Giovanna Grossi

Use of multispectral ASTER images for mapping debris-covered glaciers within the GLIMS project

The problem of mapping debris-covered glaciers using images derived from satellite-borne optical scanners is addressed in this paper. Results using also Terra-ASTER images on the Belvedere and Miage glaciers, both located in the Italian Alps, are presented. Field measurements and energy balance modeling indicate that for debris superimposed on ice, surface temperatures of some degrees colder than for pure, debris are to be expected in the morning. This fact is also confirmed by processing satellite images taking into account the thermal band. The results of black glacier detection can be useful for the project GLIMS (Global Land Ice Monitoring from Space) when debris-covered glaciers are to be mapped

Forcing intermittency and land surface hydrologic partitioning

Because of sampling problems, the precipitation estimates from satellite remote sensing are aggregated over time (typically monthly) and over space. Since land surface hydrologic processes have threshold and nonlinear dependencies on precipitation, coarse-resolution precipitation observations may not be directly used in hydrologic models. Differences in the character of intermittency of precipitation, the averaged values remaining the same, can in fact yield large differences in the hydrologic partitioning and therefore in the resulting climate. In this paper an equilibrium hydrologic model is used to study the influence of intermittency on the way precipitation is partitioned into different hydrological quantities. The parameters defining intensity and duration of storms are varied (keeping total precipitation volume constant), and the resulting effects on the partitioning into runoff, evaporation, recharge, and soil moisture storage are determined. It is found that the character of intermittency in storm arrivals has a large impact on the hydrologic partitioning. Furthermore, investigations on the sensitivity of hydrologic partitioning on soil type and water table depth show that rainfall intermittency plays a major role irrespective of these other factors. Runoff generation, evaporation, and groundwater recharge are the three main components of the water balance. Depending on the soil type and climate, the main competition is between different combinations of these three loss mechanisms. It is concluded that the temporal structure of storms has a strong influence on the long-term equilibrium state of the hydrological system.

Proposal of a semi-probabilistic approach for storage facility design

Storage facilities are key devices in mitigating the urban drainage impact on receiving water bodies, but their design is still affected by high uncertainty. The analytical-probabilistic approach has recently raised interest, because the facility performances are directly related to probability. Starting from statistically independent storm events, distributions of the meteorological variables must be fitted. Rainfall series, recorded in three Italian raingauges, were examined for appraising two main concerns: the choice of proper probability distributions for rainfall volume and the sample sensitivity with respect to the analysis criterion. The analytical derivation of the model is then finally discussed.

Ten years of monitoring areal snowpack in the Southern Alps using NOAA-AVHRR imagery, ground measurements and hydrological data

Monitoring snow cover in alpine areas is important for the estimation of the water storage during the snowmelt season, especially in view of irrigation, hydropower production and water supply. Cost-efliciency and fine temporal resolution of images from the satellite-borne NOAA-AVHRR sensor indicate this source of information as a suitable candidate for monitoring snow cover extent. This information can also be used for validation of distributed snowmelt models. As a result of a long-term study, ten years of snow covered area depletion curves have been estimated using remote sensing in seven watersheds of size larger than 400 km 2 in the Southern Alps. Coupling of satellite imagery with detailed topographic data and some ground measurements of snowpack depth and density provides regional estimates of snow water equivalent in northern Italy, upstream of Lakes Maggiore, Como, Iseo, Idro, and Garda. The basin water equivalent estimates are compared with the values obtained from the hydrological water balance equation used in two of the selected watersheds and computed for different snowmelt seasons.

Scaling properties of topologically random channel networks

Abstract The analysis deals with the scaling properties of infinite topologically random channel networks (ITRNs) fast introduced by Shreve (1967, J. Geol. , 75: 179–186) to model the branching structure of rivers as a random process. The expected configuration of ITRNs displays scaling behaviour only asymptotically, when the ruler (or ‘yardstick’) length is reduced to a very small extent. The random model can also reproduce scaling behaviour at larger ruler lengths if network magnitude and diameter are functionally related according to a reported deterministic rule. This indicates that subsets of rrRNs can be scaling and, although rrRNs are asymptotically plane-filling due to the law of large numbers, scaling ITRNs can also display fractional dimension.

Comparison of energy fluxes at the land surface-atmosphere interface in an Alpine valley as simulated with different models

Abstract. Within the framework of a research project coupling meteorological and hydrological models in mountainous areas a distributed Snow-Soil-Vegetation-Atmosphere Transfer model was developed and applied to simulate the energy fluxes at the land surface – atmosphere interface in an Alpine valley (Toce Valley - North Italy) during selected flood events in the last decade. Energy fluxes simulated by the distributed energy transfer model were compared with those simulated by a limited area meteorological model for the event of June 1997 and the differences in the spatial and temporal distribution. The Snow/Soil-Vegetation-Atmosphere Transfer model was also applied to simulate the energy fluxes at the land surface-atmosphere interface for a single cell, assumed to be representative of the Siberia site (Toce Valley), where a micro-meteorological station was installed and operated for 2.5 months in autumn 1999. The Siberia site is very close to the Nosere site, where a standard meteorological station was measuring precipitation, air temperature and humidity, global and net radiation and wind speed during the same special observing period. Data recorded by the standard meteorological station were used to force the energy transfer model and simulate the point energy fluxes at the Siberia site, while turbulent fluxes observed at the Siberia site were used to derive the latent heat flux from the energy balance equation. Finally, the hourly evapotranspiration flux computed by this procedure was compared to the evapotranspiration flux simulated by the energy transfer model. Keywords: energy exchange processes, land surface-atmosphere interactions, turbulent fluxes

Design Storm for Mixed Urban and Agricultural Drainage Systems in the Northern Delta in Vietnam

AbstractA design storm definition procedure for the sizing of channels within mixed urban and lowland rice drainage systems is developed, with reference to the Northern Delta in Vietnam. By analyzing a 20-years-long time series of rainfall observations recorded at Hanoi monitoring station, typical storm events were identified and a set of suitable design storms was determined and recommended for the optimal design storm selection. A procedure to select an optimal design hyetograph is then defined, based on a combination of the design storm method and continuous simulation. A set of simulation experiments on a fictitious basin was finally carried out to support the choice of the storm temporal pattern providing the best performance in terms of reproduction of runoff peaks.

Metals Potential Removal Efficiency of Permeable Pavement

Permeable Pavement (PP) represents a good solution to solve stormwater management problems both in quantitative and qualitative way. In this way, the potential removal efficiency of a permeable pavement in treating metals was assessed by performing a monitoring campaign at a lab-scale system constructed for the purpose. Based on literature experiences, different relatively high-level concentrations of Copper and Zinc were applied during 8 different synthetic rainfall events. Results shown that the removal rates of Cu and Zn of the lab-scale pavements range from 85% to 92% and from 65% to 82%, respectively. Results also shown that the Cu removal rates of the lab-scale pavement are higher than Zn removal rate.