Equilibrium temperatureTeis the water surface temperature at which net energy exchange to the atmosphere is zero. Since heat loss rate is a function of (Tw−Te), whereTwis the actual water surface temperature, the concept of equilibrium temperature is useful in predicting water temperatures. By selecting a set of equations to describe the heat exchange processes at the surface, one can produce curves of heat exchange rate (excluding shortwave radiation) versus (Tw−Ta), whereTais air temperature. These curves can be approximated by linear functions. The slopesqand interceptsQoof these curves are in turn linear functions of wind speed for a specified set of weather conditions (clear and low humidity or cloudy and high humidity). Specifying these weather conditions, wind speed, air temperature, and net incoming solar radiationQR, one can calculateqandQoand compute the equilibrium temperature asTe= [(QR−Qo)/q[ +Ta. This relation provides a simple yet general means of calculatingTeand can be used to investigate time variations ofTwin response to meteorologic condi