Do San Diego engineers under estimate the amount of water that falls during rain events?

Do the engineers here just completely undersize all the drainage systems in San Diego because they assume it doesn't rain much? Do they assume even if it does rain, it's a small amount of water? Is this in an effort to save a money in construction costs?

Or are their calculations and designs just totally wrong. Or for these "larger" rain events do they supposedly say it's a "1 in 1000 year event" so it doesn't need to be adequately sized for that?

All the drainage systems here get totally overwhelmed every time it rains longer than a couple hours.

From public systems to private property.