Space-time Multifractality of Remotely Sensed Rainfall Fields

A methodology aimed at characterizing the scaling properties of precipitation fields in space and time is revised and applied to remotely sensed rainfall data retrieved during two oceanic campaigns (GATE and TOGA-COARE), and a land campaign (TRMM-LBA). The presence of spatial heterogeneity induced by orography is investigated on data retrieved over land (TRMM-LBA): the performed analyses show that the orographic induced heterogeneity seems to be negligible for the examined data. Moreover, the scaling properties observed on rainfall over land are compared with those detected on ocean rainfall for several space-time events. Results of a multifractal analysis enable a common calibration of the STRAIN space-time rainfall downscaling cascade model for the three datasets. Generated synthetic fields preserve the observed rainfall space-time variability

Orographic influences in rainfall downscaling

The problem of rainfall downscaling in a mountainous region is discussed, and a simple methodology aimed at introducing spatial heterogeneity induced by orography in downscaling models is proposed. This procedure was calibrated and applied to rainfall data retrieved by the high temporal resolution rain gage network of the Sardinian Hydrological Survey

On the effect of gable roof on natural ventilation in two-dimensional urban canyons

Flow regimes occurring in urban canyons are strongly influenced by the geometrical shape of the buildings; however, fluid dynamic investigations are typically carried out using parallelepiped obstacles. The present study is focused on assessing the effect of gable roofs on the flow regimes characterizing urban canyons (skimming flow, wake interference, isolated roughness) and the implications in terms of integral parameters (air exchange rate and friction factor), which are useful in practical applications. Numerical simulations are performed by means of RANS modeling of idealized two dimensional urban canyons between series of identical gable roof buildings with pitch ranging from 0° up to 40°, and wind direction perpendicular to the canyon axis. Simulations performed for different canyon aspect ratios show the key role played by the roof pitch in enhancing turbulence and in increasing ventilation, in particular for narrow canyons. Furthermore, turbulence-driven ventilation is observed to be related to the square root of the friction coefficient by a single linear relation, despite of the roof pitch. These results may have an impact on design and planning strategies aimed at enhancing natural ventilation and promoting efficient pollutant and heat dispersion in urban areas