Long term trends in the Bologna daily rainfall time series (1813-2020)

The rainfall time series in Bologna is one of the longest daily precipitation records available.

Figure 1 presents the progress along time of cumulative annual rainfall during the observation period. Dating back to 1813 with no missing values, the time series spans over 208 years. As such, it offers a valuable opportunity to evaluate long term trends of rainfall statistics, thus offering information on past and recent precipitation changes.

In detail, we focus on the progress along time of annual and monthly precipitation as well as the annual and monthly maxima of daily precipitation, by applying linear regression. We also present an overview of historical long term droughts and estimate their frequency of occurrence by applying run theory. We also compare drought statistics of historical data with those of future climate scenarios recently presented by the literature.

The results highlight that the drought frequency is decreased in the past 50 years, while there is evidence of decreasing variability of annual rainfall during time, with no evident trend.