Flood and landslide warning based on rainfall thresholds and soil moisture indexes: the HEWS (Hydrohazards Early Warning System) for Sicily

摘要

The main focus of the paper is to present a flood and landslideearly warning system, named HEWS (Hydrohazards Early Warning System),specifically developed for the Civil Protection Department of Sicily, basedon the combined use of rainfall thresholds, soil moisture modelling andquantitative precipitation forecast (QPF).The warning system is referred to 9 different in which Sicilyhas been divided into and based on a threshold system of three differentincreasing critical levels: ordinary, moderate and high.In this system, for early flood warning, a Soil Moisture Accounting (SMA)model provides daily soil moisture conditions, which allow to select aspecific set of three rainfall thresholds, one for each critical levelconsidered, to be used for issue the alert bulletin.Wetness indexes, representative of the soil moisture conditions of acatchment, are calculated using a simple, spatially-lumpedrainfall–streamflow model, based on the SCS-CN method, and on the unithydrograph approach, that require daily observed and/or predicted rainfall,and temperature data as input. For the calibration of this model dailycontinuous time series of rainfall, streamflow and air temperature data are used.An event based lumped rainfall–runoff model has been, instead, used for the derivation of the rainfall thresholds for each catchment in Sicilycharacterised by an area larger than 50 km. In particular, a Kinematic Instantaneous Unit Hydrograph based lumped rainfall–runoff model with the SCS-CN routine for net rainfall was developed for this purpose.For rainfall-induced shallow landslide warning, empirical rainfallthresholds provided by Gariano et al. (2015) have been included in thesystem. They were derived on an empirical basis starting from a catalogue of265 shallow landslides in Sicily in the period 2002–2012.Finally, Delft-FEWS operational forecasting platform has been applied tolink input data, SMA model and rainfall threshold models to produce warningon a daily basis for the entire region.