EVALUATION OF 11 EQUATIONS FOR DETERMINING EVAPORATION FOR A SMALL LAKE IN THE NORTH CENTRAL UNITED-STATES

Eleven equations for calculating evaporation were compared with evapor ation determined by the energy budget method for Williams Lake, Minnes ota. Data were obtained from instruments on a raft, on land near the l ake, and at a weather station 60 km south of the lake. The comparisons were based on monthly values for the open-water periods of 5 years, a total of 22 months. A modified DeBruin-Keijman, Priestley-Taylor, and a modified Penman equation resulted in monthly evaporation values tha t agreed most closely with energy budget values. To use these equation s, net radiation, air temperature, wind speed, and relative humidity n eed to be measured near the lake. In addition, thermal surveys need to be made to determine change in heat stored in the lake. If data from distant climate stations are the only data available, and they include solar radiation, the Jensen-Haise and Makkink equations resulted in m onthly evaporation values that agreed reasonably well with energy budg et values.