The heavy precipitation event of 14–15 October 2018 in the Aude catchment: A meteorological study based on operational numerical weather prediction systems and standard and personal observations

Abstract

Abstract. The case of the heavy precipitation event on 14 and 15 October 2018 which has led to severe flash flooding in the Aude watershed in south-western France is studied from a meteorological point of view using deterministic and probabilistic numerical weather prediction systems, as well as a unique combination of observations from both standard and personal weather stations. This case is typical of Mediterranean heavy precipitation events due to its classic synoptic situation and its quasi-stationary convective precipitation that regenerates continuously, but with some peculiarities such as the presence of a former hurricane and a pre-existing cold air mass close to the ground. It is shown that the positive Mediterranean sea surface temperature anomaly may have played an aggravating role in the amount of precipitation that poured into the Aude basin. On the other hand, soil moisture does not seem to have played a significant role. A study of rainfall forecasts shows that the event had limited predictability, in particular given the small size of the watersheds involved. It is shown that the stationarity of precipitation, whose estimation benefits from data from personal stations, is linked to the presence near the ground of a trough and a strong potential virtual temperature gradient, the stationarity of both of which is highlighted by a combination of observations from standard and personal stations. The forecast that comes closest to the rainfall observations contains the warmest, wettest and fastest low-level jet and also simulates near the ground a trough and a marked boundary between cold air in the west and warm air in the east, both of which are stationary.

Performance of automated flood inundation mapping methods in a context of flash floods: a comparison of three methods based either on the Height Above Nearest Drainage (HAND) concept, or on 1D/2D shallow water equations

“…9.c shows in this case that a reasonable variation in the peak discharge value (set from 84.2 m 3 .s −1 to 116.5 m 3 .s −1 to remain consistent with rainfall observations) is not sufficient to compensate the underestimation effect. Since the selected roughness value (n=0.066) is already relatively high, an underestimation of the locally estimated rainfall intensities is suspected to be at the origin of the errors in this case (Caumont et al, 2020).…”

“…The last event occurred on the 15 th of October 2018 in the intermediate part of Aude river watershed (5050 km 2 ), where a accumulated rainfall of more than 300 mm in 24 hours was locally recorded (Caumont et al, 2020). Several tributaries of the Aude river had very strong flood reactions: Lauquet river (196 km 2 , peak discharge of about 880 m 3 .s −1 ), Trapel river (55 km 2 , >300 m 3 .s −1 ), and Orbiel river (253 km 2 , 490 m 3 .s −1 ).…”

A multi-sourced assessment of the spatiotemporal dynamics of soil moisture in the MARINE flash flood model

“…A very specific pattern of precipitation occurred during this event. The precipitation field was oriented along the main axis of the river, resulting in intense and devastating surface runoff (Caumont et al, 2020). This response time appears to be faster than the response time regularly considered for this station (about 5 h).…”

“…In this work, the ANTILOPE quantitative precipitation estimates (QPEs) are used for precipitation estimation (Champeaux et al, 2009). The ANTILOPE QPEs are based on a fusion between the radar data provided by the operational radar network ARAMIS (Tabary, 2007) and the measurements at rain gauges, spatialized by the kriging method.…”

A network of water vapor Raman lidars for improving heavy precipitation forecasting in southern France: introducing the WaLiNeAs initiative

“…The two most important HPEs seen in Fig. 1 are located in the Aude department and are related to the 12-13 November 1999 event (Nuissier et al 2008;Ducrocq et al 2008) and the 14-15 October 2018 event (Caumont et al 2021). Large amounts of rainfall associated with these Fig.…”