The oasis effect in an extremely hot and arid climate: The case of southern Israel

One of the definitions of the 'oasis effect' is the reduction of temperature in an isolated moisture source surrounded by an arid area. This study examined the existence of the 'oasis effect' and its diurnal dynamics in a rural settlement in the Arava Valley, southern Israel, characterized by an extremely hot and dry climate. The study site included varied types of plant covering: a grove of native desert trees, areas planted with tropical and sub-tropical vegetation (garden trees, bushes and lawn) and date plantations. Experiments were conducted during three consecutive years (2004-2006) for a period of 4 days at the height of summer. Results obtained during all the three summers demonstrate that the settlement created an 'oasis effect', but its intensity was dependant on the combined influences of synoptic conditions, time of day and type of vegetation. During the late night, dawn and early morning, all types of vegetation created a cooling effect; however, this effect was more pronounced with sub-tropical garden vegetation (up to 4 °C) as compared to local desert trees. During the daytime, garden trees caused a weaker cooling effect up to 2 °C, while local desert trees had a warming effect up to 1.0 °C.