Changes in high-intensity precipitation on the Northern Apennines (Italy) as revealed by multidisciplinary data over the last 9000 years

Abstract. Several record-breaking precipitation events have stricken the mountainous area of Emilia-Romagna Region (Northern Apennines, Italy) over the last years. As a consequence, severe geomorphological processes, like debris avalanches and debris flows, shallow landslides and overbank flooding affected the territory, causing severe damages to human-made structures. The unusual intensity of these phenomena prompted an investigation on their frequency in the past, beyond the instrumental time. Are these phenomena unprecedented in the region?

Peat bog and lake deposits can provide useful elements to reply to this question and to infer the frequency of extreme precipitation events occurred in the past.

Here we present the results of a dedicated field campaign performed in summer 2017 at Lake Moo in the Northern Apennines, a 0.15 km2 peat bog located at an altitude of 1130 m a.s.l. During the extreme precipitation event of 13-14 September 2015, several debris flows, generated by small streams, have affected the Lake Moo plain. In such a small drainage basin (< 2km2), high-density flood can be triggered only by high-intensity precipitation events.

The sedimentary succession (ca. 13 m-thick) was studied through the drilling of two cores and one trench. The sequence, characterised by clusters of coarse-grained alluvial deposits interbedded with organic-rich silty clays and peat layers, was analysed combining sedimentological, pollen, microanthracological, pedological data and radiocarbon dating (AMS 14C), in an innovative multidisciplinary approach for this area.

Original data acquired during the field campaign were also correlated with other specific paleoclimatic proxies available in the literature for the Northern Apennines area. We discover that the increase of extreme paleoflood, associated with coarse-grained deposits similar to the ones observed recently, correlates well with the warm phases of the Holocene Thermal Maximum and with the ongoing warming trend observed which started at the beginning of the last century.

 

Keywords

extreme precipitation, Holocene flood activity, Northern Apennines, climate change, water cycle, global warming

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