Anne Frigon

Climate and Climate Change over North America as Simulated by the Canadian RCM

Abstract An analysis of several multidecadal simulations of the present (1971–90) and future (2041–60) climate from the Canadian Regional Climate Model (CRCM) is presented. The effects on the CRCM climate of model domain size, internal variability of the general circulation model (GCM) used to provide boundary conditions, and modifications to the physical parameterizations used in the CRCM are investigated. The influence of boundary conditions is further investigated by comparing the GCM-driven simulations of the current climate with simulations performed using boundary conditions from meteorological reanalyses. The present climate of the model in these different configurations is assessed by comparing the seasonal averages and interannual variability of precipitation and surface air temperature with an observed climatology. Generally, small differences are found between the two simulations on different domains, though both domains are quite large as compared with previously reported results. Simulations ...

Interannual variability and expected regional climate change over North America

This study aims to analyse the interannual variability simulated by several regional climate models (RCMs), and its potential for disguising the effect of seasonal temperature increases due to greenhouse gases. In order to accomplish this, we used an ensemble of regional climate change projections over North America belonging to the North American Regional Climate Change Program, with an additional pair of 140-year continuous runs from the Canadian RCM. We find that RCM-simulated interannual variability shows important departures from observed one in some cases, and also from the driving models’ variability, while the expected climate change signal coincides with estimations presented in previous studies. The continuous runs from the Canadian RCM were used to illustrate the effect of interannual variability in trend estimation for horizons of a decade or more. As expected, it can contribute to the existence of transitory cooling trends over a few decades, embedded within the expected long-term warming trends. A new index related to signal-to-noise ratio was developed to evaluate the expected number of years it takes for the warming trend to emerge from interannual variability. Our results suggest that detection of the climate change signal is expected to occur earlier in summer than in winter almost everywhere, despite the fact that winter temperature generally has a much stronger climate change signal. In particular, we find that the province of Quebec and northwestern Mexico may possibly feel climate change in winter earlier than elsewhere in North America. Finally, we show that the spatial and temporal scales of interest are fundamental for our capacity of discriminating climate change from interannual variability.

Internal Variability of the Canadian RCM’s Hydrological Variables at the Basin Scale in Quebec and Labrador

AbstractThe effect of a regional climate model’s (RCM’s) internal variability (IV) on climate statistics of annual series of hydrological variables is investigated at the scale of 21 eastern Canada watersheds in Quebec and Labrador. The analysis is carried out on 30-yr pairs of simulations (twins), performed with the Canadian Regional Climate Model (CRCM) for present (reanalysis and global climate model driven) and future (global climate model driven) climates. The twins differ only by the starting date of the regional simulation—a standard procedure used to trigger internal variability in RCMs. Two different domain sizes are considered: one comparable to domains used for RCM simulations over Europe and the other comparable to domains used for North America. Results for the larger North American domain indicate that mean relative differences between twin pairs of 30-yr climates reach ±5% when spectral nudging is used. Larger differences are found for extreme annual events, reaching about ±10% for 10% and ...

A transition from CMIP3 to CMIP5 for climate information providers: the case of surface temperature over eastern North America

The release of new data constituting the Coupled Model Intercomparison Project—Phase 5 (CMIP5) database is an important event in both climate science and climate services issues. Although users’ eagerness for a fast transition from CMIP3 to CMIP5 is expected, this change implies some challenges for climate information providers. The main reason is that the two sets of experiments were performed in different ways regarding radiative forcing and hence continuity between both datasets is partially lost. The objective of this research is to evaluate a metric that is independent of the amount and the evolution of radiative forcing, hence facilitating comparison between the two sets for surface temperature over eastern North America. The link between CMIP3 and CMIP5 data sets is explored spatially and locally (using the ratio of local to global temperatures) through the use of regional warming patterns, a relationship between the grid-box and the global mean temperature change for a certain time frame. Here, we show that local to global ratios are effective tools in making climate change information between the two sets comparable. As a response to the global mean temperature change, both CMIP experiments show very similar warming patterns, trends, and climate change uncertainty for both winter and summer. Sensitivity of the models to radiative forcing is not assessed. Real inter-model differences remain the largest source of uncertainty when calculating warming patterns as well as spatially-based patterns for the pattern scaling approach. This relationship between the datasets, which may escape users when they are provided with a single radiative forcing pathway, needs to be stressed by climate information providers.

Sensitivity of runoff and projected changes in runoff over Quebec to the update interval of lateral boundary conditions in the Canadian RCM

An analysis was carried out of the sensitivity of runoff simulations from version 4.2 of the Canadian Regional Climate Model (CRCM) to the frequency of lateral boundary condition (LBC) forcing at 6 and 12-hour intervals. The motivation for this study was that some climate model output may only be available at a 12-hour interval and it is important to know if CRCM runs with these outputs are comparable to runs made with 6-hourly forcing. The LBC sensitivity was assessed over two different regional domains (North America and Quebec) for annual runoff simulated over 21 river basins located in the Quebec/Labrador peninsula. The sensitivity results were compared with the CRCMs internal variability and natural climate variability to reach conclusions about the relative importance of LBC update frequency. The results show that LBC frequency can have a significant influence on mean annual runoff over the investigated basins when the simulation domain is relatively small, as in the case of the Quebec, but not for the larger North American (AMNO) domain runs. The entire ensemble of five members of the Canadian Coupled Global Climate Model (CGCM3) can therefore be safely used to generate dynamically downscaled projections over the basins, even though three of the members were archived at a 12-hourly interval. Climate projections for the 2041-2070 horizon (with SRES-A2), from a five-member ensemble of CRCM 45-km runs performed over the AMNO domain (driven by each of the five CGCM3 members), project an increase of annual runoff over all investigated river basins with the largest changes towards the north. This ensemble also provides an estimate of uncertainty of projected basin runoff change related to natural variability, but there remains a need to consider additional projections (more RCMs, more driving GCMs) to produce a more complete assessment of uncertainty.

