Daily Temperature Extremes and Precipitation across Indiana over a 120-Year Period

Abstract

A database of daily maximum and minimum temperatures recorded at 17 sites across Indiana from 1 September 1897 through 31 August 2018 shows relatively warm and cool periods alternating over decadal timescales. Average values in all 17 stations were computed over 20-year intervals in order to smooth out year-to-year variability. These intervals reveal an underlying pattern in daily extreme temperatures. The
spread from the coolest 20-year period to the warmest is 1.1–1.28 C for both the mean daily maximum and minimum temperatures. Relatively warm daily maxima and minima exist in the 40-year interval 1918–1958, followed by cooler temperatures during the next two decades ending in 1978. Annual mean maxima and minima over the years 1998–2018 are warmer than in the previous 20-year period, 1978–1998, but still cooler than the peak reached earlier in the 20th century. However, when viewed over three-month intervals, daily temperature minima for March-May and June-August during the most recent 20-year period are the warmest in the record. The same is true for daily temperature maxima in March through May. However, 20-year mean daily temperature maxima for June through August have remained stable over the past 60 years. Timeintegrated precipitation amounts for the 17-station composite increased during the second half of the 20th century. Twenty-year mean annual precipitation for the period 1998–2018 is 12–13% above corresponding values for 1938–1978.