Variability of the Climate in Athens‐Greece Over the Last 165 Years of the Period 1858–2023: An Assessment Based on Thornthwaite's Climate Classification and Relevant Indices

ABSTRACT This study investigates the long‐term variability of the local climate in Athens‐Greece over the last 165 years of the period 1858–2023. Thornthwaite's water balance approach and aridity classification along with various climatic indices and variables were used, including precipitation, potential and actual evapotranspiration, water surplus and deficit, thermal concentration and efficiency, and moisture, humidity and aridity indices. The analysis was performed across multiple analysis periods, ranging from 15 to 41 years and under varying soil water holding capacities (100–300 mm) to minimise hydroclimatic uncertainties. Probable climatic periodicities were also examined. Results reveal a notable increase in potential evapotranspiration since the mid‐20th century due to increased air temperature values, though with a rather constant precipitation pattern. Increased water deficits and water demand for evapotranspiration are also detected. Despite these changes, the overall climatic classification in the area has not altered during the last 165 years of record, remaining within the thresholds of the semi‐arid (D) and mesothermal (B 3 ′) types of climates. The results highlight the climatic resilience in the Athens area in terms of aridity; however, increasing temperature‐dependent water stress may affect future water availability in the area.