Spatial and temporal variability of freshwater discharge into the Gulf of Alaska

Abstract

A study of the freshwater discharge into the Gulf of Alaska (GOA) has been carried out. Using available streamgage data, regression equations were developed for monthly flows. These equations express discharge as a function of basin physical characteristics such as area, mean elevation, and land cover, and of basin meteorological characteristics such as temperature, precipitation, and accumulated water year precipitation. To provide the necessary input meteorological data, temperature and precipitation data for a 40 year hind-cast period were developed on high-spatial-resolution grids using weather station data, PRISM climatologies, and statistical downscaling methods. Runoff predictions from the equations were found to agree well with observations. Once developed, the regression equations were applied to a network of delineated watersheds spanning the entire GOA drainage basin. The region was divided into a northern region, ranging from the Aleutian Chain to the Alaska/Canada border in the southeast panhandle, and a southern region, ranging from there to the Fraser River. The mean annual runoff volume into the northern GOA region was found to be 792 6 120 km 3 yr 21 . A water balance using MODIS-based evapotranspiration rates yielded seasonal storage volumes that were consistent with GRACE satellite-based estimates. The GRACE data suggest that an additional 57 6 11 km 3 yr 21 be added to the runoff from the northern region, due to glacier volume loss (GVL) in recent years. This yields a total value of 849 6 121 km 3 yr 21 . The ease of application of the derived regression equations provides an accessible tool for quantifying mean annual values, seasonal variation, and interannual variability of runoff in any ungaged basin of interest.

Seasonal flows of international British Columbia-Alaska rivers: The nonlinear influence of ocean-atmosphere circulation patterns

“…However, the mainland portion of the Alaskan panhandle can be only a few tens of kilometers wide, and the larger rivers tend to penetrate the Coast Mountains into the interior, spanning the international border. Most of the region is highly remote, and as a consequence, relatively few transboundary BC-AK rivers have enjoyed long-term hydrometric monitoring, n/a n/a n/a Dease Lake 1192340 58-62 480 −0.8 n/a n/a n/a resulting in only sparse hydroclimatic datasets from this region (e.g., [31,57,79]). US Geological Survey (USGS) and Water Survey of Canada (WSC) streamflow databases were screened for hydrometric stations on the main stems of unregulated transboundary BC-AK rivers having about 25 years or more of year-round daily data collection.…”

“…River flow variability here influences the strength of density-driven coastal currents (e.g., Alaska Coastal Current [72]) and spawning migration survival of transboundary salmon runs (e.g., [26]). Additionally, runoff from these basins into the Gulf of Alaska (GOA), which typically exceeds 150 km 3 year −1 [31,57,60], has the potential to be substantially altered by changes in regional glacier volume [10,42,43] and shifts in the rain/snow fraction of winter precipitation [61,73]. Such climate-driven hydrological variability propagates downstream into coastal marine ecosystems, and the corresponding suite of terrestrial, aquatic, and marine environmental effects are likely to be profoundly seasonal [64].…”

“…This is evident, for example, in the 2013-2015 California drought, which primarily reflects precipitation variations that appear to fall within the envelope of historical variability and processes [49], yet which have caused tremendous water management challenges. Near the BC-AK region, the interannual variability in freshwater discharge into the GOA regularly exceeds 20% due mainly to shifts in precipitation and glacier volume loss rates [31]. Understanding historical flow variability is a crucial first step toward rigorously predicting how watersheds may respond to longer-term climatic shifts, as an accurate portrayal of variability is essential to resolving unaliased trends in a region where hydrologic variability exceeds trend [63].…”

Influence of Basin‐ and Local‐Scale Environmental Conditions on Nearshore Production in the Northeast Pacific Ocean

“…Freshwater discharge was considered as an additional localscale variable representing a terrestrial influence on water column stratification and was estimated using either a spatially explicit discharge model for sites in the Alaska Coastal Current (Hill et al 2015; except the Alaska Peninsula site, which is beyond the domain of the discharge model) or stream 508 gauge data for sites in the California Current. In each case, the watershed for a given study site was delineated by identifying all of the coastal pour points in the marine study site and associated watersheds via use of a digital elevation model (2-arc-seconds' resolution; data available at ned.usgs.gov for U.S. sites and gdex.cr.usgs.gov/gdex for Canadian sites) following established methods for defining hydrography (Jenson and Domingue 1988).…”

“…In each case, the watershed for a given study site was delineated by identifying all of the coastal pour points in the marine study site and associated watersheds via use of a digital elevation model (2-arc-seconds' resolution; data available at ned.usgs.gov for U.S. sites and gdex.cr.usgs.gov/gdex for Canadian sites) following established methods for defining hydrography (Jenson and Domingue 1988). When the discharge model was used to estimate monthly freshwater discharge, the mean monthly discharge from a study watershed was extracted from the model (Hill et al 2015) for the years 1980-2010.…”