In an HEC-ResSim watershed, at least one meteorological station must be defined to model water temperature. HEC-ResSim water quality model allows the user to define multiple meteorological stations. Each meteorological station must contain the following weather information: atmospheric pressure, air temperature, humidity, shortwave radiation, cloudiness, and wind speed.
If local meteorology varies significantly within the model domain, or if the modeled system is large, it is necessary to use multiple meteorological datasets. The Meteorological Dataset Editor (Section 3.3) enables the user to identify a group of met stations and to specify the atmospheric variables that are measured at each station. In an HEC-ResSim water quality model, the meteorological dataset is used by the geometry dataset (linked in the Geometry Editor (Chapter 4) to assign each reach and reservoir to a met station . Each water cell (defined in the geometry dataset) in the water quality model is individually assigned to a particular meteorological dataset (in the Geometry Editor).
A time series of measured solar radiation is preferred. However, if solar radiation observations are not available, a time series of solar radiation may be computed based on the longitude and latitude of the site, the day of year, and the time of day. Note that the station latitude, longitude and standard meridian information (entered in the Station Editor, as described in Section 2.2.3) are required to compute a solar radiation time series. Furthermore, if the weather station (met station) is located close to the river, the longitude and latitude entered should be that of the location of the weather station. If the weather station is remote, or if weather data is compiled from multiple sources, a central longitude and latitude should be used.
Atmospheric pressure is a required input to the water temperature model. If an atmospheric pressure time series cannot be obtained, a value estimated from site elevation may be entered. Although a time series of atmospheric pressure is preferred, if none is available, the local atmospheric pressure is estimated from the reference elevation entered for a meteorological station. The reference elevation should correspond to an average land surface elevation. Note, the reference elevation is set from the Watershed Setup module, from the Station Editor (as described in Section 2.2.3).