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See detailMonitoring of the 2003 summer drought in Belgium with the NDWI applied on spot-vegetation data.
Horion, Stéphanie; Eerens, Herman; Tychon, Bernard ULg et al

in Veroustraete, F.; Bartholomé, E.; Verstraeten, W. W. (Eds.) Proceedings of the 2nd international vegetation user conference. 1998-2004 : 6 years of operational activities. (2005)

The summer 2003 was abnormally hot, sunny and dry. The average temperatures from June to August were the highest ever recorded in the Belgian reference meteorological station of Uccle, but also in other ... [more ▼]

The summer 2003 was abnormally hot, sunny and dry. The average temperatures from June to August were the highest ever recorded in the Belgian reference meteorological station of Uccle, but also in other countries of western and central Europe such as Portugal, Germany, Switzerland and the United Kingdom. Many human activities were affected by these particular climatic conditions, among which agriculture.The Normalized Difference Water Index (NDWI) applied on ten-daily SPOT- VEGETATION imagery is one of the drought indicators which could serve for the localisation of drought affected areas in Belgium. In this paper preliminary results show that detection of dry events is possible using historical averages of NDWI. Relative NDWI images can be used to monitor the development of the summer drought.These images are computed by the weighted difference between the NDWI values during this summer and its value at the same period in a reference year, which corresponds to a normal year in terms of rainfall availability. Analysis of the relation between NDWI and NDVI behaviours show that the green biomass influences the NDWI value especially during the growing season. More accurate study has to be done to individualize the specific NDWI behaviour during dry events. In perspectives, index validation with meteorological parameters and with the Relative Soil Moisture Index, which is an output of the Belgian Crop Growth Monitoring System, will improve this study. [less ▲]

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See detailAeolian dust falls in northern Italy in autumn 1996: chemical and mineralogical comparison
Ozer, Pierre ULg; LUCCHETTI, Gabriella

in Periodico di Mineralogia (2005), 74(2), 103-116

This paper describes two dust fall events in Genoa and Turin (northern Italy) on 12 November 1996 and 7 December 1996 respectively. Meteorological data suggest that the dust-bearing rain that fell on ... [more ▼]

This paper describes two dust fall events in Genoa and Turin (northern Italy) on 12 November 1996 and 7 December 1996 respectively. Meteorological data suggest that the dust-bearing rain that fell on Genoa originated in north-eastern Morocco, where dust mobilisation was reported two days earlier, and had been carried straight to the north-western Italian coast by very strong winds. But the dust fall observed in Turin was not characterised by any specific synoptic situation inducing dust transport from the southern Mediterranean. The analyses include a quantitative and a qualitative study of two dust samples collected in downtown Genoa and Turin. The total amounts of dust that fell give two very high values of 4.05 g m-2 for Genoa and 0.54 g m-2 for Turin. The median sizes of the dust particles were 14.6 µm and 25.8 µm respectively. Most of the dust material collected in Genoa showed a yellowish-brown to red colour due to surface weathering by ferric hydroxides, and was sometimes coated with clayey particles. This attests to the Saharan origin of the particles. On the contrary, only 15% of the material sampled in Turin was coated with red-like clayey material from the desert. A large part of the sample was covered with a carbon-like substance. In addition, the proportion of organic matter (pollen grains and seeds) and anthropogenic fibrous material was much higher. This suggests that the dust fall observed in Turin very likely originated from local pollution mixed with a low proportion of long-distance Saharan dust. [less ▲]

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See detailDésertification au Sahel : Crise climatique ou anthropique ?
Ozer, André ULg; Ozer, Pierre ULg

in Bulletin des Séances de l’Académie Royale des Sciences d’Outre-Mer = Mededelingen der Zittingen van de Koninklijke Academie voor Overzeese Wetenschappen (2005), 51(4), 395-423

Over the last decades, the Sahel suffered two dramatic contiguous droughts. At present, and since the early 1990s, rainfalls have recorded an amelioration that tends towards the average of precipitation ... [more ▼]

