Can we reduce the hail problem?
The magnitude of the hail problem in New Zealand is considered. Although there is less hail damage than in some other countries, the cost is likely to increase as the area used for horticulture increases. Methods of abating hail damage by the use of protective devices are discussed. Applications of an improved hail climatology are considered. Two methods of suppressing hail that have been widely used overseas are reviewed. One method involves the seeding of cloud with silver iodide, or other substances, that are intended to promote freezing of supercooled water at temperatures higher than those at which cloud water freezes naturally. It is shown that carefully designed scientific experiments have not demonstrated any reduction of hail resulting from cloud seeding. However there is evidence that many hail suppression operations in various parts of the world appear to have reduced hail damage. Hail cannon, which are now being introduced to New Zealand, belong to a class of attempted hail suppression methods based on explosives. Possible mechanisms for their claimed success are reviewed. The lack of firm scientific evidence for their efficacy is demonstrated.