Search

International audience; Soil erosion supplies large quantities of sediments to rivers of Southeastern Asia. It reduces soil fertility of agro-ecosystems located on hillslopes, and it degrades, downstream, water resource quality and leads to the siltation of reservoirs. An increase in the surface area covered with commercial perennial monocultures such as teak plantations is currently observed at the expanse of traditional slash-and-burn cultivation systems in steep montane environments of these regions. The impacts of land-use change on the hydrological response and sediment yields have been investigated in a representative catchment of Laos monitored for 13 years. After the gradual conversion of rice-based shifting cultivation to teak plantation-based systems, overland flow contribution to stream flow increased from 16 to 31% and sediment yield raised from 98 to 609 Mg km −2. This result is explained by the higher kinetic energy of raindrops falling from the canopy, the virtual absence of understorey vegetation cover to dissipate drop energy and the formation of an impermeable surface crust accelerating the formation and concentration of overland flow. The 25-to-50% lower 137 Cs activities measured in soils collected under mature teak plantations compared to soils under other land uses illustrate the severity of soil erosion processes occurring in teak plantations.

Soil erosion supplies large quantities of sediments to rivers of Southeastern Asia. It reduces soil fertility of agro-ecosystems located on hillslopes, and it degrades, downstream, water resource quality and leads to the siltation of reservoirs. An increase in the surface area covered with commercial perennial monocultures such as teak plantations is currently observed at the expanse of traditional slash-and-burn cultivation systems in steep montane environments of these regions. The impacts of land-use change on the hydrological response and sediment yields have been investigated in a representative catchment of Laos monitored for 13 years. After the gradual conversion of rice-based shifting cultivation to teak plantation-based systems, overland flow contribution to stream flow increased from 16 to 31% and sediment yield raised from 98 to 609 Mg km(-2). This result is explained by the higher kinetic energy of raindrops falling from the canopy, the virtual absence of understorey vegetation cover to dissipate drop energy and the formation of an impermeable surface crust accelerating the formation and concentration of overland flow. The 25-to-50% lower Cs-137 activities measured in soils collected under mature teak plantations compared to soils under other land uses illustrate the severity of soil erosion processes occurring in teak plantations.

In the Dry Zone of Myanmar, improved access to water is widely acknowledged as being vital for livelihood enhancement and the general well-being of around 10 million people, most of whom depend on agriculture. Thus, expanding the sustainable use of groundwater is of great importance for socioeconomic development. According to this study, opportunities for accessing groundwater are generally good, and development of the resource has steadily increased over the years. However, there still appears to be good prospects for expanding groundwater use for irrigation, with a view to increasing agricultural production. Provision of affordable mechanical technologies for drilling wells and support with credit facilities to purchase small-capacity motorized pumps for irrigation could improve food security and livelihoods, where there is potential to expand groundwater use. Replenishable groundwater resources of the Dry Zone are likely to be less than previously thought. Thus, it is important to find the right balance between increasing development of the resource for enhanced irrigation, while also protecting its existing beneficial use for communities and the environment.

In Northeast Thailand, about 80% of the 20 million inhabitants are engaged in rainfed agriculture. Climate vagaries combined with coarse-textured sandy and unevenly distributed saline soils explain low agriculture yields and the endemic relative poverty of the population. We conducted an in-depth analysis of change in the rainfall pattern using daily records (1953-2010) from 18 gauging stations scattered across Northeast Thailand. Based on an intimate knowledge of the local farming systems, particularly their strategies to deal with climate variability and their evolution during the past decades, we analyse and discuss how the cropping systems can adapt to the detected rainfall changes. We used the Mann–Kendall trend detection test, modified to account for serial correlation at each individual station, and the regional average Kendall's statistic designed for the detection of regional trends across the entire studied area. On-farm surveys carried out during the past two decades in both the upper and lower parts of Northeast Thailand provide a detailed understanding of the functioning of the agricultural production systems and their diversity. The analysis reveals very limited changes in rainfall frequency, intensity and extremes during the humid monsoon and therefore little change in the existing climatic constraints to agricultural production (early dry spells in the wet season and risk of floods at its peak in September). But we found a significant regional trend toward a wetter dry season that could offer new limited opportunities for agricultural production. The paper will discuss the implications of these findings and compare them with recently published research results. Differences in statistical significance between local and regional rainfall trends are also interpreted. If these trends extend, households would not face many difficulties because of their renowned adaptive capacity built over centuries of facing highly variable rainfall patterns, and due to the diversity of their resilient farming systems. (Texte intégral)

Paper presented at the International Conference on Sustainability in the Water-Energy-Food Nexus, Bonn, Germany, 19-20 May 2014

The high operating frequencies of semiconductor chips generate heat fluxes it is important to be evacuated in order to avoid the destruction of the chip. A standard module in the field of power electronics is composed of a silicon chip, an electrical insulator (substrate) and a heat sink (drain) for the evacuation of heat. This heat induces thermomechanical stresses due to differential expansion of materials.Two new concepts proposed can overcome these problems and increase the overall reliability of electronic systems. The first is the design and development of a drain composite adaptive thermal properties (thermal expansion coefficient and thermal conductivity). In the second, a new assembly method is presented. It allows, by means of a metal film Sn or Au, intermetallic compounds to create stable over time.; Les fréquences de fonctionnement élevées des puces semi-conductrices génèrent des flux de chaleurs importants qu'il est nécessaire d'évacuer pour éviter la destruction de la puce. Un module standard dans le domaine de l'électronique de puissance est composé d'une puce en silicium, d'un isolant électrique (substrat) et d'un dissipateur thermique (drain) permettant l'évacuation de la chaleur. Cette chaleur induit des contraintes thermomécaniques dues à la dilatation différentielle des matériaux.Deux concepts nouveaux proposés permettent de palier ces problèmes et d'augmenter la fiabilité générale des systèmes électroniques. Le premier est la conception et l'élaboration d'un drain composite à propriétés thermiques adaptatives (coefficient de dilatation thermique et conductivité thermique). Dans le deuxième, une nouvelle méthode d'assemblage est présentée. Elle permet, au moyen d'un film métallique Sn ou Au, de créer des composés intermétalliques stables dans le temps.

This study assessed the variability of flows under present and 'naturalized' basin conditions in the Upper Ganges Basin (UGB). Furthermore, the PRECIS regional climate model (RCM) was used to generate climate projections for the UGB, with subsequent simulations of future river flows. Results show that the annual average precipitation, actual evapotranspiration (ET) and net water yields of the whole basin were 1,192 mm, 416 mm and 615 mm, respectively. Precipitation, ET and water yields were found to be higher in the forested and mountainous upper areas of the UGB. On an annual average, present-day flows throughout UGB are about 2-8% lower than under naturalized conditions. Dry and wet season flows under climate change (CC) scenario A2 are lower than that under present climate conditions at upstream locations, but higher at downstream locations of UGB. Flows under CC scenario B2 are systematically higher and lower than that under CC scenario A2 during dry and wet seasons, respectively.