Piedmont Flood Research Articles

Post-processing rainfall in a high-resolution simulation of the 1994 Piedmont flood

Post-processing rainfall in a high-resolution simulation of the 1994 Piedmont flood

The 1994 Piedmont flood: an archetype of extreme precipitation events in Northern Italy

Extreme precipitation events (EPEs) are meteorological phenomena of major concern for the densely populated regions of northern and central Italy. Although statistically rare, they tend to be recurrent in autumn and share common characteristics in the large-scale dynamical evolution responsible for their generation. Past studies on EPEs have reported, as the main triggering factor, a meridionally elongated upper-level trough embedded in an incoming Rossby wave packet. In this respect, we show how the meteorological conditions leading to the devastating 1994 Piedmont flood represent a typical flow evolution for this type of extreme events. Exploiting the systematic classification of EPEs recently published by the authors and taking advantage of a new observational dataset, this article revisits the role of the large-scale flow on this and similar cases of past EPEs.

The Piedmont flood of November 1994: a testbed of forecasting capabilities of the CNR-ISAC meteorological model suite.

The celebration of the 25th anniversary of the Piedmont flood was organized by the University of Piemonte Orientale in Alessandria, a town that was severely affected in November 1994. It has been an opportunity to reexamine the meteorological event and assess the potential of CNR-ISAC models, after more than 20 years of development, to accurately simulate the heavy precipitation at different lead times. The predictability of this extreme event has been studied on a wide range of space and time scales, from subseasonal to convection resolving, using a variety of model setups and initial conditions. The subseasonal experiment produces a precipitation anomaly that, even if underestimated, indicates some predictability beyond the second forecast week. At shorter ranges, results indicate that there is a consistent improvement in the precipitation forecast going from low-resolution hydrostatic to high-resolution nonhydrostatic models. It is only at very high resolution (500 m) that the convective activity extending to the north of the divide line of the Ligurian Apennines, which was responsible for the flood of the Tanaro River, is predicted with an intensity comparable with rain gauge observations. The main mesoscale phenomena that played a role in the different phases of the event have been also identified.

Low cost, multiscale and multi-sensor application for flooded area mapping

Abstract. Flood mapping and estimation of the maximum water depth are essential elements for the first damage evaluation, civil protection intervention planning and detection of areas where remediation is needed. In this work, we present and discuss a methodology for mapping and quantifying flood severity over floodplains. The proposed methodology considers a multiscale and multi-sensor approach using free or low-cost data and sensors. We applied this method to the November 2016 Piedmont (northwestern Italy) flood. We first mapped the flooded areas at the basin scale using free satellite data from low- to medium-high-resolution from both the SAR (Sentinel-1, COSMO-Skymed) and multispectral sensors (MODIS, Sentinel-2). Using very- and ultra-high-resolution images from the low-cost aerial platform and remotely piloted aerial system, we refined the flooded zone and detected the most damaged sector. The presented method considers both urbanised and non-urbanised areas. Nadiral images have several limitations, in particular in urbanised areas, where the use of terrestrial images solved this limitation. Very- and ultra-high-resolution images were processed with structure from motion (SfM) for the realisation of 3-D models. These data, combined with an available digital terrain model, allowed us to obtain maps of the flooded area, maximum high water area and damaged infrastructures.

Testing the use of reimbursement data to obtain damage curves in urbanised areas: the case of the Piedmont flood on October 2000

This article analyses the assessment of economic damages in urbanised flooded areas by testing the use of reimbursement data to obtain damage curves. Data coming from field observation of the 2000 flood in Piedmont, Italy, are used and the influence of local features and topography, as well as urban patterns are studied. Our starting point is the assessment of individual flooded elements, whose damages result from slightly more than 7000 refund claims. Damage functions estimation is carried out by using water depth and flow velocities obtained by 2D inundation model. Results show the relationship of damage versus water depth and versus flow velocity are strongly nonlinear and urban patterns playing a major role in explaining the amount of damage under given conditions. Moreover, results provide useful information for future ex ante estimation of potential flood damages and rewarding risk reductions and management actions.

