Storm Duration Research Articles

Evidence of shorter more extreme rainfalls and increased flood variability under climate change

Increases in extreme rainfall intensities as a result of climate change pose a great risk due to the possibility of increases in pluvial flooding, particularly in urban and developed areas. But evidence is emerging that the observed increases in extreme rainfall are not resulting in universal increases in flooding. Indeed, on a global scale, studies consistently find more gauge stations with decreasing rather than increasing trends in the annual maxima flood magnitude. Here, we aim to improve our understanding of how rainfall and streamflow extremes are changing and why floods are not always observed to increase despite increases in rainfall extremes. To do so, we examine trends in streamflow events using 2776 stations from the Global Runoff Data Centre, with events chosen to isolate the impact of changes to their respective rainfall and antecedent soil moisture. The analysis is limited to stations with 30 years or more of active record with the majority of stations in North America, Europe, Brazil, Oceania, and southern Africa.Consistent with physical reasoning, for more frequent events such as the annual maxima, it is found the peak 1-day rainfall event intensity is increasing approximately a rate of 6–7%/°C, with rarer event intensities increasing at a rate exceeding the Clausius-Clapeyron relation. We find that storm volumes are not increasing as greatly as the peak rainfall and storm durations are decreasing, pointing to an intensification of rainfall events and a peakier temporal pattern. While rainfall is intensifying, the magnitude of frequent floods (those expected to occur on average once per year) are in general decreasing, particularly in tropical and arid regions of the world. We find that this is likely due to a dominance of drying antecedent soil moisture conditions. However, the magnitude of rarer floods has, on average been increasing. We suggest this is because, for these rarer events, the increase in rainfall outweighs the decrease in soil moisture. Our results point to a worst of both world’s scenario where small floods, responsible for filling our water supplies, are decreasing, while the large flood events which pose a risk to life and infrastructure, are increasing.

Climate Change Is Making India’s West Coast More Vulnerable to Cyclones

A new study found significant increases in the intensity, frequency, and duration of cyclonic storms over the Arabian Sea. Is the west coast prepared?

The relative influence of dune aspect ratio and beach width on dune erosion as a function of storm duration and surge level

Abstract. Dune height is an important predictor of impact during a storm event given that taller dunes have a lower likelihood of being overtopped than shorter dunes. However, the temporal dominance of the wave collision regime, wherein volume loss (erosion) from the dune occurs through dune retreat without overtopping, suggests that dune width must also be considered when evaluating the vulnerability of dunes to erosion. We use XBeach, a numerical model that simulates hydrodynamic processes, sediment transport, and morphologic change, to analyze storm-induced dune erosion as a function of dune aspect ratio (i.e., dune height versus dune width) for storms of varying intensity and duration. We find that low aspect ratio (low and wide) dunes lose less volume than high aspect ratio (tall and narrow) dunes during longer and more intense storms when the beach width is controlled for. In managed dune scenarios, where sand fences are used to construct a “fenced” dune seaward of the existing “natural” dune, we find that fenced dunes effectively prevent the natural dune behind them from experiencing any volume loss until the fenced dune is sufficiently eroded, reducing the magnitude of erosion of the natural dune by up to 50 %. We then control for dune morphology to assess volume loss as a function of beach width and confirm that beach width exerts a significant influence on dune erosion; a wide beach offers the greatest protection from erosion in all circumstances while the width of the dune determines how long the dune will last under persistent scarping. These findings suggest that efforts to maintain a wide beach may be effective at protecting coastal communities from dune loss. However, a trade-off may exist in maintaining wide beaches and dunes in that the protection offered in the short-term must be considered in concert with potentially long-term detrimental effects of limiting overwash, a process which is critical to maintaining island elevation as sea level rises.

