G. Dalla Fontana

Snowmelt modelling by combining air temperature and a distributed radiation index

High spatial variability in snowmelt phenomena was observed in the experimental watershed of the upper Cordevole (7 km2), in the Dolomites. Snowmelt depends, at a point scale, on available energy, which in turn is heavily affected by slope, aspect and shading effects of the site. A distributed hourly model of snowmelt was set up as a geographical information system (GIS) module. The model accumulates snowfall for each raster element (20 m × 20 m) using a temperature threshold. It simulates snowmelt using air temperature and a radiation index consisting of daily average values of clear sky radiation that have cumulated at selected dates since 21 December. It should be underlined that the only relevant calibration parameter of the model is the combined snowmelt factor, which is unique for the whole basin. The clear sky radiation maps were computed for a selected period of the year, based on the watershed digital terrain model and the solar path sampled at very short intervals. When run for a season, the model produces snow water equivalent maps at given dates. The model was validated, with satisfactory results, by comparing these maps with 60 snow covered area surveys and related water equivalent measures collected in six snowmelt seasons from 1986 to 1991. The classical temperature index approach to snowmelt modelling does not allow the full variability over the basin to be taken into account. Besides, it seems important to point out that this fully distributed approach allows us to avoid the use of snow covered area (SCA) depletion curves, the definition of which still proves a troublesome task.

Flood dynamics in urbanised landscapes: 100 years of climate and humans’ interaction

Raising interest in the interaction between humans and climate drivers to understand the past and current development of floods in urbanised landscapes is of great importance. This study presents a regional screening of land-use, rainfall regime and flood dynamics in north-eastern Italy, covering the timeframe 1900–2010. This analysis suggests that, statistically, both climate and land-use have been contributing to a significant increase of the contribution of short duration floods to the increase in the number of flooded locations. The analysis also suggests that interaction arises, determining land-use dynamics to couple with climatic changes influencing the flood aggressiveness simultaneously. Given that it is not possible to control the climatic trend, an effective disaster management clearly needs an integrated approach to land planning and supervision. This research shows that land management and planning should include the investigation of the location of the past and future social and economic drivers for development, as well as past and current climatic trends.

Erosion Area Assessment in Mountainous Basins Using GIS Methods

Watershed management and headwater reconstruction programmes require a reliable knowledge of sediment source dynamics. GIS techniques are a powerful tool for the assessment of active erosion areas in drainage basins. These analyses were conducted in two small drainage basins in the Italian Alps for which a DEM and detailed inventory maps of sediment sources are available. Field surveys found that active sediment sources (bare slopes, overgrazed areas, shallow landslides, eroding stream banks and debris flow channels) covered 1.1% of Cordevole Torrent basin and 5.2% of the Rio Cordon basin. The GIS techniques involve simple statistical analyses of thematic information, the use of indicators including basin topography and channel network, and the physically based modelling of shallow landslides. The model reproduces the observed distribution of landslide locations consistently and more than 80% of the observed landslide area is predicted to be unstable or to fail with low rainfall. Some 69% of the unconditionally unstable areas and 65% of the slopes predicted to become unstable with low-intensity steady-state rainfall (<_ 50 mm/day1) were identified. Avalanche sources areas and active scree slopes were closely correlated

Flood Hazard Assessment and Mitigation

A flood is an overflowing of water from rivers onto land not usually submerged. Floods also occur when water levels of lakes, ponds, reservoirs, aquifers and estuaries exceed some critical value and inundate the adjacent land, or when the sea surges on coastal lands much above the average sea level. Nevertheless, floods are a natural phenomenon important to the life cycle of many biota, not the least of which is mankind. Floods became a problem as humans began establishing farms and cities in the bottom-lands of streams and rivers. In doing so, they not only exposed their lives and properties to the ravages of floods, but also exacerbated floods by paving the soil and constructing the stream channels. Over time, continued urbanisation of natural floodplains has caused great annual losses of both wealth and human life. In this way, in many countries and regions of the World, floods are the most costly hazards in terms of both loss of human lives and material damage.