The factor that dominates the climate regime during the warm season in the Levant region is the Mediterranean Sea. Field observations of air and surface temperatures, relative humidity, solar radiation and wind were carried out around a 4-hectare pond in Begin Park, in the city of Tel Aviv, Israel, during the daytime hours of the warm season. Observations were carried out at screened meteorological stations on four randomly selected days, all associated with moderate heat stress. Two of them, one representing a warm, dry day and the other a sultry day, were analyzed in detail.

A decrease in temperature combined with an increase in relative humidity was observed on the downwind side of the pond, resulting in a net decrease in the Heat Stress Index (HSI) all four days. The observed temperature deviations of 1.5–1.60C thus reflect a significant climatic effect of this body of water, even though the body of water is very small. However, no significant change was noted in the water vapor pressure during most of the daytime hours. A positive relationship was found between the lake effect and wind speed in both types of weather. The maximum effect was observed at midday, when this factor was at its strongest, when an HSI depletion of 0.8–1.1 units was reached.

It is suggested that the temperature drop induced by the pond during the warmest hours of the day was mainly the result of a truncation of the sensible heat flux when the air that previously passed over hot surfaces swept over the relatively cool water. During the evening hours, when the temperature of the water and of the surfaces of its surroundings became equalized, latent heat cooling due to evaporation became the dominant source of the lake effect. It is concluded that even small bodies of water have a relieving effect on humans in the daytime hours under both dry and humid hot weather conditions.