Over the last decades, the Sahel suffered two dramatic contiguous droughts. At present, and since the early 1990s, rainfalls have recorded an amelioration that tends towards the average of precipitation previous to the 1970s. However, this improvement may be due to increasing rainfall intensity and it seems that the length of the rainy season did not show any extension when compared to the 1970s and 1980s. Moreover, the Sahelian population has been multiplied by 3 since 1950 and is foreseen to be multiplied by 10 by the second half of the 21st century. Increasing urban population levels are much more impressive and bring about important environmental disruptions every day. Such increasing human pressure leads to uncontrolled deforestation in order to meet the needs in fuel wood, wood for construction and shifting cultivation. In addition, the ever-increasing number of herds for contracting range conditions leads to overgrazing. All these processes cause the degradation of the vegetation cover, a constant diminution of crop yields, as well as a strong reduction of biodiversity. One of the consequences is the reactivation of previously fixed dunes that were formed during the last interpluvial phase (18,000 BP). This article provides a state-of-the-art of the present controversy about desertification processes and concludes that if the droughts of the 1970s and 1980s have had dramatic consequences for the population of the Sahel, current and coming increasing human pressure will intensify the desertification of the southern fringe of the Sahara. [less ▲]

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See detailEstimation de la pollution particulaire naturelle de l’air en 2003 à Niamey (Niger) à partir de données de visibilité horizontale
Ozer, Pierre ULg

in Environnement Risques & Santé (2005), 4(1), 43-49

There is no longer any question that air pollution in the form of large quantities of total suspended particulates (TSP) and particulate matter less than 10 µm in aerodynamic diameter (PM 10) harms human ... [more ▼]

There is no longer any question that air pollution in the form of large quantities of total suspended particulates (TSP) and particulate matter less than 10 µm in aerodynamic diameter (PM 10) harms human health. Deterioration in air quality due to high concentrations of mineral dust from Africa affects the US and Europe, although most of these countries are far from the Sahara. Surprisingly, no estimates of TSP or PM 10 levels near the Saharan dust source are available. Measurements taken at Niamey-Airport in Niger of horizontal visibility, which is reduced by the presence of dust in the atmosphere, allowed us to estimate TSP and PM 10 levels according various relations found in the literature. Both the magnitude and frequency of mineral particle concentrations are very high. The average yearly concentration is estimated at 103 µg.m -3 TSP and 67 µg.m -3 PM 10. These very high particulate levels present a real public health threat to which national and international policy-makers must respond. [less ▲]

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See detailAnalyse climatique de la région de Gouré, Niger oriental : récentes modifications et impacts environnementaux
Ozer, Pierre ULg; Bodart, Catherine ULg; Tychon, Bernard ULg

in Cybergeo : Revue Européenne de Géographie = Cybergeo - European Journal of Geography (2005)

Since the late 1960s, the Sahel is affected by a dramatic drought. This article analyses climatic variations recorded in the Gouré area, eastern Niger, between 1936 and 2003. It appears that the drought ... [more ▼]

Since the late 1960s, the Sahel is affected by a dramatic drought. This article analyses climatic variations recorded in the Gouré area, eastern Niger, between 1936 and 2003. It appears that the drought ended in the late 1980s. However, the rainfall increase did not lead to an extension of the length of the rainy season. The study of the wind shows that correct data were recorded during the two first years of the station of Gouré (1984 and 1985). Afterwards, wind speed was entached by errors and did not report since 1997. The situation is alarming as we know that neighbouring stations meet the same problems and that no synoptic station currently reports wind values in eastern Niger. However, based on wind speed and deflation data recorded in 1984, a threshold wind speed of 7 m/s was determined in Gouré. Finally, from measurements of horizontal visibility reduced by mineral dust, our results suggest that air quality is reduced because of the high frequency of wind erosion. The confrontation of our results with recent environmental studies in that region show that the end of the drought did not lead to any landscape improvement. Increasing human pressure tends to be the main driving factor of land degradation. [less ▲]

