Lower Return Periods Research Articles

Impact of climate change on Gironde estuary

Within the THESEUS European project, a simplified mathematical model for storm surge levels in the Bay of Biscay was adjusted on 10 events at Le Verdon using wind and pressure fields from CLM/SGA, so that the water levels at Le Verdon have the same statistic quantiles as observed tide records for the period [1960-2000].A numerical model of the Gironde Estuary was used to evaluate future water levels at 6 locations of the estuary from Le Verdon to Bordeaux and to assess the changes in the quantiles of water levels during the XXIst century using ONERC's pessimistic scenario for sea level rise (60 cm).The analysis of future storm surge levels shows a decrease in their quantiles at Le Verdon,, whereas there is an increase of the quantiles of total water levels. This increase is smaller than the sea level rise and gets even smaller as one enters farther upstream in the estuary.A series of flood maps for different return periods between 2 and 100 years and for four time periods ([1960-1999], [2010-2039], [2040-2069] and [2070-2099]) have been built for the region of Bordeaux. Quantiles of water levels in the floodplain have also been calculated. The impact of climate change on the evolution of flooded areas in the Gironde Estuary and on quantiles of water levels in the floodplain mainly depends on the sea level rise. Areas which are not currently flooded for low return periods will be inundated in 2100. The influence of river discharges and dike breaching should also be taken into account for more accurate results.

Assessing Financial Loss due to Pluvial Flooding and the Efficacy of Risk-Reduction Measures in the Residential Property Sector

A novel quantitative risk assessment for residential properties at risk of pluvial flooding in Eindhoven, The Netherlands, is presented. A hydraulic model belonging to Eindhoven was forced with low return period rainfall events (2, 5 and 10-year design rainfalls). Three scenarios were analysed for each event: a baseline and two risk-reduction scenarios. GIS analysis identified areas where risk-reduction measures had the greatest impact. Financial loss calculations were carried out using fixed-threshold and probabilistic approaches. Under fixed-threshold assessment, per-event Expected Annual Damage (EAD) reached €38.2 m, with reductions of up to €454,000 resulting from risk-reduction measures. Present costs of flooding reach €1.43bn when calculated over a 50-year period. All net-present value figures for the risk-reduction measures are negative. Probabilistic assessment yielded EAD values up to more than double those of the fixed-threshold analysis which suggested positive net-present value. To the best of our knowledge, the probabilistic method based on the distribution of doorstep heights has never before been introduced for pluvial flood risk assessment. Although this work suggests poor net-present value of risk-reduction measures, indirect impacts of flooding, damage to infrastructure and the potential impacts of climate change were omitted. This work represents a useful first step in helping Eindhoven prepare for future pluvial flooding. The analysis is based on software and tools already available at the municipality, eliminating the need for software upgrading or training. The approach is generally applicable to similar cities.

Vulnerability of olive orchards under the current CAP (Common Agricultural Policy) regulations on soil erosion: a study case in Southern Spain

To measure the erosive processes taking place under conditions close to those experienced by farmers and land managers; analyses on spatial units adapted to the size of the farm must be carried out; in a non-isolated way in the case of conventional plots. The objective of this study was to describe and understand the current state – in terms of high soil losses and degradation risk – of a commercial olive farm following the CAP agro-environmental requirements as well as the interaction between soil management decisions and rainfall variability. In this work, rainfall and runoff soil loss for 6.4 hydrological years (2005–2011) were monitored in the outlet of an olive orchard microcatchment of 6.7ha. The equipment used was a flume with an ultrasonic sensor to measure flow height, a rainfall gauge and a sediment sampler. Management systems and olive yields were described for the study period. Different management operations (no-tillage, conventional tillage, no herbicides with tillage and mulch) were applied in the field as a result of the farmer adapting to yearly conditions and to recommendations on good agricultural practice.Our results indicate that the interaction between the factors of annual climatological features and management determined the hydrology, soil loss and olive yield. On the annual scale, cumulative rainfall and rainfall erosivity varied between 600 and 1000mm and 600 and 1500MJMmha−1h−1, respectively. The average annual runoff coefficient was equal to 15±10%, while total sediment loss ranged from <1tha−1year−1 to >20tha−1year−1. Olive yield ranged between 5000kgha−1year−1 and 10,000kgha−1year−1. Above average annual rainfall values were associated with both high yields and soil losses >10tha−1year−1.For the study period, frequent events with a low return period resulted in soil losses >10tha−1, despite the use of different soil management techniques and the compliance of CAP agro environmental regulations. The high risk of soil degradation evaluated might mean that the criterion based on slopes >10% is not suitable for the application of agro-environmental requirements of CAP. On the other hand, further research on conservation technologies such as a more efficient use of cover crops, mulches and plant barriers, controlled traffic farming and/or changes in land use is needed.

