The North Slope regional hydrology is characterized by water fluxes and storages expressed in simulations using a spatially-distributed numerical model (Permafrost Water Balance Model, PWBM, Rawlins et al., 2019). Model input and output fields are resolved at a daily time step. The PWBM includes a multi-layer snow model that accounts for wind compaction, change in density due to fresh snowfall, and depth hoar development with time. Runoff is the sum total of surface (overland) and subsurface flow each day. Subsurface runoff occurs when the amount of water in a soil layer exceeds field capacity. Recent modifications included the incorporation of new data and parameterizations for surface fractional open water (fw) cover, soil carbon content, and transient ponded surface evaporation and runoff. Updates to the spatial estimates of fw were drawn from a product derived from brightness temperature (Tb) retrievals from the Advanced Microwave Scanning Radiometer for EOS (AMSR-E) (Du et al., 2017) to parameterize the grid cell fraction of open water (annual average) across the model domain. Properties of near surface organic-rich soils strongly control hydrological and thermal dynamics in the seasonally thawed active layer. We used soil organic carbon (SOC) estimates from version 2.2 of the Northern Circumpolar Soil Carbon Database (NCSCD), a digital soil map database linked to extensive field-based SOC storage data (Hugelius et al., 2014). The PWBM was run in a 50-year spinup over the year 1980 to stabilize soil temperature and water storage pools. This spinup was followed by a 30-year transient simulation over the period 1981–2010, the focus of our analysis. Model calibration is performed to adapt the model and optimize its performances in simulating the water cycle across the study domain and involved the surface transient storage pool and river flow velocity. To simulate river discharge (Q), model estimated R was routed through a simulated topological network (STN) (Vörösmarty et al., 2000) and expressed as a volume flux at each grid cell including coastal outlets of 42 watersheds defined at the 25 km scale draining from Utqiagvik (formerly Barrow) to just west of the Mackenzie River delta. A simple linear routing model was used given the relatively short travel times through the North Slope basins. Water transferred to the downstream grid or exported at the coast is
Qout= S(v/d)
where Qout (cubic meters per second) is grid cell flow downstream, v is flow velocity (meters per second), d is the distance between grid cells (meters), and S is volume of river water (cubic meters). Additional details of the model setup and simulations can be found in Rawlins et al. (2019).
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Rawlins, M. A., Cai, L., Stuefer, S. L., and Nicolsky, D.: Changing Characteristics of Runoff and Freshwater Export From Watersheds Draining Northern Alaska, The Cryosphere, 13, 1–16, https://doi.org/10.5194/tc-13-1-2019, 2019.
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