Early chromite mining and agricultural clearance: Opportunities for the investigation of agricultural sediment dynamics in the eastern piedmont (USA)

Many flood plains in the Eastern Piedmont (USA) are buried under deposits of sediment resulting from European agricultural clearance. Classic radioisotopic dating techniques cover temporal periods too short (¹³⁷Cs, ²¹⁰Pb) or too long (¹⁴C) to reliably date sediments deposited during periods of local European activity (1660-1900). Moreover, many potential biomarkers, such as pollen, degrade in oxic flood plain sediments. In the Baltimore, Maryland (USA) region, early chromite mining (1820 –1880) occurred during periods of rapid agricultural clearance. Use of chromium (Cr) chemostratigraphic profiles in flood plain sediments tied to historical mining activity can provide improved precision in overbank accumulation rates and timing. Sediment cores were collected from the Red Run basin, which is part of the Baltimore Ecosystem Study, an urban Long-Term Ecological Research site. Trace metal chemostratigraphic profiles were measured and peaks in Cr concentration tied to historic mining activity. Dates from Cr chemostratigraphic profiles were combined with ¹³⁷Cs dating to reconstruct flood plain sedimentation rates. Red Run early sedimentation rates (1820 –1880) were higher (0.45 –1.19 cm/yr) than more recent (1880 –1963) rates (0.08 –0.46 cm/yr). This indicates that Piedmont flood plain vertical sediment accumulation might have peaked before the peak in agricultural clearance, earlier than assumed by regional models. The Cr chemostratigraphy is applicable to a wider region including much of the Maryland and Pennsylvania (USA) Piedmont.

Water Vapor Sources of the October 2000 Piedmont Flood

Abstract Very intense mesoscale or synoptic-scale rainfall events can occasionally be observed in the Mediterranean region without any deep cyclone developing over the areas affected by precipitation. In these perplexing cases the synoptic situation can superficially look similar to cases in which very little precipitation occurs. An example is the major precipitation and flooding event that affected Piedmont, Italy, between 13 and 16 October 2000. The emphasis of this study is on the moisture origin and transport. Moisture balances are computed on different space and time scales, revealing that precipitation exceeds evaporation over an area inclusive of Piedmont and the northwestern Mediterranean region, on a time scale encompassing the event and about 2 weeks preceding it. This is suggestive of an important moisture contribution originating from outside the region. A synoptic and dynamic analysis is then performed to outline the potential mechanisms that could have contributed to the large-scale moistur...

High-Resolution Weather Forecasting over Complex Orography: Sensitivity to the Assimilation of Conventional Data

Abstract Weather forecasting for regions with complex orography, as the Alps, presents several challenges and the task becomes even more difficult when high resolution is required. Moreover, for the Alpine region, some of the problems are due to the lack of observations especially over the Mediterranean Sea. A possibility for improving forecasts is to reuse assimilation techniques locally. In this paper, results obtained through data assimilation are presented: objective analysis (OA) of observations and data analyses from the European Centre for Medium-Range Weather Forecasts (ECMWF) are used together to generate a new set of mesoscale initial (ICs) and boundary conditions (BCs). In particular, OA is applied to surface data and radiosoundings using two methods: Cressman and multiquadric. The sensitivity of the weather forecast to the number of upper-air stations assimilated by OA is tested using data from the Piedmont flood (4–6 November 1994). At first, a comparison is made between ICs, obtained through...

The Uncertainty in the Prediction of Flash Floods in the Northern Mediterranean Environment

Development of an operational flood forecasting system and assessment of forecast uncertainty are the principal topics of this paper. Flood forecasting procedures are developed for a Mediterranean environment. A procedure that uses the Ensemble Prediction System as input for a semidistributed hydrologic model is presented. A rainfall downscaling model is used to bridge the scale gap between numerical weather prediction model output and hydrologic modeling input. The results are illustrated for the November 1994 Piedmont flood.

The impact of human activities on groundwater resources in the south edge of Tarim Basin, Xinjiang

In the modern times, the population growth, development of industrial and agricultural production and the petroleum exploitation, brought about the unceasing expansion of artificial oasis and abrupt increase of water demand. The artificial hydraulic irrigation engineering took the place of the natural river system, the reservoirs took the place of natural lakes, which in turn enhanced the space-time redistribution of surface water based on the natural evolution, and so did groundwater. The groundwater recharge reduced 26.2% in 46 years from 1950 to 1995 in the southern piedmont flood plain of Tarim Basin due to mean yearly population increase rate of 27.7‰ and associated with the water use rate increasing from 24.6% to 58.4%. At the same time the artificial water system seepage give primary play to groundwater recharge, which is up to 57.6% whilst that of the natural system reduce to 33.7%. As a result, groundwater level drop 3–5m widespread except some irrigation area and surroundings of plain reservoir. Spring water discharge also reduce about 37.6% and discharge zone continuously move away to the north with the value of 0.5–1.2km in the past 40 years.

