High-resolution Near-surface Permafrost Modeling for the 21st Century, Wrangell-St. Elias National Park and Preserve, Alaska

Permafrost within most part of Wrangell-St. Elias National Park and Preserve (WRST) is discontinuous and warm i.e. within a few degrees of thawing. It is the physical foundation on which the ecosystems in the park rest. Thawing of permafrost alters this foundation, and can alter ecosystems and landscapes. Nonetheless, the data on permafrost condition and extent within WRST is limited. The current and future permafrost distribution and thickness of active layer can be modeled, given sufficient data about ground properties, vegetation, topography, and climate. We used GIPL 1.0 (Spatially Distributed Model of Permafrost Dynamics in Alaska) model; and downscaled climate forcing from 5 Global Circulation Models (GCM) that work best for Alaska and high-resolution soil landscape and ecotype maps from National Park Service (NPS) as model inputs to develop high-resolution permafrost maps for the recent past (2001-10) and the future decades (2050s and 2090s). The soil landscape and ecotype maps were derived from Landsat TM scenes (Jorgenson et al. 2008). The modeling effort resulted in recent and future permafrost maps of WRST at a spatial resolution of 28.5 m, the best resolution permafrost maps available for any part of Alaska. The model mapped 80% of WRST as underlain by near-surface permafrost during the decade of 2001-10 (Fig. 1) and predicted 50% decrease in the near-surface permafrost extent by 2050s owing to a 2 °C increase in the mean decadal air temperature and slightly higher precipitation. According to the 5 GCM projections, the decadal air temperature will increase by another 2 °C between 2050s and 2090s which will likely cause further increase in the ground temperature and decrease in the permafrost extent. The model predicts a meager 15% of WRST would still remain underlain by near-surface permafrost toward the end of the 21st century. Comparison of the modeled permafrost distribution with in situ observation of permafrost presence/absence at 430 sites showed 95% agreement. Thus, the modeled permafrost distributions are reliable representation of near-surface permafrost extent within WRST. These maps are critical to understand the permafrost condition and to identify the sites vulnerable to thawing. These maps also facilitate informed decision making on resource management. Figure 1: Near-surface permafrost map of WRST (2001-10) at 28.5 m spatial resolution. MDGT is the Mean Decadal Ground Temperature at the bottom of active layer (negative values) or seasonally frozen layer (positive values). The negative and positive MDGT values represent presence and absence of permafrost, respectively.