Vol. 16:1, pp. 51-64
The Physical Climatology of Alpine Tundra,
Scout Mountain, British Columbia, Canada
I. R. SAUNDERS AND W. G.
BAILEY, Department of Geography, Simon Fraser University
Eleven months of radiation budget measurements from an alpine tundra site in
southern British Columbia encapsulated a wide range of atmospheric and surface
conditions and provide insights into the controlling factors affecting energy
and mass exchanges in the high mountain environment. The seasonal snow cover
exerts a strong surface control on energy exchange, the high albedo suppressing
solar radiation absorption and the cold surface temperatures limiting net long
wave radiation losses. Turbulent energy fluxes during winter were very small and
driven by the negative net radiation. The very thin snowpack that persisted
throughout the winter meant that energy storage changes within the snow were
negligible and the snowmelt period was very brief.
When the tundra is snow-free, cloud cover is the most important determinant
of the radiation budget through its influence on atmospheric transmissivity and
long wave radiation fluxes. Local orographic cloud development provided an
important negative feedback which countered the large solar irradiances that
would otherwise be expected in high mountains during the summer.
Both energy- and moisture-limiting evapotranspiration regimes occurred during
both field seasons, governed largely by the frequency, rather than the
magnitude, of precipitation events. In the absence of precipitation, the tundra
desiccated rapidly due to the efficient drainage, limited soil moisture storage
capacity, and the presence of quick-drying rock surfaces. Surface resistance
measurements demonstrated the lack of efficiency in the transfer of subsurface
moisture to the atmosphere during dry periods, and show that the change from a
wet-surface evaporative regime to a dry-surface one is achieved very quickly.
Vol. 16:1, pp. 65-75
Climate of the Summit Region of Mount
Kinabalu (Borneo) in 1992, an El Niño Year
KANEHIRO KITAYAMA, The
Japanese Forestry and Forest Products Research Institute
An extensive El Niño, which normally causes droughts on the western side of
the tropical Pacific basin, occurred from the spring of 1991 to May 1992.
Measurements were taken of climatic variables associated with this irregular but
reoccurring event in a high-altitude environment at 3,780 m near the upper
timberline on Mount Kinabalu, Borneo, for one year in 1992. These included
temperature above and below ground, vapor pressure, global radiation,
photosynthetically active radiation, and rainfall. Mean monthly air temperatures
at 1.5 m ranged from 6.6 (October) to 9.7°C (March) with an annual mean of
8.1°C. Relatively dry periods with monthly rainfall less than 100 mm occurred
from January to April and in August. Total rainfall for the year was 2,418 mm.
Monthly rainfall minus potential evapotranspiration indicated net negative water
budgets in the dry periods for all albedo values (0.1-0.5) which were used in
the calculation. Associated with these droughts were freezing ground-air
temperatures and an extremely high soil temperature. It is inferred that the
marked aridity resulted from the occurrence of air subsidence which
adiabatically becomes dry and isolates the summit from uplifting moist air.
However, the mechanisms causing putative subsidence remain unknown and I cannot
conclude if the 1992 drought on Mount Kinabalu is attributable to the El Niño
only. Nevertheless, this study suggests the possibility of extensive water
stress to plants in the summit region. Small-sized leaves and sclerophylly,
which characterize the site, appear to be morphological adaptations primarily to
such water stress.