Observations of Evapotranspiration in the Russian River basin, California

Abstract Observations of Evapotranspiration in the Russian River basin, California Robert Zamora1; Chengmin Hsu2; Lynn Johnson3; and Rob Cifelli1 1NOAA Earth System Research Laboratory, Physical Science Division, Boulder, Colorado, USA 2Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder / NOAA Earth System Research Laboratory, Physical Science Division, Boulder, Colorado, USA 3Cooperative Institute for Research in the Atmosphere, Colorado State University / NOAA Earth System Research Laboratory, Physical Science Division, Boulder, Colorado, USA

The NOAA Hydrometeorology Program (HMT) in collaboration the California Department of Water Resources has deployed a network of soil moisture observing stations in the Russian River basin. The basin encompasses 1,485 square miles within Sonoma and Mendocino Counties, California. The soil moisture observations have been used to investigate the hydrological response of the basin to heavy wintertime precipitation associated with land falling atmospheric rivers (ARs) during the winter-spring seasons, and in the evaluation of the Sacramento Model Heat Transfer (SAC-HT) soil moisture parameterization used by the NOAA National Weather Service Office of Hydrologic Development Research Distributed Hydrological Model (HL-RDHM). Evapotranspiration is a crucial process that must be accounted for in hydrological modeling. Evapotranspiration is controlled by both surface meteorological forcing, canopy, and soil water storage. Thus, is advantageous to have collocated in-situ observations of net radiation, sensible, latent, and ground heat fluxes when evaluating hydrological models. The HMT program recently added such observing capability to one of the observing sites located near the headwaters of the Austin Creek tributary of the Russian River. The site is located 15 km northwest of Cazadero, CA. Beginning in May 2012 soil moisture and temperature probes were added at depths of 5, 20, 50 and 100 cm. Probes at 10 and 15 cm have been in place since December 2008. A sonic anemometer, and fast response gas analyzer were installed at the 9-m level of a tall tower. A suite of radiometers capable of making high-accuracy surface radiative flux observations became operational, in addition to ground heat flux plates. In this paper we will discuss the instrumentation used, the component summation method of measuring downwelling solar insolation, and provide a preliminary look at surface energy balance estimates made at the site with a focus on evapotranspiration. Finally we will compare the flux observations with the climatological averages used by HL-RDHM along with simulations of streamflow, and soil moisture. Key Words: evapotranspiration, soil moisture, distributed hydrologic modeling, Russian River basin, surface energy balance