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I heard (example article) that the Chinese government caused it to rain before and during the Olympics to reduce pollution levels.
Does reliable technology currently exist that could trigger rain within a reasonable area and does technology exist that would dissipate rain clouds and prevent it from raining?
The biggest study I can find concludes that it is ineffective:
In the most comprehensive reassessment of the effects of cloud seeding over the past fifty years, new findings from Prof. Pinhas Alpert, Prof. Zev Levin and Dr. Noam Halfon of Tel Aviv University's Department of Geophysics and Planetary Sciences have dispelled the notion that seeding is an effective mechanism for precipitation enhancement.
'Cloud Seeding' Not Effective at Producing Rain as Once Thought, New Research Shows
It's a hard problem to decide though - effectively "hypothetical meteorology" i.e. you must decide when, where and how much would it have rained anyway, had you not done anything.
Other peer-reviewed studies have come to a different conclusion:
a 2010 study by Bernard Silverman, a consulting meteorologist based in Colorado, published in the peer-reviewed journal Atmospheric Research. Silverman reviewed 11 Sierra Nevada cloud-seeding programs and found that six were successful in boosting streamflow. In the remaining five, the evidence was not conclusive whether they were successful.
Cloud seeding, no longer magical thinking, is poised for use this winter
In summary: No, a reliable technology does not exist. It's still unclear, despite several scientific studies, how effective the technology is. It might still useful, at least in some situations, but we can say for sure it's not yet "a reliable technology".
