In order to define a dry period, a threshold for wet days is usually considered to account for measurement errors and evaporation. In the present study, we compare the threshold of 1 mm d⁻¹, the most commonly used threshold, to a time-varying threshold describing evapotranspiration to compare how the risk of extreme dry spells is estimated with both thresholds. Results indicate that considering a fixed threshold can underestimate extreme dry spells during the extended summer.