In this study, the surface energy balance of 10 sites in the western and central Canadian subarctic is examined. Each research site is classified into one of five terrain types (lake, wetland, shrub tundra, upland tundra, and coniferous forest) using dominant vegetation type as an indicator of surface cover. Variations in the mean summertime values (15 June-25 August) of the energy balance partitioning, Bowen ratio (), Priestley-Taylor alpha (␣), and surface saturation deficit (D o) are compared within and among terrain types. A clear correspondence between the energy balance characteristics and terrain type is found. In addition, an evaporative continuum from relatively wet to relatively dry is observed among terrain types. The shallow lake and wetland sites are relatively wet with high Q E /Q* (latent heat flux/net radiation), high ␣, low , and low D o values. In contrast, the upland tundra and forest sites are relatively dry with low Q E /Q*, low ␣, high , and high D o values.
This study details seasonal characteristics in the annual surface energy balance of upland and lowland tundra during the 1998-99 water year (Y2). It contrasts the results with the 1997-98 water year (Y1) and relates the findings to the climatic normals for the lower Mackenzie River basin region. Both years were much warmer than the long-term average, with Y1 being both warmer and wetter than Y2. Six seasons are defined as early winter, midwinter, late winter, spring, summer, and fall. The most rapid changes in the surface energy balance occur in spring, fall, and late winter. Of these, spring is the most dynamic, and there is distinct asymmetry between rates of change in spring and those in fall. Rates of change of potential insolation (extraterrestrial solar radiation) in late winter, spring, and fall are within 10% of one another, being highest in late winter and smallest in spring. Rates of change in air temperature and ground temperature are twice as large in spring as in fall and late winter, when they are about the same. Rates of change in components of the energy balance in spring are twice and 4 times as large as in fall and late winter, respectively. The timing of snowpack ripening and snowmelt is the major agent determining the magnitude of asymmetry between fall and spring. This timing is a result of interaction between the solar cycle, air temperature, and snowpack longevity. Based on evidence from this study, potential surface responses to a 1ЊC increase in air temperature are small to moderate in most seasons, but are large in spring when increases range from 7% to 10% of average surface energy fluxes.
Abstract:In this study, 10 years of summertime data collected at a representative sedge fen in the Hudson Bay Lowland (HBL) are used to investigate the energy and water balance dynamics of subarctic wetlands. The summertime climatic characteristics at the study site during the 10 year study period are also examined. It is shown that mean cumulative summertime precipitation P avg for the study decade closely approximates the 30 year mean P avg . However, the mean summertime air temperature T avg for the study decade is 1°C higher than the 30 year mean T avg .To examine the energy and water balance dynamics at the study site, the variation in each of their respective components throughout the study decade is considered. Little variation is observed in cumulative summertime net radiation Q Ł cum and cumulative summertime ground heat flux Q Gcum ; however, substantial year-to-year variation is evident in cumulative summertime water deficit WD cum , cumulative summertime precipitation P cum , cumulative summertime sensible heat flux Q Hcum , and cumulative summertime latent heat flux Q Ecum . It is noted that the variability in Q Ecum is particularly significant because it consumes the largest proportion of the available summertime energy, and is the largest component of the summertime water balance at this subarctic wetland.Past research has suggested that Q Ł , P, and T have the most influence on summertime Q E at high-latitude wetlands. To test this hypothesis at our study site, Q Ecum , P cum , T avg and Q Ł cum from each year in the study decade were examined. It is observed that high Q Ecum is associated with high P cum , T avg and Q Ł cum , and that low Q Ecum is associated with low P cum and T avg . To identify the hydroclimatological variables that are most responsible for controlling Q Ecum dynamics at the sedge fen, a stepwise linear regression was performed. This analysis indicates that P cum and Q Ł cum are the most important hydroclimatological controls over Q Ecum . However, it is demonstrated that the variability in P cum is more responsible than the variability in Q Ł cum for the variability in Q Ecum during the study decade because of its higher coefficient of variation. The results of this study have broader applicability to wetlands in other parts of the subarctic ecoregion, including the Mackenzie River Basin (MRB). For example, past studies have shown similarities in the energy balance regimes at wetland sites from the HBL and MRB.
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