NEX-GDDP-CMIP6

Summary Description

NASA’S Earth Exchange Global Daily Downscaled Projections (NEX-GDDP-CMIP6) is an ensemble of global climate model simulations bias-adjusted by NASA. It downscales 9 variables from 35 climate models over a historical period (1950–2014) and four future emission pathways (SSP1-2.6, SSP2-4.5, SSP3-7.0, SSP5-8.5) using the bias correction/spatial disaggregation (BCSD) bias-adjustment method. The reference dataset used is the Global Meteorological Forcing Dataset (GMFD). A detailed description of the dataset is available in Thrasher et al. (2022).

Dataset Characteristics

Current version: v2.0
Available variables: temperature, precipitation, wind, humidity, longwave and shortwave radiation (see variables section below)
Temporal coverage: 1950–2100
Temporal resolution: daily
Spatial coverage: global
Spatial resolution: 0.25 degree
Data type: Bias-adjusted climate projections
Data format: netCDF and Cloud optimized GeoTIFF (COG)
Web references:
NASA website
Reference:
Thrasher et al. (2022)
Contact: Dr. Bridget Thrasher and Dr. Ian Brosnan, NASA NEX
Data Support: Nasa Center for Climate Simulation (NCCS) Support

When to use NEX-GDDP-CMIP6

When you need CMIP-based, bias-adjusted future climate projections at a global scale
When you need bias-adjusted wind, humidity and radiation data in addition to temperature and precipitation
When you need downscaled climate data suitable for impact studies at medium spatial resolution that better represent local processes (e.g., topography, coastlines) than global models
When you need climate projections under four future emissions pathways (SSPs)
When you need scenario-based projections with improved agreement with a global reference dataset
When you want to avoid performing bias correction and post-processinng workflows on CMIP6 data, particularly outside of Canada

Strengths and Limitations

Key Strengths of NEX-GDDP-CMIP6

Strength	Description
Large multi-model ensemble	Makes use of a large number of climate models, which allows to sample the (structural) uncertainty associated with climate projections.
Multiple emission scenarios	Simulations driven by four different emission scenarios were processed to span a wide range of possible futures.
Multiple variables	Nine climate variables are available.

Key Limitations of NEX-GDDP-CMIP6

Limitation	Description
Lower resolution	The resolution is relatively low compared to other bias-adjusted datasets, although it is improved compared to the GCM’s resolution.
Few references	There is little documented experience using this dataset over Canada.

Expert Guidance

Click to toggle section collapse

NEX-GDDP-CMIP6 stands out from other bias-adjusted datasets by providing data for the entire globe as opposed to a limited domain. It also provides 9 different variables: mean temperature, maximum temperature, minimum temperature, precipitation, relative humidity, specific humidity, longwave downwelling radiation, shortwave downwelling radiation, near surface wind speed.

The dataset is composed of 35 different models, but not all models are available for all variables and emissions scenarios. Users should be careful when comparing ensembles that have a different composition.

The trend of the original simulations is preserved in the bias-adjusted product. This means that “the hot model problem” (Hausfather et al. (2022)), i.e. the over representation of models that warm up too quickly, will also be present for this dataset. See the “Expert Guidance” section on the CMIP6 data page.

The dataset might not be realistic over smaller islands as the reference dataset (Global Meteorological Forcing Dataset - GMFD; Department of Civil and Environmental Engineering, Princeton University (2006)) has not been validated over oceans.

The dataset is accompanied by the following warning: “This dataset is intended for use in scientific research only, and use of this dataset for other purposes, such as commercial applications, and engineering or design studies is not recommended without consultation with a qualified expert.”

Because there are very few studies that have looked at this dataset specifically over Canada in the literature, the quality and limitations of the dataset over the country have not been well established. Users are strongly encouraged to validate the data for their region before using them.

The dataset includes the high emission scenario SSP5-8.5 which can be considered unlikely to realize under current established climate policy. See the section on the unlikeliness of RCP8.5 and SSP5-8.5 greenhouse gas emission scenarios

Variables available in NEX-GDDP-CMIP6

For details click on variable group to uncollapse

Temperature

Daily Near-Surface Air Temperature (tas) [K]
Daily Maximum Near-Surface Air Temperature (tasmax) [K]
Daily Minimum Near-Surface Air Temperature (tasmin) [K]

Precipitation

Precipitation (average daily precipitation rate, pr) [kg m-2 s-1]

Wind

Daily-Mean Near-Surface Wind Speed (sfcWind) [m s-1]

Humidity

Near-Surface Relative Humidity (hurs) [%]
Near-Surface Specific Humidity (huss) [dimensionless ratio (kg/kg)]

Radiation

Surface Downwelling Longwave Radiation (rlds) [W m-2]
Surface Downwelling Shortwave Radiation (rsds) [W m-2]

Data Access

Data can be accessed through Amazon Web Services (AWS) or THREDDS to allow for subsetting of the very large dataset. Instructions are provided by the NASA Center for Climate Simulations - NCCS.

References

Department of Civil and Environmental Engineering, Princeton University. (2006). Global Meteorological Forcing Dataset for Land Surface Modeling, Boulder, CO: NSF National Center for Atmospheric Research. doi:10.5065/JV89-AH11

Hausfather, Z., Marvel, K., Schmidt, G. A., Nielsen-Gammon, J. W., & Zelinka, M. (2022). Climate simulations: Recognize the ’hot model’ problem. Nature, 605(7908), 26–29.

Thrasher, B., Wang, W., Michaelis, A., Melton, F., Lee, T., & Nemani, R. (2022). NASA global daily downscaled projections, CMIP6. Scientific Data, 9(1), 262.