An assessment of tropical cyclones in North American CORDEX WRF simulations

This work presents an assessment of tropical cyclones (TCs) in the 25 km and 50 km resolution reanalysis-forced and baseline and future (RCP8.5) global climate model (GCM) forced simulations produced for the North American branch of the international Coordinated Regional climate Downscaling Experiment (NA-CORDEX) using the Weather Research and Forecasting (WRF) model. A set of complementary 12 km resolution simulations produced as a part of a different project is also included in this assessment.Before examining the projections from the GCM-driven simulations, the ability of the simulations to minimally produce a realistic spatial distribution of historical TC occurrence was assessed in simulations forced by reanalysis and the three different GCMs used herein. Then, projections for occurrence, TC related mean precipitation and precipitation intensity, storm duration, the intensity measured by minimum pressure and maximum wind speed, storm size, and translation speed were examined. Several of these characteristics show little to no change in the future in trend or in distribution across the ensemble. However, many simulations suggest a westward shift or increase in TC occurrence over the East Pacific basin and a decrease in occurrence over the Caribbean and Gulf of Mexico. Increases (decreases) in total storm-related precipitation are projected where TC occurrence increases (decreases). TC precipitation intensity is found to increase in all simulations over the East Pacific, but projections are mixed over the North Atlantic. Finally, the ensemble projects a distribution shift towards more intense TC over the East Pacific, and a shift toward faster translation speeds over the North Atlantic.

Non-stationary Investigation of Extreme Rainfall

Natural or human-induced variability emerged from investigation of the traditional stationary assumption regarding extreme precipitation analyses. The frequency of extreme rainfall occurrence is expected to increase in the future and neglecting these changes will result in the underestimation of extreme events. However, applications of extremes accept the stationarity that assumes no change over time. Thus, non-stationarity of extreme precipitation of 5, 10, 15, and 30 minutes and 1-, 3-, 6-, and 24-hour data of 17 station in the Black Sea region were investigated in this study. Using one stationary and three non-stationary models for every station and storm duration, 136 stationary and 408 non-stationary models were constructed and compared. The results are presented as non-stationarity impact maps across the Black Sea Region to visualize the results, providing information about the spatial variability and the magnitude of impact as a percentage difference. Results revealed that nonstationary (NST) models outperformed the stationary model for almost all precipitation series at the 17 stations. The model in which time dependent location and scale parameter used (Model 1), performed better among the three different time variant non-stationary models (Model 1 as time variant location and scale parameters, Model 2 as time variant location parameter, and Model 3 as time variant scale parameter). Furthermore, non-stationary impacts exhibited site-specific behavior: Higher magnitudes of non-stationary impacts were observed for the eastern Black Sea region and the coastal line. Moreover, the non-stationary impacts were more explicit for the sub-hourly data, such as 5 minutes or 15 minutes, which can be one of the reasons for severe and frequent flooding events across the region. The results of this study indicate the importance of the selected covariate and the inclusion of it for the reliability of the model development. Spatial and temporal distribution of the nonstationary impacts and their magnitude also urges to further investigation of the impact on precipitation regime, intensification, severity. Doi: 10.28991/cej-2021-03091748 Full Text: PDF

Evaluation of regional climate models and future wind characteristics in the Black Sea

AbstractThe main objective of the present study is to provide a comprehensive image of the expected wind patterns along the 21st century in the Black Sea using the wind fields simulated by Regional Climate Model (RCM), namely Rossby Centre regional atmospheric model (version RCA4). Long‐term averages, long‐term variability, and long‐term trends in wind characteristics over the Black Sea are evaluated in two future time slices (near future 2021–2060 and middle future 2061–2100) under the two climate scenarios (RCP4.5 and 8.5). Detailed analysis of wind (annual mean and 99th percentile wind speeds) and storm characteristics (number and duration of storms) are conducted for three different locations selected on the same meridional section to assess the variability on the wind characteristics from west to east. Spatiotemporal variability on the wind characteristics indicates that the eastern Black Sea will be characterized by lower mean wind speed, stronger 99th percentile wind speed, and higher variability. Considering the global indicators of climate change (e.g., increasing frequency and intensity of extreme events), the eastern Black Sea, characterized by complex atmospheric circulation due to surrounding mountains, is more likely to be subjected to the impacts of climate change as the occurrence of extreme wind speeds in future periods is more prominent in this region. In the future periods, the 100‐year return period wind speeds increase approximately 7% and 27% in the western and eastern Black Sea, respectively, compared to the historical period. The strong and relatively stable winds with low variability in the western Black Sea indicate a reliable, persistent, and sustainable wind energy potential in this region in the future.

