Characteristics of Heat and Water Budget of two Arctic Permafrost Sites: Dominant Processes and Observed Changes
Permafrost plays a significant role in the land surface energy and moisture balance, and thus in the climate and hydrologic system. The goal of our group is to establish spatial and temporal linkages between water and energy fluxes at the plot and landscape scales at different permafrost affected ecosystems. We chose typical Arctic ecosystems spanning contrasting bioclimatic zones with different climate and landcover conditions: (i) warm, maritime conditions with low above ground biomass (Spitsbergen) and (ii) cold, continental conditions with medium biomass (Lena River Delta, Siberia). At these sites, automatic weather stations have been operating for more than 10 years. This data record was recently extended with temporally and spatially highly resolved data of eddy covariance and soil thermal stations. Furthermore, longer term climate data (partly dating back to 1911) are available from long term weather stations (Longyearbyen, Svalbard and Stolb Station, Siberia). Spitsbergen has a mild, maritime winter climate due to the influence of the Atlantic currents. The summer ground heat flux ranges between 10 to 30 %. Interannual variation in thickness and duration of the snow cover can be large (for example, the number of snow free days in 2000 was about half compared to 1999), affecting the total amount of energy transferred towards the surface and thus the ground thermal regime. Warming is observed in permafrost temperatures, presumably due to recently warmer winter air temperature and an increase of snow depth. In contrast, the site in the Lena River Delta is characterized by wetland polygonal tundra. Warming is observed in air, but not in soil temperatures. Latent heat fluxes, such as sublimation of snow during spring and evapotranspiration during the summer are important components of the energy balance. During the summer of 1999, the surface became much drier (i.e. the water level of polygonal ponds fell below the surface) due to decreased precipitation input. This resulted in reduced evapotranspiration and increased active layer thaw depths.
Observational Evidence of an Intensifying Hydrological Cycle in Northern Canada
This talk will present an overview of recent trends and variability of river discharge in northern Canada, with a focus on our contributions to the IPY project "Arctic Freshwater Systems". We will first introduce the pan-Arctic domain, with a focus on northern Canada, and its hydroclimatology. Trends and variability in the 1964-2007 annual streamflow for 45 rivers spanning 5.2 × 106 km2 of northern Canada will then be discussed. We will present a trend analysis for the 44-year period that reveals a modest increase in the annual flows, with a recent trend reversal owing to much-above average values recorded over the past decade. Trends in the coefficient of variation computed from 11-year moving windows of annual streamflows exhibit spatially coherent signals with increasing variability across most of northern Canada, excluding some rivers with outlets to the Labrador Sea and eastern James Bay. This study therefore provides observational evidence of an intensifying hydrological cycle in northern Canada.
Permafrost Melt in the Wetland-Dominated Zone of Discontinuous Permafrost - Implications for Basin Runoff
Field studies were initiated in 1999 at Scotty Creek in the lower Liard River basin, NWT, Canada, to improve the understanding and model-representation of the major water flux and storage processes within this wetland- dominated zone of discontinuous permafrost. Over this period, permafrost melt has led to appreciable landscpae change. As a result, permafrost plateaus have been replaced by flat bogs and channel fens. Because these three peatland types have very different functions in the overall cycling and storage of water in the basins of this region, there is good reason to suspect that permafrost melt will lead to changes in basin runoff production. This paper documents the rates and patterns of permafrost loss in this region using a variety of ground-based and remotely sensed measurements. A mechanistic-based conceptual model of landscape evolution is presented that offers insights for water scientists and managers into how the on-going landscape change in this region resulting from climate and human disturbances may influence the basin hydrograph.
Comparison and Analysis of 30-year NCEP/NLDAS Products for the Winter Season
Noah snow physics is upgraded based on the collaboration between NCEP Environmental Model Center Land-Hydrology Group and Hydrological Group of University of Washington by constraining sublimation on snow surfaces, increasing maximum snow albedo and including snow age. The upgraded Noah is used to run 30-year (1979-2008) North-America Land Data Assimilation System (NLDAS) forcing and generate 30-year NLDAS products. Besides the Noah, the NASA Mosaic, the OHD SAC and the Princeton VIC land models were also run for the same period using a common 1/8th degree grid using common hourly land surface forcing. The non-precipitation surface forcing is derived from NCEP's retrospective and realtime North American Regional Reanalysis System (NARR). The precipitation forcing is anchored to a daily gauge-only precipitation analysis over CONUS that applies a Parameter-elevation Regression on Independent Slopes Model (PRISM) correction. This daily precipitation analysis is then temporally disaggregated to hourly precipitation amounts using radar and satellite precipitation. The NARR-based surface downward solar radiation is bias-corrected using seven years (1997-2004) of GOES satellite-derived solar radiation retrievals. The NCEP/NLDAS products from the four land models such as snow water equivalent, snow cover, sublimation, and snowmelt are compared for different time scales from daily to monthly. Observed USGS streamflow is used to assess timing of snowmelt simulation in mountainous regions over the Continental United States (CONUS) and snow cover retrieved from satellite is employed to evaluate the performance of the four models. Water and energy fluxes are analyzed and compared for four models in the winter season.
