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Constantin de Magny G.,IRD Montpellier | Thiaw W.,National Centers for Environmental Predictions | Kumar V.,National Centers for Environmental Predictions | Manga N.M.,Clinique Des Maladies Infectieuses Du Center National Et University Of Fann | And 6 more authors.
PLoS ONE | Year: 2012

Cholera is an acute diarrheal illness caused by Vibrio cholerae and occurs as widespread epidemics in Africa. In 2005, there were 31,719 cholera cases, with 458 deaths in the Republic of Senegal. We retrospectively investigated the climate origin of the devastating floods in mid-August 2005, in the Dakar Region of Senegal and the subsequent outbreak of cholera along with the pattern of cholera outbreaks in three other regions of that country. We compared rainfall patterns between 2002 and 2005 and the relationship between the sea surface temperature (SST) gradient in the tropical Atlantic Ocean and precipitation over Senegal for 2005. Results showed a specific pattern of rainfall throughout the Dakar region during August, 2005, and the associated rainfall anomaly coincided with an exacerbation of the cholera epidemic. Comparison of rainfall and epidemiological patterns revealed that the temporal dynamics of precipitation, which was abrupt and heavy, was presumably the determining factor. Analysis of the SST gradient showed that the Atlantic Ocean SST variability in 2005 differed from that of 2002 to 2004, a result of a prominent Atlantic meridional mode. The influence of this intense precipitation on cholera transmission over a densely populated and crowded region was detectable for both Dakar and Thiès, Senegal. Thus, high resolution rainfall forecasts at subseasonal time scales should provide a way forward for an early warning system in Africa for cholera and, thereby, trigger epidemic preparedness. Clearly, attention must be paid to both natural and human induced environmental factors to devise appropriate action to prevent cholera and other waterborne disease epidemics in the region.

Mahe G.,Mohammed V University | Lienou G.,University of Yaounde I | Descroix L.,LTHE IRD | Bamba F.,University of Sfax | And 8 more authors.
Hydrological Processes | Year: 2013

In this paper, we study the impact of climate change on river regimes in several parts of Africa, and we look at the most probable causes of these changes either climatically or anthropogenically driven. We study time series of updated monthly and annual runoff of rivers of North Africa, West Africa (Sahelian and humid tropical regions) and Central Africa, including the largest river basins: Niger and Volta rivers in West Africa, and Congo and Ogooue rivers in Central Africa. The recent years are studied in the perspective of multi-decadal variability. In West Africa and in a part of Central Africa, the climate has changed since 1970, and rainfall has not returned to previous annual amounts, except in Equatorial Africa. The consequences of the long-lasting drought are, depending on the area concerned, the modification of seasonal regimes (Equatorial area), the groundwater table decrease (Tropical humid area) and the land cover degradation (Sahelian area). The increasing number of dams and of agricultural areas also plays a major role on the modification of river regimes. The population increase will continue to impact on the environment: land cover change, deforestation, agriculture and increasing number of dams will be associated with a reduction of water and sediment discharges to the sea, and major impacts on downstream ecosystems and coastal areas. It seems necessary to share with stakeholders a comprehensive approach of the water cycle from the basin to the sea, to prevent long-lasting damages to ecosystems and infrastructures. © 2013 John Wiley & Sons, Ltd.

Donat M.G.,University of New South Wales | Peterson T.C.,National Oceanic and Atmospheric Administration | Brunet M.,Rovira i Virgili University | Brunet M.,University of East Anglia | And 21 more authors.
International Journal of Climatology | Year: 2014

