Patterns of river width and surface area newly revealed by the satellite-derived North American River Width (NARWidth) dataset

Abstract:

The total surface area of rivers and streams is a key quantity for estimating gaseous emissions from fluvial networks to the atmosphere. Presently, the most sophisticated evaluations of continental-scale river surface area rely on: 1) calculating river width from digital elevation models (DEMs) by scaling width to upstream drainage area via downstream hydraulic geometry (DHG) relationships; 2) extrapolating river width and length from large to small river basins using Horton ratios; and 3) extrapolating empirical relationships between climate and percentage water cover to from low- to high-latitude basins where hydrologically conditioned topographic data does not exist. Here we use the recently developed North American River Width (NARWidth) dataset to estimate the total surface area of North American rivers and streams. NARWidth is the first fine-resolution, continental-scale river centerline and width database. The database is derived from Landsat satellite imagery and contains measurements of >2.4×10⁵ km of rivers wider than 30 m at mean annual discharge. We find that datasets that estimate river width by applying DHG relationships to DEMs underestimate the abundance of wide rivers and do not capture the widest rivers observed by NARWidth. We attribute these differences to: 1) the tendency of stream gauges to be located at stable, single channel sites, leading to a potential bias of measured river width relative to the representative river width throughout a river’s entire length; and 2) physiographic conditions that are not captured by DHG and can cause substantial deviation from strict width-discharge relationships. We then calculate the total surface area of North American rivers by extrapolating the strong observed relationship between total river surface area and width at different widths (r²>0.996 for 100-2000 m widths) to narrow rivers and streams. We find that the total surface area of North American rivers is ~1.38×10⁵ km² for all rivers wider than 1 m and ~2.30×10⁵ km² for all rivers wider than 0.1 m, values ~32-121% greater than the most robust previous estimate used to evaluate greenhouse gas efflux from rivers. Our estimation of North American river surface area indicates that present evaluations of gaseous emissions from rivers to the atmosphere should likely be revised upwards.