Rivoire P. auteur aut IRD Tramblay Yves auteur aut IRD Neppel L. auteur aut IRD Hertig E. auteur aut IRD Vicente-Serrano S. M. auteur aut IRD text journalArticle eng text/pdf reformatted digital access To define a dry day, the most common approach is to identify a fixed threshold below which precipitation is considered equivalent to zero. This fixed threshold is usually set to account for measurement errors and precipitation losses due to the atmospheric evaporation demand. Yet, this threshold could vary in time according to the seasonal cycle and in the context of long-term trends, such as the increase in temperature due to climate change. In this study, we compare extreme dry spells, defined either with a fixed threshold for a dry day (1 mm) or with a time-varying threshold estimated from reference evapotranspiration (ET0), for a large database of 160 rain gauges covering large parts of the Mediterranean basin. Results indicated positive trends in ET0 during summer months (June, July and August) in particular. However, these trends do not imply longer dry spells since the daily precipitation intensities remain higher than the increase in the evaporative demand. Results also indicated a seasonal behavior: in winter the distribution of extreme dry spells is similar when considering a fixed threshold (1 mm) or a time-varying threshold defined with ET0. However, during summer, the extreme dry-spell durations estimated with a 1 mm threshold are strongly underestimated in comparison to extreme dry spells computed with ET0. We stress the need to account for the atmospheric evaporative demand instead of using fixed thresholds for defining a dry day when analyzing dry spells, with respect to agricultural impacts in particular. specialized ZONE MEDITERRANEENNE 062 072 19 8 1629-1638 2019 1561-8633 https://www.documentation.ird.fr/hor/fdi:010076544 10.5194/nhess-19-1629-2019 1561-8633 [F B010076544] https://www.documentation.ird.fr/hor/fdi:010076544 https://horizon.documentation.ird.fr/exl-doc/pleins_textes/divers19-08/010076544.pdf IRD - Base Horizon / Pleins textes 2019-09-19 2025-02-24 fdi:010076544 fre