Investigating event-based temporal patterns of design rainfall in a tropical region

ABSTRACT This study investigated the temporal rainfall pattern in order to facilitate rainfall design, which normally requires a good understanding of the temporal patterns of rainstorm events. The analysis employed a storm-event-based approach using the concept of inter-event time definition (IETD) and rainfall depth/duration/intensity thresholds. The 5-min rainfall data at three raingauge stations were analysed to determine representative quartiles of a design storm in a tropical city. The temporal characteristics of the design storm could be determined from the rainfall depth ratios of consecutive peak rainfalls for each interval of storm duration, and time to the first peak rainfall depending on each quartile’s rainstorm events. The determination of the quantile distribution of tropical rainfall could help improve the representativeness of design rainfall and facilitate rainfall–runoff modelling for urban flood control in a tropical region.

Implications of Distinct Methodological Interpretations and Runoff Coefficient Usage for Rational Method Predictions

AbstractThe Rational Method is one of the most widely used methods for estimating peak discharge in small catchments. There are at least three forms of the Rational Method in use: deterministic, stochastic, and hybrid Rational Methods. These different forms are associated with distinct definitions of the runoff coefficient and produce distinct design flows, each of which has different risks associated with their exceedence. In this study, we firstly differentiate these forms of the Rational Method and show that a key point of difference between the forms lies in their interpretations of the runoff coefficient parameter. We then focus on the widely used hybrid Rational Method and demonstrate that the runoff coefficient is not only challenging to interpret, but is also dependent on land cover types, storm duration, and infiltration losses. With the understanding that most design manuals treat the runoff coefficient as a constant dependent on land cover and independent of storm properties, we explore the magnitude of error in design flows resulting from these assumptions. They suggest that the magnitudes of error associated with the conventional application of the Rational can be >500%. These issues with interpretation and internal consistency in the treatment of terms in the Rational Method suggest that it may not be possible to achieve reliable or consistent peak flow estimates using the Rational Method, motivating the use of more complex design tools.

Alfvénicity-related Long Recovery Phases of Geomagnetic Storms: A Space Weather Perspective

Abstract This paper reports, for the first time on a statistical basis, on the key role played by the Alfvénic fluctuations in modulating the recovery phase of the geomagnetic storms, slowing down the restoration of the magnetosphere toward its pre-storm equilibrium state. Using interplanetary and geomagnetic measurements collected over more than one solar cycle, a high correlation between the durations of Alfvénic streams and concurrent recovery phases is found, pointing to a clear coupling between Alfvénic turbulence and magnetospheric ring current dynamics. By exploiting current solar wind models, these observations also provide space weather opportunities of predicting the total duration of any geomagnetic storm induced by any solar driver provided that it is followed by an Alfvénic stream, a crucial piece of information for ground technologies and infrastructures that are affected by time-integrated effects throughout the duration of the storm.

Development and Assessment of High-Resolution Radar-Based Precipitation Intensity-Duration-Curve (IDF) Curves for the State of Texas

Conventionally, in situ rainfall data are used to develop Intensity Duration Frequency (IDF) curves, which are one of the most effective tools for modeling the probability of the occurrence of extreme storm events at different timescales. The rapid recent technological advancements in precipitation sensing, and the finer spatio-temporal resolution of data have made the application of remotely sensed precipitation products more dominant in the field of hydrology. Some recent studies have discussed the potential of remote sensing products for developing IDF curves. This study employs a 19-year NEXRAD Stage-IV high-resolution radar data (2002–2020) to develop IDF curves over the entire state of Texas at a fine spatial resolution. The Annual Maximum Series (AMS) were fitted to four widely used theoretical Extreme Value statistical distributions. Gumble distribution, a unique scenario of the Generalized Extreme Values (GEV) family, was found to be the best model for more than 70% of the state’s area for all storm durations. Validation of the developed IDFs against the operational Atlas 14 IDF values shows a ±27% difference in over 95% of the state for all storm durations. The median of the difference stays between −10% and +10% for all storm durations and for all return periods in the range of (2–100) years. The mean difference ranges from −5% for the 100-year return period to 8% for the 10-year return period for the 24-h storm. Generally, the western and northern regions of the state show an overestimation, while the southern and southcentral regions show an underestimation of the published values.