Characterization of the hydraulic performance of a gully under drainage conditions

During rainfall events with low return periods (1-20 years) the drainage system can provide some degree of protection to urban areas. The system design is based not only on good hydraulic performance of the surface and the sewer network but also on their linking elements. Although the linking elements are of utmost importance as they allow the exchange of flow between the surface and the sewer network, there is a lack of studies that thoroughly characterize them. One crucial structural part of those elements is the gully. State-of-the-art dual-drainage models often use simplified formulae to replicate the gully hydraulic behaviour that lacks proper validation. This work focuses on simulating, both numerically and experimentally, the hydraulic performance of a 0.6 × 0.3 × 0.3 [m] (L × W × D) gully located inside an 8 × 0.5 × 0.5 [m] rectangular channel. The numerical simulations are conducted with the OpenFOAM toolbox and validated with water level measurements in the Multiple-Linking-Element experimental installation located at the Laboratory of Hydraulics of the University of Coimbra. The results provide a complete three-dimensional insight of the hydraulic behaviour of the flow inside the gully, and discharge coefficient formulae are disclosed that can be directly applied in dual-drainage models as internal boundary conditions.

Cumulative Prospect Theory and Momentum Crashes: Evidence from Asia

We provide robust evidence of momentum crashes within the Asian region, which occurred following the Asian financial crisis and the global financial crisis. The probability of a momentum crash is time-varying; it increases after periods of low market returns and high cross-sectional return dispersion when the beta of the zero-investment momentum portfolio becomes negative. Under cumulative prospect theory, investors overweight the probability of a momentum crash when estimating their value function, resulting in the price of “winners” decreasing and future average returns increasing. Consistent with this theory, we show that momentum returns in Asia are substantially lower following periods where the probability of a momentum crash is higher. Therefore, we argue that the negative (positive) skewness of winner (loser) portfolios is priced and may explain the momentum premium.

URBFEP Model for Basin Scale Simulation of Urban Floods Constrained by Sewerage's Size Limitations

Rain drainage in urban catchments is highly complex and depends on numerous and widespread restrictions to water flows caused by the layout of urban areas and building morphology, as well as by the size of sewers which are usually designed for low return period values (2÷10 years). The higher the rainfall return period, the higher the influence of such limitations and the correspondent hydrographs show reductions in peak values due to the reservoir effect generated by flood waters. The modelling of such processes is based on mathematical algorithms of transients associated with rainfall-runoff phenomena and with 1D/2D flow routing processes that, during more intense rainfall, occur simultaneously in the sewer and on the surface (dual drainage systems). However, when flood risk planning relates to the catchment scale for a vast territory with many urban areas, the model no longer focuses on a detailed simulation of what happens inside each urban area, but rather on an estimate of the main characteristics of the urban floods and of the hydrographs discharged into the receivers. In this case, it is necessary to use simpler models, but which are still able to provide a reliable representation of such phenomena. For such purpose, the conceptual model URBFEP (URBan Flood Equivalent Pipe) has been developed in order to obtain a reliable representation of these restricted urban flood processes. This model is presented here, demonstrating its ability to represent the real behaviour of urban sub-catchments in comparison to the results obtained in physically based simulations in a set of real urban areas selected as pilot cases.

Impacts of Land Cover and Climate Changes on Peak Floods Probability Distribution Function

Climate and land cover are the main regulators of discharge formation. We combined here 5 alternative land cover case with 2 different precipitation scenarios. Land cover scenarios are: (a) present land cover according to CORINE 2006 maps, (b) ICES scenario at 2050, (c) IMAGE scenario at 2050, (d) cementification scenario C1 and (e) cementification scenario C2. The ICES and IMAGE scenarios are based on consideration of economy and population growth, cementification scenarios 1 and 2 are intended as exemplificative what-if scenarios for urbanization of rural areas. Precipitation is modelled as (a) the observed one and (b) increasing of 10% the average value. Peak flood probability distributions are analytically for each of the 10 land cover-climate combinations. The case study is the Secchia river basin in Emilia Romagna region. Results show that in absence of changes in the precipitation regime, the peak flood associated to low return period (