Mechanisms of Intense Alpine Rainfall

Abstract Numerical studies by the authors and others of the 1994 Piedmont flood show that the orographically modified flow was a critical element for the production of extraordinary rainfall. To uncover the precise mechanism of orographic rainfall occurring in full-physics MM5 simulations of the 1994 Piedmont flood, the authors carried out simulations with the same real-data initial and boundary conditions, but with the real orography replaced by an idealized one. With excellent agreement between real and idealized orography on the rainfall rate versus time in the Piedmont area, analysis of the idealized-orography simulation provides a clear picture of the model's mechanism of orographically induced rainfall. As noted in previous studies of the 1994 Piedmont case, a moist saturated airflow has a reduced effective static stability and tends to flow over the mountains, while an unsaturated airstream is stable and tries to flow around (toward the left in the Northern Hemisphere). In the 1994 Piedmont case, t...

Western Mediterranean cyclones and heavy rain. Part 1: Numerical experiment concerning the Piedmont flood case

AbstractHeavy rain events constitute a major operational problem in the Mediterranean area. The present work tries to contribute to a better understanding of this problem by considering the possible indirect influence of surface depressions in the triggering and location of the heavy rain. The idea is that any surface low contributes to the organisation of the low‐level flow. This then affects the creation/intensification of a low‐level feeding current of warm and wet air that can sustain heavy rain if there is convective instability. Two approaches have been used: (a) a numerical and synoptic approach, Part 1, and (b) a statistical approach, Part 2. In Part 1, the differences between a control run and a numerical experiment without the Iberian mountains for the ‘MAP Piedmont flood event’ are discussed. Among other effects, the Iberian orography seems to intensify a secondary low near Liguria as well as increase the mixing ratio convergence and the rainfall intensity near it. A few other cases of heavy rain are also briefly reviewed in order to identify the presence of a Mediterranean depression in the vicinity. Copyright © 2000 Royal Meteorological Society

Numerical simulations of the Piedmont flood of 4-6 November 1994

Numerical simulations of the Piedmont flood of 4-6 November 1994

Numerical simulations of the Piedmont flood of 4–6 November 1994

A case study of the 1994 Piedmont flood is carried out by performing several numerical experimentsusing the MM5 model. We report on sensitivity tests and analyses that suggest thefollowing description of the events leading to the flood: rising motion ahead of an upper-leveltrough, progressing from Spain towards Italy, initiated deep convection within the conditionallyunstable air existing over the Mediterranean. Thus, a band of intense precipitation and lowlevelsoutherly winds formed and moved eastward with the upper trough. As the rain band andstrong southerlies encountered the western Alps, moist air was lifted, resulting in large amountsof rainfall. The associated latent-heat-related upward motion produced a strong positive vorticityanomaly over the western Alps with associated low-level easterlies in the Po Valley whichappear to have played a major role in retarding the generally eastward progress of the rainband over Piedmont.

Numerical Simulations of the 1994 Piedmont Flood: Role of Orography and Moist Processes

The intense precipitation event that occurred between 3 and 6 November 1994 and caused extensive flooding over Piedmont in northwestern Italy is simulated and tested with respect to various physical aspects, using a meteorological mesoscale model (BOLAM). The period when the most intense rain occurred, mainly covering the second half of 4 and all of 5 November, is examined. A control experiment, starting at 1200 UTC 4 November, simulates the two observed precipitation peaks and captures the magnitude and timing of the most intense precipitation well even at relatively low horizontal resolution (about 30 km). The European Centre for Medium-Range Weather Forecasts analyses are used to provide the initial and boundary conditions. Model output diagnostics and comparison with observations indicate that most of the precipitation is associated with a prefrontal low-level jet, ahead of the cold front, impinging upon the orography of the region (Alps and Apennines). The model simulates a multiple rainband and frontal structure whose evolution determines both intensity and location of the prefrontal warm and moist flow. Almost all of the simulated precipitation over the Alps forms in the middle–low troposphere through forced ascent, whereas part of the secondary maximum, observed over the Apennines, is of convective type. Sensitivity experiments have been conducted to investigate the effects of orography, surface fluxes, and latent heat exchange processes in the atmosphere. The role of the orography is crucial in determining distribution and amount of precipitation, whereas sensible and latent heat fluxes from the Mediterranean Sea (over the period considered) enhanced only the convective precipitation. Distinct dynamical effects, important for the amount and the spatial distribution of precipitation, are found to be associated with warming due to condensation and cooling due to evaporation and melting of precipitation. The latter process seems to be responsible for the simulated formation of rainbands and complex evolution of the cold front over the western Mediterranean. The multiple front life cycle and propagation feeds back on the simulated precipitation distribution, affecting the location of the prefrontal moist flow. Condensation affects the atmospheric effective stratification where the flow impinges on the orography, determining the flow regime (orographic lifting vs blocking and flow around), which, in turn, has an important impact on precipitation.

Stratigraphy and Recent evolution of Maryland Piedmont flood plains

Stratigraphy and Recent evolution of Maryland Piedmont flood plains