Is current irrigation sustainable in the United States? An integrated assessment of climate change impact on water resources and irrigated crop yields.

While climate change impacts on crop yields has been extensively studied, estimating the impact of water shortages on irrigated crop yields is challenging because the water resources management system is complex. To investigate this issue, we integrate a crop yield reduction module and a water resources model into the MIT Integrated Global System Modeling framework, an integrated assessment model linking a global economic model to an Earth system model. We assess the effects of climate and socioeconomic changes on water availability for irrigation in the U.S. as well as subsequent impacts on crop yields by 2050, while accounting for climate change projection uncertainty. We find that climate and socioeconomic changes will increase water shortages and strongly reduce irrigated yields for specific crops (i.e., cotton and forage), or in specific regions (i.e., the Southwest) where irrigation is not sustainable. Crop modeling studies that do not represent changes in irrigation availability can thus be misleading. Yet, since the most water-stressed basins represent a relatively small share of U.S. irrigated areas, the overall reduction in U.S. crop yields is small. The response of crop yields to climate change and water stress also suggests that some level of adaptation will be feasible, like relocating croplands to regions with sustainable irrigation or switching to less irrigation intensive crops. Finally, additional simulations show that greenhouse gas (GHG) mitigation can alleviate the effect of water stress on irrigated crop yields, enough to offset the reduced CO2 fertilization effect compared to an unconstrained GHG emission scenario

A Bayesian approach for energy-based estimation of acoustic aberrations in high intensity focused ultrasound treatment

High intensity focused ultrasound is a non-invasive method for treatment of diseased tissue that uses a beam of ultrasound to generate heat within a small volume. A common challenge in application of this technique is that heterogeneity of the biological medium can defocus the ultrasound beam. Here we reduce the problem of refocusing the beam to the inverse problem of estimating the acoustic aberration due to the biological tissue from acoustic radiative force imaging data. We solve this inverse problem using a Bayesian framework with a hierarchical prior and solve the inverse problem using a Metropolis-within-Gibbs algorithm. The framework is tested using both synthetic and experimental datasets. We demonstrate that our approach has the ability to estimate the aberrations using small datasets, as little as 32 sonication tests, which can lead to significant speedup in the treatment process. Furthermore, our approach is compatible with a wide range of sonication tests and can be applied to other energy-based measurement techniques

Impact du changement climatique sur le climat de vagues en zone côtière, par régionalisation dynamique : application à la côte aquitaine