Monte Carlo analysis of the effect of spatial distribution of storms on prioritization of flood source areas

Implementation of structural and non-structural flood control measures in flood-prone watersheds is on increasing demand. Different watershed areas are not necessarily hydrologically similar and impose variable effects on the outlet flow hydrograph. Meanwhile, prioritization of watershed areas in terms of flood generation is essential for economic flood control planning. Previous works have focused on the definition of a flood index that quantifies the contribution of each subwatershed unit or grid cell to the outlet flood hydrograph through the application of unit flood response (UFR) approach. In the present research, for the first time, the effect of spatial pattern of storm events on the flood index variation was assessed via a Monte Carlo uncertainty analysis. To do so, the UFR approach was carried out for a large number of randomly generated rainfall spatial pattern. The proposed methodology was adopted to the Tangrah watershed in northern Iran. The watershed is frequently hit by floods that have historically caused loss of life and properties. The results indicated that for the more frequent flood events, the flood index is quite sensitive to the spatial distribution of rainfall such that for the highest ranked subwatershed (SW6), the standardized variation of the flood index values (i.e., the uncertainty range) decreases from 1.0 to 0.5 when the rainfall depth increases from 20 to 150 mm, respectively. The results further revealed that increasing the rainfall depth from 20 to 150 mm would cause the effect of rainfall spatial distribution on subwatersheds’ flood indices to diminish. The implications are that if flood control measures are designed for more frequent floods with lower return periods, an uncertainty analysis is required to identify the range of flood index variations.

Time-Varying Risk Aversion in the Cross-Section of Mutual Fund Flows

Analyzing cross sectional determinants of fund flows, this study finds evidence that investors’ risk aversion is time-varying. In particular, the periods over which the increases in risk aversion are observed are associated with contemporaneously low market returns, suggesting that increases in aggregate risk aversion increases the discount rate thereby lowering market prices. While the relation is more pronounced across equity funds, a marginally significant increase in risk-aversion during periods of low bond returns was also observed. Furthermore, the study finds that bond investors are generally more risk averse than equity investors, and that equity and bond investors engage in comparatively less performance chasing during periods with low market returns. This study adds to the growing body of research, which suggests that risk-aversion and consequently risk premia are time-varying, providing a risk-based explanation for phenomena such as long-run stock return predictability.

What are We Meeting For? The Consequences of Private Meetings with Investors

Using a unique dataset of all one-on-one meetings between senior management and investors for an NYSE-traded firm, we investigate the impact of these private meetings on investor decisions. We find evidence that investors who meet privately with management make more informed trading decisions in periods when they meet, increasing their position before periods of high returns and decreasing their positions before periods of low returns. This improved timing ability is concentrated in hedge funds, and does not appear to be driven by fixed investor skill, investors communicating with each other, or investors endogenously choosing to meet simply when they have pre-existing private information. The increase in timing ability is larger during periods of greater uncertainty and more public information availability, consistent with a mosaic theory of investing. Our results suggest that, despite the passage of Regulation Fair Disclosure, private meetings help a subset of investors make more informed trading decisions.

Fluxes and storage of fine-grained sediment and associated contaminants in the Na Borges River (Mallorca, Spain)

Abstract Samples of suspended and fine channel bed sediment were used to examine the spatial and temporal variability in the amount of fine-grained sediment and associated contaminants temporarily stored in the Na Borges River (319 km 2 ) in Mallorca and the relationship of such channel storage to the fluxes of fine sediment and associated contaminant through the system. This Mediterranean groundwater-dominated river drains a predominantly agricultural catchment, although urbanisation during the twentieth century has changed the catchment hydrology. A re-suspension technique was used to obtain estimates of channel storage at monthly intervals during the 2004–2005 hydrological year at eight locations along the main stem of the stream (i.e. 26 km). The estimates of fine sediment storage ranged between 0 and 13,000 g m − 2 , with a mean value of 2400 g m − 2 . Only Cu exceeded the critical threshold (36 μg g − 1 ), established by existing guidelines for the contaminant content of fluvial sediment. The results demonstrated significant spatial and temporal variability, in response to the influence of urban point sources, agricultural practises, seasonal groundwater interactions and the first-flush effect. The amount of fine sediment entering storage during the study period was 515.2 t, representing the net increase in storage over the study period. As a result, the mean specific storage was 21 t km − 1 . Suspended-sediment load and temporary fine sediment storage are the two basic components of the channel sediment budget that interact to determine sediment transport through a channel system, and they can therefore be used to compute the total input of sediment and associated contaminants to the system. Accordingly, storage values were compared with estimates of suspended sediment load and associated contaminant load values at three measuring stations along the river. During the study period, storage in the main channel system represented 87% of the sediment input and 68% of the contaminant input, indicating that deposition was more important than transport. The low gradient of the main channel and the low return period (i.e. 0–2.5 years) of the flood events that occurred during the study period meant that remobilised bed sediment and associated contaminants were redeposited downstream rather than being flushed to the catchment outlet as suspended sediment. Furthermore, the river bed is dry during the summer months, allowing sealing and crusting processes to stabilise the sediment deposited during the wet season and thereby reduce its availability for remobilisation at the beginning of the next wet season. Together, these factors promote sediment deposition and storage, with the result that sediment progressively accumulate over several hydrological years until a major flood event (i.e. return period ≈ 5 years) evacuates the stored sediment.

