Possible impacts of anthropogenic aerosols on water resources of the Jordan River and the Sea of Galilee

Insights are provided to the hitherto unexplained decreasing trends in the available water for consumption from the Sea of Galilee and in the outflow of the main springs of the Jordan River with respect to the nearby rainfall. The loss of available water of about 110 million m³ yr^-1 (about 6.5% of the national water consumption in Israel) is shown to be caused by a decreasing trend in the factor of precipitation enhancement by uplifting on topographic barriers. Previous studies, reviewed here, show that the most probable cause of this decreasing trend is an increasing trend in the concentrations of submicron air pollution particles during the last half century. These particles slow down the conversion of cloud drops into raindrops and snow flakes, thus decreasing precipitation from short-lived clouds such as form in moist air that crosses topographic barriers. This decreasing trend was partially mitigated by cloud seeding for rain enhancement, but apparently, the air pollution dominated and caused a net loss of orographic precipitation. A large portion of the water resources in this semiarid part of the world results from orographic precipitation. Therefore this is an issue with major economic and societal implications, not only to the study area but to many other densely populated parts of the world where the livelihood of the inhabitants depends on water resulting from orographic precipitation, which might be compromised by the air pollution produced by the very people who depend on that water.