Determining the Frequency and Duration of Elevated Temperature-Humidity Index

Extreme temperatures and humidities can be harmful or even fatal to livestock if proper precautions are not taken. An indicator often used to measure stressful conditions is the Temperature-Humidity Index (THI). Using seven years of hourly data from 17 sites in Oklahoma, total annual hours were determined for THI ³ 84 and THI ³ 79 with and without evaporative cooling. To provide a tool to determine the effect of employing evaporative cooling to reduce THI levels, a Poisson loglinear regression model was used to predict the average annual hours that an evaporative cooler could reduce THI levels to below 79 throughout Oklahoma. Predicted rates of THI reduction ranged from 64.3 to 100%.