Objective Calibration of Regional Climate Models: Application over Europe and North America

AbstractAn important source of model uncertainty in climate models arises from unconfined model parameters in physical parameterizations. These parameters are commonly estimated on the basis of manual adjustments (expert tuning), which carries the risk of overtuning the parameters for a specific climate region or time period. This issue is particularly germane in the case of regional climate models (RCMs), which are often developed and used in one or a few geographical regions only. This study addresses the role of objective parameter calibration in this context. Using a previously developed objective calibration methodology, an RCM is calibrated over two regions (Europe and North America) and is used to investigate the transferability of the results. A total of eight different model parameters are calibrated, using a metamodel to account for parameter interactions. The study demonstrates that the calibration is effective in reducing model biases in both domains. For Europe, this concerns in particular a ...

Change in North American Atmospheric Conditions Associated with Deep Convection and Severe Weather using CRCM4 Climate Projections

Abstract Severe weather has important social and economic impacts. Some studies have indicated that its intensity may increase over this century as a consequence of climate change induced by greenhouse gases. This study aims to investigate the possibility of a future increase in deep convective events over North America resulting from the evolution of favourable atmospheric conditions. Our analysis is based on an ensemble of projections performed using the Canadian Regional Climate Model (CRCM) at 45 km resolution, driven by different Global Climate Models (GCMs) and reanalyses. We concentrate our study on Convective Available Potential Energy (CAPE), vertical wind shear, and convective precipitation. Based on two different approaches to linking atmospheric conditions and severe weather, we find that the number of extreme weather events is expected to increase during the twenty-first century. In agreement with other studies on this subject, we find that CAPE is expected to increase, whereas wind shear is expected to decrease slightly. Through the analysis of the CRCMs convective precipitation outputs, we show that severe convective liquid precipitation events may become both more frequent and slightly more intense. Sensitivity experiments show that results depend on the driving GCM although they confirm the general conclusions. Additional experiments conducted with reduced humidity input at the lateral boundaries show the significant role that the humidity level of the driving GCMs has on simulated extreme regional events. At the regional level results are, in general, consistent with those found at the continental scale, but large inter-regional variations exist.

Investigation of the hydrologic cycle simulated by the Canadian Regional Climate Model over the Québec/Labrador territory

This paper discusses the surface hydrology of a two-year simulation conducted over the Quebec/Labrador territory with the Canadian Regional Climate Model (CRCM). The CRCM was driven by NCEP (National Center for Environmental Protection) atmospheric objective analyses and was run at a 30 km horizontal grid-point spacing. Model results are compared with available observations for the period from June 1992 to June 1994. A spatial analysis of the CRCM annual runoff shows that the model is in good agreement with basin observations although the simulated precipitation and surface evaporation are too important. The main features of seasonal runoff variation are captured by the CRCM with differences mainly attributed to the oversimplification of the surface processes in the single-layer surface scheme. We also find that spring peak runoffs are quite well synchronized with the observations but with some overestimation when a lumped hydrologic model is fed by CRCM meteorological outputs. Despite the fact that the hydrologic model was not recalibrated with the CRCM data, this first experience shows the potential use of the CRCM to feed a hydrologic model. In summary, even though our analysis shows the usefulness of the CRCM simulated surface hydrology information, results from this experience indicate the need to refine the surface scheme to represent more accurately surface hydrology processes.

A study of a CASP storm: Analysis of radar data

Abstract The morphology and time evolution of a winter storm is studied using radar data taken during the Canadian Atlantic Storms Program (CASP). The vertical motions that generate the snow are derived from reflectivity measurements. The study reveals a banded structure in the precipitation pattern with ascending and descending air associated with the bands. Vertical velocities averaged over the radar‐covered area reach values close to 1 m s‐1 . The region of large‐scale uplifting moves horizontally at about half the horizontal air velocity. A persistent precipitation pattern results from the continuously renewed air within the uplifting region.

Timescales associated with climate change and their relevance in adaptation strategies

Anthropogenic greenhouse gas emissions that induce changes in the Earth’s climate affect particular variables and locations differently. A key part of this difference is the timescale at which this change takes place, which will eventually have important consequences for adaptation requirements. This idea of timescale associated with climate change has been used several times in the past to estimate the urgency of adaptation in particular regions. The definition of climate-change timescale is, however, not unique. For example, we can think of it in terms of an expected trend (e.g. in temperature) reaching a given threshold, or think of it in terms of the time it may take this trend to become statistically significant. We may also wonder about the validity of this speculation given that, due to natural variability, the expected trend may in fact not be realized. In this article we explore alternative ways of defining the timescale of climate-change, compare their properties, and illustrate them with an example for the case of projected surface temperature over North America. It is shown that these timescales are analytically related but may differ substantially in magnitude under certain conditions. In particular, it is shown that climate change impact on vulnerable systems may arrive before statistical detection of the variable’s trend takes place. This fact may have implications on how climate change impacts are seen by those with diverging interests.