Seasonality in the Surface Energy Balance of Tundra in the Lower Mackenzie River Basin

Abstract

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.

Parameterization of Lakes and Wetlands for Energy and Water Balance Studies in the Great Lakes Region*

“…Thus, lakes and wetlands significantly changed the partitioning of precipitation to ET and total runoff within the study domain. Similar results were identified by Bowling and Lettenmaier (2010) and Rouse et al (2008) for modeling and observations based studies, respectively.…”

“…As ET increased, annual average total runoff decreased from 35%-31% with the inclusion of lakes and wetlands. Rouse et al (2008) reported similar characteristics (i.e., more ET and less total runoff) for lake/wetland dominated regions in the central Mackenzie River basin, relative to upland areas. During the summer, the water balance deficit in the lake-dominated region was increased twofold during the dry years (Rouse et al 2008) compared to average conditions.…”

“…Rouse et al (2008) reported similar characteristics (i.e., more ET and less total runoff) for lake/wetland dominated regions in the central Mackenzie River basin, relative to upland areas. During the summer, the water balance deficit in the lake-dominated region was increased twofold during the dry years (Rouse et al 2008) compared to average conditions. This suggests that effects of lakes and wetlands on the surface water balance could be more substantial (depending on season) under changing climatic conditions.…”

“…Lakes and wetlands altered the simulated partitioning of energy balance components with 6% higher LH and 5% lower SH with lakes represented. Rouse et al (2008) observed a 59% increase in LH and 61% decrease in SH for lake surfaces relative to land surfaces in central Canada. The simulated results for a domain with maximum water extent on the order of 20% seem comparable.…”

“…Water stored in lakes and wetlands helps to control land surface temperature and energy fluxes Rouse et al 2003;Lofgren 1997;Eaton et al 2001;Bonan 1995;Coe and Bonan 1997). Specifically, lakes and wetlands decrease summer temperatures, increase winter temperatures (Bonan 1995), and reduce daily air temperature variability (Hostetler et al 1993).…”