A workshop was held in Casablanca, Morocco, in March 2012, to enhance knowledge of climate extremes and their changes in the Arab region. This workshop initiated intensive data compilation activities of daily observational weather station data from the Arab region. After conducting careful control processes to ensure the quality and homogeneity of the data, climate indices for extreme temperatures and precipitation were calculated. This study examines the temporal changes in climate extremes in the Arab region with regard to long-term trends and natural variability related to ENSO and NAO. We find consistent warming trends since the middle of the 20th Century across the region. This is evident in the increased frequencies of warm days and warm nights, higher extreme temperature values, fewer cold days and cold nights and shorter cold spell durations. The warming trends seem to be particularly strong since the early 1970s. Changes in precipitation are generally less consistent and characterised by a higher spatial and temporal variability; the trends are generally less significant. However, in the western part of the Arab region, there is a tendency towards wetter conditions. In contrast, in the eastern part, there are more drying trends, although, these are of low significance. We also find some relationships between climate extremes in the Arab region and certain prominent modes of variability, in particular El Niño-Southern Oscillation (ENSO) and North Atlantic Oscillation (NAO). The relationships of the climate extremes with NAO are stronger, in general, than those with ENSO, and are particularly strong in the western part of the Arab region (closer to the Atlantic Ocean). The relationships with ENSO are found to be more significant towards the eastern part of the area of study. © 2013 Royal Meteorological Society.

Nabat P.,French National Center of Weather Research | Somot S.,French National Center of Weather Research | Mallet M.,CNRS Laboratory for Aerology | Michou M.,French National Center of Weather Research | And 9 more authors.
Atmospheric Chemistry and Physics | Year: 2015

The present study investigates the radiative effects of dust aerosols in the Mediterranean region during summer 2012 using a coupled regional aerosol-atmosphere-ocean model (CNRM-RCSM5). A prognostic aerosol scheme, including desert dust, sea salt, organic, black-carbon and sulphate particles, has been integrated to CNRM-RCSM5 in addition to the atmosphere, land surface and ocean components. An evaluation of this aerosol scheme of CNRM-RCSM5, and especially of the dust aerosols, has been performed against in situ and satellite measurements, showing its ability to reproduce the spatial and temporal variability of aerosol optical depth (AOD) over the Mediterranean region in summer 2012. The dust vertical and size distributions have also been evaluated against observations from the TRAQA/ChArMEx campaign. Three simulations have been carried out for summer 2012 with CNRM-RCSM5, including the full prognostic aerosol scheme, only monthly-averaged AOD means from the aerosol scheme or no aerosols at all, in order to focus on the radiative effects of dust particles and the role of the prognostic scheme. Surface short-wave aerosol radiative forcing variability is found to be more than twice as high over regions affected by dust aerosols, when using a prognostic aerosol scheme instead of monthly AOD means. In this case downward surface solar radiation is also found to be better reproduced according to a comparison with several stations across the Mediterranean. A composite study over 14 stations across the Mediterranean, designed to identify days with high dust AOD, also reveals the improvement of the representation of surface temperature brought by the use of the prognostic aerosol scheme. Indeed the surface receives less radiation during dusty days, but only the simulation using the prognostic aerosol scheme is found to reproduce the observed intensity of the dimming and warming on dusty days. Moreover, the radiation and temperature averages over summer 2012 are also modified by the use of prognostic aerosols, mainly because of the differences brought in short-wave aerosol radiative forcing variability. Therefore this first comparison over summer 2012 highlights the importance of the choice of the representation of aerosols in climate models. © Author(s) 2015.

Abdou K.,Direction de la Meteorologie Nationale | Parker D.J.,University of Leeds | Brooks B.,University of Leeds | Kalthoff N.,Karlsruhe Institute of Technology | Lebel T.,LTHE IRD
Quarterly Journal of the Royal Meteorological Society | Year: 2010

