Air temperature and precipitation, in the words of Chattopadhyay and Edwards (2016), are “two of the most important variables in the fields of climate sciences and hydrology.” Understanding how and why they change has long been the subject of research, and reliable detection and characterization of trends in these variables is necessary, especially at the scale of a political decision-making entity such as a state. Chattopadhyay and Edwards evaluated trends in precipitation and air temperature for the Commonwealth of Kentucky in the hopes that their analysis would “serve as a necessary input to forecasting, decision-making and planning processes to mitigate any adverse consequences of changing climate.”

Data used in their study originated from the National Oceanic and Atmospheric Administration and consisted of time series of daily precipitation and maximum and minimum air temperatures for each Kentucky county. The two researchers focused on the 61-year period from 1950-2010 to maximize standardization among stations and to ensure acceptable record length. In all, a total of 84 stations met their initial criteria. Next, Chattopadhyay and Edwards subjected the individual station records to a series of statistical analyses to test for homogeneity, which reduced the number of stations analyzed for precipitation and temperature trends to 60 and 42, respectively. Thereafter, these remaining station records were subjected to non-parametric Mann-Kendall testing to assess the presence of significant trends and the Theil-Sen approach to quantify the significance of any linear trends in the time series. What did these procedures reveal?

For precipitation, Chattopadhyay and Edwards report only two of the 60 stations exhibited a significant trend in precipitation, leading the two University of Kentucky researchers to state “the findings clearly indicate that, according to the dataset and methods used in this study, annual rainfall depths in Kentucky generally exhibit no statistically significant trends with respect to time.” With respect to temperature, a similar result was found. Only three of the 42 stations examined had a significant trend. Once again, Chattopadhyay and Edwards conclude the data analyzed in their study “indicate that, broadly speaking, mean annual temperatures in Kentucky have not demonstrated a statistically significant trend with regard to time.”

Given such findings, it would seem that the vast bulk of anthropogenic CO2 emissions that have been emitted into the atmosphere since 1950 have had little impact on Kentucky temperature and precipitation, because there have been no systematic trends in either variable.

Reference

Chattopadhyay, S. and Edwards, D.R. 2016. Long-term trend analysis of precipitation and air temperature for Kentucky, United States. Climate 4: 10; doi:10.3390/cli4010010.