Momentum and reversals in Taiwan index futures returns during periods of extreme trading imbalance

The study analyzes the relation between a trading imbalance metric that captures data observable by investors, and future momentum and reversals in Taiwan index futures returns. Standard regression analyses do not show any significant dynamic relations between daily index futures returns and the trading imbalance, regardless of whether the trading imbalance metric is lagged, contemporaneous, or leads the index futures return. However, when the analyses are focused on periods with extreme trading imbalances I find that the daily index futures returns exhibit significant reversals following periods of extreme (low) trading imbalances and low returns. I also find some evidence of residual momentum in consecutive daily index futures returns following periods of extreme (high) trading imbalances and high returns. Trading simulation, directional accuracy, and market timing tests show these effects to be economically significant, even after accounting for transaction costs.

The effect of the conditions of a landscape on its retention capacity

The effect of the conditions of a landscape on its retention capacityQuestions related to the occurrence, frequency, intensity, duration, characteristics and causes of floods have been discussed more in recent years. Two basic approaches to flood control often conflict. The first is based on the assumption of the considerable effect of a landscape's retention capacity, which can in fact prevent surface runoff generation and flood formation and can significantly transform flood wave. The second approach asserts that the retention capacity of a landscape is nearly negligible and that the only reliable flood protection can be provided by extending the technical structures of flood control measures mainly and directly on water courses. Two different approaches were applied to assess the effect of landscape conditions and revitalization measures on surface runoff and flood formation within a catchment and floodplain. The conclusion shows that the effect of landscape revitalization is very important, but mainly for low return periods of flood events, while for extreme events, the effect on landscapes and floodplains becomes less important and even negligible.

A generalized regional design storm rainfall model for Botswana

Design of drainage and dam structures involves a full understanding of the duration, magnitude and volume of peak flood flows anticipated. For gauged catchments a number of established flood frequency models and rainfall-runoff models are used widely. However, most planned developments for bridge or dam or any other water development structures in a catchment are located at a site in a stream where there are no discharge records. In a catchment, records of short duration rainfall data might not also be available in order to transform them to design flood. In this study, a generalized parametric model for rainfall intensity-duration-frequency (IDF) relations is developed for the estimation of rainfall extremes in Botswana. The model is calibrated on available records on rainfall IDF relationships that are in use by the Botswana Roads Department. The proposed formulation allows one to estimate the expected rainfall depth for a duration ranging from 5 minutes to 2 hours and beyond and for low and medium return periods (up to 50 years) in any location within Botswana. A simplified experiment is developed in order to assess the reliability of the proposed formulation, whose performances are tested also in comparison with other regionalization approaches recently proposed by the scientific literature. The proposed model reproduced the observed IDF both qualitatively and quantitatively with high values of R2 ranging between 92.9 to 99.9 % during model calibration and 92.3 to 99.8% during model verification. Given the lack of recorded continuous and short duration rainfall information, the model can be used to assist hydrologists in the design of drainage and other water control structures for ungauged sites in Botswana.Keywords: Design storms, IDF model, Calibration, verification, parameter sensitivity analysis, Botswana

Frequency Analysis as a Tool for Assessing Adverse Conditions During a Massive Fish Kill in the St. Lawrence River, Canada

