About OWEN
The Open Water Evaporation Network was developed and funded through a collaboration between the U.S. Bureau of Reclamation, California Department of Water Resources, and the Desert Research Institute. The aim of the network is to improve estimates of reservoir evaporation through continuous and near real-time monitoring of over water weather variables and water temperature. OWEN operates four weather and evaporation monitoring buoys at Lahontan (NV), American Falls (ID), Folsom (CA), and Stampede (CA). Data is freely available and the OWEN data portal allows custom graphing and downloading of variables.
Open Water Evaporation
Evaporation from open water is primarily a function of water temperature, humidity, air temperature, wind speed, stability of the atmosphere, net radiation, water temperature and flow in and out of the water body, and heat storage. Evaporation pans are typically used to estimate lake and reservoir evaporation. However the timing and magnitude of pan evaporation is not representative of actual evaporation from a lake or reservoir due to difference in water temperature, heat storage, wind speed, and many other variables. Freezing conditions also limit the use of pans for estimating evaporation in winter months. Heat storage impacts both the rate and timing of evaporation, and is dependent on the volume, depth, geometry, clarity, and surrounding environment of the water body. Shallow water bodies have smaller amounts of heat storage, whereas deep water bodies can have significant heat storage, creating seasonal shifts in monthly evaporation. By measuring water temperature and radiative and advective drivers of evaporation at each reservoir, enhanced evaporation estimates can be made and provide benchmark datasets to compare gridded weather data and other estimates of evaporation.
Measurements
Over Water
  • Incoming and outgoing short wave radiation
  • Incoming and outgoing long wave radiation
  • Air temperature at two heights
  • Vapor pressure at two heights
  • Wind speed
In Water
  • Thermal infrared water skin temperature
  • Water temperature at depth intervals
Additional information is presented on the Sensors and Measurements page.
Past 7 Days of Selected Data