Heat waves analysis and the heat load of agricultural workers during the heat waves in 2017 (using index WBGT)

Abstract

Workers in agriculture are regularly exposed to heat stress during summer, which can affect reduced labour productivity and income losses. Air temperatures in Slovenia have been rising in recent decades, and climate change projections show that this trend will continue along with an increase in the number of days with heat stress risk. Changes in the number of heat waves in central and south-western Slovenia for the period 1961–2017 were analysed as well as the risk of the heat stress for workers during heat waves in the year 2017. The heat wave occurs if the temperature threshold for the average daily temperature is reached or exceeded on at least three consecutive days, with the threshold for the mild continental climate (Ljubljana) 24 °C and the mild Submediterranean climate (Bilje) 25 °C. The WBGT (Wet Bulb Globe Temperature) index, assessing the risk of heat stress, was calculated from relative humidity and air temperatures. At both locations, the number of days in heat waves increased as well as their intensity, average daily air temperatures were significantly higher than in the first half of the considered period. The time span, in which the heat waves occur, also extended, as until 1990 they did not appear in early June and late August, as in recent years. The calculated values of the WBGT show that for most days in the heat waves in 2017 in Ljubljana and Bilje, the WBGT 23 °C threshold was exceeded practically all day, which shows a high level of heat stress risk for physically intense work. In the case of exceeded WBGT reference values, employers or farmers themselves should take actions to reduce the risk of heat stress.