Why do scientists classify climates according to precipitation instead of relative humidity?

Because it's easier to scale hustle then relative humidity. and high relative humidity and high precipitation rate are the associates. I should know because I grew up in both greater New Orleans, which is subtropical, and the Oklahoma panhandle, which is semi-arid 5% relative humidity or higher is normal in New Orleans. While 6% relative humidity is relatively familiar in the Oklahoma and Texas panhandles.