Pretty much exactly what it says on the tin. This is a history, not a science, text. But as a history of rain, it's 100% more interesting than a book on rain would generally sound. Filled with anecdotes that bring the history to life, and raise it a notch above a dry (ha!) academic narrative, once I got past the parts of history I always find slow (ie, any part we have to speculate about) I found it hard to put the book down.
The author tries tackle the subject globally, but generally, it's US-centric (which, if I remember right, she disclaims at the start). There's a certain amount of doom and gloom when she gets to present day human vs. rain (spoiler: rain always wins), but I was incredibly please and very inspired by the stories she told about how certain cities are learning from their mistakes. In a global culture that is so, I'm sorry, collectively stupid about climate change, it often feels like we're being beat about the head with it; we haven't yet figured out that, just as this tactic doesn't work on children, it doesn't work on humanity in general. But a story about people learning from the past and taking steps to remediate the problems - that's what, in my opinion - is going to inspire the long-term change we so desperately need.
She ends the book with the most telling irony - her trip the the rainiest place on the planet, Mawsynram, where she experiences 5 cloud free, sunny days, while back home in Florida her family lives through the rainiest weather in the state's recorded history.
A pleasant, informative and well-written read.