Recovering, correcting, and reconstructing precipitation data affected by gaps and irregular readings: The Padua series from 1812 to 1864

The aim of this work is to reconstruct the 1812–1864 period of the Padua precipitation series at the daily level, using a local precipitation Log. Missing readings, cumulative amounts, and gaps often affect early precipitation series, as observers did not follow a precise protocol. Therefore, the daily amount and frequency reported in the register of observations are not homogeneous with other periods, neither comparable with other contemporary series, and need a correction. The correction methodology has been based on the daily weather notes written in the Log in parallel to the readings. Taking advantage of periods in which both weather observations and instrumental readings were regularly taken, the terms used to describe the precipitation type and intensity have been classified, analyzed statistically, calibrated, and transformed into numerical values. The weather notes enable the distribution of precipitation to be determined based on the cumulative amounts collected on consecutive rainy days into the likely precipitation that occurred on every single rainy day. In the case of missing readings, the presence of weather notes enables the missing amounts to be estimated using the relationships found previously. Finally, the recovery of additional contemporary documents made it possible to fill some gaps in this period. Using this approach, 52 years of the long Padua precipitation series have been corrected: precipitation collected for two or more rainy days has been distributed according to the actual rainy days; the rain amount fully recovered and most of the missing values reconstructed; the false extreme events corrected.