A millennium-long reconstruction of damaging hydrological events across Italy

Abstract

Damaging hydrological events are extreme phenomena with potentially severe impacts on human societies. Here, we present the hitherto longest reconstruction of damaging hydrological events for Italy, and for the whole Mediterranean region, revealing 674 such events over the period 800–2017. For any given year, we established a severity index based on information in historical documentary records, facilitating the transformation of the data into a continuous time-series. Episodes of hydrological extremes disrupted ecosystems during the more severe events by changing landforms. The frequency and severity of damaging hydrological events across Italy were likely influenced by the mode of the Atlantic Multidecadal Variability (AMV), with relatively few events during the warm Medieval Climate Anomaly dominated by a positive phase of the AMV. More frequent and heavier storms prevailed during the cold Little Ice Age, dominated by a more negative phase of the AMV. Since the mid-19 th century, a decreasing occurrence of exceptional hydrological events is evident, especially during the most recent decades, but this decrease is not yet unprecedented in the context of the past twelve centuries.

Historical predictability of rainfall erosivity: a reconstruction for monitoring extremes over Northern Italy (1500–2019)

“…We use these factors (amounts of precipitation and weather anomalies) to develop a parsimonious model for reconstructing annual rainfall erosivity over the period 1500-2019 CE, allowing us to capture a wide range of climate variability, and identifying landscape-stress changes. The results of this study complement, for the past five centuries (1500-2019 CE), the twelve century-long (800-2018 CE) reconstructions of extreme hydro-meteorological events across Italy 56 and in the Po River Basin 70 .…”

“…Rainfall erosivity model calibration and validation For the reconstruction of annually resolved storm erosivity (MJ mm ha −1 h −1 yr −1 ) for the PRL, we developed and calibrated the Rainfall Erosivity Historical Model (REHM, Eq. 1), based on summer and autumn precipitation data and Gaussian-filtered values of the reconstructed annual severity storm index sum (ASSIS(GF)) from Diodato et al 56 . For the calibration period 1993-2015 CE, we obtained the coefficients A = 1.968 MJ ha −1 h −1 yr −1 , α = 0.32 mm −1 , k = 1 mm −1 , β = 2 mm −1 and η = 2 in Eqs.…”

“…Long documentary records can help relating local and regional hydrological extreme features to impacts 52,53 and climatic forcing 54,55 , and in integrated multi-disciplinary approaches to climatic variability in hazard-exposed areas 56,57 . Studies in historical climatology can contribute with valuable new perspectives to the research of landscape preservation in the light of climate change, especially in terrestrial river systems that are highly dynamic and regulated by intricate climatic, geomorphic and ecological processes 58 .…”

Communicating Hydrological Hazard-Prone Areas in Italy With Geospatial Probability Maps

“…Changes in the frequency of severe weather events determine the occurrence of damaging hydrological events (Diodato et al, 2019;Petrucci et al, 2019), which in turn affect many natural and human systems (Corella et al, 2016;Sofia et al, 2017). Modeling rainfall intensity can help to quantifying the effect of these extreme phenomena that involve complex landscape and ecosystem scenarios within multiple event feedback forms (e.g., Thomas, 2001;Mulligan and Wainwright, 2013;Harris et al, 2018).…”

“…Local interactions between environmental context and climate variability are provided as comprehensive explanation for landscape changes and impact evaluation (Bintliff, 2002). The diverse geomorphology characterizing the Mediterranean region has important consequences for the atmospheric and sea circulations, with an uneven distribution of weather types (Lionello et al, 2006) and a broad spectrum of hydro-geomorphological hazard potentials across Italy (Diodato et al, 2019).…”