China Vows to Stop the Rain
Since the Olympic stadium doesn't have a roof, the Beijing Meteorological Bureau has been given the task of making sure the games remain dry. According to Zhang Qian, head of weather manipulation (best title to have on a business card ever) at the bureau, they've had success with light rain but heavy rain remains tough to control. I see a hurricane cannon in some lucky country's future.
He always wanted to know "who'll stop the rain?" The Chinese.
P226
Not exactly 'new' tech...the silver iodide version's been around forever, and the liquid nitrogen version doesn't sound particularly revolutionary.
It does, however, go along with the Chinese cultural desire to control the elements, which heretofore has been embodied mostly with the rivers--the legendary "Yellow Emperor" was the first to stop the flooding of the Yang Tze; the current government has thrown massive resources into the Three Gorges dam. Controlling the rivers has been traditionally (as far as I recall, anyway) seen as evidence of controlling the land, and thus of being a legitimate government.
Controlling the rain, then, would be an extension of this.
In Xanadu did Kubla Khan
A stately pleasure dome decree
They don't actually *stop* the rain. It's most likely cloud seeding and similar... removing all the water from the clouds by making it fall early one way or another. Now, large scale weather manipulation is bad... but a few weeks in one city isn't going to hurt anything. Yea yea, butterfly effect and all... but also dynamic equilibrium.