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Changes in Freeze-Thaw Cycle and Permafrost Dynamics, and their Hydrological Implications over the Russian Arctic Drainage Basin

NSFThis project is funded by NSF ARC grant 0229766


To conclude data rescue and produce and distribute a gridded Northern Hemisphere freezing/thawing index product


Tingjun Zhang is the PI, Roger Barry is Co-PI, and Oliver Frauenfeld is Co-Investigator.

Project Summary

Research efforts pertaining to this project saw the creation of a temporally and spatially continuous long-term 25 kilometers by 25 kilometer gridded Northern Hemisphere freezing/thawing index product. Variability in the ground thermal regime in high-latitude cold regions has important ramifications for surface and subsurface hydrology, carbon exchange, the surface energy and moisture balance, and ecosystem diversity and productivity. However, assessing these variations, particularly in light of reported widespread atmospheric and terrestrial changes over recent decades, remains a challenge due to the sparse observing networks in high latitudes. The annual freezing/thawing (F/T) index can be used to predict and map permafrost and seasonally frozen ground distribution, active layer and seasonal freeze depths, and has important engineering applications, thereby providing important information on climate variability in cold regions. The freezing/thawing index is generally defined based on daily observations, which are not readily available for many high-latitude locations. However, we established the reliability of using monthly temperature observations, which are readily available from a variety of sources. Based on a comprehensive evaluation, we select the University of East Anglia's Climatic Research Unit (CRU) temperature product, available for 1901 to2002, which enabled us to produce and analyze a 25 kilometer by 25 kilometer gridded Northern Hemisphere freezing/thawing index product. Long-term climatologies of the freezing/thawing index delineate the cold regions of the Northern Hemisphere, as well as areas of seasonally frozen ground and permafrost. Objective trend analysis indicates that in recent decades, no significant changes have occurred in Russian permafrost regions; however, seasonally frozen ground areas are experiencing significant warming trends. Over North America, Canadian and Alaskan permafrost regions are experiencing a decrease in freezing index during the cold season, while coastal areas and eastern Canada are seeing significant increase in warm season thawing index.

2005 saw the conclusion of our data rescue under this present effort, updating our database of Russian observing stations with monthly soil temperature measurements at 13 depths, ranging from close to the surface to a depth of 3.2 meters. These data are also now available through the year 2000, and the total database includes over 400 sites. Future projects will focus on obtaining additional data, and the continued analyses and investigation of this data set.

Arctic map of freezing index from 1901 to 2000
Long-term climatology of the 1901 to 2001 freezing index in °C-days for the Northern Hemisphere north of 15 degrees north.

Arctic map of thawing index from 1901 to 2000
Long-term climatology of the 1901 to 2001 thawing index in °C-days for the Northern Hemisphere north of 15 degrees north.

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