Water Isotope Model Intercomparison Project (WisoMIP)
WisoMIP is a coordinated intercomparison of water isotope-enabled atmospheric general circulation models (AGCMs). It is the first project in which multiple isotope-enabled AGCM simulations have been designed and conducted under a common experimental protocol.
By combining simulations from multiple models, the WisoMIP ensemble helps identify robust features of the global water cycle and can provide more reliable estimates than any individual simulation.
WisoMIP is the successor to the Stable Water Isotope Intercomparison Group (SWING). WisoMIP Phase 1 serves as the continuation of the SWING intercomparison effort and replaces the originally anticipated SWING3 phase.
On this page: Overview · Participating Models · Data Access · Reference — Legacy Archive: SWING1 · SWING2
Phase 1: Present-Day Climate with Reanalysis Nudging
In WisoMIP Phase 1, Working Group 1 focuses on simulations of the present-day climate from 1979 to 2023 using isotope-enabled AGCMs, each nudged toward ERA5 reanalysis data. The eight participating models include all isotope-enabled AGCMs worldwide capable of simulating water isotopes while being nudged globally toward reanalysis circulation fields. The ensemble therefore covers the full set of models capable of conducting the WisoMIP Phase 1 experiment.
Figure 1. Multi-model mean annual δ18O (left) and inter-model spread (right) for δ18O in precipitation (top), surface humidity (middle), and total column water vapor (bottom), 1979–2023.
Figure 2. Taylor diagram comparing the WisoMIP models and reanalyses for surface temperature (1), precipitation (2), δ18O of precipitation (3), and deuterium excess of precipitation (4). Black stars mark the WisoMIP ensemble mean.
By prescribing identical winds, sea surface temperatures, and sea ice conditions, the experiment isolates differences in model physics related to the water cycle and its isotopic behavior, while controlling for variability in atmospheric dynamics.
The ensemble mean generally agrees more closely with observations than most individual models because biases and outlying behavior among models partially cancel. The resulting nudged ensemble can serve as one benchmark for isotope-enabled model development, comparisons with satellite retrievals, and applications as an “isotope reanalysis” product, ranging from the investigation of responses to major modes of climate variability to paleoclimate reconstruction.
Full details are provided in Bong et al. (2026).
Participating Models
Native resolutions are given as longitude × latitude × vertical levels. All models are additionally provided interpolated to a common 128 × 64 grid on 17 pressure levels (1000, 925, 850, 700, 600, 500, 400, 300, 250, 200, 150, 100, 70, 50, 30, 20, 10 hPa).
| Model | Native resolution | Principal points of contact |
|---|---|---|
| iCAM5 | 144 × 96 × 17 | Qinghua Ding, Jiang Zhu |
| iCAM6 | 288 × 192 × 17 | Richard P. Fiorella, Jiang Zhu |
| ECHAM6-wiso | 192 × 96 × 26 | Martin Werner, Alexandre Cauquoin |
| GISS-E2.1 | 144 × 90 × 17 | Allegra N. LeGrande, Hayoung Bong |
| IsoGSM3 | 188 × 94 × 17 | Kei Yoshimura, Hayoung Bong |
| LMDZ6 | 144 × 143 × 79 | Camille Risi, Cécile Agosta |
| MIROC5-iso | 128 × 64 × 17 | Atsushi Okazaki, Hayoung Bong |
| NICAM-WISO | 180 × 90 × 18 | Masahiro Tanoue |
Data Access
The WisoMIP Phase 1 archive (v1, 26 June 2025, 180 files, approximately 96 GB) is hosted on the NASA Center for Climate Simulation (NCCS) data portal and is available for direct download:
- WisoMIP1 data archive (top-level directory)
- README.txt (authoritative description of contents, variables, and contacts)
Files are netCDF, named following the pattern Total.<MODEL>_<PRODUCT>.nc, where <MODEL> is one of CAM5, CAM6, ECHAM, GISS, GSM (for IsoGSM3), LMDZ, MIROC, NICAM, or ENSEMBLE.
Direct Downloads
Each link is a single netCDF file containing all 28 variables. Monthly and Yearly are time series spanning 1979–2023. The remaining products are climatological means over that period. All fields are on the common 128 × 64 grid at 17 pressure levels, except Native grid, which preserves each model's own resolution and so varies in size from model to model.
