Hurricane/Tropical Storm Hilary dumped a lot of rain (by their standards) across southern California. Looking at Palm Springs, for example, their normal rainfall as of August 22 is 3.21 inches. They got that much from Hilary over the weekend, 3.23 inches. The previous record for the 20th of August was 0.21 inches. They got 10 times that amount on Saturday, over 2 inches. Many other stations reported records the last few days, getting their normal annual rainfall in 48 hours or less.
As I discussed in other posts, desert landscapes don’t handle rain the same way that other regions do. Here in Savannah, GA, we often see event rainfalls of 3 inches in a single event. Aside from a few places (where rather than fix the problem, the city puts up very helpful, permanent “street closed when flooding” signs) it takes a lot more than that to cause a problem. The soils in the high desert can’t handle rain coming down that fast – no matter how much they may “need” the rain, it just runs off, quickly. The arroyos (dry river beds) quickly become destructive torrents, and the situation quickly gets out of hand when human structures get in the way because they were built without taking the unique hydrology of the region in to consideration. Here is a picture I shot while flying over I-10 somewhere east of the also aptly named “Desert Center” … notice the huge diversion channels, to prevent rapid runoff from the desert from undermining the interstate by intercepting the arroyos and routing it to bridges/culverts:
So how bad was it? Not horrific unless it was your house or business that got flooded, but a lot of widely spread damage. I’m seeing over 1000 reports of flash floods and dozens of debris flows and mudslides. Most of these are local inconveniences, but there is significant, scattered damage across the region. Here is a map showing the distribution of the reports, with storm track also shown …
Overall, Hilary probably did cross the Billion dollar threshold of US damage, when all the disruption is accounted for.
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Almost every post you make educates us as well as comforts us, even when we may be in the path of a storm. Knowing what to expect is so much better than guessing.