The Aquitanian coast, as well as most coastal regions, is influenced by several hydrodynamical factors. Those factors can be modified by climate change. This study aims at studying climate change impact mainly on wave conditions which affect the Aquitanian coast.Using dynamical downscaling, waves are modelled from the North Atlantic Ocean towards the Bay of Biscay at a 10 km spatial resolution exclusively from wind fields. Waves are simulated with WAVEWATCH III spectral wave model, for the present climate (wind fields issued from the ERA-40 reanalysis) and for a control scenario and three future greenhouse gas emission scenarios (A2, A1B, B1) (wind fields issued from the RETIC simulations of ARPEGE-Climat). The database calibration and validation are based on local buoy measurements. Wind fields issued from climate model present systematic biases, therefore, a quantile-quantile correction is applied to wave projections.Wave climate evolution analysis is done in two steps. Firstly, present wave climate (1958-2001) is investigated regarding multi-decadal trends and interannual variability. A significant increase of summer wave height is identified on the period 1970-2001 (0.54 cm/y at the Biscay buoy). Concerning largest wave heights, a significant shift of directions is noticed for autumn (up to −0.47°/y from 1974 to 2001 at the Biscay buoy) and spring (0.3°/y from 1958 to 2001 at the Biscay buoy). The strong interannual variability of wave conditions is correlated to several general atmospheric circulation preferential modes (teleconnexion patterns and weather regimes). This underlines a strong link between local wave conditions and climate. For instance, the winter wave height and direction anomalies within the Bay of Biscay are strongly correlated to the North Atlantic Oscillation and the East Atlantic teleconnection pattern indices. Secondly, wave condition changes between present climate (1961-2000) and future scenarios (2061-2100) are investigated and analysed. A general decrease of wave heights is noticed in the Bay of Biscay (decrease averaged over the Bay of Biscay ranges from −4.7 to −11.4% depending on the season, for the A2 scenario), as well as a clockwise shift of summer wave directions (5.1° averaged over the Bay of Biscay, for the A2 scenario) and of winter swell directions. Those local changes are linked to wind changes in different wave generation areas, from the North Atlantic Ocean to the Bay of Biscay. Concerning sediment transport, the identified wave condition changes could reduce the longshore sediment flux by 10%.La côte aquitaine, comme la majeure partie des régions côtières, est soumise à différents facteurs hydrodynamiques qui sont susceptibles d'être modifiés par le changement climatique. Cette thèse propose d'étudier l'impact de ce changement, principalement sur les conditions de vagues auxquelles est soumise la côte aquitaine.Une régionalisation dynamique est mise en œuvre pour modéliser les vagues depuis l'Océan Atlantique Nord jusqu'au Golfe de Gascogne avec une résolution spatiale de 10 km. On utilise une stratégie d'emboîtement de modèles, ces modèles étant forcés uniquement par des champs de vent. Les vagues sont simulées avec le modèle spectral de vagues WAVEWATCH III pour le climat actuel (champs de vents de la réanalyse ERA-40) et pour un scénario de contrôle et trois scénarios futurs d'émissions de gaz à effet de serre (A2, A1B, B1) (champs de vents issus des simulations RETIC d'ARPEGE-Climat). La base de données ainsi construite est calibrée et validée à partir de mesures de bouées locales. Les champs de vent issus du modèle climatique comportant des biais, une correction quantile-quantile est appliquée aux projections de vagues.L'analyse de l'évolution des climats de vagues dans le Golfe de Gascogne s'articule en deux étapes. La première étape consiste à analyser les champs de vagues du climat actuel (1958-2001) en termes de tendances multi-décennales et de variabilité interannuelle. Une augmentation significative des hauteurs de vague estivales est visible sur la période 1970-2001 (0.54 cm/an à la bouée Gascogne) ainsi qu'une importante rotation des directions des plus hautes vagues en automne (jusqu'à -0.47°/an de 1974 à 2001 à la bouée Gascogne) et au printemps (0.3°/an de 1958 à 2001 à la bouée Gascogne). La forte variabilité interannuelle des vagues se trouve être corrélée à différents indices de certains modes préférentiels de la circulation atmosphérique générale (modes de téléconnexion et régimes de temps), mettant en lumière un lien important entre conditions de vagues locales et climat. Par exemple, en hiver, les anomalies de hauteur et de direction de vague dans le Golfe de Gascogne sont fortement corrélées aux indices des modes de téléconnexion North Atlantic Oscillation et East Atlantic pattern . La seconde étape de ce travail consiste à identifier et analyser les changements des conditions de vagues entre le climat actuel (1961-2000) et le climat futur (2061-2100). Une baisse généralisée des hauteurs de vague se dégage (baisse comprise entre −4.7% et −11.4% suivant la saison, en moyenne dans le Golfe de Gascogne pour le scénario A2), ainsi qu'une rotation horaire des vagues estivales (5.1° en moyenne dans le Golfe de Gascogne pour le scénario A2) et des houles hivernales. Ces changements locaux sont reliés aux changements des conditions de vent dans les différentes zones de génération des vagues arrivant dans le Golfe de Gascogne. En termes de transport sédimentaire, les changements de conditions de vagues identifiés pourraient réduire le flux sédimentaire longshore de 10%

Drought and stand susceptibility to attacks by the European spruce bark beetle: A remote sensing approach

Several time-series analyses have demonstrated that after extreme summer droughtbark beetle damage increased. However, studies predicting stand susceptibility overlarge spatial extents are limited by technical constraints in obtaining detailed,spatially-explicit data on infestation spot occurrence.2. Using a unique dataset of georeferenced bark beetle infestation data, we testedwhether the spatial variation of local growing conditions of forest stands, topogra-phy, and landscape variables modified the local occurrence ofIps typographusinfes-tations after a severe hot drought in Central Europe.3. Bark beetle infestation occurrence depended on soil-related aridity intensity, eleva-tion, slope, and soil conditions. We showed that elevation interacted with growingconditions and topography. At low elevations, spruce forests growing on flat areasand wetter soils were more sensitive to the infestations. On the contrary, forestson steep slopes and soils with low water availability were rarely attacked. At thelandscape scale, bark beetle damage increased with host tree cover but decreasedwith compositional diversity.4. Our findings are generally consistent with the growth-differentiation balancehypothesis that predicts that trees growing under chronic dry conditions tend to bemore resistant against biotic disturbances.5. Spruce stands at low elevations located in homogeneous landscapes dominated byspruce were those more exposed to bark beetles in the initial phase of a drought-induced outbrea