Measurements of lower boundary-layer winds collected from four Sonic Detection And Ranging (SODAR) systems during the African Monsoon Multidisciplinary Analysis (AMMA) are presented. The SODARs were located in a mesoscale network in the vicinity of Niamey, Niger, in the period 31 May to 17 August 2006; from this network 41 days of good measurements have been obtained from at least one of the SODARs, while there are several days in which two or more SODARs produced good simultaneous data. The average variation of the winds in the lower boundary layer is here presented, as a function of height and of time of day. The results confirm previous studies of the diurnal cycle of winds, and quantify the variation of this diurnal cycle with height at low altitudes. On many nights, a distinct nocturnal low-level jet was observed, at 200-400 m altitude. In profiles averaged over all of the sample days, the peak wind shear was in the layer below 300 m, with the strongest wind shear from 0000 to 0600 UTC. In particular, the magnitude of low-level wind shear, which is a significant hazard for aviation, is shown to be strongly dependent on time of day. Strong low-level wind shear (more than 4 m s-1 per 100 m), was observed on more than 35% of days in the 0000-0300 UTC period. © 2009 Royal Meteorological Society.

Khomsi K.,Direction de la Meteorologie Nationale | Mahe G.,IRD Montpellier | Tramblay Y.,IRD Montpellier | Sinan M.,Ecole Hassania des Travaux Publics | Snoussi M.,Mohammed V University
Natural Hazards and Earth System Sciences | Year: 2016

In Morocco, socio-economic activities are highly vulnerable to extreme weather events. This study investigates trends in mean and extreme rainfall, run-off and temperature, as well as their relationship with large-scale atmospheric circulation. It focuses on two Moroccan watersheds: the subhumid climate region of Bouregreg in the north and the semi-arid region of Tensift in the south, using data from 1977 to 2003. The study is based on a set of daily temperature, precipitation and run-off time series retrieved from weather stations in the two regions. Results do not show a homogeneous behaviour in the two catchments; the influence of the large-scale atmospheric circulation is different and a clear spatial dependence of the trend analysis linked to the distance from the coast and the mountains can be observed. Overall, temperature trends are mostly positive in the studied area, while weak statistically significant trends can be identified in seasonal rainfall, extreme rainfall events, average run-off and extreme run-off events.

Khomsi K.,Direction de la Meteorologie Nationale | Mahe G.,Mohammed V University | Sinan M.,Ecole Hassania des Travaux Publics EHTP | Snoussi M.,Mohammed V University
IAHS-AISH Proceedings and Reports | Year: 2013

The increase of temperature over Morocco, projected by climate models, should affect hydro-climatic regimes and ecological and socio-economic systems. In order to investigate the evolution of these regimes in the large basins of Tensift and Bouregreg, we compared the trends of observed temperature, rainfall and runoff variability. Annual temperature time series show significant increasing trends ranging between 0.07 and 0.25°C per decade in both basins. Shifts in annual and monthly temperature trends were recorded between the mid-1970s and mid-1980s and also in the early-1990s. In both basins, total annual rainfall decreased and changed its regime in the late-1970s, monthly rainfall regime changed only in the Tensift basin between early and mid-1970s. Runoff in both basins showed no significant trend for most of the stations, but a consistent decreasing trend since the early-1970s in the Tensift basin and the late-1970s and the early-1980s in the Bouregreg basin. Significant hydro-climatic changes occurred first in the southern basin (Tensift). Ruptures are most frequent in the spring and summer monthly time series. Copyright © 2013 IAHS Press.

Bari D.,Direction de la Meteorologie Nationale | Bergot T.,Meteo - France | El Khlifi M.,Hassan II University
Journal of Applied Meteorology and Climatology | Year: 2016

