HR: 1340h
AN: H33D-1407    [Abstracts]
TI: Daily Energy-Budget and Penman Evaporation From Upper Klamath Lake, Oregon
AU: Janssen, K D
EM: kjanz@pdx.edu
AF: Portland State University, Department of Geology 17 Cramer Hall 1721 SW Broadway, Portland, OR 97201 United States
AU: * Cummings, M L
EM: cummingsm@pdx.edu
AF: Portland State University, Department of Geology 17 Cramer Hall 1721 SW Broadway, Portland, OR 97201 United States
AB: To better constrain the hydrologic budget of Upper Klamath Lake, open-water evaporation rates were calculated on a daily basis from 7-June-03 to 30-September-03 using the energy-budget method. Results show evaporation rates to range from as low as -0.8 mm d^-1 to as high as 10.2 mm d^-1 with an overall average of 4.5 mm d^-1. Monthly evaporation totals compared to land-pan evaporation produced pan-to-lake coefficients of 0.66, 0.70, 0.52 and 0.47 for the months of June through September. Total energy-budget evaporation over the entire period was 525 mm or 14,200 ha-m (0.53 ha-m ha^-1) and was 46 percent of total inflow to the lake. Continuous measurements of hydrologic and atmospheric conditions at the lake used to calculate energy-budget evaporation rates were also used to calculate evaporation rates using the modified Penman method. Results from the two methods were compared in order to evaluate the efficacy of the Penman method to estimate open-water evaporation in a semi-arid, high-steppe climate. Penman evaporation rates overestimated energy-budget evaporation rates by an average of 1.0 ±0.6 mm d^-1 (root mean square error of 1.2 mm d^-1) and were greater than previously determined for lakes in more humid, less windy settings. Overestimates by the Penman method were greatest at Upper Klamath Lake on days with greater wind speeds and larger vapor pressure deficits suggesting that the mass transfer component of the Penman method is too sensitive to drier, windier conditions. Total Penman evaporation was 641 mm or 17,400 ha-m (0.64 ha-m ha^-1) and was 56 percent of total inflow to the lake. Incorporating meteorological data from land-based weather stations near the lake and using more practical methodologies led to energy-budget evaporation rates that overestimated best estimates by an average of 0.1 ±0.7 mm d^-1.
DE: 1884 Water supply
SC: Hydrology [H]
MN: Fall Meeting 2005