What have we learned from over 50 years of artificial rain enhancement experiments and operations in Israel?

A number of experiments and a long period of operational cloud seeding for rain enhancement have been carried out in Israel since the late 1950s. For many years these activities have been considered as the best example of successful attempts to artificially modify the weather. However, since the mid-1990s a number of papers appeared challenging the results of the Israeli experiments. These also followed by a long debate in the literature, leaving unresolved the question about the possible success of such cloud seeding operations.

Recently, the Israeli Water authority, accepting the previous cloud seeding operations as successful, decided to embark on a new experiment, Israel 4. The plan is to basically duplicate the method of operations used since the early 1960s, except shift the seeding lines to take advantage of the possible orographic enhancement east of the old target area.

We decided that before such operations and experiments begin, a complete re-analysis of the results from cloud seeding in northern Israel should be conducted. The analysis covers the period of the randomized Israel II experiment (1969–1975) and the subsequent period (1975 to the present) where operational seeding is being conducted. We analyzed the precipitation data in the north of Israel before and during the seeding period using the double ratio method. In the analysis we stratified the data based on the depth and position of the low pressure systems and the time of the rain during the season, in order to identify the possible effects of these factors on the target/control rainfall ratios. Furthermore, we compared the results with an area to the south that had been unseeded on the seeded days in the north. The lecture will describe the results of the analysis, raising questions about the success of the cloud seeding experiments and operations in Israel during the past 50 years.