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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . transport processes and allowed simulation of the meteorological and microphysical processes involved in cloud seeding." However, the level-ot- evidence issue regarding estimations of winter orographic cloud seeding effectiveness remains a topic of debate. Objective evaluations of non- randomized operational cloud seeding programs continue to be a difficult challenge. The World Meteorological Organization (WMO) recognized the potential of cloud seeding in favored locations in a statement on the status of weather modification issued in Geneva in June 2001. That statement says under orographic mixed-phase cloud systems: "In our present slate of knowledge, it is considered that the glaciogenic seeding of clouds formed by air flowing over mountains offers the best prospects for increasing precipitation in an economically-viable manner. These types of clouds attracted great interest in their modification because of their potential in terms of water management, i.e. the possibility of storing waler in reservoirs or in the snowpack at higher elevations. There is statistical evidence that, under certain conditions, precipitation from supercooled orographic clouds can be increased with existing techniques. Statistical analyses of surface precipitation records from some long term projects indicate that seasonal increases have been realized.~ Operational cloud seeding programs aimed at enhancing precipitation exist in more than 24 countries (see Figure 1.1). ~ . CountritJ with.UNt cloud 5HCIinl P"'IIJIIIIlIf1 I i i , i i Figure 1.1. Countries with active cloud seeding programs .1