Recurrence of Drought Events Over Iberia. Part I: Methodology and Application for Present Climate Conditions

Abstract

Seasonal drought is a typical feature of the Mediterranean climate that may lead to strong socioeconomic and ecological impacts. We investigate the occurrence and intensity of historical extreme drought events over the Iberian Peninsula (IP) for the past decades, with special focus on recurrent drought events. With this aim, we introduce and apply a new set of indices: The Recurrent Dry Year Index (RDYI) and the Consecutive Drought Year (CDY) Index. Additionally, three drought indices are considered for individual events: A simple Drought Index (DI) based on precipitation deficits and the number of affected grid points, the Effective Drought Index (EDI), and the Standardized Precipitation Index (SPI). Different gridded observational (E-OBS V20e, IBERIA01) and reanalysis datasets (ERA5) are analysed at several spatial resolutions, ranging roughly between 10km and 25km. Results show that extreme droughts are a common feature in the IP, with roughly three individual events per decade. Especially the southern and central parts of IP are exposed to recurrent events. These events typically last two to three years, but may reach a length of six consecutive years. Sensitivity in the number of drought years is found regarding the spatial resolution. Moreover, drought is identified more often with EDI, leading to an enhanced number of recurrent droughts. (Recurrent) Droughts in IP are driven by precipitation deficits in winter (rainiest season) as there is hardly any precipitation during summer over most of IP. Still, deficits in spring and autumn may also be decisive, and some sensitivity is identified regarding the choice of index and the affected region. We conclude that the new indices are suitable for the detection and analysis of recurrent drought events. They are a first step towards a systematic worldwide evaluation of recurrent drought events under present and future climate conditions.