| Model | Monthly | DJF | MAM | JJA | SON | Yearly | Annual mean | Native grid |
|---|---|---|---|---|---|---|---|---|
| Ensemble mean | 2.5 GB | 5 MB | 5 MB | 5 MB | 5 MB | 207 MB | 5 MB | N/A |
| iCAM5 | 2.5 GB | 5 MB | 5 MB | 5 MB | 5 MB | 207 MB | 5 MB | 4.2 GB |
| iCAM6 | 2.5 GB | 5 MB | 5 MB | 5 MB | 5 MB | 206 MB | 5 MB | 16.7 GB |
| ECHAM6-wiso | 2.5 GB | 5 MB | 5 MB | 5 MB | 5 MB | 206 MB | 5 MB | 8.1 GB |
| GISS-E2.1 | 2.5 GB | 5 MB | 5 MB | 5 MB | 5 MB | 206 MB | 5 MB | 3.9 GB |
| IsoGSM3 | 2.5 GB | 5 MB | 5 MB | 5 MB | 5 MB | 206 MB | 5 MB | 5.5 GB |
| LMDZ6 | 2.5 GB | 5 MB | 5 MB | 5 MB | 5 MB | 207 MB | 5 MB | 25.6 GB |
| MIROC5-iso | 2.5 GB | 5 MB | 5 MB | 5 MB | 5 MB | 206 MB | 5 MB | 2.5 GB |
| NICAM-WISO | 2.5 GB | 5 MB | 5 MB | 5 MB | 5 MB | 207 MB | 5 MB | 5.1 GB |
Monthly Climatology
Climatological mean for each calendar month over 1979–2023.
| Model | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Ensemble mean | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB |
| iCAM5 | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB |
| iCAM6 | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB |
| ECHAM6-wiso | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB |
| GISS-E2.1 | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB |
| IsoGSM3 | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB |
| LMDZ6 | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB |
| MIROC5-iso | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB |
| NICAM-WISO | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB | 5 MB |
Variables
Every file contains all 28 variables listed below, so you can choose a file by the time period you need rather than by variable. Twenty-one of the variables are single-level maps on the latitude-longitude grid. The remaining seven vary with height (d18O, dD, dexcess, ta, ua, va, and hus) and have one extra vertical dimension, named p, which holds the 17 pressure levels listed above.
| Name | Units | Description |
|---|---|---|
| Isotopes: precipitation | ||
| d18Op | ‰ | δ18O of precipitation |
| dDp | ‰ | δD of precipitation |
| dexcessp | ‰ | Deuterium excess of precipitation |
| Isotopes: evaporation | ||
| d18Oe | ‰ | δ18O of evaporation |
| dDe | ‰ | δD of evaporation |
| dexcesse | ‰ | Deuterium excess of evaporation |
| Isotopes: surface specific humidity | ||
| d18Os | ‰ | δ18O of specific humidity (surface) |
| dDs | ‰ | δD of specific humidity (surface) |
| dexcesss | ‰ | Deuterium excess of specific humidity (surface) |
| Isotopes: specific humidity on pressure levels | ||
| d18O | ‰ | δ18O of specific humidity (pressure level) |
| dD | ‰ | δD of specific humidity (pressure level) |
| dexcess | ‰ | Deuterium excess of specific humidity (pressure level) |
| Isotopes: vertically integrated water vapor | ||
| d18Ow | ‰ | δ18O of vertically integrated water vapor |
| dDw | ‰ | δD of vertically integrated water vapor |
| dexcessw | ‰ | Deuterium excess of vertically integrated water vapor |
| Water cycle and meteorology | ||
| pr | mm/day | Precipitation (surface) |
| ev | mm/day | Evaporation (surface) |
| huss | kg/kg | Specific humidity (surface) |
| hus | kg/kg | Specific humidity (pressure level) |
| prw | kg/m2 | Atmospheric column precipitable water |
| tas | °C | Temperature (surface) |
| ta | °C | Temperature (pressure level) |
| ps | hPa | Pressure (surface) |
| ua | m/s | u-wind (pressure level) |
| va | m/s | v-wind (pressure level) |
| iuq | kg/m/s | Vertically integrated moisture u-flux |
| ivq | kg/m/s | Vertically integrated moisture v-flux |
| pref | % | Precipitation efficiency, (pr/qvsum) × 100 |
Note: WisoMIP covers the atmosphere. For water isotope data in the ocean, see the Global Seawater Oxygen-18 Database.
Reference
Bong, H., et al., 2026: Water Isotope Model Intercomparison Project (WisoMIP): Present-day climate. J. Geophys. Res. Atmos., 131, e2025JD044985, doi:10.1029/2025JD044985. An open-access version is available from the ESS Open Archive.
Credits
Acknowledgment is given to Hayoung Bong and Allegra N. LeGrande for compiling and processing the WisoMIP Phase 1 data, managing the archive at NASA GISS, and analyzing the model results, to Sylvia Dee for coordinating the project, to all participating modeling groups listed above, and to the providers of the global ground-based and satellite observations used for model evaluation and analysis.
Contact
Please contact Dr. Allegra N. LeGrande or Dr. Gavin Schmidt if you have any questions or comments about these data.