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See detailEvolution des ressources forestières en Afrique de l’Ouest soudano-sahélienne au cours des 50 dernières années
Ariori, Serge Léopold; Ozer, Pierre ULg

in Geo-Eco-Trop (2005), 29

On the basis of an exhaustive consultation of the literature describing the temporal evolution of land cover in arid, semiarid and dry subhumid regions of West Africa, this study shows that the ... [more ▼]

On the basis of an exhaustive consultation of the literature describing the temporal evolution of land cover in arid, semiarid and dry subhumid regions of West Africa, this study shows that the deforestation trend has been very important during the second half of the 20th century. This trend to deforestation is globally large (2% per year) and is clearly alarming. Although our results differ from FAO's official data, it is demonstrated that those are questionable. In addition, if dense woody formations have been strongly reduced in the study area, our study indicates that degraded woody formations are currently declining. Our results clearly go against the recent conclusions of some authors preaching the idea of a 'greening Sahel'. [less ▲]

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See detailMesure des retombées au sol des aérosols désertiques durant l’hivernage 2005 à Mâle, Mauritanie méridionale.
Gassani, Jean; Bent Mohamed, Aminetou; Duchesne, Jean et al

in Geo-Eco-Trop (2005), 29

The Sahara and its margins largely contribute to the global injection of mineral dust into the northern hemisphere, about half of the yearly global mineral dust production. In this study, we have placed a ... [more ▼]

The Sahara and its margins largely contribute to the global injection of mineral dust into the northern hemisphere, about half of the yearly global mineral dust production. In this study, we have placed a pyramidal receptacle in Mâle (southern Mauritania) during the rainy season 2005 in order to measure daily Saharan dust deposition. The dust quantity collected totals 78.38 g/m2 during the 3 months experimented. Comparing our results to previous works achieved in the southern border of the Sahara shows that the levels of deposition in Mâle are extremely high. This could suggest a continuous environmental degradation resulting from always increasing human pressure. [less ▲]

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See detailBulletin agrométéorologique - Août 2004
Tychon, Bernard ULg; Ozer, Pierre ULg; Horion, S. et al

in Bulletin Agrométéorologique (2004), 3(5), 1-4

Le mois d’août a été caractérisé par des précipitations, des vitesses de vent et une humidité anormalement élevées. Les valeurs de rayonnement étaient par contre anormalement faibles. Les rendements ... [more ▼]

Le mois d’août a été caractérisé par des précipitations, des vitesses de vent et une humidité anormalement élevées. Les valeurs de rayonnement étaient par contre anormalement faibles. Les rendements prévus pour le maïs fourrager sont légèrement inférieurs à ceux observés au cours des cinq années antérieures. Par contre, concernant la betterave sucrière et la pomme de terre mi-hâtive, la tendance est inverse avec des estimations globalement supérieures à la moyenne des cinq dernières années. [less ▲]

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See detailBulletin agrométéorologique - Juillet 2004
Tychon, Bernard ULg; Ozer, Pierre ULg; Horion, S. et al

in Bulletin Agrométéorologique (2004), 3(4), 1-4

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See detailBulletin agrométéorologique - Juin 2004
Tychon, Bernard ULg; Ozer, Pierre ULg; Horion, S. et al

in Bulletin Agrométéorologique (2004), 3(3), 1-5

Les paramètres climatiques du mois de juin furent tous proches de la moyenne, exception faite de l'ensoleillement qui fut largement déficitaire sur l’est du pays. La situation des céréales d’hiver et de ... [more ▼]

Les paramètres climatiques du mois de juin furent tous proches de la moyenne, exception faite de l'ensoleillement qui fut largement déficitaire sur l’est du pays. La situation des céréales d’hiver et de la pomme de terre est globalement favorable laissant entrevoir des rendements généralement supérieurs à ceux de 2003. Par contre, les prévisions relatives au maïs fourrager et à la betterave sucrière montrent que ces cultures pourraient connaître, au niveau national, une légère baisse par rapport à l’année passée. [less ▲]

