Centennial Temperature Variability in Semiarid La Rioja, Northwestern Argentina: Insights from Historical and Modern Daily Records

A 117-year daily temperature record (1903–2019) from La Rioja, Argentina, is constructed and homogenised by combining rescued historical observations from the archives of the Oficina Meteorológica Argentina (1903–1940) with modern operational data from the Servicio Meteorológico Nacional (1941–2019). Analysing such extensive historical records is essential for identifying long-term temperature trends and for understanding recent changes within the context of the climate system’s natural variability. This record is then examined to characterise centennial trends, multidecadal variability, extreme temperature events, and the association with major modes of Pacific and Atlantic oceanic variability. Over the full period, no significant trends were found in the maximum (Tmax) or minimum (Tmin) temperature series or in the diurnal temperature range (DTR). Since the mean series show no significant trend, the dominant pattern of variability was characterised through Lomb–Scargle spectra of the daily anomaly series, which revealed dominant multidecadal peaks of ~37 years for Tmax and DTR and around 27 years for Tmin. Cross-correlation with the oceanic indices shows that Tmin is weakly but consistently associated with two of the considered tropical Pacific indices, while Tmax appears to be decoupled from the four considered modes. The frequency of warm days declines significantly, at −3.82% per century, despite the stationary Tmax mean, indicating a contraction of the upper tail of the daytime distribution. A pronounced day–night asymmetry runs through all diagnostics. The findings illustrate the importance of complementing linear trend analysis with spectral diagnostics in records exhibiting strong multidecadal variability and contribute a long-term reference for a previously underexplored semiarid station.