Abstract
The effects of climate change on landslide activity may have important environmental, socio-economic, and political consequences. In the last decades, several short-term extreme rainfall events affected Mediterranean regions, resulted in damaging geo-hydrological processes and casualties. It is unequivocal that the impact of landslides in several Mediterranean countries is increasing with time, but until now, there has been little or no quantitative data to support these increases. In this paper, both rainfall conditions for the occurrence of shallow landslides and rainfall trends were investigated in the Portofino promontory, which extends in the Ligurian Sea, where heavy rainfall and related ground effects often occur. Adopting a frequentist approach, the empirical intensity-duration threshold was estimated. Our findings highlight that the rainfall intensity required to trigger landslides is lower for the same duration than those expected in other similar environments, suggesting a high susceptibility to rainfall-induced landslides in the Portofino territory. Further, the Mann-Kendall test and Hurst exponent were used for detecting potential trends. Analysis of long-term rainfall time series showed statistically significant increasing trends in short duration precipitation occurrence and rainfall rates, suggesting a possible future scenario with a more frequent exceedance of the threshold triggering value and an increase of landslide risk.
Highlights
The occurrence of rainfall-induced landslides and the effects of climate change on rainfall has been among the most debated and controversial scientific issues for some years because of the difficulty in forecasting and their serious environmental, socio-economic and political consequences, both at a global and regional scale.In the last years, it has become apparent that the number of casualties and amount of economic losses due to shallow landslides and mud-debris flows have been dramatically increasing in Europe and worldwide [1,2,3,4,5,6,7,8,9,10]
Analysis developed for European and Mediterranean regions show different trends; an increase in total annual precipitation, rainfall intensity, and frequency of extreme rainfall events has been observed in several countries in Central and Northern Europe, whereas a common negative trend in annual precipitation has been detected in several Mediterranean areas [10,14,15,16]
Different methods have been proposed in the literature to extract rainfall duration [41]. We identified this parameter by measuring the period between the time of the landslides and the time when the rain started in the rainfall record of the representative gauge [95]
Summary
The occurrence of rainfall-induced landslides and the effects of climate change on rainfall has been among the most debated and controversial scientific issues for some years because of the difficulty in forecasting and their serious environmental, socio-economic and political consequences, both at a global and regional scale.In the last years, it has become apparent that the number of casualties and amount of economic losses due to shallow landslides and mud-debris flows have been dramatically increasing in Europe and worldwide [1,2,3,4,5,6,7,8,9,10]. The quantification of the increasing impact of rainfall-induced landslides is still poor and supported by little empirical evidence. It is commonly recognized by a large part of the scientific community that a change in the patterns of precipitation is unequivocal but irregular in space and time; an increase in global mean. In regards to Italian regions, a decreasing trend in the annual rainfall amount and the number of rainy days per year has been commonly recorded, with an increase in rainfall intensity [17,18,19]. It has been observed that the most intense events are often associated with high lightning activity [20] and convective systems
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