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Pan-Arctic Land Surface Modeling


NSFThis project is funded by NSF

Objective

To investigate the future state of permafrost in the near-surface soil layers in collaboration with the National Center for Atmospheric Research (NCAR)

Collaborators

Andrew Slater

Project Summary

Observations clearly indicate that the climate is changing. Observations already suggest that the terrestrial Arctic is experiencing the largest change of any world region in terms of temperature, and modeling studies and current trends suggest that this change will continue.

This study investigates the future state of permafrost in the near-surface soil layers. These upper layers are important due to their potential impact upon hydrology, ecology, and trace gas emissions. Results from the high-resolution (T85) version of the Community Climate System Model (version 3; CCSM3) agree quite well with current estimates of continuous permafrost extent, providing a mean value of 10.6 million square kilometers for the period from 1980 to 1999. A century later in time (2080 to 2099), the model projects more than an 80 percent reduction in continuous permafrost in the upper 3.5 meters of the ground under the current emissions scenario. Additional experiments show that there is still "heat in the pipeline," meaning that if greenhouse gas levels remain at current levels, we would still see a 10 to 15 percent reduction in the extent of continuous nearsurface permafrost. Perhaps the most concerning result was the rapid thaw of very large regions over a period of only 40 years.

Under the projected climate change scenario, freshwater discharge into the ocean will increase by 28 percent, 15 percent of which can be attributed to melting ground ice. The seasonal hydrograph for the period 2080 to 2099 shows higher baseflow and higher springtime runoff, though summer runoff remains similar to present day estimates. The current simulations do not account for the consequences of increased carbon and methane fluxes from Arctic soils; this is an area of ongoing research and is perhaps the area of largest uncertainty for future Arctic climate.

In additional, related studies, we compared the performance of five land surface models (CHASM, Noah, CLM, VIC, ECMWF), in the simulation of hydrological processes across the terrestrial Arctic drainage system for the period 1980-2001. The models represent a wide range of physics, particularly with respect to high-latitude processes and are forced with surface meteorology derived from the ERA-40 reanalysis. Our objective is to assess the ability of the models to capture various aspects of Pan-Arctic hydrology as well as identify those features that contain the largest uncertainty. Compared to station data, all models produce similar errors in snow water equivalent; yet they differ widely in their snow regimes in terms of snowfall quantity, estimated snow depths and most importantly, sublimation rates. Additionally, model albedo is consistently higher than observations in the presence of snow. No single model was the best or worst performing when compared to a range of observations.

Hydrographs of the four major Arctic catchments
Seasonal hydrographs of the four major Arctic catchments. Note that baseflow is difficult to capture, particularly in the MacKenzie and Yenesi basins.

Related Resources

None

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