Aqpi: Systems Requirements for Hydrological Functions

San Francisco Bay (SF Bay) is a highly urbanized estuary and the surrounding communities are susceptible to flooding in inland rivers and creeks that drain to the SF Bay, and along the SF Bay shoreline. An integrated forecast system, Advanced Quantitative Precipitation Information (AQPI), that involves watershed and oceanic drivers is being developed for predicting flooding in the SF Bay area tributaries and estuaries.

This project focuses on the AQPI watershed flood prediction modeling using the National Oceanic and Atmospheric Administration's National Water Model (NWM). The NWM is a distributed hydrologic model which computes the hydrologic balance on a 250 m grid, aggregates excess precipitation to a 1 km grid, and routes these flood flows using the NHD-PlusV2 stream network. The system updates to include USGS gaged flows (-3 to 0 hrs), along with three forecast configurations (short- (0 to 18 hrs; 1-hr update), medium- (0 to 10 days; 6-hr update) and long-range (0 to 30 days; 1-day update). The NWM can provide a variety of flood forecast products, including hydrographs at any location (peak flow, time-to-peak, duration of high flow), and grid displays of soil moisture, snowpack, and ponded water depth. As part of the AQPI, additional products including grids of flood recurrence levels and at-risk bridge crossings will be provided to stakeholders. Various verification analyses are being conducted to characterize the NWM accuracy.

Coordination with Bay area flood response agencies is intended to help assure that the AQPI system products are acceptable and usable. To this end, we are asking local agency leaders to describe how they currently conduct their flood awareness, warning and response activities; how these procedures could be supported by the NWM products; and to review NWM outputs and recommend how these products could be formulated to support their operations. Results of these reviews are presented to reflect how users' assessments are informing design of the real-time AQPI system.