of the driving model. The comparison of climate statistics of the LB to those of the PBB provides an estimate of the errors resulting solely from nesting with imperfect LBCs. The simulations are performed over the East Coast of North America using the Canadian RCM, for five consecutive February months (from 1990 to 1994). It is found that the errors contained in the large scales of the IBB driving data are transmitted to and reproduced with little changes by the LB. In general, the LB restores a great part of the IBB small-scale errors, even if they do not take part in the nesting process. The small scales are seen to improve slightly in regions with important orographic forcing due to the finer resolution of the RCM. However, when the large scales of the driving model have errors, the small scales developed by the LB have errors as well, suggesting that the large scales precondition the small scales. In order to obtain correct small scales, it is necessary to provide the accurate large-scale circulation at the lateral boundary of the RCM.
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  • Projected Changes to Mean and Extreme Surface Wind Speeds for North America Based on Regional Climate Model Simulations

    Jeong, Dae Il   Sushama, Laxmi  

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