Evolution of Surface Hydrology in the Sahelo-Sudanian Strip: An Updated Review

In the West African Sahel, two paradoxical hydrological behaviors have occurred during the last five decades. The first paradox was observed during the 1968–1990s ‘Great Drought’ period, during which runoff significantly increased. The second paradox appeared during the subsequent period of rainfall recovery (i.e., since the 1990s), during which the runoff coefficient continued to increase despite the general re-greening of the Sahel. This paper reviews and synthesizes the literature on the drivers of these paradoxical behaviors, focusing on recent works in the West African Sahelo/Sudanian strip, and upscaling the hydrological processes through an analysis of recent data from two representative areas of this region. This paper helps better determine the respective roles played by Land Use/Land Cover Changes (LULCC), the evolution of rainfall intensity and the occurrence of extreme rainfall events in these hydrological paradoxes. Both the literature review and recent data converge in indicating that the first Sahelian hydrological paradox was mostly driven by LULCC, while the second paradox has been caused by both LULCC and climate evolution, mainly the recent increase in rainfall intensity

Initiation à la nématologie : application aux cultures maraichères : rapport de stage des techniciens supérieurs en protection des végétaux

Les nématodes du genre #Meloidogyne (Goeldi, 1892) constituent un groupe important dans les régions de production maraîchère du Sénégal où leur virulence et leur large spectre d'hôte en font un parasite redoutable. L'association de cette espèce à des baisses de rendement justifie l'attention particulière qu'accorde le laboratoire de nématologie de l'Institut Français de la recherche Scientifique pour le Développement en Coopération (ORSTOM) à une recherche d'alternatives nouvelles pour le contrôle de ce nématode. Ce stage fut orienté à l'étude (la description, la morphologie, la biologie, la lutte...) de ce genre, ainsi que les techniques nématologiques appliquées depuis l'échantillonnage, l'extraction jusqu'à la reconnaissance des espèces de #Meloidogyne par électrophorèse monodimensionnelle d'isoenzymes et des montages de spécimens sur lame de Cobb. (Résumé d'auteur

Seasonal fractional ARIMA with stable innovations

We develop the theory of seasonally fractionally differenced ARIMA time series with stable infinite variance innovations establishing conditions for existence and invertibility. This is a finite parameter model which exhibits long range dependence, seasonality and high variability. We perform some simulations to illustrate the behavior of the model.

Biomorphometric characteristics of different types of sensilla detected on the antennaof Helicoverpa armigera by scanning electron microscopy

A morphometric study on H. armigera antenna showed four styles of sensilla, i.e., styloconica, chaetica, coeloconica, and trichodea, and their numbers were estimated. Sensilla trichodea detect inter and intraspecific communication signals and was the most numerous. They were divided into three types: type I, the longest, with a length of 34.04 ± 3.16 μm and about 2.16 to 2.42 μm in diameter at its base; 2) type II, intermediate, with a length of 22.58 ± 0.77 μm and basal diameter of 1.8–2.52 μm; 3) type III, the shortest sensilla trichodea, with a length of 7.62 ± 0.4 μm and a range in diameter similar to that of type II. The length of the female sensilla trichodea was longer than that of the male. The total number of sensilla trichodea was estimated to be 7520 on the antenna of the female, and 6831 on the male antenna. The lengths of the sensilla trichodea type I and type III were significantly different on male (t = 4.6881, P = 0.0034) and female antenna (t = 18.9852, P = 0.0001). An estimation of the predicted surface area of the most numerous type I on sampled segments between the 12th and 20th segments from a female of H. armigera showed a surface area of 5 × 103 μm2 and a sensillar density of 38 sensilla/103 μm2. The fraction of sensilla-occupied surface area was 0.4 μm2

Estimation of Fractional ARIMA Process with Stable Innovations: A Monte Carlo Study

This paper considers estimation of the parameters for fractionally integrated processes with infinite varianceinnovations introduced by Kokoszka and Taqqu (1995). This is a finite parameter model which exhibitslong-range dependence and large fluctuations (heavy-tailed distributions). We introduce two proceduresto estimate the dierencing parameter and ARMA coecients. The first one is the Conditional Sum ofSquares (CSS) method and the second is the Minimum Hellinger Distance (MHD) estimator. Monte Carloexperiments are used to evaluate the finite sample performance of the proposed estimators, and compare itto the Markov chains Monte Carlo (MCMC) Whittle approach developed by Ndongo et al. (2010)

Evolution of Surface Hydrology in the Sahelo-Sudanian Strip: An Updated Review

In the West African Sahel, two paradoxical hydrological behaviors have occurred during the last five decades. The first paradox was observed during the 1968–1990s ‘Great Drought’ period, during which runoff significantly increased. The second paradox appeared during the subsequent period of rainfall recovery (i.e., since the 1990s), during which the runoff coefficient continued to increase despite the general re-greening of the Sahel. This paper reviews and synthesizes the literature on the drivers of these paradoxical behaviors, focusing on recent works in the West African Sahelo/Sudanian strip, and upscaling the hydrological processes through an analysis of recent data from two representative areas of this region. This paper helps better determine the respective roles played by Land Use/Land Cover Changes (LULCC), the evolution of rainfall intensity and the occurrence of extreme rainfall events in these hydrological paradoxes. Both the literature review and recent data converge in indicating that the first Sahelian hydrological paradox was mostly driven by LULCC, while the second paradox has been caused by both LULCC and climate evolution, mainly the recent increase in rainfall intensity