4. HYBAM: un observatorio para medir el impacto del Cambio Climático sobre la erosión y los flujos de sedimentos en la zona Andino-Amazónica

La cuenca Amazónica es la más grande del mundo. La instalación del observatorio HYBAM con una amplia red de estaciones hidrológicas ubicadas desde el piedemonte andino hasta el océano Atlántico permite, desde el 2003, la generación de registros periódicos y confiables (nivel del agua, caudal, concentración de sedimentos y otros parámetros físico-químicos de la calidad del agua) a lo largo de toda la cuenca. Hoy en día, el desarrollo de técnicas satelitales, como la altimetría, permite completar eficientemente los datos obtenidos por las redes de medición en los ríos. El recrudecimiento de eventos extremos en la Amazonia (Inundaciones, sequias,) por efecto del cambio climático actual asociado a un cambio acelerado de ocupación de los suelos (deforestación, prácticas agrícolas), tiene una incidencia directa sobre la producción sedimentarla. Conocer los flujos de materiales transportados por los ríos es esencial tanto para la navegación fluvial como para guiar la explotación de los recursos naturales (agua, petróleo, minerales), para conocer el transporte de partículas contaminantes o para diseñar infraestructuras.Le bassin de l’Amazone est le plus grand du monde. La mise en œuvre de l’observatoire HYBAM avec un vaste réseau de stations hydrologiques situées sur les contreforts des Andes jusqu’á l’océan Atlantique permet de générer, depuis 2003, des données régulières et fiables tout le long du bassin (hauteur d’eau, débit, concentration de sédiments et d’autres paramètres physico-chimiques de qualité de l’eau). De nos jours, la mise au point des techniques par satellite, tels que l’altimétrie, permet de compléter efficacement les données obtenues par les réseaux de mesure dans les rivières. L’intensification des événements extrêmes dans la région amazonienne (inondations, sécheresses), liés au changement climatique actuel associé á un changement rapide de l’utilisation des terres (déforestation, pratiques agricoles), ont un impact direct sur la production de sédiments. Connaître les flux de matières transportés par les rivières est essentiel pour la navigation fluviale ainsi que pour guider l’exploitation des ressources naturelles (eau, pétrole, minéraux), connaître le trajet de particules polluantes ou concevoir des infrastructures.The Amazon basin is the largest basin in the world. The implementation of the HYBAM observatory, which has installed a large network of hydrological stations located from the Andean foothills down to the Atlantic Ocean, allows since 2003, generate periodical and reliable records (such as water level, flow, sediment concentration and other physicochemical parameters of water quality) along the entire basin. Nowadays, the development of satellite techniques, (such as altimetry), makes it possible to efficiently complete the data obtained by the measurement networks in rivers. The intensification of extreme events in the Amazon region (floods, droughts) occurred as a result of the current Climate Change associated with a more rapid change of land use (deforestation, agricultural practices) have a direct impact on sediment production. It is essential to know the flows of the materials transported by rivers, both for river navigation as well as to guide the exploitation of natural resources (water, oil, minerals), to know the transport of particulate pollutants, or to design infrastructures

Performance of ALICE AD modules in the CERN PS test beam

Two modules of the AD detector have been studied with the test beam at the T10 facility at CERN. The AD detector is made of scintillator pads read out by wave-length shifters (WLS) coupled to clean fibres that carry the produced light to photo-multiplier tubes (PMTs). In ALICE the AD is used to trigger and study the physics of diffractive and ultra-peripheral collisions as well as for a variety of technical tasks like beam-gas background monitoring or as a luminometer. The position dependence of the modules' efficiency has been measured and the effect of hits on the WLS or PMTs has been evaluated. The charge deposited by pions and protons has been measured at different momenta of the test beam. The time resolution is determined as a function of the deposited charge. These results are important ingredients to better understand the AD detector, to benchmark the corresponding simulations, and very importantly they served as a baseline for a similar device, the Forward Diffractive Detector (FDD), being currently built and that will be in operation in ALICE during the LHC Runs 3 and 4.Peer reviewe

From drought to flooding: understanding the abrupt 2010-11 hydrological annual cycle in the Amazonas River and tributaries

In this work we document and analyze the hydrological annual cycles characterized by a rapid transition between low and high flows in the Amazonas River (Peruvian Amazon) and we show how these events, which may impact vulnerable riverside residents, are related to regional climate variability. Our analysis is based on comprehensive discharge, rainfall and average suspended sediment data sets. Particular attention is paid to the 2010–11 hydrological year, when an unprecedented abrupt transition from the extreme September 2010 drought (8300 m3s−1) to one of the four highest discharges in April 2011 (49 500 m3s−1) was recorded at Tamshiyacu (Amazonas River). This unusual transition is also observed in average suspended sediments. Years with a rapid increase in discharge are characterized by negative sea surface temperature anomalies in the central equatorial Pacific during austral summer, corresponding to a La Nina-like mode. It originates a geopotential height wave train over the ˜subtropical South Pacific and southeastern South America, with a negative anomaly along the southern Amazon and the southeastern South Atlantic convergence zone region. As a consequence, the monsoon flux is retained over the Amazon and a strong convergence of humidity occurs in the Peruvian Amazon basin, favoring high rainfall and discharge. These features are also reported during the 2010–11 austral summer, when an intense La Nina event ˜ characterized the equatorial Pacific

Sediment budget in the Ucayali River basin, an Andean tributary of the Amazon River

