Global river inflow with Navy Coastal Ocean Model

Abstract

One of the primary concerns driving the development of U.S. Navy global models has been improved performance and nesting support in shelf and nearshore regions with short notice applicability anywhere on the globe. A global implementation of the Navy Coastal Ocean Model (NCOM) is a product of some of the efforts to meet this need. One purpose of Global NCOM is to provide a global capability for initializing, nesting, and evaluating fixed and relocatable coastal ocean models. In support of that objective, a database of river flow estimates is needed. Perry et al. (1996) provides a start with estimates of annual mean river discharges for 981 of the largest global rivers. However, many rivers exhibit a strong seasonal variability, which we would like to reflect in our ocean models. Through the use of multiple Internet sources and published data sets we have expanded on the Perry (1996) data to provide a global database of monthly mean river discharge and incorporated this data in global and nested NCOM runs. Where sufficient data is unavailable to construct monthly means, a seasonal cycle is imputed from nearby rivers and scaled to the appropriate annual mean. Real time discharge rates are routinely available for almost no rivers outside of the United States, so a monthly mean is likely to be the most appropriate estimate of real time flow for analyses and forecasts in most areas. The monthly river outflow can contribute to more accurate seasonal representation of areas near coastlines. Seasonality particularly affects the polar areas, where river outflow can become quite small during winter months and quite large during the summer melting season. Multiannual daily USGS observations for selected US rivers are used to quantify the improvement in estimation of daily flow by the monthly means versus a multiannual mean. Case studies examine the impact of river input into NCOM.