A roof pond with gunny bags floating on water surface (RPWGB) has been proven to be an efficient evaporative based cooling technique in the previous studies of the authors due to the creation of thermal stratification inside the pond. In this paper, a mathematical model is developed for the investigation of its cooling performance as compared to a roof pond with a movable insulation (RPWMI) under hot dry climatic conditions. This one-dimensional model is based on the new empirical correlations of water evaporation rate from a wetted surface and a free water surface to the ambient air proposed by the authors, and takes into account the response of buildings as a whole to evaporative cooling. Results by simulations indicated that RPWGB performed slightly better than RPWMI, which is widely considered as the most efficient evaporative based roof cooling techniques, except when they are applied to a building: with poorly insulated light walls and roof. (c) 2004 Elsevier Ltd. All rights reserved.