Climate change impact on waves in the Bay of Biscay, France

International audienceThe knowledge of offshore and coastal wave climate evolution towards the end of the twenty-first century is particularly important for human activities in a region such as the Bay of Biscay and the French Atlantic coast. Using dynamical downscaling, a high spatial resolution dataset of wave conditions in the Bay of Biscay is built for three future greenhouse gases emission scenarios. Projected wave heights, periods and directions are analysed at regional scale and more thoroughly at two buoys positions, offshore and along the coast. A general decrease of wave heights is identified (up to -20 cm during summer within the Bay of Biscay), as well as a clockwise shift of summer waves and winter swell coming from direction. The relation between those changes and wind changes is investigated and highlights a complex association of processes at several spatial scales. For instance, the intensification and the north-eastward shift of strong wind core in the North Atlantic Ocean explain the clockwise shift of winter swell directions. During summer, the decrease of the westerly winds in the Bay of Biscay explains the clockwise shift and the wave height decrease of wind sea and intermediate waves. Finally, the analysis reveals that the offshore changes in the wave height and the wave period as well as the clockwise shift in the wave direction continue toward the coast. This wave height decrease result is consistent with other regional projections and would impact the coastal dynamics by reducing the longshore sediment flux

Contact resistances in spark plasma sintering: From in-situ and ex-situ determinations to an extended model for the scale up of the process

tHeating in spark plasma sintering is a key point of this manufacturing process that requires advancedsimulation to predict the thermal gradients present during the process and adjust them. Electric andthermal contact resistances have a prominent role in these gradients. Their determination is difficult asthey vary with pressure and temperature. A calibration method is used to determine all of the contactresistances present within tools of different sizes. Ex situ measurements were also performed to validatethe results of the in-situ calibrations. An extended predictive and scalable contacts model was developedand reveals the great importance and diversity of the contact resistances responsible for the generalheating of the column and high thermal gradients between the parts. The ex/in situ comparison highlightsa high lateral thermal contact resistance and the presence of a possible phenomenon of electric currentfacilitation across the lateral interface for the high temperatures

Vagues sur la côte aquitaine : régionalisation dynamique de 1958 à 2002

National audienceUn système de modélisation de vagues, forcé uniquement par des champs de vent a été mis en place avec le code WAVEWATCH IIITM sur une période de 44 ans (1958 à 2002) en vue d'étudier l'impact de la variabilité climatique passée sur les états de mer et sur l'érosion de la côte aquitaine. Les emboîtements hauturiers forcés par les champs de vent de la réanalyse ERA-40 ont été calibrés sur la période 1998-2002 sur 8 points de mesures. Les résultats sur 44 ans ont ensuite été validés sur 11 bouée

Dendrite growth morphologies in rapidly solidified Al-4.5wt.%Cu droplets

International audienceThe impulse atomization process developed at the University of Alberta (Canada) enables metallic powders to be solidified with controlled process parameters and improved properties. In order to investigate the microstructure morphologies in droplets of Al- 4.5wt.%Cu alloys, three-dimensional reconstructions of several droplets are obtained by using synchrotron X-ray micro-tomography, allowing a visualization of the inner microstructure in three dimensions. The analysis of the reconstructed volumes reveals that a wide range of morphology, from highly branched to "finger-bundle", can be obtained for different droplets of similar diameter and produced in the same batch. Unexpectedly for this alloy, microstructural features also indicate that the development of the dendrite arms (primary and of higher orders) occurs in most droplets along crystallographic axes, instead of the usual directions observed in conventional casting technologies

On the use of rigorous microwave interaction models to support remote sensing of natural surfaces

A study has been undertaken which objective is to contribute to the investigation of the validity of microwave surface scattering models used in remote sensing applications, particularly when applied to realistic representations of natural surfaces. These investigations are based on recent implementations of rigorous methods (MoM and FDTD) and cover a wide range of configurations of observation (mono- and bi-static). Both land (bare soils) and sea surfaces are being investigated