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WMO Precipitation Enhancement Project: 25 years since
 the Site Selection Phase 2

A large group of colleagues and friends gathered in Valladolid, Spain, in May 2005 to remember the project in which they had participated 25 years before and to reflect on the progress of precipitation enhancement science since then. That project was the WMO Precipitation Enhancement Project (PEP).



By the early 1979s, a large number of "rain enhancement" and "hail prevention" projects had been run by several countries and there was a need for some definitive indication of whether they were scientifically justified, or not, as well as guidance on ways to improve the efficacy of such projects.  Recognition of that need and the hope that a well-conducted international project would gain wide acceptance led to the Precipitation Enhancement Project. The project had its origins in deliberations of the Panel on Weather Modification in Toronto, Canada, in 1974, under the chairmanship of Professor Roland List, and was formally established in 1975 by the approval of World Meteorological Congress. The aim of the project was to create a scientifically planned and executed project of precipitation enhancement that could serve Member countries as an example for worldwide practice.  The magnitude of the project was ambitious: US$ 3 million.  The project was placed in the hands of the Intergovernmental Board consisting of representatives of interested countries (W. Godson, Canada; J. Zillman, Australia; B.J. Mason, UK; Y. Israel, USSR; R. Wright and G. Benton, USA).

The Board initiated the search for a suitable site for the experiment by charging a group of prominent scientists that included J. Warner (Australia), A. Gagin (Israel) and E. Bolley and R. Cunningham (USA) to visit potential host countries.  This led to the selection of the site in the vicinity of Valladolid, Spain, and to the Site Selection Phase 2 (SSP2) that became three years of observations (1979-1981) of clouds by aircraft, radar and satellites to determine the potential for augmentation of precipitation by cloud seeding.  No cloud seeding was to take place during this phase, just the assessment of the potential for profitably doing so.

The celebration in May 2005 coincided with the 25th anniversary of the fiesta in the Castle of Fuensaldaa that marked the end of the second (middle) year of the field campaign.  It was also almost 30 years since the formulation of the idea for PEP.

The conclusion of the SSP2 studies was that the potential for significant rain augmentation in the region, during the winter months, was insufficient to warrant a full-scale seeding effort.  Although the result of PEP was negative in that sense, it did, however, serve the useful role of foreclosing an experiment that would probably have failed and, much more importantly, set an example for the logical and non-political planning of weather modification efforts. This aspect of PEP was the keynote of the 25th reunion.

The  project had a significant impact on scientific work and international collaboration within the National Meteorological Institute (INM) of Spain: an aspect of PEP that was manifest in the talks given during the reunion by various directors and group leaders from the INM. 

Gabor Vali et al.







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