Stress hydrique (écologie) | EPFL Graph Search

vignette|Niveau de stress hydrique, par pays, en 2019 (carte établie par le World Resources Institute). Un stress hydrique, qui peut également être une pénurie d'eau, est une situation dans laquelle la demande en eau dépasse les ressources en eau disponibles. Le manque d’eau dans le monde repose essentiellement sur le déséquilibre géographique et temporel entre la demande et la disponibilité en eau douce. Plus d'une personne sur six dans le monde souffre de stress hydrique, ce qui signifie qu'elle n'a pas suffisamment accès à de l'eau potable. Les pays du Proche-Orient, du Moyen-Orient, d'Afrique et de l'Asie sont considérablement touchés par ce phénomène. Selon les Nations unies, les deux tiers de la population mondiale vivront en situation de stress hydrique en 2025. Généralités Définitions et mesures alt=Population ayant accès à l'eau potable en 2007|vignette|Population ayant accès à l'eau potable en 2007. Une pénurie d'eau ou un stress hydrique est une

Tall and old Amazonian forests are more resilient to precipitation variability

Francesco Giardina

Climate change is altering the natural equilibrium of the Amazon ecosystem, which is in turn deeply connected to the Earth’s biogeochemical cycles. Understanding this relationship aids optimal rainforests management in the future. Previous research has investigated the role of environmental variables and climatic drivers, neglecting the influence of forest height and age. This study uses remote sensing observations of precipitation, vapour-pressure deficit and canopy height along with model estimates of tree age and aboveground biomass to show that tall and old Amazonian trees are three times less sensitive to precipitation variability than younger and smaller forests. Canopy size is found to be equally important to mean precipitation in controlling the response to interannual climate variability. Our results align with those of in-situ experiments. These findings could help better predict the response of the Amazon forest to future droughts and water stress.

2017

Optimization of drip irrigation using a sensor network in Sahel Region (Burkina Faso) - Analysis of soil water and plant dynamics in the framework of project Info4Dourou 2.0

Tom Müller

The research project Info4Dourou 2.0 's main goal is to improve agriculture in semi-arid regions by developing a support system that optimizes agricultural production and water consumption based on continuous soil humidity measurements using a sensor network. In this context, the main purpose of the study was to give more scientific support to the agronomic model on which the sensor network is based. In particular the research aims at understanding the soil water and plant dynamics in order to give recommendations on the system design. The main feature of the system is to indicate when irrigation must be triggered and in which soil moisture conditions. The thesis developed a numerical model based on the software HYDRUS 2D to acquire a precise knowledge on the soil water dynamics and was calibrated and coupled with field experiments on two vegetable crops of eggplant and cabbage in Burkina Faso using drip kit irrigation systems. A great focus was given on the plant response to different irrigation schedules and to water stress, considering aerial biomass development, root distribution and final yields. Water stress was linked to continuous measurements of the soil matrix potential at different depth and locations. The field experiments showed that a daily irrigation frequency resulted to better canopy development during the first part of the growth but that great water savings are possible by optimizing the schedule. Water stress was difficult to track precisely by following daily sap flow behaviour which suggested that plant stress occurs before transpiration reduction, especially when biomass is building up. The adaptability of the root distribution was demonstrated and was clearly correlated with the wetted zone which depended on the irrigation schedule. From the numerical model, it was shown that using one sensor at a depth of about 10 cm was most appropriate in order to pilot irrigation during the whole crop growth. The analysis showed that most of the water savings could be achieved at relatively high threshold values and that low thresholds mainly resulted to transpiration reduction which was not advisable. A threshold of -20 kPa was proposed for the beginning of the growth stage which then decreases to a value of -50 kPa at full canopy development. These thresholds are believed to be adequate for most vegetable crops since they allow keeping the soil matrix potential in the root zone at values that are tolerated by most plants. An analysis of the influence of the soil texture also showed that similar values seem to perform well for most soils, if assuming an adaptation of the root distribution to the wetted zone. The study focused mainly on water stress but more research could be done on the impact of the irrigation system on nutrients availability for example.

2015

Effects of groundwater on desalinization in coastal reservoir and adjacent aquifer

David Andrew Barry, Jing Xu

Coastal reservoir provides the additional storage capacity of freshwater in coastal zone which greatly alleviate the water shortage in stressed areas, and the salinization of reservoir water degrade the utility of coastal reservoir. Salinization may result from inadequate desalinization in early operation stage, and groundwater as the important source of freshwater to coastal reservoir and adjacent aquifer was obviously have significant impacts on salinization which was in a dearth research. Laboratory experiments and mathematical model were designed to further discuss the influence of groundwater on the desalinization. The results from experiments shown that with the groundwater discharge rate increased, residual saltwater distribution result from intruded fresh groundwater was further moderated. Coastal reservoirs also greatly changed groundwater discharge pathways to sea. Without coastal reservoir, groundwater discharge to sea directly, while with coastal reservoir, part of groundwater would firstly discharge to coastal reservoir, desalinate the reservoir water, and then to sea. Mathematical model was designed for the prediction of the salinity of reservoir water, and the results from model could indicate the accuracy groundwater discharge pathways in coastal reservoir and adjacent aquifer. These results demonstrate the complexity of the groundwater system in adjacent aquifer of coastal reservoir, and may have great implications for future investigations on the predication of water quality during the full operational period.

2019

Optimization of drip irrigation using a sensor network in Sahel Region (Burkina Faso) - Analysis of soil water and plant dynamics in the framework of project Info4Dourou 2.0

Tom Müller

2015