The Hydrologic Regime At Sub-Arctic And Arctic Watersheds: Present And Projected

Abstract

The wetlands in the Arctic Coastal Plain, Northern Alaska, support a multitude of wildlife and natural resources that depend upon the abundance of water. Observations and climate model simulations show that surface air temperature over the Alaskan arctic coast has risen in recent history. Thus a growing need exists to assess how the hydrology of these arctic wetlands will respond to the warming climate. A synthesis study was conducted combining the analysis of an extensive field campaign, which includes direct measurements of all components of the water balance, with a physically-based hydrologic model forced by downscaled climate projections. Currently, these wetlands exist despite a desert-like annual precipitation and a negative net summer water balance. Although evapotranspiration is the major pathway of water loss, there are multiple non-linear controls that moderate the evapotranspiration rates. At the primary study site within the Barrow Environmental Observatory, shallow ponding of snowmelt water occurs for nearly a month at the vegetated drained thaw lake basin. Modeling studies revealed that the duration and depth of the ponding are only replicated faithfully if the rims of low-centered polygons are represented. Simple model experiments suggest that the polygon type (low- or high-centered) controls watershed-scale runoff, evapotranspiration, and near-surface soil moisture. High-centered polygons increase runoff, while reducing near-surface soil moisture and evapotranspiration. Soil drying was not projected by the end-of-the century but differential ground subsidence could potentially dominate the direct effects of climate warming resulting in a drying of the Arctic Coastal Plain wetlands. A drier surface would increase the susceptibility to fire, which currently is a major part of the Alaskan sub-arctic but not the arctic landscape. High quality pre- and postfire data were collected in the same location in central Seward Peninsula, uniquely documenting short-term soil warming and wettening following a severe tundra fire. Overall, this research concludes that arctic and sub-arctic watershed-scale hydrology is affected by changes in climate, surface cover, and microtopographic structures. It is therefore crucial to merge hydrology, permafrost, vegetation, and geomorphology models and measurements at the appropriate scales to further refine the response of the Arctic Coastal Plain wetlands to climate warming.