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Base map indicating the locations of the observing networks being installed in California by NOAA/ESRL and partners as part of CA-DWR's EFREP Program.
Base map indicating the locations of the observing networks being installed in California by NOAA/ESRL and partners as part of CA-DWR's EFREP Program.
Map showing observing networks being installed for HMT-West legacy project. Click image for more detail.
EFREP Handout
EFREP handout, click image to download.

HMT-West Legacy Project

During northern hemisphere winters, the western coast of North America is battered by landfalling storms. The impact of these storms is a paramount concern to California, where water supply and flood protection infrastructure are being challenged by the effects of age, increased standards for urban flood protection and projected climate change impacts. In addition, there is a built-in conflict between providing flood protection and the other functions of major water storage facilities in California: water supply, water quality, hydropower generation, water temperature and flow for at risk species, and recreation.

The California Department of Water Resources (CA-DWR) has signed a five-year agreement with NOAA's Earth System Research Laboratory (ESRL). The joint project between CA-DWR, ESRL, and the Scripps Institute for Oceanography (SIO) is part of CA-DWR's Enhanced Flood Response and Emergency Preparedness (EFREP) program. This project builds on research conducted under HMT and will provide CA-DWR with a 21st-century solution to their water management and flood control issues.

Because preceding soil conditions can determine whether a storm produces a flood, soil moisture sensors are being placed at 43 sites across the state. CA-DWR is partnering with SIO to install soil moisture sensors in the upper elevations of CA by taking advantage of existing infrastructure at interagency Remote Automated Weather Station (RAWS) sites. ESRL is installing soil moisture sensors at lower elevation sites and primarily at California Department of Forestry fire station (CalFire) facilities.

Water vapor is the juice that fuels precipitation, and GPS technology provides a viable method of measuring the column-integrated water vapor. Hundreds of GPS receivers exist in California for geodetic science. By installing surface meteorology sensors with the GPS receivers and by upgrading real-time communications, these GPS receiver sites can provide water vapor measurements in real time. ESRL is partnering with UNAVCO, the operators of the Plate Boundary Observatory (PBO) where many GPS receivers already exist, to provide water vapor measurements from 37 locations across the state.

The snow level is also a significant variable with respect to flooding in mountainous watersheds because it determines the surface area throughout the watershed that is exposed to snow versus rain. Engineers at ESRL have invented a new compact, frequency-modulated, continuous wave radar at S-band designed to measure the snow level at much reduced cost compared to the traditional pulsed-Doppler radars used by ESRL scientists for this purpose. These "snow-level radars" are being installed in ten key watersheds across the state.

The winds contained in the low-level jets of landfalling winter storms contribute to the heavy orographic precipitation on the windward slopes of the coastal and inland mountain ranges of California. These jets are often accompanied by enhanced water vapor in the so-called warm conveyor belt of extratropical storms. The narrow band of enhanced integrated water vapor is also referred to as an atmospheric river (AR). ESRL scientists have combined a wind profiler with a GPS receiver and other meteorological sensors to form an AR observatory (ARO). Four coastal AROs are being installed as part of this project.

To take full advantage of the observing networks being installed and to provide advanced lead time of high impact weather, this project involves a numerical weather prediction component using the HMT WRF ensemble. Special display systems that can provide this value-added information in the Weather Forecast Office and River Forecast Center settings are also being implemented. Finally, decision support tools, that will allow water managers and other decision makers to make optimal use of the information, are being developed. Observation and modeling datasets are available on dedicated ESRL web pages. Observation datasets are also available through the NOAA MADIS program and are sent to NWS Western Region with SHEF-encoding.