Extreme precipitation

Could a multidisciplinary approach shed some light on the increase frequency of these events?

In the Emilia-Romagna region, we are witnessing more high intensity precipitation events, probably attributable to the increase of temperature and water vapor in the atmosphere. In the event of 14 September 2015 many debris and hyper-concentrated flows has been observed in the Northern Apennine, some of them flowing in a peat-bog environment. Our plan is to characterize the observed deposits and use them as a marker for high intensity precipitation events in the past. The peat-bog sedimentary deposit could represent a complementary archive, beyond the instrumental chronological time, to register singular events in the recent past. This natural archive could reveal additional information about past frequency of these events and shed new perspective on future precipitation distribution and intensity due to climate change.

Predicting Extreme-Precipitation Effects on the Geomorphology of Small Mountain Catchments: Towards an Improved Understanding of the Consequences for Freshwater Biodiversity and Ecosystems.

                                                                                                                            Abstract: In 2015 an intense rainfall event hit the Valleys of the Trebbia, Nure, and Aveto watercourses in the Northern Apennines. In about 6 h a mesoscale convective system deployed a stunning amount of precipitation of 340 mm, with an extreme hourly rainfall intensity of >100 mm/h. It triggered debris flows along slopes and stream channels, landslides and floods, which caused serious damages. Through the optimal combination of rainfall data and radar volumes, in this work we present a detailed rainfall analysis, which will serve as a basis to create a quantitative correlation with debris flows over elementary hydrological units. We aim at providing an objective basis for future predictions, starting from the recognition of the forcing meteorological events, and then arriving at the prediction of triggering phenomena and to the debris-flow type. We further provide seven observations/case studies on the effects of extreme-precipitation events on freshwater environments in small mountain catchments. Extreme-precipitation events are becoming more frequent and widespread globally but their ecological effects are still insufficiently understood. In general, the effects of extreme events on inland-waters’ ecosystems are highly context-dependent, ranging from deleterious to beneficial. We therefore highlight the necessity of further studies to characterize these effects in more depth to be able to include appropriate mitigation measures in environmental planning and stewardship.

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EGU General Assembly 2019: Session ITS4.2/CL4.21/HS11.21/OS2.11 Past and ongoing climate changes in the Mediterranean region and their impacts on the environment and the human societies

Multidisciplinary analysis at Lake Moo peat bog site: New data from a natural archive to gouge past and future trends in heavy rainfall events over Northern Apennines (Italy).

Segadelli Stefano(1), Federico Grazzini(2), Margherita Aguzzi(2), Alessandro Chelli(3), Roberto Francese(3), Veronica Rossi(4), Francesca Staffilani(1), Maria Teresa De Nardo(1), Sandro Nanni(2),

A series of record breaking precipitation events have stricken the mountainous area of Emilia-Romagna Region (northern Apennines, Italy) over the last years. As consequence, several geomorphological processes, like widespread debris flows along the slopes and hyperconcentrated flood in the stream channels, shallow landslides and overbank flooding affected the territory, causing serious damages to man-made structures.

The stratigraphic study of current and fossil peat bog and lake deposits can provide useful insight to support a strong match between precipitation intensity and warm climatic phases in antecedent climatic periods.

Here we present the results of the field campaign performed in summer 2017 at Lake Moo a 0.15km2 peat bog located at an altitude of 1130m a.s.l. The chosen area has been affected, during the flooding of the upper Trebbia and Nure valleys 13-14 September 2015, by several high-density flows  generated by the stream that flow into the plain. Our main assumption is that, in such a small drainage basin (area <2 km2), with favourable geologic and geomorphic characteristics implying advantageous sediment transfer into lake, high density flood can be triggered only by high precipitation intensity events (HPI) lasting a sufficient amount of time for water to infiltrate and mobilize large quantities of debris. In the Trebbia-Nure case, a detailed analysis of precipitation over Lake Moo site microbasin, showed that the observed debris flow occurred with a peak intensity of 112mm/3h. This is a very high value compared to shallow landslide and debris flow thresholds find in literature for nearby areas, like the Apuane and Garfagnana regions, which can be explained by the dense vegetation cover in the area.

The sedimentary succession (ca. 13 m-thick) was studied through the extraction of two cores and one trench. The facies/paleoenvironmental interpretation of the sedimentary succession, characterized by clusters of coarse-grained alluvial deposits interbedded with organic-rich silty clays and peaty layers, was achieved combining sedimentological and pollen data with pedological data and radiocarbon dating (AMS 14C). The results of radiocarbon dating will be matched with information deriving from targeted historical analysis on the effects local heavy rainfalls.

The lack of surrounding anthropic activities, the vicinity of the lake to main Appenine crest, very exposed to maritime moist airflow coming from the central mediterranean sea, make this site particularly suitable for a reconstruction of HPI events.

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1° Convegno Nazionale AISAM

10-13 Settembre 2018 – Bologna – Italy

Partecipazione alla prima edizione del Congresso Nazionale dell’Associazione Italiana Scienze dell’Atmosfera e Meteorologia (CN1-AISAM) che si tenuto a Bologna dal 10 al 13 settembre 2018.

Per maggiori informazioni consultare il seguente link oppure scarica la presentazione e il programma:

 https://eventi.unibo.it/aisam-cn1

 AISAM presentation

 AISAM pocket programme

Precipitazioni estreme ed effetti al suolo sul reticolo minore: il caso del 14 Settembre 2015

Facendo seguito al report d’evento sull’alluvione che ha colpito la Val Trebbia e la Val Nure nel Settembre 2015, abbiamo svolto un ulteriore lavoro di approfondimento che ha lo scopo di illustrare nel dettaglio gli effetti che precipitazioni di elevatissima intensità, come quelle cadute durante quell’episodio, possono apportare sul territorio, modificandone in alcuni casi la morfologia a livello macroscopico. Il sistema temporalesco, stazionario per quasi 6 ore, ha scaricato circa 300 mm/in 6 ore con punte d’intensità oraria superiori ai 100mm/h registrate dalle stazioni meteorologiche della rete osservativa regionale RIRER. Aspetto innovativo di questo lavoro è la combinazione del dato puntuale delle stazioni con il dato radar e la sua comparazione degli effetti al suolo rilevati da ulteriori indagini. Emerge chiaramente una relazione monotòna e crescente fra intensità di pioggia e gli oltre trecento fenomeni di colate di detrito censiti nell’area di studio. Viene proposto uno schema evolutivo (o modello geologico) dei movimenti in massa, tipo colate di detrito, a carico del reticolo idrografico minore scatenati da piogge intense. Questa analisi conferma che le zone dell’Appennino Tosco-Emiliano, a forte acclività (sopra i 25°) e con adeguata copertura detritica, possono essere soggette a colate di detrito se sollecitate da precipitazione di forte intensità e di durata di alcune ore, quasi univocamente imputabili a sistemi convettivi organizzati.

Reporto effetti precipitazioni estreme