Heat waves in Finland: present and projected summertime extreme temperatures and their associated circulation patterns

Abstract

The number and intensity of individual hot days affecting Finland in the current and future climate is investigated together with the circulation patterns associated with the hot days. In addition, the number, length and intensity of heat waves lasting at least 3 days is also considered. ERA‐Interim reanalysis data and both direct model output and bias‐corrected data for historical and future climate [representative concentration pathway 4.5 (RCP4.5) scenario] simulations from 17 global climate models are analysed. Three intensities of heat waves and hot days are defined based on daily mean temperature thresholds of 20, 24 and 28 °C. The percentage of summertime days which exceed these temperature thresholds is shown to increase in the future. In ERA‐Interim, 24% of summertime days in southern Finland exceed the lowest temperature threshold while none exceed the highest temperature threshold. Under the RCP4.5 scenario these values increase to 47 and 1%, respectively. Larger relative changes occur in northern Finland. Heat waves are also longer in the RCP4.5 simulations than in the historical simulations. In southern Finland, the mean length of a heat wave where the 20 °C daily mean temperature is exceeded is 6.1 days in the historical simulations but increases to 9.4 days in the RCP4.5 simulations. The hot days in both northern and southern Finland are associated with a statistically significant positive pressure anomaly over Finland and to the east to Finland and a statistically significant negative pressure anomaly over Russia between 90 and 120°E. These pressure anomalies were evident for all intensities of hot days in the current climate and the future climate. The magnitude of the pressure anomalies increases as the daily mean temperature threshold increases. However, for hot days which exceed the same daily mean temperature threshold, the pressure anomalies are weaker in the RCP4.5 simulations than in the historical or ERA‐Interim data.

Response of Urban Heat Stress to Heat Waves in Athens (1960–2017)

“…It is known that literature lacks a universal definition of HWs (e.g., [16]). The use of upper percentiles in T max and the choice of the least duration of three consecutive days in the adopted definition is consistent (or more strict) with definitions used in other relevant studies [41][42][43][44].…”

The summer 2018 heatwave in Finland

“…This result resonates somewhat with the results of Kim et al . (), who analysed climate model projections and concluded that the relative change in heatwave duration and occurrence in Finland was larger for northern Finland than southern Finland (they did not consider the magnitude of temperature anomalies). The positive temperature anomalies in May and July 2018 were found to extend throughout the whole depth of the troposphere, from the surface up to ~10km.…”

Heat waves in Berlin and Potsdam, Germany – Long‐term trends and comparison of heat wave definitions from 1893 to 2017

“…In Europe, for example, HWs cause more human fatalities than any other natural hazard (period 1998–2009; European Environment Agency (EEA), ). As many studies have shown, the occurrence of HWs has increased until today (e.g., Alexander et al ., ; Moberg et al ., ; Della‐Marta et al ., ; Perkins et al ., ; Russo et al ., ; Kim et al ., ; Piticar et al ., ). Other studies show further increase for the coming decades in HW frequency, duration, and magnitude due to projected global climate change (e.g., Meehl and Tebaldi, ; Beniston et al ., ; Koffi and Koffi, ; Fischer and Schär, ; Russo et al ., ; ; Zacharias et al ., ; Kim et al ., ; Lhotka et al ., ).…”