ALBERT

Description: We present a generalized version of SnowTran-3D (version 2.0), that simulates wind-related snow distributions over the range of topographic and climatic environments found globally. This version includes three primary enhancements to the original Liston and Sturm (1998) model: (1) an improved wind sub-model, (2) a two-layer sub-model describing the spatial and temporal evolution of friction velocity that must be exceeded to transport snow (the threshold friction velocity) and (3) implementation of a three-dimensional, equilibrium-drift profile sub-model that forces SnowTran-3D snow accumulations to duplicate observed drift profiles. These three sub-models allow SnowTran-3D to simulate snow-transport processes in variable topography and different snow climates. In addition, SnowTran-3D has been coupled to a high-resolution, spatially distributed meteorological model (MicroMet) to provide more realistic atmospheric forcing data. MicroMet distributes data (precipitation, wind speed and direction, air temperature and relative humidity) obtained from meteorological stations and/or atmospheric models located within or near the simulation domain. SnowTran-3D has also been coupled to a spatially distributed energy- and mass-balance snow-evolution modeling system (SnowModel) designed for application in any landscape and climate where snow is found. SnowTran-3D is typically run using temporal increments ranging from 1 hour to 1 day, horizontal grid increments ranging from 1 to 100 m and time-spans ranging from individual storms to entire snow seasons.

Description: The consistency of long-term yearly precipitation and runoff trends over the largest Arctic watersheds (Ob, Yenisei and Lena Rivers) is examined. Three gridded precipitation datasets (Climatic Research Unit, University of Delaware, NCEP) are used for comparative analyses with runoff data collected at basin outlets. The results generally demonstrate inconsistency in long-term changes of basin precipitation and runoff. The Yenisei River runoff increases significantly, while precipitation data show mostly negative trends. The Ob River does not show any significant trend either in precipitation or runoff. Positive trend in the Lena River runoff is accompanied by a weak precipitation increase; however, the precipitation increase is not strong enough to support the observed runoff change. The inconsistency identified in basin precipitation and runoff trends suggests uncertainty in both the quality of basin precipitation and runoff datasets, as well as the perceived hydrologic factors impacting runoff change.

Description: This study systematically analyzes long-term (1950-1992) stream temperature records for the major sub-basins within the Lena River watershed in order to describe water temperature regimes over the various parts of the Lena watershed and document significant stream temperature changes induced by reservoir regulation, and by natural variations/changes. The results show that the open water season can be divided into three consecutive stages---"increasing temperature stage" in the early open water season, "stable temperature stage" in the mid-warm season, and "decreasing temperature stage" in the late open water season. Temperature conditions are similar over the Aldan and Upper Lena regions. However, stream temperatures at the Lena basin outlet are up to 8 °C lower than those over the southern sub-basins. This suggests that the latitudinal difference in climatic variables, such as air temperature, might be the major control on stream temperature regime. Results also demonstrate that the reservoir regulation has a strong influence on the regional water temperature regime and change in the regulated sub-basin. Reservoir regulation has increased (decreased) the downstream water temperatures in the Vilui valley during the early (mid) open water season. Trend analyses show consistent warming trends across the entire Lena River basin in the early open water season. This may indicate a response to earlier snowmelt over the Lena River watershed. Trend results also demonstrate that the Aldan tributary, without much human impact, experiences warming (cooling) trends in the first (second) half of the open water season, leading to a stream temperature regime shift toward early open water season. The upper Lena River has warming (cooling) trends in the early (mid-late) open water season. Over the regulated Vilui tributary, however, stream temperatures have significantly increased in the early and late parts of the warm season due to combined effects of natural changes and reservoir regulation. Over the Lena basin as a whole, strong positive correlations have been found between the basin mean monthly air and water temperatures during the warm season. Increasing water temperatures were observed during the early and mid-June. Because of stream temperature increase in this peak flow period, the Lena River heat flux has gone up by 23% in June. This may have considerable impact on the thermal conditions of the Laptev Sea in the early summer season.