Abstract
Intense meteorological events are the primary cause of geohazard phenomena in mountain areas. In this paper, we present a study of the intense rainfall event that occurred in the provinces of Lecco and Sondrio from 11 to 12 June 2019. The aim of our work is to understand the effect of local topography on the spatial distribution of rainfall and to attempt the reconstruction of a realistic rainfall field relative to that extreme event. This task represents a challenge in the context of complex orography. Classical rain-gauge interpolation techniques, such as Kriging, may be too approximate, while meteorological models can be complex and often unable to accurately predict rainfall extremes. For these reasons, we tested the linear upslope model (LUM) designed for estimating rainfall records in orographic precipitation. This model explicitly addresses the dependence of rainfall intensification caused by the terrain elevation. In our case study, the available radio sounding data identified the convective nature of the event with a sustained and moist southern flow directed northward across the Pre-Alps, resulting in an orographic uplift. The simulation was conducted along a smoothed elevation profile of the local orography. The result was a reliable reconstruction of the rainfall field, validated with the ground-based rain gauge data. The error analysis revealed a good performance of the LUM with a realistic description of the interaction between the airflow and local orography. The areas subjected to rainfall extremes were correctly identified, confirming the determinant role of complex terrain in precipitation intensification.
Highlights
In alpine environments, hydrogeological hazards are mainly triggered by heavy rainfall events that can occur across the seasons in different ways [1,2,3]
Bearing in mind that a unique technique to determine rainfall amounts for ungauged regions does not exist, especially for remote places in mountain territories, we focused on a model able to reconstruct a reliable rainfall field
The aim of our study was to attempt to overcome the poor accuracy of classical interpolation techniques, while avoiding the complexities of running a Limited Area Models (LAMs)
Summary
Hydrogeological hazards are mainly triggered by heavy rainfall events that can occur across the seasons in different ways [1,2,3]. The autumn is the most critical season, where extratropical cyclone structures can strike the alpine range frequently, affecting its southern flank slope [4,5,6]. These episodes can cause extensive damage, injuries, and deaths due to the possible triggering of critical events, such as floods and landslides [7,8]. One of the most important is the elaboration of the intensity–duration curves where precipitation features are intended as predictors for the event triggering These curves correlate the intensity and the duration of a precipitation event, defining a critical rainfall event with respect to a threshold above which landslide failures are highly expected [9,10,11,12,13]. The information acquired about rainfall characteristics is fundamental for the correct assessment of these hydrogeological events
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