NEX-GDDP-CMIP6

Summary Description

NASA’S Earth Exchange Global Daily Downscaled Projections (NEX-GDDP-CMIP6) is a set of global simulations bias-adjusted by NASA. It downscales 9 variables for 35 global climate models over a historical period (1950–2014) and four future 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) reference set. A detailed description of the method is available in Thrasher et al. (2022).

Dataset Characteristics

Current version: (v2.0)[https://www.nccs.nasa.gov/sites/default/files/NEX-GDDP-CMIP6-v2-Tech_Note.pdf]
Temporal coverage: 1950–2100
Temporal resolution: daily
Spatial coverage: global
Spatial resolution: 0.25 degree
Data type: netCDF
Web references:
NASA website
Reference publications: Thrasher et al. (2022),

Strengths and Limitations

Key Strengths of NEX-GDDP-CMIP6

Strength	Description
Multi-Model Ensemble	One member of each available GCM was adjusted to give all models equal representation.
Multiple emission scenarios	The ensemble includes simulations driven by four different emission scenarios, which allows it to span a wide range of possible futures.
Multiple variables	Nine variables have been adjusted.

Key Limitations of NEX-GDDP-CMIP6

Limitation	Description
Lower resolution	The resolution is not as high compared to other bias-adjusted datasets.

Expert Guidance

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NEX-GDDP-CMIP6 stands out from other bias-adjusted datasets as it covers the whole globe, not only a small domain, and it adjusts 9 variables (tas, tasmax, tasmin, pr, hurs, huss, rlds, rsds, sfcWind).

The authors of the dataset highlight a few limitations. First, there is a possible underestimations of the extremes due to diffusion over the spatial distribution when performing the statistical downscaling. Second, the method (like all bias-adjustment methods) makes the assumption that the relative spatial patterns will remain constant under future climate change. Third, the frequency of extremes is not adjusted. The information from the GCM is kept. Fourth, the dataset might not be realistic over smaller islands as the reference dataset (GMFD) have not been validated over the oceans.

Similarly to ESPO-G6, the trend of the GCMs is preserved in the bias-adjusted product. This means that “the hot model problem” (Hausfather et al. (2022)) will also be present for this dataset. However, the authors of the dataset provide no guidance on this issue. should this be in a general section ?.

Note that the SSP5-8.5 scenario is available for this dataset. According to the recommendation of Working Group III, this scenario is currently considered unlikely.

The dataset has 35 different models, but not all models are available for all variables and emissions scenarios. The inclusion or exclusion of some models might affect the results when comparing subgroups who don’t have the same members.

Note that some of that data ended up in a non-physical range, either because of the bias-adjustement method and/or the initial data was already out-of-range. In these rare cases, the extremes values were clipped to a physical limit.

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.”

Example Applications

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Available Variables 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 (mean of the daily precipitation rate, pr) [kg m-2 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]

Wind

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

Data Access

Data can be accessed through Amazon Web Services (AWS) or THREDDS. Instructions are available here: https://www.nccs.nasa.gov/services/data-collections/land-based-products/nex-gddp-cmip6

References

Hausfather, Z., Marvel, K., Schmidt, G.A., Nielsen-Gammon, J.W., Zelinka, M., 2022. Climate simulations: Recognize the ’hot model’ problem. Nature 605, 26–29. https://doi.org/10.1038/d41586-022-01192-2

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