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

Abstract

Heat waves (HWs) are natural hazards characterised by episodes of hot weather. However, in the absence of a universal definition a wide variety of definitions is applied. In this study, ten different air temperature (T) based HW definitions are applied to the urban region of Berlin, Germany, to investigate and compare the occurrence and duration of HWs, and their long‐term trends from 1893 to 2017. We studied how long‐term trends depend on different definition of HWs, as well as if long‐term mean values and trends differ between inner‐city and peripheral locations of Berlin. Generally, results show significant increases in HW occurrence and duration for most definitions, although large differences exist between them. Temporal agreement between the definitions is low, 15 episodes in 125 years are identified by all definitions as HWs. Inner‐city regions of Berlin are subject to more frequent and longer HWs than peripheral regions, if definitions based on daily minimum or mean T are applied. Results also show that trend estimations of HW characteristics for HW definitions with “extreme” values for their detection criteria (e.g., in terms of duration or threshold) are highly sensitive to the applied method. We conclude that depending on the question under investigation, different HW definitions might be optimal and hence attempts for the development of “universal” definitions need to take this into account.

Contrasting changes of urban heat island intensity during hot weather episodes

“…Urban Rural arise when heat wave definitions applying daily minimum or daily mean T are investigated. These contrasts could not be found when using heat wave definitions that apply daily maximum T (Fenner et al 2019). Note that given the diverse findings in other studies concerning UHIIs during HWEs, our findings might not be transferable to other regions, as only one mid-latitude city was investigated.…”

“…Similarly, Fenner et al (2019) showed that in Berlin urban-rural contrasts in heat wave characteristics only Table 1. Mean differences (Δ) in weather conditions between hot weather episodes (HWEs) and normal conditions (NC) during 2015-2018, May-September.…”

“…Since most of these studies applied different methods to identify the subsequently analysed HWEs, it could be hypothesized that the contrasting results are at least partly due to the application of different methods to identify these episodes. The definition of heat waves, as well as whether they are identified at an urban or a rural location, can substantially affect their frequency, duration, and long-term trends (Fenner et al 2019). Further, it could be hypothesized that by applying different methods, both increased and decreased UHIIs during HWEs can be detected, even for a single city.…”

A Consistent Methodology to Evaluate Temperature and Heat Wave Future Projections for Cities: A Case Study for Lisbon

“…They devised a HW hazard index and found that most of the capitals revealed significant positive trends of HW hazard characteristics especially in central-eastern and southeastern Europe. They also concluded that minor index increases were observed in most of the northern capitals and decreases in several northern and especially southwestern cities.Fenner et al [17] applied different HW definitions to study long-term (1893-2017) trends of HW duration and frequency for Berlin. They found a general positive trend amongst HW definitions but with the respective magnitude depending on the definition and trend estimation method.…”

“…Fenner et al [17] applied different HW definitions to study long-term (1893-2017) trends of HW duration and frequency for Berlin. They found a general positive trend amongst HW definitions but with the respective magnitude depending on the definition and trend estimation method.…”