Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Monsoon in West Africa: Classic continuity hides a dual-cycle rainfall regime

28.01.2003


Since the end of the 1960s West Africa has continuously been suffering hard drought. The rainfall deficit for the 1970s and 1980s, calculated to compare with the 1950s and 1960s, thus reached as high as 50% over the northern part of the Sahel. The hydrological cycle as a whole is affected by this drought, which results in serious consequences for agriculture and food security.



IRD researchers, aiming to understand the mechanisms behind this situation, examined rainfall data from 1950 to 1990. Two sub-periods emerge : a wet one (1951-1969), followed by a dry one (1970-1990). This finding led them to modify drastically the classic model which presents the monsoon as a process that unfurls in a continuous sweep from South to North. Two rainfall dynamics regimes are in evidence, distinct in time and in space, separated by a sharp transition. The mean date for this, a jump heralding the monsoon onset, is around 22 June, which proved to be highly constant for both the wet and the dry sub-periods.

The proposed model predicts that the first monsoon phase starts off from the Atlantic coast in February and propagates steadily northwards. By May it has reached the central Sahel (13°N longitude, Niamey). After a period of stabilization, rainfall abruptly becomes much heavier. It touches the whole Sahel zone simultaneously. A short dry season then appears on the coast before a second rainy season arises there from September, linked to the retreat of the monsoon towards the South.


Rainfall variations within the first phase of the monsoon, which corresponds to a stable oceanic regime, are only small. However, the second phase, regulated by the prevailing conditions in the continental regime, shows wide inter-annual differences. So much of the Sahel’s rainfall is the fruit of a continental-derived cycle - 90% in fact - that any loss of monsoon intensity during this second phase can favour severe drought. The duration of the rainy season did not, however, vary much over the two periods, the research team found. The drought is therefore expressed by a lengthening of the average time between two rainfall events, which increases the risk of a dry spell intervening at the core of what should be the rainy season and rendering crop plants such as millet more vulnerable to stress.

Since a severe drought that hit the Sahel between 1971 and 1974, several investigations have been devoted to determining the different factors (relief, oceanic parameters and so on) that could explain this climatic event. These latest studies have prompted IRD researchers to postulate a discontinuous, non-linear, model for monsoon development. Such a model broadens the field of investigation in terms of potentially relevant parameters in drought development in West Africa. The approach the team is adopting favours advances in the identification of mechanisms behind the decline in rainfall-event frequency after the monsoon jump. It also provides the foundation for the international programme AMMA* devoted to improving systems for predicting the monsoon.

___________________
* AMMA = Analyse multidisciplinaire de la mousson africaine (Multidisciplinary Analysis of the African Monsoon), a programme launched at the beginning of 2002 on the initiative of the IRD, the CNES, the CNRS, Météo-France and the African organizations ACMAD (African Center for Meteorological Applications to Development) and AGRHYMET (Centre d’Agro-hydro-meteorologie, Niamey, Niger)

Marie-Lise Sabrie | alfa

More articles from Ecology, The Environment and Conservation:

nachricht International network connects experimental research in European waters
21.03.2017 | Leibniz-Institut für Gewässerökologie und Binnenfischerei (IGB)

nachricht World Water Day 2017: It doesn’t Always Have to Be Drinking Water – Using Wastewater as a Resource
17.03.2017 | ISOE - Institut für sozial-ökologische Forschung

All articles from Ecology, The Environment and Conservation >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Giant Magnetic Fields in the Universe

Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.

The results will be published on March 22 in the journal „Astronomy & Astrophysics“.

Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...

Im Focus: Tracing down linear ubiquitination

Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.

Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...

Im Focus: Perovskite edges can be tuned for optoelectronic performance

Layered 2D material improves efficiency for solar cells and LEDs

In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...

Im Focus: Polymer-coated silicon nanosheets as alternative to graphene: A perfect team for nanoelectronics

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...

Im Focus: Researchers Imitate Molecular Crowding in Cells

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

International Land Use Symposium ILUS 2017: Call for Abstracts and Registration open

20.03.2017 | Event News

CONNECT 2017: International congress on connective tissue

14.03.2017 | Event News

ICTM Conference: Turbine Construction between Big Data and Additive Manufacturing

07.03.2017 | Event News

 
Latest News

Argon is not the 'dope' for metallic hydrogen

24.03.2017 | Materials Sciences

Astronomers find unexpected, dust-obscured star formation in distant galaxy

24.03.2017 | Physics and Astronomy

Gravitational wave kicks monster black hole out of galactic core

24.03.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>