Estimates of Freshwater Discharge from Continents: Latitudinal and Seasonal Variations
Abstract
Annual and monthly mean values of continental freshwater discharge into the oceans are estimated at 1Њ resolution using several methods.The most accurate estimate is based on streamflow data from the world's largest 921 rivers, supplemented with estimates of discharge from unmonitored areas based on the ratios of runoff and drainage area between the unmonitored and monitored regions.Simulations using a river transport model (RTM) forced by a runoff field were used to derive the river mouth outflow from the farthest downstream gauge records.Separate estimates are also made using RTM simulations forced by three different runoff fields: 1) based on observed streamflow and a water balance model, and from estimates of precipitation P minus evaporation E computed as residuals from the atmospheric moisture budget using atmospheric reanalyses from 2) the National Centers for Environmental Prediction-National Center for Atmospheric Research (NCEP-NCAR) and 3) the European Centre for Medium-Range Weather Forecasts (ECMWF).Compared with previous estimates, improvements are made in extending observed discharge downstream to the river mouth, in accounting for the unmonitored streamflow, in discharging runoff at correct locations, and in providing an annual cycle of continental discharge.The use of river mouth outflow increases the global continental discharge by ϳ19% compared with unadjusted streamflow from the farthest downstream stations.The river-based estimate of global continental…
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