On the improvements in precipitation, temperature and streamflow forecasts from the Hydrologic Ensemble Forecast Service after upgrading from the GEFSv10 to the GEFSv12

Abstract:

The Hydrologic Ensemble Forecast Service (HEFS) of the U.S. National Weather Service (NWS) has utilized meteorological forecasts from the Global Ensemble Forecast System version 10 (GEFSv10) for medium-range ensemble streamflow forecasting. The recent upgrade to the GEFS (GEFSv12) includes, among others, the Finite Volume Cubed Sphere (FV3) dynamical core and increased spatial resolution. To assess the impact of upgrading from GEFS v10 to v12 on HEFS performances prior to its operational implementation in the NWS River Forecast Centers (RFCs), an evaluation is conducted over a set of 200 testbed basins in the US, which were selected according to representative basin attributes (objective criteria) and feedback from the RFCs (subjective criteria). The ensemble means of the raw meteorological forecasts from both GEFSv12 and GEFSv10 are verified against precipitation and temperature observations from the Analysis of Record for Calibration (AORC). The ensemble meteorological forecasts are post-processed by the HEFS Meteorological Ensemble Forecast Processor (MEFP). The MEFP forecasts are also validated against forcing observations. Finally, we verify ensemble streamflow forecasts generated with meteorological forecasts from the MEFP using forcing inputs from the GEFSv10 and GEFSv12, respectively. Both forcing and streamflow datasets are created via hindcasting for a 31-year period (1989-2019) using the Community Hydrologic Prediction System (CHPS), a software architecture based on the Delft-FEWS platform. The Ensemble Verification System (EVS) is used to produce ensemble verification statistics of precipitation, temperature, and streamflow. This presentation discusses findings from hindcasting and validation experiments and summarizes the impact of upgrading from GEFS v10 to v12 on the quality of the HEFS forecasts.