Spatiotemporal Interaction of Near-Surface Soil Moisture Content and Frost Table Depth in a Discontinuous Permafrost Environment
The ubiquitous presence of frozen ground in cold regions creates a unique dynamic boundary issue for subsurface water movement and storage. We examined the relationship between ground thaw and spatiotemporal soil moisture patterns at three sites (peatland, wetland and valley) near Yellowknife NT. Thaw depth and near-surface soil moisture were measured along a systematic grid at each site. Energy and water budgets were computed for each site to explain the soil moisture patterns. At the peatland, overall soil moisture decreased through the summer and became more spatially homogeneous with deepened thaw, increased subsurface storage capacity, and drying from evapotranspiration. In the peatland and wetland, accumulated water in depressions maintained soils at higher soil moistures for a longer duration than the hummock tops. The depressions had deeper frost tables than the drier hummock tops because the organic mats covering the hummocks insulated the ground and retarded ground thaw. The wettest soils were often locations of deepest thaw depth due to surface ponding and the transfer of latent heat accompanying surface runoff from upslopes. For example, the 3.3 ha wetland received 3.08x105 m3 of surface inflow from a lake with 2.32 kJm-2 of convective heat available to be transferred into the frozen ground over the study period. Soil moisture patterns also revealed preferential surface and subsurface flow routes. The findings indicate that the presence of frozen ground and differential thawing have a diverse and dynamic relationship with near-surface soil moisture content. When the impermeable boundary is dynamic, and controlled by water and energy fluxes, thicker soil layers are associated with higher moisture. This contrasts findings from temperate regions with a fixed impermeable boundary which show that surface soil moisture content can be lower in areas with thick soil.
Investigating groundwater flow and storage within a proglacial moraine in the Canadian Rockies using multiple geophysical methods
Unconsolidated sedimentary deposits like talus slopes and moraines play an important yet largely undetermined role in storing and transmitting groundwater within alpine watersheds. To investigate their subsurface flow regime, and in conjunction with ongoing hydrological and chemical measurements, we have undertaken several geophysical surveys over a characteristic moraine-talus field within the Lake O'Hara alpine watershed, located in Yoho National Park, British Columbia. Here, we present results from multiple electrical resitivity, ground-penetrating radar (GPR), and seismic refraction lines recorded across the toe of a proglacial moraine deposit that is discharging groundwater into a nearby pond. Groundwater chemistry data sampled from the pond indicate separate flowpaths within the moraine that originate from at least three distinct sources. Model inversions of the electrical resistivity lines and the processed GPR profiles allow us to delineate the bedrock topography that underlies the moraine. A topographic depression within the bedrock surface is interpreted to control groundwater flow from within the interior of the moraine-talus field to the pond. By comparing a P-wave velocity tomogram determined from inversion of seismic refraction data with a coincident GPR profile, we show that in places the bedrock exhibits a low-velocity (<2000 m/s) weathering layer of up to 5 m in thickness. A corresponding electrical resistivity tomogram indicates that the weathered layer may be partially saturated with groundwater. Based on our interpreted datasets, we suggest that: 1) the underlying bedrock topography controls much of the groundwater flow through the moraine to the groundwater outlet pond, and 2) the fractured weathering layer of the shallow bedrock has the capacity to store some of this groundwater.
Development of the MESH hydrological model in two Canadian arctic basins
The research network "Improved Processes and Parameterisation and Prediction in Cold Regions" (IP3) intends to improve the scientific understanding of processes and predictions and improve understanding of the ways in which these challenges affect human health and the natural environment in addition to strengthening Canada's scientific capacity. Through this network there are close interactions between researchers in the field examining the hydrological processes and modellers simulating those processes using hydrological models. This study examines the results of this collaboration in two research basins located in northern Canada: Scotty Creek and Baker Creek. The Scotty Creek watershed flows into the Liard River near its confluence with the Mackenzie River at Fort Simpson, it has a drainage area of approximately 150 km2. The watershed consists of a broad peatland complex with islands of sparse woodland, underlain by permafrost, surrounded by channel fens and flat bogs. The Baker Creek watershed is a series of interconnected lakes draining an area of 150 km2 located north of Great Slave Lake. Typical of Canadian Shield drainage basins, the landscape is taiga woodland and boreal forest. The hydrological model MESH, currently being developed by Environment Canada, was used to simulate the hydrological processes in the basins. Results were compared to the detailed field measurements available from the basins for such variables as soil moisture, soil temperature, and snow water equivalent. Based on this comparison, various processes such as the partitioning of flow within a grid square and the contributing area of the basin were modified in the model. These modifications led to an improvement in the MESH simulations and a better understanding of the important hydrological processes occurring in these northern basins.