Using nowcasting technique and data assimilation in a meteorological model to improve very short range hydrological forecasts

Abstract

Abstract. Forecasting flash floods with anticipation of some hours is still a challenge especially in environments made by a collection of small catchments. Hydrometeorological forecasting systems generally allow to predict the possibility of having very intense rainfall events on quite large areas with good performances even with 12–24 hours of anticipation. However, they are not able to predict exactly rainfall location if we consider portions of territory of 10 to 103 km2 as order of magnitude. The scope of this work is to exploit both observations and modeling sources to improve the discharge prediction in small catchments with time horizon of 2–8 hours. The models used to achieve the goal are essentially three i) a probabilistic rainfall nowcasting model able to extrapolate the rainfall evolution from observations; ii) a non hydrostatic high-resolution numerical weather prediction (NWP) model; iii) a distributed hydrological model able to provide a streamflow prediction in each pixel of the studied domain. These tools are used, together with radar observations, in a synergistic way, exploiting the information of each element in order to complement each other: observations are used in a frequently updated data assimilation framework to drive the NWP system, whose output is in turn used to improve the information in input to a nowcasting technique; finally nowcasting and NWP outputs are blended, generating an ensemble of rainfall scenarios used to feed the hydrological model and produce a prediction in terms of streamflow. The flood prediction system is applied to three major events occurred on Liguria Region (Italy) first to produce a standard analysis on predefined basin control sections, then using a distributed approach that exploit the capabilities of the employed hydrological model. The results obtained for these three analyzed events show that the use of the present approach is promising. Even if not in all the cases, the blending technique clearly enhances the prediction capacity of the hydrological nowcasting chain with respect to the use of input coming only from the nowcasting technique; moreover, a worsening of the performance is rarely observed and it is nevertheless ascribable to the critical transition between the nowcasting and the NWP model rainfall field.

Spatial and Temporal Evaluation of Radar Rainfall Nowcasting Techniques on 1,533 Events

“…We find this in this study too, with increasing forecast skill in the downwind direction of the operational radars with south‐westerlies as the main wind direction. Hence, whereas the application of nowcasting in flood forecasting is likely to be beneficial (e.g., Berenguer et al., 2005; Liguori et al., 2012; Moreno et al., 2013; Pierce et al., 2005; Poletti et al., 2019; Vivoni et al., 2006, 2007), the catchment properties will influence the eventual skill.…”

The Piedmont flood of November 1994: a testbed of forecasting capabilities of the CNR-ISAC meteorological model suite

“…They have been used for numerous scientific studies and applications, as for instance: sensitivity and impact studies, and diagnostics of meteorological phenomena including severe weather and storms (e.g. Malguzzi et al 2006 ; Cavaleri et al 2010 ; Fantini et al 2012 ; Cioni et al 2016 ; Davolio et al 2016 , 2017a ; Buzzi et al 2020 ); model coupling with hydrological and ocean models (Davolio et al 2015 ; Lombardi et al 2018 ; Ferrarin et al 2013 , 2019 ; Poletti et al 2019 ); theoretical and idealized studies of instability processes (Davolio et al 2009 ; Fantini and Malguzzi 2008 ); applications to probabilistic and ensemble forecasting, and atmospheric predictability studies (Uboldi and Trevisan 2015 ; Corazza et al 2018 ); data assimilation studies (Tiesi et al 2016 ; Davolio et al 2017b ); model validation and intercomparison projects (Nagata et al 2001 ; Casaioli et al 2013 ). The ISAC NWP models have also been employed as basic tools in many international field experiments such as the international forecasting demonstration project called MAP D-PHASE (Rotach et al 2009 ) and the HyMeX campaign SOP1 (Ducrocq et al 2014 ; Ferretti et al 2014 ), and in numerous European scientific projects.…”

Large‐Sample Evaluation of Radar Rainfall Nowcasting for Flood Early Warning

“…In addition, we cannot conclude if these results also hold for urban areas, even though the smallest catchments in this study have the size of urban areas. Nevertheless, promising results have been reported in discharge forecasting studies using nowcasting for mountainous regions (e.g., Berenguer et al., 2005; Germann et al., 2009; Moreno et al., 2013; Poletti et al., 2019) and for urban areas (e.g., Liguori et al., 2012; Sharif et al., 2006).…”

“…Nowcasted rainfall has already been successfully used as input for various hydrological models and forecasting systems (Berenguer et al., 2005; Germann et al., 2009; Heuvelink et al., 2020; Liguori et al., 2012; Liguori & Rico‐Ramirez, 2013; Moreno et al., 2013; Pierce et al., 2005; Poletti et al., 2019; Sharif et al., 2006; Vivoni et al., 2006, 2007). Berenguer et al.…”