Overview of the first HyMeX special observation period over Croatia

Abstract

Abstract. The HYdrological cycle in the Mediterranean EXperiment (HyMeX) is intended to improve the capabilities of predicting high-impact weather events. Within its framework, the aim of the first special observation period (SOP1), 5 September to 6 November 2012, was to study heavy precipitation events and flash floods. Here, we present high-impact weather events over Croatia that occurred during SOP1. Particular attention is given to eight intense observation periods (IOPs), during which high precipitation occurred over the eastern Adriatic and Dinaric Alps. During the entire SOP1, the operational model forecasts generally well represented medium intensity precipitation, but heavy precipitation was frequently underestimated by the ALADIN model at an 8 km grid spacing and was overestimated at a higher resolution (2 km grid spacing). During IOP2, intensive rainfall occurred over a wider area around the city of Rijeka in the northern Adriatic. The short-range maximum rainfall totals were the largest ever recorded at the Rijeka station since the beginning of measurements in 1958. The rainfall amounts measured in intervals of 20, 30 and 40 min were exceptional, with return periods that exceeded a thousand, a few hundred and one hundred years, respectively. The operational precipitation forecast using the ALADIN model at an 8 km grid spacing provided guidance regarding the event but underestimated the rainfall intensity. An evaluation of numerical sensitivity experiments suggested that the forecast was slightly enhanced by improving the initial conditions through variational data assimilation. The operational non-hydrostatic run at a 2 km grid spacing using a configuration with the ALARO physics package further improved the forecast. This article highlights the need for an intensive observation period in the future over the Adriatic region to validate the simulated mechanisms and improve numerical weather predictions via data assimilation and model improvements in descriptions of microphysics and air-sea interactions.

Modelling extreme precipitation over the Dinaric Alps: An evaluation of the CNRM‐ALADIN regional climate model

“…For the investigation of CNRM-ALADIN skill in reproducing the extreme precipitation at the event scale, that is, the HPE, we focus on six IOPs during HyMeX SOP1 (Drobinski et al, 2014;Ivančan-Picek et al, 2016). The details about the IOPs, their duration and area they affected, are presented in Table 3.…”

“…The highest precipitation recorded during this HPE was 220 mm day −1 at meteorological station Rijeka, and consequently, the intensity of this HPE caused severe flooding and damage. The synoptic and mesoscale situation was thoroughly described in Ferretti et al (2014) and Ivančan-Picek et al (2016).…”

“…This flow, often organized in a convergence line, is then forced to rise due to the steep orography, thus triggering or reinforcing convection and generating, usually, prefrontal orographic precipitation and enhancing frontal precipitation (e.g., Kozari ć and Ivančan-Picek, 2006;Ivančan-Picek et al, 2014;Davolio et al, 2016). The HPEs observed during the first Hydrological cycle in the Mediterranean Experiment (HyMeX; Ducrocq et al, 2014) Special Observation Period (SOP1) developed under similar conditions (Ivančan-Picek et al, 2016). During the SOP1, the northern Adriatic was one of the most affected areas, with more than 1,000 mm of precipitation recorded at several stations.…”

“…The Dinaric Alps and Adriatic regions are no exception to hazards caused by HPEs (Ruti et al, 2016). HPEs are most common in autumn when the sea surface temperature is still high, leading to large thermal differences between the sea and atmosphere (e.g., Ivančan-Picek et al, 2016). Triggering mechanisms of all HPEs occurring in the Adriatic are similar.…”

“…Intense observation periods (IOPs) date, area affected(Ivančan-Picek et al, 2016) and selected radiosounding…”