Rainfall spatial-heterogeneity accelerates landscape evolution processes

Catchment hydro-morphological response is mainly conditioned on rainfall properties, such as rainfall intensity, storm duration and frequency, and the timing of these events. Rainfall spatial variability is likewise a major determinant affecting streamflow, erosion, and sediment transport, and is explored largely in the context of heavy rain triggering floods and fast morphological changes on hillslopes and in channels. In this study, we examine how the spatial structure of rainfall influences landscape evolution at the catchment scale over hundreds of years. To achieve this, multiple realizations of hourly rainfall fields, each differing only by their spatial distribution but identical in all other respects, were simulated using a weather generator. The impact of storm spatial-heterogeneity on the catchment morphology was then assessed with a landscape evolution model (CAESAR-Lisflood). A virtual “open-book” type catchment was used for this numerical experiment. The mean streamflow and low-flows remained the same while the magnitude of the annual peak streamflow increased by up to 12% in response to higher rainfall spatial heterogeneity. However, the erosion and deposition rates significantly increased (up to 50%) and the net erosion and deposition areas changed (increased by up to 9% and decreased by 13.5%, respectively) when the rain became less uniform in space. Furthermore, new gullies were found to be longer, deeper, and more branched in response to increased rainfall heterogeneity. The results suggest that heterogeneity in rainfall spatial patterns speeds up landscape development, even when rainfall volumes and temporal structures are the same. This implies that the spatial structure of rainfall may have more of an influence on catchment morphology at long time scales than previously thought.

Effects of climate change on depression‐focused groundwater recharge in the Canadian Prairies

AbstractSmall topographic depressions are ubiquitous in the glaciated terrain of the Northern Prairies characterized by a cold semiarid climate. Groundwater recharge in this region is focused in topographic depressions, which receive lateral inputs of snowmelt runoff in addition to vertical inputs of precipitation. The response of depression‐focused recharge to climate change is largely unknown due to the difficulty of representing the complex interaction between depressions and surrounding uplands in hydrological models. This study evaluates climate change effects on recharge using a process‐based hydrological model and the pseudo‐global warming (PGW) approach representing a climate of 2092–2100, which has a higher mean annual temperature (+4.9 °C) and precipitation (+135 mm or +27%) compared with the present climate. The recharge model is conditioned using field data from an instrumented grassland site in the Canadian Prairies. Under the present climate, snowmelt runoff occurred in March–April over frozen soil, which accounted for the majority of water transfer from the upland to the depression. Under the PGW scenario, the amount of snowmelt runoff in March–April decreased due to lower snow accumulation and shorter periods of frozen soil. Instead, runoff occurred in midwinter and also in summer months due to increased intensity and duration of summer storms. Despite the increased precipitation, mean annual recharge rates decreased from 10.2 to 3.2 mm yr–1, indicating the importance of considering the complex effects of warmer and wetter climate on hydrological processes in cold semiarid regions.

A multi-sensor evaluation of precipitation uncertainty for landslide-triggering storm events.

