Hydrological responses to precipitation extremes: an investigation of the National Water Model system in the San Francisco Bay Area using AQPI Gap-Filling Radar

It remains a challenge to provide accurate and timely precipitation and flash flood warning information in many parts of the western U.S., including California. Complex terrain combined with sparse observations often result in underestimation or complete misses of extreme precipitation and hydrologic events, especially in small watersheds. The Advanced Quantitative Precipitation Information (AQPI) project is being implemented to improve monitoring and forecasting of precipitation, streamflow, and coastal flooding in the San Francisco (SF) Bay Area. The backbone of AQPI is a gap-filling radar network consisting of a coastal C-band weather radar and four X-band radar units to augment the existing NEXRAD radar network and improve Quantitative Precipitation Estimation (QPE), which is of importance for hydrological applications. As part of the AQPI project, NOAA and the Cooperative Institute for Research in the Atmosphere (CIRA) at Colorado State University are assessing the performance of the gap-fill radar QPE and its impact on streamflow forecasts. This study initially explores the impacts of AQPI radar-based precipitation on the hydrological processes during selected rainfall events in the SF Bay region. The NOAA National Water Model (NWM), built on the WRF-Hydro community modelling system, is implemented for testing the hydrological responses. A set of experiments are conducted on selected watersheds using different rainfall inputs, model initialization approaches, and calibration techniques. The presentation will demonstrate the sensitivity between AQPI radar rainfall extremes and hydrological extremes in the SF Bay Area.