Assessing Compound Drought and Heatwave Events in Urban Areas of the Eastern Mediterranean and Middle East Region: A Multivariate Approach Using CMIP6 Climate Model Simulations

Urban areas in the Eastern Mediterranean and Middle East (EMME) region are increasingly vulnerable to droughts and heatwaves, whose frequency and severity are intensified by climate change.This study focuses on Compound Drought and Heatwave (CDHWs) events and assesses their impacts on the urban areas across the EMME region. Climate simulations for the recent past and future (1981 to 2060), derived from CMIP6 models, are utilized under various Shared Socioeconomic Pathways (SSPs) to enable a more comprehensive understanding of socioeconomic and climate interactions. Following the IPCC framework, the CDHW hazard, exposure, and vulnerability are assessed over urban areas in the EMME region, incorporating climatic and non-climatic factors, such as sensitive population groups. Focusing on the hazard component two different approaches are employed: the first detects concurrent exceedances of climate indices, and the second utilizes a copula-based approach to model the dependence structure of the driving variables of drought and heatwaves (i.e., temperature and precipitation), and thus to estimate the bivariate return period from the fitted copula. Copulas are advantageous because they describe the dependence structure between variables in a multivariate distribution independently of the marginal distributions, allowing for a more accurate analysis, including tail dependencies. Drought months are defined using the SPI and SPEI, while heatwave days are identified using the Excess Heat Factor (EHF) and percentile-based indicators based on the daily maximum temperature. The results underscore the importance of considering statistical dependencies between droughts and heatwaves in risk assessments and exhibit that traditional univariate approaches may significantly underestimate the risks associated with CDHW events in urban areas. The study highlights the need for a multivariate perspective to more accurately assess the severity and frequency of droughts and heatwaves and to develop more effective climate adaptation strategies in urban areas.