Evaporative cooling is especially effective in hot dry climates. Temperature drops of 30 to 40 degrees are rather easy to achieve. It is not too unusual to achieve lower temperatures with evaporative cooling than with mechancial refrigeration during very low humidity periods due the lowered performance of mechanical refrigeration equipment in these conditions. In the Southwest, it is a common practice to use both methods. Evaporative cooling can be used during the hot dry periods and mechanical refrigeration during high humidity periods.
Most homes have an evaporative cooler and an air conditioner on the roof.
Evaporative cooling can be successfully used anywhere the wet bulb temperature is lower than the dry bulb which is almost everywhere. The Middle East is an excellent example of the ideal climate for evaportive cooling. This mentality views this technology as if it had not progressed any during the past 60 or 70 years. A heat stratification layer will form at the roof level which will not adversely affect the cooling process provided that space is not used. Remember cold air drops and hot air rises.