Dynamics of evaporation from saline water bodies

Abstract

The sensitivity of evaporation from saline solutions resulting from a variation in their salinity/activity coefficients (β) is investigated. The calculations are based on a theoretically derived parameter (γ = ∂T/∂β), which accounts for the temperature change following a departure in the salinity/activity coefficient. Results reveal that γ is a function of saline temperature, the level of the activity coefficient, and the transfer coefficients for water vapor and sensible heat. For a transfer coefficient of 15 W m−2 kPa−1, γ ranges from ≈−6 K for a saline temperature of 5°C and activity coefficient of 0.95 to ≈−27 K for a saline temperature of 40°C and activity coefficient of 0.4. The present formulation provides a robust method that can be used to identify lower and upper theoretical limits for the variations of saline temperatures, and also to derive the departures of the activity coefficient and evaporation rates for saline solutions from routine meteorological observations only. Calculations with the Penman equation reveal that the aerodynamic term is the most sensitive parameter influencing evaporation from saline solutions following a departure in their salinity/activity coefficients, with a contribution ranging from ≈50%–65% of total annual evaporation departure. Alterations to net radiation following a variation in β accounts for a contribution of about 25% of total annual change in evaporation.