Extreme precipitation can have profound consequences for communities, resulting in natural hazards such as rainfall‐triggered landslides that cause casualties and extensive property damage. A key challenge to understanding and predicting rainfall‐triggered landslides comes from observational uncertainties in the depth and intensity of precipitation preceding the event. Practitioners and researchers must select from a wide range of precipitation products, often with little guidance. Here we evaluate the degree of precipitation uncertainty across multiple precipitation products for a large set of landslide‐triggering storm events and investigate the impact of these uncertainties on predicted landslide probability using published intensity–duration thresholds. The average intensity, peak intensity, duration, and NOAA‐Atlas return periods are compared ahead of 177 reported landslides across the continental United States and Canada. Precipitation data are taken from four products that cover disparate measurement methods: near real‐time and post‐processed satellite (IMERG), radar (MRMS), and gauge‐based (NLDAS‐2). Landslide‐triggering precipitation was found to vary widely across precipitation products with the depth of individual storm events diverging by as much as 296 mm with an average range of 51 mm. Peak intensity measurements, which are typically influential in triggering landslides, were also highly variable with an average range of 7.8 mm/h and as much as 57 mm/h. The two products more reliant upon ground‐based observations (MRMS and NLDAS‐2) performed better at identifying landslides according to published intensity–duration storm thresholds, but all products exhibited hit ratios of greater than 0.56. A greater proportion of landslides were predicted when including only manually verified landslide locations. We recommend practitioners consider low‐latency products like MRMS for investigating landslides, given their near‐real time data availability and good performance in detecting landslides. Practitioners would be well‐served considering more than one product as a way to confirm intense storm signals and minimize the influence of noise and false alarms.

Forecasting Occurrence and Intensity of Geomagnetic Activity With Pattern‐Matching Approaches

AbstractVariability in near‐Earth solar wind conditions gives rise to space weather, which can have adverse effects on space‐ and ground‐based technologies. Enhanced and sustained solar wind coupling with the Earth's magnetosphere can lead to a geomagnetic storm. The resulting effects can interfere with power transmission grids, potentially affecting today's technology‐centered society to great cost. It is therefore important to forecast the intensity and duration of geomagnetic storms to improve decision making capabilities of infrastructure operators. The 150 years aaH geomagnetic index gives a substantial history of observations from which empirical predictive schemes can be built. Here we investigate the forecasting of geomagnetic activity with two pattern‐matching forecast techniques, using the long aaH record. The techniques we investigate are an Analogue Ensemble (AnEn) Forecast, and a Support Vector Machine (SVM). AnEn produces a probabilistic forecast by explicitly identifying analogs for recent conditions in the historical data. The SVM produces a deterministic forecast through dependencies identified by an interpretable machine learning approach. As a third comparative forecast, we use the 27 days recurrence model, based on the synodic solar rotation period. The methods are analyzed using several forecast metrics and compared. All forecasts outperform climatology on the considered metrics and AnEn and SVM outperform 27 days recurrence. A Cost/Loss analysis reveals the potential economic value is maximized using the AnEn, but the SVM is shown as superior by the true skill score. It is likely that the best method for a user will depend on their need for probabilistic information and tolerance of false alarms.

Hydrodynamic Сonditions of the Bakalskaya Spit Degradation (Western Crimea) over the Past 30 Years

urpose. The paper is aimed at studying the morphodynamic features of the Bakalskaya Spit evolution being influenced by the sea wind waves and swell, namely assessment of inter-annual variations in the alluvial (erosion) areas of the Bakalskaya Spit coastline, analysis of inter-annual variability of the wind wave parameters, determination of the surface wave characteristics (or a combination of a few ones) responsible for the processes of the bottom material erosion or accumulation in the coastal zone. Methods and Results. Based on the analysis of satellite images for 1984–2016, the areas of the bottom material accumulation or erosion of the Bakalskaya Spit coastline were determined. Application of the spectral wave model permitted to obtain time series of the main parameters of wind waves and swell (significant wave heights and propagation directions) in the Bakalskaya Spit coastal zone with the 1 hr time resolution for the period from 1984 to 2016. The characteristics of surface waves responsible for the coastline deformation were revealed using the discriminant analysis. Conclusions. Analysis of satellite images of the spit made it possible to distinguish three periods in the history of the Bakalskaya spit evolution: 1985–1997, 1998–2007 and 2007–2016. The first period was characterized by relative stability. The strongest erosion took place in 1998; after that the alluvial and erosion cases alternated for 10 years weakly tending to general erosion that constituted the second period. The third one that began in 2007 can be defined as the period of spit degradation accompanied by the irreversible loss of beach material. The basic parameters conditioning hydrodynamics of the Bakalskaya Spit water area are: total duration of storms; mean and maximum values of significant heights of wind waves and swell. Statistical characteristics of the wind waves’ parameters are of a fairly strong inter-annual variability. According to the mean and maximum indices, the wind waves directed close to the normal to the coastline (WSW and WNW) are the most developed. The applied discriminant analysis permitted to draw a statistically reliable conclusion that the direction of the final (mean annual) wave impact on the coastal zone, conditioning the processes of sand accumulation or erosion was set by the waves directed to NNW, at that the swell contribution was dominant. The impact degree is determined by strong storms with the directions close to the normal to the coastline, namely, the WSW ones.

