Statistically downscaled climate scenarios and indices from CMIP6 global climate models
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Environment and Climate Change Canada has a mandate to provide Canadians with past and future climate change information for climate impact assessments, adaptation planning and mitigation policy development. There is a growing demand in Canada and internationally for global climate model (GCM) projections to be downscaled at high spatial resolutions. ECCC’s Climate Research Division (CRD) and the Pacific Climate Impacts Consortium (PCIC) previously produced statistically downscaled climate scenarios based on simulations from climate models that participated in the Coupled Model Intercomparison Project phase 5 (CMIP5) in 2015. These have been widely used and are referenced in Canada’s Changing Climate Report.Reference1 The CMIP5 downscaled scenarios are available on ECCC’s Canadian Climate Data and Scenarios website and PCIC’s climate change scenarios data portal.
ECCC and PCIC have now updated the CMIP5-based downscaled scenarios with a new set of downscaled scenarios based on the next generation of climate projections from the Coupled Model Intercomparison Project phase 6 (CMIP6). CMIP6 climate projections are based on both updated global climate models and new emissions scenarios called “Shared Socioeconomic Pathways” (SSPs).Reference7 Statistically downscaled datasets have been produced from 26 CMIP6 GCMs (Table 2) under three different emission scenarios (i.e., SSP1-2.6, SSP2-4.5, and SSP5-8.5) using the same downscaling method (BCCAQv2)Reference2Reference9 and downscaling target data (NRCANmet)Reference6 as the CMIP5-based downscaled scenarios. Downscaled daily maximum and minimum temperatures and daily precipitation are available across Canada at 10km grid spatial resolution for the 1950-2014 historical period and for the 2015-2100 period following each of the three emission scenarios.
Table 1. Main characteristics.
CanDCS-U6: Canadian Downscaled Climate Scenarios–Univariate method from CMIP6
|Variables and unit||
Daily maximum temperature (°C)
Daily minimum temperature (°C)
Daily precipitation (mm)
1/12° (10km) grid resolution
1950 to 2100
Historical emissions: 1950-2014
Future emissions scenarios: 2015-2100
|Future emissions scenarios||
31 climate indices (Table 3)
Downscaling methodology and data
Proper usage of statistically downscaled data requires a basic understanding of how climate models simulate the climate system and how outputs from climate models are combined with historical observations to create downscaled climate scenarios. Uncertainties are present in each step of the climate modelling and downscaling chain and it is recommended that users familiarize themselves with basic principles of climate modelling and downscaling before using these data.Reference3
Statistically downscaled multi-model ensembles have been constructed using output from 26 CMIP6 GCMs that are available at the Earth System Grid Federation (ESGF) Data Nodes, including 10 initial-condition members of the CanESM5 model produced by the Canadian Centre for Climate Modelling and AnalysisReference8 and one run from each of 25 other CMIP6 models (Table 2).
Bias Correction/Constructed Analogues with Quantile mapping (BCCAQ) is a hybrid downscaling algorithm that combines downscaling by BCCA (Bias Correction/Constructed Analogues)Reference5 with quantile mapping. The use of Quantile Delta MappingReference2, a change-preserving form of quantile mapping, distinguishes BCCAQv2 from the previous version of the algorithm. Details are provided by Werner and Cannon (2016).Reference 9 Code implementing the BCCAQv2 method is also available from the Comprehensive R Archive Network (CRAN) repository via the R package “ClimDown”.Reference4
Daily minimum temperature (°C), daily maximum temperature (°C), and daily precipitation (mm/day) outputs from 26 CMIP6 GCMs were downscaled using the BCCAQv2 algorithm. Historical 1/12° (~10km) gridded NRCANmet dataset of daily minimum temperature, maximum temperature and precipitation for CanadaReference6 were used as the respective downscaling “targets” (training data used to calibrate BCCAQv2) so that the historical downscaled climate model output has statistical characteristics that resemble those of NRCANmet as closely as possible during the 1951-2010 period. Once calibrated for a particular climate model and variable for the historical 1951-2010 reference period, BCCAQv2 is applied to the climate simulations of that variable for the selected model under three emission scenarios (SSP1-2.6, SSP2-4.5, and SSP5-8.5). This process is repeated separately for each variable and model, and hence is termed a “univariate” downscaling scheme.
Table 2. List of CMIP6 global climate models used in the statistically downscaled multi-model ensembles.