Abstract During the summer of 2001, the largest fish kill in the recorded history of the St. Lawrence River occurred. More than 25,000 dead carp were recovered. Preliminary analyses suggested hydroclimatic factors may have triggered the fish kill. Long time series of hydroclimatic variables were available upstream and downstream from the study area. In order to investigate if hydroclimatic conditions were extreme during the summer of 2001, frequency analyses were performed on time series of air and water temperature, water level, and solar radiation. During this period, the daily maximum water temperature was abnormally high (return period of 47 years) relative to other years. Air temperature was also high (return period of 22 years) and water level was very low (return period of 67 years). Results showed that hydroclimatic forcings were acting at two different time scales. First, short-term extremes are more likely to have direct impacts on ecosystems, such as lethal stress caused by oxygen depletion in shallow areas. Long-term extremes have indirect effects, which are more difficult to detect, such as immunosuppression. These results reiterate the importance of water temperature in aquatic habitat, particularly in the present context of global warming and climate change.

Evaluation and inter-comparison of Global Climate Models’ performance over Katonga and Ruizi catchments in Lake Victoria basin

Regional impact assessments of climate change on hydrological extremes require robust examinations of climate model simulations. The climate models may satisfy mean statistics but fail to reproduce extreme quantiles which are crucial for applications of climate change impact analysis on water resources. Through statistical analysis, this paper evaluates and inter-compares the performance of Global Climate Model (GCM) simulations for their ability to predict changes in hydrological extremes for given locations or catchments in the Nile basin. Two catchments were considered: Katonga and Ruizi catchments in the Lake Victoria basin. Models that differ significantly from the observed extremes were considered unreliable for impact assessments on hydrological extremes. A graphical approach (rainfall quantile/frequency analysis), which allows for easy spotting of discordant models, in combination with several statistics, was used to evaluate 18 GCM control simulations against observed rainfall data. Standard deviation, coefficient of variation and root mean squared error (about the mean) of the observed rainfall, were used to derive error margins against which GCM simulations were evaluated. Model results outside the error margins were considered inconsistent with the observed rainfall. Model inter-comparison was also carried out for the rainfall change projections till the 2050s and 2090s through analysis of perturbations and percentage changes based on A1B, A2, and B1 SRES scenarios. It is noted that the GCM outputs are more consistent in reproducing rainfall signatures at annual aggregation level than at monthly aggregation levels with tendency of overestimation of the rainfall depths but with significant variation among different GCM simulations. The GCMs perform better in reproducing rainfall frequency with higher return periods compared with lower return periods. Most of the GCMs perform better for the wet months than the drier months. The GCMs CGCM3.2a, CM3.O, CM4.1, PCM1, CGCM3.1T47, MIROC3.2.HIRES, CCSM3.0 and FGOALS, are the most inconsistent with the observed rainfall for both catchments. Good performing models are MK3.5, MK3.0, ECHAM5, CM2.1U.H2 and CM2.0. In general, most GCMs perform poorly for both catchments. This signals the need for significant improvements in the rainfall modelling of the climate models for the study region. There is no strong evidence to suggest that GCM performance improves with higher spatial resolution. Models which are highly inconsistent with other models in reproducing the observed rainfall are not necessarily inconsistent with other models in the future projections. Differences in projections for the A1B, B2, and B1 scenarios were found to be smaller than the differences between the GCM simulations.

Time-Varying Predictability in Mutual Fund Returns

We provide novel evidence that mutual fund returns are predictable after periods of high market returns but not after periods of low market returns. The asymmetric conditional predictability in relative performance cannot be fully explained by time-varying differences in transaction costs, in style exposures, or in survival probabilities of funds. Performance predictability is more pronounced for funds catering to retail investors than for funds catering to institutional investors, suggesting that unsophisticated investors make systematic mistakes in their capital allocation decisions.

Assessing and modelling changes in rainfall erosivity at different climate scales