Influence of Wave Climate on Intra and Inter-Annual Nearshore Bar Dynamics for a Sandy Beach

The study investigates cross-shore outer sand bar dynamics in an open-coast non-tidal beach at the Bulgarian Black Sea due to wave climate. On seasonal to short-term (1–2 years) time scale, monthly field measurements of the outer bar profiles were related to respective modeled nearshore wave data. Hereby, seaward-shoreward bar migration was examined depending on the wave forcing, wave non-linearity, wave transformation scenarios, storms and direction of wave incidence. Analysis revealed that intra-annually highly non-linear waves were responsible for outer bar displacement, while the direction of migration depended on wave period, duration of conditions with wave steepness >0.04, angle of approach and total duration of storms. Short-term bar evolution was mainly governed by wave height and storms’ parameters as the angle of approach and duration. The correlation between the outer bar location and wave height annual variations initiated the first for the explored Black Sea region examination of possible connection between wave height’s temporal fluctuations and the variability of climatic indices the North Atlantic Oscillation (NAO), the Atlantic Multi-decadal Oscillation (AMO), the East Atlantic Oscillation (EA), the Arctic Oscillation (AO), the East Atlantic-Western Russia (EA/WR) and the Scandinavian (SCAND) patterns. According to the results the inter-annual outer bar location may vary depending on periods of maximum annual wave fluctuations, which in turn predominantly depend on indices the EA (4–5, 10–11, 20–30 years), the EA/WR (2–4, 9–13 years) and the NAO (15 years).

Influence of storm events on surf zone zooplankton in a Southwestern Atlantic sandy beach: A preliminary methodology using high-frequency physical data

Here we present a preliminary methodology and unprecedented data for sandy beach surf zones, focused on understanding the effects of the passage of storm events in surf- zooplankton communities. The main objectives of the present study were to analyze the variation of surf zone physical parameters during several storm events, which have occurred on Pehuen Co beach (PC), using high-frequency physical data and to explore the influence of these events on surf zooplankton taking into account some ecological community indicators such as taxa richness, abundance and diversity. We observed that the zooplankton community structure was significantly altered after the storms, mainly in terms of abundance, but also in the number of taxa and general diversity. In addition, important differences between storm duration were registered. The short-duration storms (< 6 h) were associated with an increase of zooplankton abundances after the events, whereas the long-duration ones (> 6 h) showed a sharp decrease in the number of organisms. Based on the present results, the coastal biological system could be completely altered during storm events, considering that the observed changes in the zooplankton community probably affect other species that interact with them, altering the trophic relationships in surf waters. Additionally, the high-frequency data provided us valuable information not only to visualize the hydrodynamic consequences of the storms, but also to explain the changes in the zooplankton community. The present contribution provides an initial step toward comprehensive research about the physical-biological interactions in surf zone waters during storms, even more in the actual context of climate change where extreme events are expected to increase in frequency and intensity.

Gidrodinamicheskiye usloviya degradatsii Bakal'skoy kosy (Zapadnyy Krym)

