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Impact of initial conditions on modelling extreme precipitation: case of November 29–30, 2010 floods over Morocco

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Modeling Earth Systems and Environment
Authors:
Zahra Sahlaoui at Moroccan meteorology
Zahra Sahlaoui
  • Moroccan meteorology
Fatima Zahra Hdidou at Moroccan Meteorology
Fatima Zahra Hdidou
  • Moroccan Meteorology
Khalid Elrhaz at DGM moroccan meterology
Khalid Elrhaz
  • DGM moroccan meterology
Soumia Mordane at University of Hassan II Casablanca
Soumia Mordane
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Abstract and Figures

Extreme Precipitation is a weather hazard that affects the society directly and harmfully. Because of the process involved in the formation of precipitation at several spatial and temporal scales, the forecast of precipitation is still challenging the weather models. The aim of this work is to evaluate the impact of initial condition on the modelling of extreme precipitation by the Numerical Weather Prediction (NWP) limited area model ALADIN (Aire Limitée Adaptation dynamique Developpement INternational) at 10 km horizontal resolution. The case study corresponds to the extreme flooding event of November 29–30, 2010 across Morocco with daily precipitation reaching 178 mm over Casablanca city. A detailed description of the atmosphere dynamic during this event is given to help the understanding of the precipitation generation. Several experiments were performed to assess the impact of conventional and satellite data. Furthermore, sensitivity studies were carried out for the surface initialisation and the start mode. The assimilation experiment with an optimal setting had produced dynamical fields that were more favourable for the heavy precipitation occurrence. The evaluation of precipitation forecast has been performed by comparison to the surface precipitation observations. The results showed that the combined surface/upper-air assimilation of both conventional and satellite observations produced a clear improvement in term of precipitation location and intensity forecast.
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Vol.:(0123456789)
1 3
Modeling Earth Systems and Environment (2022) 8:5683–5693
https://doi.org/10.1007/s40808-022-01468-6
ORIGINAL ARTICLE
Impact ofinitial conditions onmodelling extreme precipitation: case
ofNovember 29–30, 2010 floods overMorocco
ZahraSahlaoui1,2 · FatimaZahraHdidou1,2· KhalidElRhaz1· SoumiaMordane2
Received: 31 May 2022 / Accepted: 13 July 2022 / Published online: 26 July 2022
© The Author(s), under exclusive licence to Springer Nature Switzerland AG 2022
Abstract
Extreme Precipitation is a weather hazard that affects the society directly and harmfully. Because of the process involved
in the formation of precipitation at several spatial and temporal scales, the forecast of precipitation is still challenging the
weather models. The aim of this work is to evaluate the impact of initial condition on the modelling of extreme precipitation
by the Numerical Weather Prediction (NWP) limited area model ALADIN (Aire Limitée Adaptation dynamique Developpe-
ment INternational) at 10km horizontal resolution. The case study corresponds to the extreme flooding event of November
29–30, 2010 across Morocco with daily precipitation reaching 178mm over Casablanca city. A detailed description of the
atmosphere dynamic during this event is given to help the understanding of the precipitation generation. Several experiments
were performed to assess the impact of conventional and satellite data. Furthermore, sensitivity studies were carried out for
the surface initialisation and the start mode. The assimilation experiment with an optimal setting had produced dynamical
fields that were more favourable for the heavy precipitation occurrence. The evaluation of precipitation forecast has been
performed by comparison to the surface precipitation observations. The results showed that the combined surface/upper-air
assimilation of both conventional and satellite observations produced a clear improvement in term of precipitation location
and intensity forecast.
Keywords Atmospheric modelling· Heavy precipitation event· Data assimilation· Morocco
Introduction
The precipitation is among the most impact-relevant meteor-
ological phenomena. It has a direct impact on human safety,
activity and economy. Flash floods are the most widespread
and harmful weather-related natural disasters, which are
closely related to the precipitation frequency and intensity.
Furthermore, taking into account the connection between
the climate changes and the precipitation intensity, several
studies had shown an increase of extreme precipitation
event occurrence over large parts of the globe (Bulti etal.
2021; Tabari 2020). Therefore, high-resolution precipitation
forecasts are highly needed for a better risk management
and decision making. Additionally, accurate precipitation
forecast is also highly required for urban (Moujahid etal.
2018), industrial and agricultural applications. It is also a
crucial input for flood forecasting systems and hydrological
models (El Khalki etal. 2020).
The precipitation forecast, at short and medium range,
is mainly based on Numerical Weather Prediction (NWP)
models. Former studies (Igri etal. 2015, Rao etal. 2020)
showed that the precipitation forecast accuracy is closely
linked to the model initial conditions, especially in case of
extreme events. During the last years, the data assimilation
methods used in meteorology had been widely improved,
which allowed taking advantages from the widespread and
diversified observation network.
The numerical weather prediction was developed in the
Moroccan Meteorological Service within the framework of
ALADIN (Aire Limité Adaptation dynamique Developpe-
ment INternational) consortium (ALADIN 1997). It is an
international cooperation, led by Météo-France that started
in 1990, in association with Eastern Europe countries.
Morocco joined the project in 1993 as the first non-European
country. The Moroccan operational forecast suite has started
* Zahra Sahlaoui
sahlaoui_zahra@yahoo.fr
1 CNRM, Direction Générale de La Météorologie, Casa-Oasis,
B.P:8106, 20240Casablanca, Morocco
2 LPPSMM, Faculty ofSciences Ben M’Sik, University
Hassan II, 20085Casablanca, Morocco
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