Climatology of heat waves characteristics based on different metrics- Application on a centennial air temperature record of the eastern Mediterranean

Today, there is a strong scientific consensus that severe weather phenomena and climatic extremes represent an increasing threat in the background of climate change, with profound and unpredictable impacts on the environment, economy and humans.  Heat waves (HWs) in particular, are among the most disastrous phenomena across the globe, imposing significant pressure on human health, with severe heat waves being associated with thousands of excess deaths in the past. Considerable recent research focuses on the study of the main characteristics of HWs (e.g. amplitude, duration or frequency) and their long-term trends, using different approaches and metrics. Such approaches differ with respect to the used climatic index (maximum, minimum, mean air temperature or combination), the use of fixed or dynamic temperature thresholds, the duration and others. The plethora of existing indices in literature and the lack of a universal metric to define HWs is underlined  in most studies.

  This research attempts to investigate how and to what extent are the long-term statistics and trends in HWs characteristics affected by the use of different definitions. The analysis was based on the centennial, uninterrupted records of air temperature of the National Observatory of Athens which constitute a unique material for the study of climatology of HWs in the long-term. Yet, capital cities of the eastern Mediterranean have been assigned as hot spots among other European cities, with respect to future heat-related risk.

The analysis revealed substantial deviations in HWs features among different definitions, as for instance changes in seasonal occurrence of HWs, or an eightfold increase in the number of HWs since the late 19th century, when the six-days minimum duration of HWs was replaced by three-days.

The better understanding of the impact of different HWs indices on their long-term statistics is crucial for better future projections, especially at a vulnerable to heat-related risk area, like the eastern Mediterranean.