Permission has been granted for seeding clouds to generate rainfall in three provinces: Tehran, West Azarbaijan and East Azarbaijan.
The cloud seeding operations which were supposed to be implemented earlier this calendar year (started March 21) were postponed due to the delay in licensing by the Civil Aviation Organization (CAO), said Mohammad Mehdi Javadian Zadeh, head of the National Cloud Seeding Research Center (NACSER), in Yazd Province.
The center has two plans for cloud seeding. Prior permission from the CAO before the aircraft for the operations could take off was required and the license was issued finally on December 28, he said. Cloud seeding operations are to be implemented in 12 provinces including Tehran and some of the provinces in the North, Central Plateau and also West Azarbaijan and East Azarbaijan.
The annual water year in Iran starts on October 1 and ends on September 30 of the next year; the best time for cloud seeding is late November. In fact, the cold clouds which have seed-ability enter the country in late November; therefore the cloud seeding operations were supposed to commence from November 5-10, and continue till early May, IRNA reported.
Delay
Since cloud seeding should be undertaken by specific planes, the clearance from the CAO was required. CAO experts have inspected the planes and issued two licenses. The final permit however was issued late December, he noted, and hence the delay in the operations.
The center is geared up for the seeding operations, the commencement of which depends “on the time of entry of suitable precipitation in the provinces.”
From among the two cloud seeding aircrafts, one has been allocated to Tehran, West Azarbaijan and East Azarbaijan and the other to the country’s central plateau.
Javadian Zadeh emphasized the importance of clouds seeding and said the World Meteorological Organization believes cloud seeding should be considered as an effective strategy along with other water resources management strategies in arid regions. In fact the cloud seeding operation should be conducted on an ongoing basis; it shouldn’t be postponed even in times of water crises.
He also said “all operations are conducted by local manpower, including prediction, operation implementation, and evaluation” and the energy ministry has also agreed with the implementation of cloud seeding.
Precipitation
Cloud seeding process started 60 years ago. It is a form of weather modification which attempts to change the amount or type of precipitation in clouds, by dispersing substances into the air that serve as cloud condensation or ice nuclei, which alter the microphysical processes within the cloud.
The most common chemicals used for cloud seeding include silver iodide, potassium iodide and dry ice (solid carbon dioxide).
Silver iodide can cause temporary incapacitation or possible residual injury to humans and mammals with intense or continued but not chronic exposure. However, there have been several detailed ecological studies that show negligible environmental and health impacts. The toxicity of silver and silver compounds (from silver iodide) was shown to be of low order in some studies.
These findings likely result from the minute amounts of silver generated by cloud seeding, which are 100 times less than industry emissions into the atmosphere in many parts of the world, or individual exposure from tooth fillings.
Accumulations in the soil, vegetation, and surface runoff have not been large enough to measure.
