Ninth International Conference on Permafrost ... - IARC Research

Permafrost, Parameters, Climate Change, and UncertaintyAndrew G. SlaterNSIDC, University of Colorado, Boulder, CO, USADavid M. LawrenceNational Center for Atmospheric Research, Boulder, CO, USAIntroductionRecently observed changes in the state of permafrostare many and varied. Appearance and disappearance oflakes, degradation of ice wedges, and changes in riverchannel morphology are several of the processes that havebeen linked to thawing of permafrost and warming of soiltemperatures. Osterkamp (2007) suggests that permafrost atWest Dock, Alaska, has warmed about 3.7°C since 1976 andmay have warmed greater than 6°C since 1900. While mostmodeling efforts to assess the effects of future climate changeon permafrost and frozen ground indicate that there will besubstantial change, the magnitude and extent of the changeis still uncertain (e.g., Lawrence & Slater 2005; Zhang etal. 2008). Part of the uncertainty in permafrost simulationscan be associated with somewhat external factors such assimulation of snow or specification of soil and vegetationparameters. Here we present a sensitivity study of suchinputs and parameters.MethodsModelA simple analytic model following the method ofKudryavtsev (Sazonova & Romanovsky 2003) was appliedto estimate the current and future state of permafrost. Themodel produces a steady-state solution under the assumptionof constant sinusoidal temperature forcing. The model alsoaccounts for the presence of snow, vegetation, and theorganic matter above the mineral soil. The primary inputsto the model are the mean annual air temperature, annualamplitude of air temperature, and the mean snow depth overthe winter period. Parameters required by the model includesoil texture, so as to compute thermal conductivity and heatcapacity as well as estimates of snow thermal conductivity.The model is applied on a 100 x 100 km EASE equal-areagrid for the region covered by the pan-arctic drainage basins;this region extends down to 45°N in places.DataTemperature data was derived from the ECMWF 40-yearreanalysis project. This data has been shown to produce.Average snow depth and density was obtained as theensemble average from five land surface models (CHASM,CLM, ECMWF, NOAH, and VIC) that had performed 23-year simulations over the region (Slater et al. 2007). Theestimates from the models are more consistent with stationbasedmeasurements than the available passive microwavesatellite data; this is particularly so in the eastern Siberianuplands, where satellite products have known biases.Parameter data for soil texture properties is based on themap of Zobler (1986) and has been used extensively inlarge-scale modeling experiments. To simplify matters andmaintain a conservative estimate of change, soil moisturewas prescribed at 99% of saturation.Figure 1. Analytic model simulation of present-day permafrost. Temperature is in degrees Celsius. Disregard results for Greenland.293