Trends in Observed Summer Daily Temperature Maximum Across Colorado

Abstract:

Increases in the anthropogenic greenhouse forcing are expected to increase

the tendency for longer and stronger heat waves in summer. We examine if there is

a trend in the observed daytime extreme temperature (Tmax) during summer

between 1900-2014 at select high quality stations (n=9) across Colorado. We

compile daily observations of Tmax and other variables during summer (JJA), and

derive and analyze trends in five different extreme metrics from this data that

include the maximum five-day Tmax average, warm spell duration index, and the

number of days when Tmax exceeds the 95th, 99th, and 99.9th percentile

conditions. We find that the 1930s and 2000s in Colorado had some outstandingly

hot years, when we also find exceptionally high count of summer Tmax extremes.

Five out of the nine stations show increases in extreme temperature indicators in

the more recent decades. The variability in trends in the daily summer Tmax

extremes across the nine stations correspond with the mean annual warming trends

at those stations. We also find that wetter summers have much smaller instances of

Tmax extremes as compared to drier summers.