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See detailBulletin agrométéorologique - Mai 2004
Tychon, Bernard ULg; Ozer, Pierre ULg; Horion, S. et al

in Bulletin Agrométéorologique (2004), 3(2), 1-5

Les températures et l'ensoleillement du mois de mai furent légèrement inférieurs à la moyenne. En revanche, les précipitations déficitaires furent généralisées et les périodes sans pluie ont atteint près ... [more ▼]

Les températures et l'ensoleillement du mois de mai furent légèrement inférieurs à la moyenne. En revanche, les précipitations déficitaires furent généralisées et les périodes sans pluie ont atteint près de trois semaines en certaines régions. La situation des cultures est globalement favorable laissant entrevoir des rendements généralement semblables, voire supérieurs à ceux de 2003. [less ▲]

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See detailBulletin agrométéorologique - Avril 2004
Tychon, Bernard ULg; Ozer, Pierre ULg; Horion, S. et al

in Bulletin Agrométéorologique (2004), 3(1), 1-4

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See detailAnalyse de la campagne agricole 2003 en terme de stress hydrique
De Longueville, Florence ULg; Horion, Stéphanie ULg; Tychon, Bernard ULg et al

in Bulletin de la Société Géographique de Liège (2004), 44

This article presents the evaluation of the crop water stress in 2003 using the Belgian Crop Growth Monitoring System (B-CGMS). The indicator used is the Relative Soil Moisture Index (RSMI), and is based ... [more ▼]

This article presents the evaluation of the crop water stress in 2003 using the Belgian Crop Growth Monitoring System (B-CGMS). The indicator used is the Relative Soil Moisture Index (RSMI), and is based on a calculation integrating soil moisture data. This index shows the differences between needed and effectively available soil water for different crop types. It is one of the outputs of the B-CGMS agrometeorological model. Based on a fixed threshold, days affected by water stress have been identified and computed for specific periods during which lack of soil water is likely to have dramatic impacts on crop production. The cumulative number of days affected by water stress indicator has then been integrated into a GIS to spatially represent the situation of winter wheat and maize during the 2003 crop season. Results suggest that only maize was affected by the water stress in northern and southern Belgium. In the latter area, the lack of water at key periods provoked a yield reduction ranging between 2 and 50%. [less ▲]

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See detailMise en évidence des zones touchées par la désertification par télédétection a basse résolution au Niger
Hountondji, Yvon ULg; Ozer, Pierre ULg; Nicolas, Jacques ULg

in Cybergeo : Revue Européenne de Géographie = Cybergeo - European Journal of Geography (2004)

In order to identify areas where desertification may have occurred over the last two decades, 109 stations located in three bioclimatic zones of Niger are analyzed. Time series of remote sensing data are ... [more ▼]

In order to identify areas where desertification may have occurred over the last two decades, 109 stations located in three bioclimatic zones of Niger are analyzed. Time series of remote sensing data are well suited to this task. Here, we use time series of NOAA AVHRR normalized difference vegetation index (NDVI) data and rainfall data. In this study, trend analysis is used to identify areas within the biomes from 1981 to 1999 in Niger with apparent land degradation in semi-arid areas. It appears that most of Niger (98%) recorded increasing rainfall while only 76% experienced increasing maximum NDVI. However, the combination of the two variables through the ratio shows a widespread reduction of the rain-use efficiency with non significant trend for the stations located in northern Sahel (p=0.52), highly significant for those located in central Sahel (p=0.00009) and significant in southern Sahel (p=0.041). Overall, 75.3% of the sample recorded a significant reduction of the NDVIMax/RR ratio. Only one station out of four (24.7%) presented a stability of the ratio. These negative trends suggest a progressive diminution of the vegetation productivity as highlighted by the lowering of the NDVIMax/RR ratio. This situation suggest a consistently environmental degradation and that desertification processes continued during the last two decades over most of the Sahelian belt of Niger. [less ▲]

