Meccanica 31: 3-14, 1996. © 1996 KluwerAcademic Publishers. Printed in the Netherlands. The Role of Cloud Tracking and Passive Microwave Techniques in the Short-term Prediction of Flood Hazard on a Regional Scale L. LANZA, G. BONI, M. CONTI, R LA BARBERA and E SICCARDI Universith di Genova, Hydraulic Institute, Via Montallegro 1; 16145 Genova, Italy (Received: 26 June 1995) Abstract. The role of remote sensing in enhancing the monitoring capabilities and the short-term prediction of the risk of flooding on a regional scale is addressed in this paper by means of the application of storm identification and cloud tracking techniques to a few case studies where cluster analysis based on infrared satellite imagery is used as the primary source of information. Polar satellite sensors, which provide passive microwave images, were also proposed in the literature for application in flood forecasting operational problems, though the accuracy of passive microwave techniques is only acceptable when rainfall estimates are integrated over quite large spatial and temporal scales. Climatological studies are well suited to make use of such data while the measure of instantaneous rainfall is still lacking of an adequate validation. A theoretical and numerical framework for the assessment of the reliability of passive microwave estimates of instantaneous rainfall within the typical resolution scales of polar satellite sensors is provided in the paper. Sommario. II ruolo delle tecniche di monitoraggio da sensori remoti nell'incrementare le potenzialita di pre- visione a breve termine del rischio di inondazione a scala regionale ~ analizzato nel presente lavoro attraverso l'applicazione di tecniche di identificazione ed inseguimento dei corpi nuvolosi ad alcuni casi di studio in cui le immagini satellitarie nella banda dell'infrarosso termico sono utilizzate come principale strumento di monitorag- gio. In letteratura viene inoltre proposta l'utilizzazione, in applicazioni operative di previsione delle inondazioni, di sensori alle microonde passive montati su satelliti ad orbita polare: l'accuratezza di tali tecniche ~ tuttavia accettabile solo quando le stime di precipitazione vengono integrate su ampie scale spaziali e temporali. Mentre l'uso di tali tecniche per studi climatologici ~ di notevole utilith, la misura della precipitazione alle piccole scale spazio-temporali necessita ancora di un adeguato processo di validazione. Nel presente lavoro viene proposto un approccio teorico per la stima dell'affidabilit~ di tali stime di precipitazione alle scale tipiche della risoluzione spaziale del sensore. Key words: Remote sensing, Rainfall, Flood forecasting, Hydrometeorology. 1. Introduction The noticeable research effort recently undertaken by the scientific community towards the detection of some clear evidence of changes in climate characteristics on a planetary scale points to a deeper understanding of the physical processes that are likely to play, at the land-atmosphere interface, any significant role in affecting climate through an interaction with the energy balance of the earth. The enhancement of the present capabilities to obtain reliable measurements of the hydrometeorological variables involved is one of the outstanding research objectives in hydrology, which are expected to provide the experimental basis where the evidence of trends or modifications can be soundly discussed and eventually enucleated from the underlying variance characteristics of the processes observed. Among these variables rainfall is the most familiar and commonly measured among hydrologists, at least where traditional rain gauge networks are concerned and the distribution of space-time rainfall over the land areas is investigated.