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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.

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.

Filahi S.,Direction de la Meteorologie Nationale | Filahi S.,Hassan II University | Tanarhte M.,Max Planck Institute for Chemistry | Tanarhte M.,Hassan II University | And 3 more authors.
Theoretical and Applied Climatology | Year: 2015

The purpose of this paper is to provide a summary of Morocco’s climate extreme trends during the last four decades. Indices were computed based on a daily temperature and precipitation using a consistent approach recommended by the ETCCDI. Trends in these indices were calculated at 20 stations from 1970 to 2012. Twelve indices were considered to detect trends in temperature. A large number of stations have significant trends and confirm an increase in temperature, showing increased warming during spring and summer seasons. The results also show a decrease in the number of cold days and nights and an increase in the number of warm days and nights. Increasing trends have also been found in the absolute warmest and coldest temperatures of the year. A clear increase is detected for warm nights and diurnal temperature range. Eight indices for precipitation were also analyzed, but the trends for these precipitation indices are much less significant than for temperature indices and show more mixed spatial patterns of change. Heavy precipitation events do not exhibit significant trends except at a few locations, in the north and central parts of Morocco, with a general tendency towards drier conditions. The correlation between these climate indices and the large-scale atmospheric circulations indices such as the NAO, MO, and WEMO were also analyzed. Results show a stronger relationship with these climatic indices for the precipitation indices compared to the temperature indices. The correlations are more significant in the Atlantic regions, but they remain moderate at the whole country scale. © 2015 Springer-Verlag Wien

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.

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