Surface-Atmosphere Moisture Coupling in Eurasian Frozen Ground Regions

Abstract:

Permafrost represents an impermeable barrier to moisture, resulting in a saturated or near-saturated surface layer during the warm season in many continuous and discontinuous permafrost zones. These surface conditions could lead to enhanced convection and precipitation during the warm season, and significant local recycling of moisture. In areas underlain by sporadic or isolated permafrost, or in seasonally frozen areas, the moisture can drain away more readily, resulting in much drier soil conditions. As climate change causes frozen ground degradation, this will thus also alter the patterns of atmospheric convection, moisture recycling, and the hydrologic cycle in high-latitude land areas. In this study, we analyze evaporative fraction (EF) as a proxy for evapotranspiration, and precipitation from the Modern-Era Retrospective analysis for Research and Applications (MERRA-land) reanalysis dataset. We focus on 1979-2012 and document patterns and changes in EF over the Eurasian high latitudes. We find strong, positive April EF trends over the study period, particularly in the Lena River Basin, 80% of which is underlain by continuous permafrost. In fact, these significant positive trends in spring EF are strongest over continuous permafrost across the Eurasian high latitudes, but negative for sporadic and isolated permafrost. In addition, we find a strong, statistically significant relationship between EF anomalies and the probability of subsequent precipitation over the Lena Basin during April. This association therefore suggests a potential land-atmosphere coupling between frozen ground and precipitation. As the permafrost and seasonally frozen ground distribution changes in the future, this will likely have repercussions for the Arctic hydrologic cycle.