An Online Chill Calculator for South Carolina Counties Using Maximum and Minimum Daily Temperatures

Highlights An online tool was developed to calculate and plot chill hours, chill units, and chill portions in South Carolina. Calculations are based on hourly air temperatures reconstructed from daily maximum and minimum temperatures. The tool is freely available at https://etcman.shinyapps.io/SC_Chill_App_2022/. Abstract. The buds of temperate perennial plants typically enter dormancy in late fall, remaining dormant throughout winter and early spring. Dormancy is broken, and bloom/leaf-out begins after the plants are exposed to a certain winter chill and spring heat. There is a lack of user-friendly tools that provide winter chill information to local farmers. This study aimed to develop an online chill calculator for South Carolina using daily air temperature data from each county in the state. A website was created that (1) automatically downloads daily maximum (T max ) and minimum (T min ) temperature data from the selected county and date range and (2) calculates and plots the daily and cumulative chill hours, chill units, and chill portions using four chill models. The app reconstructs hourly temperatures (T(t)) from daily T max and T min from the Applied Climate Information System (ACIS). Chill hours are calculated using the T(t)<7.2°C and 0°C<T(t)<7.2°C models, while chill units and chill portions are calculated using the Utah and Dynamic models, respectively. The app results for the years 2019 to 2022 were shown for Spartanburg, Barnwell, and Beaufort counties in South Carolina, with mean annual temperatures of 11.2°C, 13.5°C, and 15.9°C, respectively. The chill results from the four models were linearly and inversely correlated (0.94 = r 2 = 0.99) with the counties’ mean annual temperature. The cumulative chill values from the T(t)<7.2°C, 0°C<T(t)<7.2°C, and Dynamic models all tended to increase and follow similar trends over time. However, the Utah model followed a more erratic trend. Farmers can utilize the new website to easily visualize local chill data enabling them to make informed farming decisions. Keywords: Chill hours, Chill portions, Chill units, Decision support system, Software, Temperature.