“The size of rainstorms hitting Los Angeles has been getting bigger over the past 60 years, according to a new report released today by the Environment California Research and Policy Center.“
That much could certainly be true. Cities do heavily influence local weather through a variety of effects – paving absorbing more insolation, trombe wall effect, wind spoiling and so on. This tends to create additional lofting and accentuate local storm activity (may even create local thunderstorms). IIRC studies in Tokyo began highlighting this back in the 1980s.
The environmental advocacy group measured rainfall in the Los Angeles metro area since 1948 and found that a storm large enough to occur only once a year decades ago is now happening every 8.8 months.
Similar trends were seen throughout much of California and nationwide. Overall, California experienced a 13 percent increase in extreme rainstorms and snowstorms between 1948 and 2011, one of 43 states to see statistically significant increases.