|Beijing Climate Center (China)||BCC-CSM2-MR||r1i1p1f1|
|Canadian Centre for Climate Modelling and Analysis (Canada)||CanESM5||r1i1p2f1 ~ r10i1p2f1|
|Euro-Mediterranean Centre for Climate Change (Italy)||CMCC-ESM2||r1i1p1f1|
|Institute of Atmospheric Physics (China)||FGOALS-g3||r1i1p1f1|
|NOAA-Geophys. Fluid Dyn. Lab (USA)||GFDL-ESM4||r1i1p1f1|
|Met Office Hadley Centre and NERC (UK)||HadGEM3-GC31-LL||r1i1p1f3|
|Institute for Numerical Mathematics (Rus.)||INM-CM4-8||r1i1p1f1|
|Institute for Numerical Mathematics (Rus.)||INM-CM5-0||r1i1p1f1|
|Institut Pierre-Simon Laplace (France)||IPSL-CM6A-LR||r1i1p1f1|
|National Institute of Meteo. Sciences and Korea Meteo. Administration (Korea)||KACE-1-0-G||r2i1p1f1|
|Korea Institute of Ocean Science and Technology (Korea)||KIOST-ESM||r1i1p1f1|
|University of Tokyo JAMSTEC, NIES, and AORI (Japan)||MIROC6||r1i1p1f1|
|University of Tokyo JAMSTEC, NIES, and AORI (Japan)||MIROC-ES2L||r1i1p1f2|
|Max Planck Institute for Meteo. (Germany)||MPI-ESM1-2-HR||r1i1p1f1|
|Max Planck Institute for Meteo. (Germany)||MPI-ESM1-2-LR||r1i1p1f1|
|Meteorological Research Institute (Japan)||MRI-ESM2-0||r1i1p1f1|
|Norwegian Climate Center (Norway)||NorESM2-LM||r1i1p1f1|
|Norwegian Climate Center (Norway)||NorESM2-MM||r1i1p1f1|
|Research Center for Env. Changes (Taiwan)||TaiESM1||r1i1p1f1|
|Met Office Hadley Centre and NERC (UK)||UKESM1-0-LL||r1i1p1f2|
For each downscaled GCM, 31 climate indices have been calculated (Table 3). The climate indices include 27 Climdex indices established by the Expert Team on Climate Change Detection and Indices (ETCCDI)Reference10 and 4 additional indices that are slightly modified from the Climdex indices. These indices are calculated from daily precipitation and temperature values from the downscaled simulations and are available at annual or monthly temporal resolution, depending on the indices.
Table 3. List of 31 climate indices (27 indices recommended by ETCCDI and 4 additional indices considered in this project (in bold).
|1||FD||Number of frost days||days|
|2||SU||Number of summer days (> 25°C)||days|
|3||SU30||Number of summer days (> 30°C)||days|
|4||ID||Number of icing days||days|
|5||TR||Number of tropical nights||days|
|6||GSL||Growing season length||days|
|7||TXx||Monthly maximum value of daily maximum temperature (TX)||°C|
|8||TNx||Monthly maximum value of daily minimum temperature (TN)||°C|
|9||TXn||Monthly minimum value of TX||°C|
|10||TNn||Monthly minimum value of TN||°C|
|11||TN10p||Percentage of days when TN < 10th percentile||%|
|12||TX10p||Percentage of days when TX < 10th percentile||%|
|13||TN90p||Percentage of days when TN > 90th percentile||%|
|14||TX90p||Percentage of days when TX > 90th percentile||%|
|15||WSDI||Warm spell duration index||days|
|16||CSDI||Cold spell duration index||days|
|17||DTR||Daily temperature range||°C|
|18||Rx1day||Monthly maximum 1-day precipitation||mm|
|19||Rx2day||Monthly maximum consecutive 2-day precipitation||mm|
|20||Rx5day||Monthly maximum consecutive 5-day precipitation||mm|
|21||SDII||Simple precipitation intensity index||mm|
|22||R1mm||Annual count of days when daily precipitation amount (PRCP) ≥ 1mm||days|
|23||R10mm||Annual count of days when PRCP ≥ 10mm||days|
|24||R20mm||Annual count of days when PRCP ≥ 20mm||days|
|25||CDD||Maximum length of dry spell, maximum number of consecutive days with PRCP < 1mm||days|
|26||CWD||Maximum length of wet spell, maximum number of consecutive days with PRCP ≥ 1mm||days|
|27||R95p||Annual total accumulation of precipitation on wet days (PRCP > 95th percentile)||mm|
|28||R99p||Annual total accumulation of precipitation on very wet days (PRCP > 99th percentile)||mm|
|29||PRCPTOT||Annual total precipitation in wet days||mm|
|30||R95day||Number of days where daily precipitation exceeds the 95th percentile||days|
|31||R99day||Number of days where daily precipitation exceeds the 99th percentile||days|
Downscaled simulations have been organized into separate directories containing one simulation for each GCM, variable, realization, and shared socioeconomic pathway. For example, the downscaled simulation of daily precipitation from the first realization (r1i1p1f1) of ACCESS-CM2 following the SSP1-2.6 pathway is contained within the directory:
In view of the large file size of the downscaled simulations (57 Gb per file), each complete simulation has been split into 5-year subsets. Each 5-year file is labeled following the same filename format to describe the simulation and time interval contained within the file. For example, the first file within the directory listed above is the following:
Components of the filename format include:
- Variable: "pr"
- Timestep: "day"
- Downscaling method and target: "BCCAQv2+ANUSPLIN300"
- GCM: "ACCESS-CM2"
- Past and future pathway: "historical+ssp126"
- Realization: "r1i1p1f1"
- Grid Label: "gn"
- Time interval: "19500101-19551231"
Each simulation directory contains one 6-year file (1950-1955, 2.3 Gb) and 29 5-year files (1.9 Gb each) that together comprise the 151-year Canada-wide downscaled simulation for that GCM, variable, realization, and socioeconomic pathway. The grid label identifier denotes whether GCM simulations are provided using the native grid of the model ("gn") or have been regridded ("gr") to another primary grid by the modelling centre. Instances where simulations from a GCM are provided at more than one grid resolution are indicated using an integer designation (e.g. "gr2").
Files of climate indices are labeled following the same filename format. For example, the first file within the Climdex directory of ACCESS-CM2 is the CDD at annual (ann) time resolution is the following:
Components of the filename format for the climate indices include:
- ETCCDI climate index: "cddETCCDI"
- Time resolution: “ann”
- Time interval: “1950-2100”
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