AbstractAn understanding of the weather drivers of soil erosion necessitates an extended instrumental meteorological series and knowledge of the processes linking climate and hydrology. The nature of such linkages remains poorly understood for the Mediterranean region. This gap is addressed through a composite analysis of long‐term climatic controls on rain erosivity in the Calore River Basin (southern Italy) for the period 1869–2006. Based on a parsimonious interpretation of rainstorm processes, a model (comparable with the Revised Universal Soil Loss Equation) was adapted to generate erosivity values on different time‐aggregation scales (yearly and seasonal). The evolution of the generated series of cumulated and extreme erosivity events was assessed by two return period (T) quantiles via a 22‐year moving window analysis (low return period, T = 2 years; high return period, T = 50 years). Erosivity extremes are shown to be characterized by increasing yearly trends (at a 100‐year rate of ∼150 MJ mm ha–1 h–1 for T = 2 years and ∼800 MJ mm ha–1 h–1 for T = 50 years), especially during the spring and autumn seasons. Quantile patterns on the extremes are also shown to be decoupled from trends in the cumulated values. The Buishand test was applied to detect the presence of temporal change points, and a wavelet spectrum analysis used for time‐frequency localization of climate signals. A change‐point in the evolution of climate is revealed over the 1970s in the spring series, which correlates to a distinct rain erosivity increase. The results indicate that soil erosion risk tends to rise as a consequence of an escalation of the climate erosive hazard, predominantly between April and November (associated with cultivation and tillage practices). Copyright © 2009 John Wiley &amp; Sons, Ltd.

Effects of multiscale rainfall variability on flood frequency: Comparative multisite analysis of dominant runoff processes

We present results of a comparative modeling analysis of the effects of multiscale rainfall variability (within‐event, between‐event, seasonal, interannual, and interdecadal) on estimated flood frequency curves for three catchments located in Perth, Newcastle, and Darwin, Australia. The analysis is performed using the derived distribution approach by combining long‐term rainfall time series generated by a stochastic rainfall model with a continuous rainfall‐runoff flood model that is able to generate runoff variability over a multiplicity of timescales. Similarities and differences of the flood frequency curves (FFCs) in these rather diverse catchments are then interpreted on the basis of differences in the dominant runoff generation processes. In Newcastle, annual maximum flood peaks are caused by saturation excess overland flow over the entire range of annual exceedance probabilities (AEPs) or return periods. On the other hand, in Darwin, the shape of the FFC is determined strongly by seasonal climatic variability, which, in combination with deep soils, leads to a switch of dominant runoff mechanisms contributing to annual maximum flood peaks, from subsurface stormflow at high AEPs (low return periods) to saturation excess overland flow at low AEPs (high return periods). This leads to FFCs exhibiting a consistent break in slope in the Darwin catchment but not so in Newcastle. On the other hand, the FFCs in Perth are affected by both seasonality and long‐term climate variability and produce a variety of shapes depending on the relative strengths of these climatic controls. Because of the fact that in Perth and Darwin the shapes of the flood frequency curves depend on a possible switch of the dominant runoff generation mechanisms with increasing return period, uncertainty in hydrological model parameters relating to landscape properties contributes significantly to the uncertainty in the flood frequency curves. This uncertainty is much less pronounced in Newcastle because of the absence of such a switch of runoff generation mechanisms.

The study of past damaging hydrogeological events for damage susceptibility zonation

Abstract. Damaging Hydrogeological Events are defined as periods during which phenomena, such as landslides, floods and secondary floods, cause damage to people and the environment. A Damaging Hydrogeological Event which heavily damaged Calabria (Southern Italy) between December 1972, and January 1973, has been used to test a procedure to be utilised in the zonation of a province according to damage susceptibility during DHEs. In particular, we analyzed the province of Catanzaro (2391 km2), an administrative district composed of 80 municipalities, with about 370 000 inhabitants. Damage, defined in relation to the reimbursement requests sent to the Department of Public Works, has been quantified using a procedure based on a Local Damage Index. The latter, representing classified losses, has been obtained by multiplying the value of the damaged element and the percentage of damage affecting it. Rainfall has been described by the Maximum Return Period of cumulative rainfall, for both short (1, 3, 5, 7, 10 consecutive days) and long duration (30, 60, 90, 180 consecutive days), recorded during the event. Damage index and population density, presumed to represent the location of vulnerable elements, have been referred to Thiessen polygons associated to rain gauges working at the time of the event. The procedure allowed us to carry out a preliminary classification of the polygons composing the province according to their susceptibility to damage during DHEs. In high susceptibility polygons, severe damage occurs during rainfall characterised by low return periods; in medium susceptibility polygons maximum return period rainfall and induced damage show equal levels of exceptionality; in low susceptibility polygons, high return period rainfall induces a low level of damage. The east and west sectors of the province show the highest susceptibility, while polygons of the N-NE sector show the lowest susceptibility levels, on account of both the low population density and high average rainfall characterizing these mountainous areas. The future analysis of further DHEs, using the tested procedure, can strengthen the obtained zonation. Afterwards, the results can prove useful in establishing civil defence plans, emergency management, and prioritizing hazard mitigation measures.