Using a fog event approach, the local meteorological and synoptic characteristics of fogs that formed over the Grand Casablanca (GCB) region during a 9-yr period (2001-09) are investigated. A climatological study of fog, with emphasis on the fog temporal variability and spatial distribution, is carried out on the basis of hourly surface meteorological observations at two synoptic stations in the region. The fog events are classified into fog types, using an objective classification algorithm, and are characterized by their duration, intensity, and times of onset and dissipation. In addition, fog events are classified into two distinct categories (isolated and widespread) on the basis of their spatial extent. K-means cluster analysis is applied to the patterns of mean sea level pressure in ERA-Interim reanalyses at 0000 UTC to determine the synoptic circulation types associated with fog occurrence in the GCB region. Results show that the fog frequency at the inland suburban station is more recurrent than at the coastal urban station. The fog events are predominantly of the advection-radiation type, with a marked tendency of nighttime occurrence during the winter. The spatial distribution analysis points out the localized character of fog and reveals the possibility of different fog types occurring when fog is present near the two stations simultaneously. Furthermore, the interaction between local- and large-scale mechanisms suggests that advective processes associated with sea-breeze circulation during daytime, followed by radiative processes early in the night, often lead to fog formation over the GCB region. © 2016 American Meteorological Society.

Bari D.,Direction de la Meteorologie Nationale | Bergot T.,French National Center of Weather Research | El Khlifi M.,Hassan II University
Quarterly Journal of the Royal Meteorological Society | Year: 2015

This numerical study focuses on a dense fog event that occurred during the night of 21-22 January 2008 in the Grand Casablanca region, on the northwestern coast of Morocco. This fog event, which lasted for 15 h, is simulated by the mesoscale non-hydrostatic model Meso-NH and analyzed using conventional meteorological observations from two synoptic stations of the region, Meteosat Second Generation (MSG) satellite imagery and the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-Interim reanalysis. Results demonstrate that this fog event included the formation of radiation fog over a continental zone and its extension to the coastal zone through the lowering of low-stratus clouds, which is in agreement with observations and is captured well by the Meso-NH model. Sensitivity experiments show that coastal fog prediction improves with improved sea-surface temperature. Model skill also depends on the adjustment of microphysical parameters when a single-moment microphysical scheme is used, and on reliable initial conditions. © 2015 Royal Meteorological Society.

Jarlan L.,CNRS Center for the Study of the Biosphere from Space | Driouech F.,Direction de la Meteorologie Nationale | Tourre Y.,Meteo - France | Duchemin B.,CNRS Center for the Study of the Biosphere from Space | And 5 more authors.
International Journal of Climatology | Year: 2014

The dominant patterns of vegetation cover interannual variability over Morocco are isolated using rotated extended empirical orthogonal functions applied to AVHRR NDVI data (1982-2008). The three leading modes capture the NDVI signal at the vegetation peak for three distinct locations: mode 1 (18.7% of total variance) is located along the Atlantic coastline, mode 2 (13.1%) is southwest of the Riff Mountain whilst mode 3 (11.2%) is along the Mediterranean coastline. Correlations between the NDVI time coefficients for the modes 'Atlantic' and 'Mediterranean' dominated by annuals and precipitation amount during the early stage of the vegetation cycle (NDJ) are found. Significant fluctuations of NDVI time coefficients are isolated: a quasi-biennial signal is present in the three modes and an additional quasi-quadriennial (∼4.4 years) signal is identified for the 'Atlantic' mode only. Connection between vegetation activity and atmospheric and oceanic climate signals are sought using time-lag correlation analyses. The NAO during fall-beginning of winter (NDJ) is found to impact vegetation peak for the 'Atlantic' mode while the Scandinavian Pattern is related to NDVI peak over the 'Atlantic' and 'Riff' latter in the season (DJF). A significant connection is also found between vegetation over the 'Atlantic' mode and the 'Riff' and the 'Atlantic Niño' mode leading the SST variability in the equatorial Atlantic with a 6-months lag. Finally, linkages between NDVI and climate information are used to build a seasonal prediction model for NDVI using multiple linear regression. The NDVI anomalies during March-April may be predicted with a reasonable accuracy from January with 79% of explained variance, 60% and 72% for the 'Atlantic', the 'Riff' and the 'Mediterranean' regions, respectively. Results have (1) direct impacts for a better understanding of the role of large-scale climate signals on vegetation cover over Morocco and (2) contribute to the implementation of an agricultural early warning system. © 2013 Royal Meteorological Society.

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