Hydrological and meteorological aspects of floods in the Alps: an overview

International audienceThis introductory paper presents and summarises recent research on meteorological and hydrological aspects of floods in the Alps. The research activities were part of the international research project RAPHAEL (Runoff and Atmospheric Processes for flood HAzard forEcasting and controL) together with experiments within the Special Observing Period-SOP conducted in autumn 1999 for the Mesoscale Alpine Programme ?MAP. The investigations were based on both field experiments and numerical simulations, using meteorological and hydrological models, of ten major floods that occurred in the past decade in the European Alps. The two basins investigated were the Ticino (6599 km2) at the Lago Maggiore outlet on the southern side of the Alps and the Ammer catchment (709 km2) in the Bavarian Alps. These catchments and their sub-catchments cover an appropriate range of spatial scales with which to investigate and test in an operational context the potential of both mesoscale meteorological and distributed hydrological models for flood forecasting. From the data analyses and model simulations described in this Special Issue, the major sources of uncertainties for flood forecasts in mid-size mountain basins are outlined and the accuracy flood forecasts is assessed

Hydrologic vulnerability to climate change of the Mandrone glacier (Adamello-Presanella group, Italian Alps)

In order to assess the annual mass balance of the Mandrone glacier in the Central Alps an energy- balance model was applied, supported by snowpack, meteorological and glaciological observations, together with satellite measurements of snow covered areas and albedo. The Physically based Distributed Snow Land and Ice Model (PDSLIM), a distributed multi-layer model for temperate glaciers, which was previously tested on both basin and point scales, was applied. Verification was performed with a network of ablation stakes over two summer periods. Satellite images processed within the Global Land Ice Measurements from Space (GLIMS) project were used to estimate the ice albedo and to verify the position of the simulated transient snowline on specific dates. The energy balance was estimated for the Mandrone and Presena glaciers in the Central Italian Alps. Their modeled balances (-1439 and -1503 mm w.e. yr-1, respectively), estimated over a fifteen year period, are in good agreement with those obtained with the glaciological method for the Caresèr glacier, a WGMS (World Glacier Monitoring Service) reference located in the nearby Ortles- Cevedale group. Projections according to the regional climate model COSMO-CLM (standing for COnsortium for Small-scale MOdeling model in CLimate Mode) indicate that the Mandrone glacier might not survive the current century and might be halved in size by 2050

Snow precipitation measured by gauges: Systematic error estimation and data series correction in the central Italian Alps

Precipitation measurements by rain gauges are usually affected by a systematic underestimation, which can be larger in case of snowfall. The wind, disturbing the trajectory of the falling water droplets or snowflakes above the rain gauge, is the major source of error, but when tipping-bucket recording gauges are used, the induced evaporation due to the heating device must also be taken into account. Manual measurements of fresh snow water equivalent (SWE) were taken in Alpine areas of Valtellina and Vallecamonica, in Northern Italy, and compared with daily precipitation and melted snow measured by manual precipitation gauges and by mechanical and electronic heated tipping-bucket recording gauges without any wind-shield: all of these gauges underestimated the SWE in a range between 15% and 66%. In some experimental monitoring sites, instead, electronic weighing storage gauges with Alter-type wind-shields are coupled with snow pillows data: daily SWE measurements from these instruments are in good agreement. In order to correct the historical data series of precipitation affected by systematic errors in snowfall measurements, a simple ‘at-site’ and instrument-dependent model was first developed that applies a correction factor as a function of daily air temperature, which is an index of the solid/liquid precipitation type. The threshold air temperatures were estimated through a statistical analysis of snow field observations. The correction model applied to daily observations led to 5–37% total annual precipitation increments, growing with altitude (1740 ÷ 2190 m above sea level, a.s.l.) and wind exposure. A second ‘climatological‘ correction model based on daily air temperature and wind speed was proposed, leading to errors only slightly higher than those obtained for the at-site corrections

Land cover changes since the 19th century detected from historic maps for environmental applications: toward a “CORINE 1800” project?

The value of cartographic heritage for environmental applications is demonstrated with a test case in the Central Italian Alps. Land cover changes since the early 19th century are detected from sample maps of the Second Military Survey of the Habsburg Empire in Lombardy (1818-1829), available on the portal www.mapire.eu. They are compared with 1954 areal sur-veys and successive land cover classification until 2018. Issues as land use classes homogeni-zation, data vectorization, georeferencing errors are addressed. The dynamics of main land cover classes (woods, bush, meadows, crops) are investigated on sample areas and the potential use of this exercise for hydrological applications is explored. In fact, the impact of the observed natural afforestation on changes in hydrological losses due to evapotranspiration and its influ-ence as a likely cause for the decrease in runoff monitored since 1845 in the Adda river basin and needs to be assessed in a systematic way. The proposed test case can pave the road for a project extended at European scale, a sort of “CORINE 1800 land cover” Geographic Infor-mation System, which could have several environmental, cartographic and socio-economic ap-plications

The Adige River map in 1:20,736 scale by Leopoldo de Claricini-Dornpacher (1847)

In the 50th year anniversary of the November 1966 Adige river flood, which hit at the same time Florence and Venice 14 map sheets of the Adige river valley between Meran and Borghetto, in northern Italy, were scanned in high-quality and printed for the public ac-cess and use. The lithograph was printed in 1847 in a 1:20.736 scale (1”:288° i.e. 1 Zoll=288 Klafter) in Innsbruck by Leopoldo de Claricini-Dornpacher (1812-1888) and depicts the river and its valley as it was in almost natural conditions when the river training works just started in the intermediate reach. A georeferencing of one sample sheet shows that a RMSE between 10 and 15 meters can be reached. A comparison with the actual geomorphology of the river especially in its southern reach is possible thanks to the map. One of the objectives of this study is, also, to make a beautiful map accessible to a wide public, to let people enjoying the river landscape as it was and will never return, until the next glacial era. Introductio

Profiles and species of Mn, Fe and trace metals in soils near a ferromanganese plant in Bagnolo Mella (Brescia, IT)

For the last forty-five years (from 1974 to present) ferroalloy production in Bagnolo Mella, Northern Italy, has generated particulate emissions enriched in potentially toxic metals and metalloids including arsenic (As), lead (Pb) and manganese (Mn). Of these, Mn is unique in that it has a significant background concentration and is seldom studied as a contaminant but is potentially a significant toxin derived from dusts regionally. Here we examine the distribution, redistribution, speciation and bioavailability of the Mn-contaminated top soils affected by atmospheric emissions adjacent to the ferroalloy plant. Four sites, variably located in the study area in terms of both distance and direction from the plant, were considered as representative of increasing levels of industrial influence. Soil profiles showed that metal concentrations (measured by X-ray fluorescence) varied considerably by location, i.e. higher in the sites closer to the plant and also at the surface level, although distributed throughout the top 15 cm, suggesting appreciable redistribution possibly due to soil mixing or infiltration. Most metal concentrations were correlated, except Mn which was independent and more variable across the sites than the other elements. Sequential chemical extractions indicated that Pb was primarily associated with Mn oxides, while As was most significantly associated with iron oxides. When Mn concentration significantly exceeded background levels, it was present in phases that were resistant to acid dissolution, very different from typical uncontaminated soils. X-ray Absorption Near Edge Spectroscopy (XANES) analyses suggested this recalcitrant Mn phase is likely a Mn-bearing spinel such as magnetite, that can be particularly toxic if ingested or inhaled. These first results highlight the legacy of ferroalloy production on surrounding soils, as well as the importance of Mn speciation for soil apportionment evaluation and human exposure estimation