Permafrost

180
Change in hydro-thermal regimes in the soil-freezing regions in the
Global Warming simulation by a CGCM of moderate- and
high-resolution
Kazuyuki SAITO 1 , Seita EMORI 2 , Masahide KIMOTO 3
(1.Frontier Research Center for Global Change (FRCGC), JAMSTEC, Yokohama, Japan; 2.National Institute
of Environmental Sciences (NIES), Tsukuba, Japan; 3.Center of Climate System Research (CCSR),
University of Tokyo, Kashiwa, Japan)
Abstract: The land cryosphere, mostly underlain by permanently or seasonally frozen ground,
is projected to experience a largest increase of near-surface temperatures under the Global
Warming at the end of this century. Degradation of permafrost, or changes in the active layer
depths and seasonally-frozen layers will exert a large impact both on the socio-economy and on
the eco-climate system in the regions. Such changes, however, may not be contained at a local
scale but will affect other regions through several physiochemical and biological pathways.
Therefore, the changes in the soil-freezing regions cannot be neglected for an adequate
estimation of the impacts due to the Global Warming. As a first step for such estimation,
change in hydro-thermal regimes was examined by a global land-ocean-atmosphere coupled
model (CGCM) of a moderate (T42) and high (T106) horizontal resolutions, including
soil-freezing processes.
The model was developed by CCSR/NIES/FRCGC, and run at the Earth Simulator at
JAMSTEC. The 200-year integration from 1900 to 2100 followed the IPCC AR4
specification; climate of the 20 th century (20c3m) and 720 ppm stabilization experiment (SRES
A1B). The land surface scheme includes ground heat and water transfer, and canopy structure
and vegetation biophysical processes. Typical land grid interval is about 50 km and 250 km
for T106 and T42, respectively, and the ground down to 4 m was divided into five layers of
different depths. Two 20-year periods (1980 to 1999, and 2080 to 2099) were selected as the
reference periods for present-day and projected climatology, respectively. 200-year times
series was also used for the analysis.
Due to the limitation in the horizontal dimensions and the resolved depth, we employed a
new classification of the frozen ground. The area is classified as a multi-year frozen ground
(MFG) when soil temperatures at any depth are kept below the freezing point during the
analyzed period. Similarly, it is seasonally frozen ground (SFG) if a soil layer at any depth is
frozen at some time of year. The geographical mapping of present-day MFG and SFG showed
reasonably good correspondence with the respective current distribution of continuous
permafrost and seasonally-frozen ground. The former occupied about 17% of the Northern
Hemisphere open land surface. MFG were found only in eastern Siberia and Arctic Canada
(about 6% of the open surface) at the end of the 21 st century, implying of the deepening of the
active layers and/or degradation to SFG in large areas. Changes in the hydro-climate of the
high-latitude will be discussed in the presentation. Impact of the horizontal resolution
difference in the simulated distribution of the frozen soil and the hydro-thermal regimes will
also be reported.
Key words: climate change; permafrost; seasonally-frozen ground; global climate model; thermal regime;
hydroclimate