A new definition of heat waves under climate change

Abstract

For the last few decades, changes in frequency, intensity, and duration of extreme climate events have been detected, and these observations are linked to human-induced climate change. To state the amount of change in these extreme events is difficult, due to many variables such as internal modes of climate variables and land use changes. Also, because of rarity of reliable climate records and extreme climate events, taking the data of climate extremes which occurred in the past into consideration is risky. The definition of an extreme event is a rare occurrence, so their records are not abundant [1]. Since the meaning of extreme can change from region to region, generic explanations must be comparative with its own values. In this study, changes in heat index (HI) and wind chill index (WCI) values are stated, according to RCP 4.5 and RCP 8.5 scenarios, and analyzed by comparing each city by its own former data. This study covers ten most crowded cities in MENA (Middle East and North Africa) region: Alexandria, Amman, Ankara, Baghdad, Cairo, Istanbul, Izmir, Jeddah, Riyadh, and Tehran. The aim of this study is to assess frequency, intensity and duration changes in index values for these cities. To achieve that, four definitions are made for each index: extremely hot days, hot days, cold days, and extremely cold days. Firstly, the total counts of each term from past and model outputs are compared to observe the change in frequencies. Secondly, consecutive day counts are compared between past values and model outputs to assess the differences in duration. As a result, according to both RCP 4.5 and RCP 8.5 scenarios, number of hot days and number of extremely hot days will increase in future. Also, their durations will be longer and their observed values will be higher for each city. Nevertheless, increase rate of frequency, intensity, and duration will vary in each city.