Evaluation of terms in the energy budget is an integral part of the prediction of thermal changes in natural water bodies. The net advective heat flux is often zero, in which case the radiation components are the dominant causes of temperature changes. Predictive methods for the two radiation components have been developed as a function of meteorological parameters alone, (e.g. temperature, humidity, cloudiness, opaqueness). These predictive methods can be used in areas where there are no records of radiation measurements since the required meteorological variables are commonly measured at weather stations and airports. A better predictive equation was found for shortwave radiation than for longwave radiation, due possibly to local climatic conditions and possible errors in portions of the longwave radiation measurements. Use of the shortwave equations in evaluating temporal temperature changes in a Florida lake resulted in good agreement with measured values. (Author)