Climate at Bonanza Creek Experimental Forest
Introduction
Interior Alaskan forests are part of the circumpolar band of boreal forests. Interior Alaska
is bounded on the south by the Alaska Range and on the north by the Brooks Range,
mountains that provide an effective barrier to coastal air masses. As a result, the
climate is strongly continental with cold winters and warm relatively dry summers.
These forests are also unique for their association with an environment characterized
by drastic seasonal fluctuation in day length (more than 21 hours on June 21 and less
than 3 hours on December 21). Temperature ranges from extremes of -50°C in January
to over +33°C in July, with a short growing season (100 days or less). The average annual
precipitation is only 269 mm, 30% of which falls as snow. Snow covers the ground
from mid-October until mid- to late April, and maximum accumulation averages 75-100 cm.
Soil temperatures are consistently low.
One characteristic of the continental climate of interior Alaska is the wide range
of air temperatures that occur between summer and winter and the large fluctuations
around the means. Mean annual temperatures in the Tanana valley area average between
-2 oC and -5 oC with the long-term average at the Fairbanks International Airport being
-3.1 oC. The warmest month, July, averages 16.3 oC whereas in January the average is
a cold -23.5 oC. Periods of extreme cold ranging in the vicinity of -40 oC to -45 °C
can occur at any time from late November through February. In contrast, daily maximum
temperatures may occasionally reach into 35 oC to 37 oC in June and July, often with
only modest night cooling because of the persisting daylight.
Annual precipitation in interior Alaska is low, from 250 to 500 mm, with a 50-year average
for Fairbanks of 287 mm. About 35 percent of precipitation falls as snow between October
and April. Summer and winter precipitation is generated from major frontal systems that
cross the State, but convection storms that produce abundant lightning add significantly
to the summer precipitation. Although precipitation amounts during the growing season may
below, evaporation rates are also low because of the relative short growing season and cool
temperatures. Even so, as much as 76 to 100 percent of the summer precipitation may be lost
as evapotranspiration.
Climate monitoring information
Climate is monitored at two main climate stations , nine of the successional study sites at
BCEF and one site in the Survey line fire study area. In the fall of 1987, BNZ joined the
network of Long-Term Ecological Research (LTER) sites, and two permanent weather stations
were established--LTER1 on a broad ridge at 365 m, about midway in an elevational transect
in the Forest (lat. 64°44'34"N long. 148°18'59"W), and LTER2 one on the floodplain of the
Tanana River (lat 64o41'57'N, long. 148°15'03"W) at 120 m elevation. Two stations were
established to accurately characterize the different climate regimes of the two major
topographic subdivisions of the Forest. Weather stations were also established at each
of 8 experimental sites, one in each successional stage being studied (See BCEF Experimental Design).
Climate parameters measured at Bonanza Creek Experimental Forest
SITES
|
PARAMETERS
|
DATA INITIATION
|
FREQUENCY
|
DATA RETRIEVAL
|
Main climate stations:
(LTER1 and LTER2) |
Air temperature
Relative humidity
Soil temperature at (5, 10, 20, 50,
100, and 200 cm depths)
Precipitation (rain and snow)
Wind speed and direction
Solar radiation (global, PAR, UV)
Evaporation
Snow depth
Soil moisture (TDR)
Depth of thaw (spring only)
|
June 1988
(UV sensors
installed May 1993.
Snow depth sensors
installed Sept 1994) |
Logged hourly |
Data retrieved
daily via modem. Summarized and
available seasonally |
| LTER1 |
Sun Photometer |
June 1994 |
Continously
during summer |
Hourly to GOES
satellite |
Successional sites:
111 (UP1A)
121 (UP2A)
131 (UP3A)
211 (FP1A)
221 (FP2A)
231 (FP3A)
241 (FP4A)
251 (FP5A)
253 (FP5C) |
Air temperature
Relative humidity
Soil temperature at (5, 10, 20, 50,
100, and 200 cm depths)
PAR |
June 1989-----
UP2A and FP3A (6/88)
FP5C (8/93) |
Logged
hourly |
Data retrieved
monthly |
| |
Precipitation--rain
Soil moisture (TDR)
Depth of thaw (spring until out)
|
Rain: 5/88
(FP5A--5/89)\
TDR: 5/92
Thaw: 5/88 |
Weekly in
summer |
Summarized and
available seasonally |
| |
Precipitation--snow depth |
Sept 1988 |
Occasionally
in winter |
Summarized and
available annually |
211 (FP1A)
231 (FP3A)
241 (FP4A) |
River height |
Intermittent since 1985 |
Weekly |
Seasonally |
|
|
