How Certain Is Your Uncertainty When It Comes to Rainfall In Managing Sanitary Sewer Overflows

One component of managing wastewater flows through real-time control is accurate current and forecast rainfall. However, precipitation estimates contain uncertainty, especially as the forecast horizon extends further into the future. Rainfall measurement relies on sensors specialized for precipitation monitoring, including weather radar and rain gauges. Rainfall monitoring should be accurate, with forecast horizons consistent with the response time of the urban drainage system. In addition to current or near-real time rainfall estimates from gauge adjusted radar rainfall (GARR), two sources of forecast rainfall will be considered here. One is derived from weather radar, called nowcasting, and the other from Numerical Weather Prediction (NWP) models such as the High-Resolution Rapid Refresh (HRRR) model with hourly intervals out to 18 hours. We review the available resolution and forecast horizons of these products and analyze forecast reliability at spatio-temporal scales relevant to managing sanitary sewer overflows and for making operational streamflow forecasts.