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See detailL’enseignement en gestion des risques naturels.
Ozer, Pierre ULg; Tychon, Bernard ULg; Ozer, André ULg et al

in Demarée, Gaston; De Dapper, Morgan; Alexandre, Jean (Eds.) Tropical Climatology, Meteorology and Hydrology: Climate-related risk analysis and sustainable development in tropical areas. (2004)

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See detailUtilisation de la visibilité horizontale pour l’estimation de la qualité de l’air à Niamey, Niger
Ozer, Pierre ULg

in Bulletin de la Société Géographique de Liège (2004), 44

It is now irrefutable that air pollution caused by large amounts of Total Suspended Particulates (TSP) has numerous undesired consequences on human health. Air quality deterioration in the US and in ... [more ▼]

It is now irrefutable that air pollution caused by large amounts of Total Suspended Particulates (TSP) has numerous undesired consequences on human health. Air quality deterioration in the US and in Europe caused by high concentration of African dust is seen as a major health threat although most of these countries are very distant from the Sahara. Surprisingly, no estimates of TSP levels near the Saharan dust source are available. Based on horizontal visibility measurements reduced by dust in the air, TSP levels are estimated at Niamey-Aéroport (Niger) by using different relations found in the literature. It appears that excessive TSP concentration levels are very important in magnitude and frequency. These very high TSP levels represent a tremendous public health threat that should be absolutely taken into consideration by national and international decision makers. [less ▲]

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See detailBois de feu et déboisement au Sahel: mise au point
Ozer, Pierre ULg

in Science et changements planétaires / Sécheresse (2004), 15(3), 243-251

A major environmental issue of the XXIst century, deforestation due to firewood consummation is an increasing problem within the Sahel of West Africa. This article underlines the difficulties to obtain ... [more ▼]

A major environmental issue of the XXIst century, deforestation due to firewood consummation is an increasing problem within the Sahel of West Africa. This article underlines the difficulties to obtain reliable statistics to correctly monitor deforestation. Field data on firewood consumption are dramatically lacking and inventories of forest cover are very poor. In this context, scientists and policymakers often use the data published by FAO to understand the deforestation topic. Unfortunately, we clearly demonstrate that those data are also inaccurate and not coherent. The analysis of several official documents shows that no institution is currently able to produce any reliable data on firewood and its impact on the environment. [less ▲]

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See detailAre the 1999 and 2000 urban floods in Senegal due to exceptional rainfall events?
Sene, Souleymane; Ozer, Pierre ULg

in Demarée, Gaston; De Dapper, Morgan; Alexandre, Jean (Eds.) Tropical Climatology, Meteorology and Hydrology: Climate-related risk analysis and sustainable development in tropical areas. (2004)

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See detailCan dust variability be a regional indicator of land degradation trend in arid and semi-arid areas? Analysis in the Sahel.
Ozer, Pierre ULg

in Demarée, Gaston; De Dapper, Morgan; Alexandre, Jean (Eds.) Tropical Climatology, Meteorology and Hydrology: Climate-related risk analysis and sustainable development in tropical areas. (2004)

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See detailMonitoring drought stress in north-eastern China by means of rainfall data and diachrone indices derived from Pathfinder AVHRR-imagery.
Ozer, Pierre ULg; Tychon, Bernard ULg; Eerens, Herman

in Smits, Paul; Bruzzone, Lorenzo (Eds.) Analysis of Multi-Temporal Remote Sensing Images (2004)

For climatic stress detection and monitoring in the Heilongjiang Province, north-eastem China, an indicator on the interannual vegetation state was extracted from the AVHRR Pathfinder image set (1981-2000 ... [more ▼]

For climatic stress detection and monitoring in the Heilongjiang Province, north-eastem China, an indicator on the interannual vegetation state was extracted from the AVHRR Pathfinder image set (1981-2000) and compared to the rainfall variations over the growing season (June to August). The results show that the vegetation status does not closely depend on rainfall variations in this region. Temperatures, which showed a rapid augmentation in the northern high latitudes since the early 1980s, seem to be a more crucial limiting factor for vegetation growth. Rapid land cover change and large natural disasters are also likely to impact the relationship between rainfall and vegetation. [less ▲]

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