Purpose. The paper is aimed at studying the morphodynamic features of the Bakalskaya Spit evolution being influenced by the sea wind waves and swell, namely assessment of inter-annual variations in the alluvial (erosion) areas of the Bakalskaya Spit coastline, analysis of inter-annual variability of the wind wave parameters, determination of the surface wave characteristics (or a combination of a few ones) responsible for the processes of the bottom material erosion or accumulation in the coastal zone. Methods and Results. Based on the analysis of satellite images for 1984–2016, the areas of the bottom material accumulation or erosion of the Bakalskaya Spit coastline were determined. Application of the spectral wave model permitted to obtain time series of the main parameters of wind waves and swell (significant wave heights and propagation directions) in the Bakalskaya Spit coastal zone with the 1 hr time resolution for the period from 1984 to 2016. The characteristics of surface waves responsible for the coastline deformation were revealed using the discriminant analysis. Conclusions. Analysis of satellite images of the spit made it possible to distinguish three periods in the history of the Bakalskaya Spit evolution: 1985–1997, 1998–2007 and 2007–2016. The first period was characterized by relative stability. The strongest erosion took place in 1998; after that the alluvial and erosion cases alternated for 10 years weakly tending to general erosion that constituted the second period. The third one that began in 2007 can be defined as the period of spit degradation accompanied by the irreversible loss of beach material. The basic parameters conditioning hydrodynamics of the Bakalskaya Spit water area are: total duration of storms; average and maximum values of significant heights of wind waves and swell. Statistical characteristics of the wind waves’ parameters are of a fairly strong inter-annual variability. According to the average and maximum indices, the wind waves directed close to the normal to the coastline (WSW and WNW) are the most developed. The applied discriminant analysis permitted to draw a statistically reliable conclusion that the direction of the final (average annual) wave impact on the coastal zone, conditioning the processes of sand accumulation or erosion was set by the waves directed to NNW, at that the swell contribution was dominant. The impact degree is conditioned by strong storms with the directions close to the normal to the coastline, namely, the WSW ones

Analysis of the Duration of High Winds During Landfalling Hurricanes

The duration of wind storms over a threshold wind speed value is known to be an important parameter in determining damage and losses, with losses tending to increase with the duration. This is because peak pressures tend to increase with longer duration, many building components and cladding systems are vulnerable to different types of fatigue mechanisms, and the yielding of linear elastic materials in the plastic range depends on the number of load cycles. A hurricane model was used to examine the duration of high winds in the United States at Miami, Galveston, and Charleston with the goal of establishing duration statistics for hurricanes as a function of peak wind speed. It was found that the duration of high winds, defined as the time that the 10 min wind speeds are within 30% of the peak 10 min wind speed, had a significant variation with a range from tens of minutes to more than 20 h, depending on location. The median duration ranged from 1.5 to 4 h at the three locations, depending on location and the design wind speed level (i.e., the risk Category of the building). These results were used to establish a simple normalized model for wind speed as a function of time, which could be used together with the design wind speed to establish load cycles for design.

Recurrent rainfall-induced landslides on the slopes with pyroclastic cover of Partenio Mountains (Campania, Italy): Comparison of 1999 and 2019 events

Abstract Rainfall-induced shallow landslides occurring along slopes of mountains around the city of Naples (southern Italy), characterized by pyroclastic covers laying upon fractured limestone bedrock, pose serious threat to settlements and towns located at their foot. Although the triggering mechanism, related to suction reduction in the initially unsaturated soil cover is quite clear, there is still debate about the hydrological processes which predispose the slopes to failure. In this paper, the predisposing factors are analyzed with reference to two intense storms, both with about 300 mm rainfall, occurred in the same period of the year in 1999 and 2019. The two storms triggered several shallow landslides in an area of few km2 of the northeast-facing slopes of Partenio Mountains. The two events are compared analyzing both the characteristics of antecedent and event precipitations, as well as simulating the response of the slopes to rainfall with the help of a mathematical model. Specifically, two slopes are analyzed: one, near the town of Cervinara, where landslides were triggered only in 1999; another, near the town of San Martino Valle Caudina, where landslides occurred during both the events. The results of the model simulations indicate that rainstorm duration (shorter in 1999) and antecedent precipitation during the weeks before the event (smaller in 1999) are the main reasons of the different responses of the slopes to the two rainfall events. In fact, both drier initial conditions at the base of the soil cover and shorter storm duration limit the possibility of drainage of infiltrating water out of the soil cover through the soil-bedrock interface, thus favoring the suction reduction required for slope failure. The obtained results provide a key for the interpretation of landslides, often occurring in late autumn-early winter in the area.