Identifying Past Droughts in El Hierro (Canary Islands) With ERA5 Climate Reanalysis and SPI

The island of El Hierro, situated as the southwesternmost territory within the Canary Islands archipelago, is renowned for its distinctive climate. Global warming is anticipated to increase the frequency and severity of droughts in the area, posing a significant threat to its inhabitants, economy, and delicate ecosystems.

The main aim of this research is to identify droughts that affected El Hierro Island between 1941 and 1970. This will be achieved through by analyzing of hourly total precipitation data obtained from the ERA5 climate reanalysis.

In addition to precipitation data, this study also integrated various variables from ERA5 that influence droughts, including surface pressure, mean sea level pressure, geopotential height at 500 hPa, temperature at 2 meters above the land surface, sea surface temperature, volumetric soil water content, wind components (U and V), and surface downward solar radiation. To assess the accuracy of ERA5 estimates, precipitation data from eight stations provided by the Spanish State Meteorological Agency (AEMET) were utilized. Furthermore, documentary research was conducted to identify droughts prior to 1941, involving a thorough examination of digital repositories such as the National Library of Spain (BNE) and the Virtual Library of Historical Press (Spain).

The Standardized Precipitation Index (SPI) was employed to assess the severity, magnitude, and duration of the droughts. Additionally, R packages such as TIDYVERSE, DPLYR, SP, SPEI, and PSYCH were utilized for the analysis of the variables. Moreover, CLIMATOL and TREND were used to ensure the quality of the observational records.

This research pioneers the quantitative analysis of the droughts that affected El Hierro Island between 1941 and 1970. This period has been largely overlooked in previous studies and is characterized by a scarcity of high-quality observational records. The findings reveal that droughts are recurrent on the island, with at least one persistent drought per decade. Notably, the 1947-1949 drought stands out as the most prolonged and severe, impacting hydrological, agricultural, and socioeconomic aspects.

In conclusion, this analysis offers valuable insights into the historical patterns and future trends of droughts on El Hierro Island, laying the groundwork for the development of informed adaptation strategies. Moreover, it contributes to enhancing our understanding and monitoring of droughts, which could reduce their impact on the population in the future.