Formation of mountain ranges results from complex coupling between lithospheric deformation, mechanisms linked to subduction and surface processes: weathering, erosion, and climate. Today, erosion of the eastern Andean cordillera and sub-Andean foothills supplies over 99% of the sediment load passing through the Amazon Basin. Denudation rates in the upper Ucayali basin are rapid, favoured by a marked seasonality in this region and extreme precipitation cells above sedimentary strata, uplifted during Neogene times by a still active sub-Andean tectonic thrust. Around 40% of those sediments are trapped in the Ucayali retro-foreland basin system. Recent advances in remote sensing for Amazonian large rivers now allow us to complete the ground hydrological data. In this work, we propose a first estimation of the erosion and sedimentation budget of the Ucayali River catchment, based on spatial and conventional HYBAM Observatory network. Copyrigh

Sediment dynamics from the summit to the sea

Formation of mountain ranges results from complex coupling between lithospheric deformation, mechanisms linked to subduction and surface processes: weathering, erosion, and climate. Today, erosion of the eastern Andean cordillera and sub-Andean foothills supplies over 99% of the sediment load passing through the Amazon Basin. Denudation rates in the upper Ucayali basin are rapid, favoured by a marked seasonality in this region and extreme precipitation cells above sedimentary strata, uplifted during Neogene times by a still active sub-Andean tectonic thrust. Around 40% of those sediments are trapped in the Ucayali retro-foreland basin system. Recent advances in remote sensing for Amazonian large rivers now allow us to complete the ground hydrological data. In this work, we propose a first estimation of the erosion and sedimentation budget of the Ucayali River catchment, based on spatial and conventional HYBAM Observatory network

Variabilidad espacio-temporal de las lluvias en la cuenca amazónica y su relación con la variabilidad hidrológica regional : un enfoque particular sobre la región andina

La variabilidad de las precipitaciones en la cuenca amazónica (CA) es analizada para el período 1964-2003. Este análisis está basado en 756 estaciones pluviométricas distribuidas en todos los países de la cuenca incluyendo datos de Bolivia, Perú, Ecuador y Colombia. En particular, la reciente disponibilidad de datos de precipitación de los países andinos hace posible completar estudios anteriores. Se subraya el impacto de la cordillera de los Andes sobre las lluvias. La mayor precipitación en la CA es observada en regiones bajas expuestas a los vientos húmedos del este, y menor lluvia es registrada en las estaciones de altura y protegidas por las primeras montañas de los Andes de los vientos húmedos del este. Además, los regímenes de las precipitaciones son más diversificados en las regiones andinas que en el llano amazónico. La variabilidad espacio-temporal de las precipitaciones es estudiada mediante un Análisis de Componentes Principales (ACP). La variabilidad a largo plazo muestra una precipitación decreciente desde 1980 que es predominante en los meses de junio-julio-agosto (JJA) y en septiembreoctubre-noviembre (SON). Durante la temporada más lluviosa, es decir, diciembre-enero-febrero (DEF) y marzo-abril-mayo (MAM), la principal variabilidad se da en la escala de tiempo decadal e interanual. La variabilidad interdecadal está relacionada con los cambios a largo plazo en el Océano Pacífico, mientras que la variación decadal, que opone al noroeste y sur de la CA, está asociada a los cambios en la intensidad de los vientos a bajo nivel (incluyendo el low level jet) a lo largo de los Andes. La variabilidad interanual caracteriza principalmente el noreste de la cuenca y los Andes tropicales del sur y se relaciona con El Niño Oscilación del Sur (ENOS) y el gradiente de la tempe ratura superficial del mar (TSM) sobre el Atlántico tropical. La precipitación media en la cuenca disminuye durante el período 1975-2003 a una tasa anual estimada en –0.32%. Diferentes test de ruptura muestran que esta disminución de lluvias ha sido especialmente importante desde 1982. Finalmente, la variabilidad espacio-temporal de las lluvias es puesta en paralelo con la variabilidad hidrológica en las principales subcuencas del Amazonas.Rainfall variability in the Amazon Basin (AB) is analyzed for the period 1964-2003. This analysis is based on 756 pluviometric stations distributed throughout the countries located in this basin; including data from Bolivia, Peru, Ecuador and Colombia. In particular, the recent availability of rainfall data from the Andean countries makes it possible to complete previous studies. It is worth mentioning the impact of the Andes on rainfall. Most rainfall, in the AB is observed in low regions exposed to low humid winds from the east, and less rainfall is registered in stations located at higher altitude and protected by the first mountains of the Andes, from the humid easterly winds. Moreover, precipitation regimes are more diversified in the Andean regions than in the Amazon plains. Spatio-temporal variability of rainfall is studied using the Principal Component Analysis (PCA). The long-term variability shows a decrease in rainfall from 1980 that prevails during June-July-August (JJA) and in September-October-November (SON). During the rainy season, ie December-January-February (DJF) and MarchApril-May (MAM), the main variability occurs at a decadal and interannual time scale. The interdecadal variability is related to long-term changes in the Pacific Ocean, while the decadal variation, which opposes the north and south of the AB, is associated with changes in the intensity of low-level winds (including low level jet) along the Andes. Interannual variability is a main characteristic of the northeastern part of the basin and the southern tropical Andes and is related to El Niño Southern Oscillation (ENSO) and the gradient of sea surface temperature (SST) over the tropical Atlantic. During the period 1975-2003, mean rainfall in the basin decreases at an annual estimated rate of -0.32%. Different rupture tests hows that this decrease in rainfall has been especially important since 1982. Finally, the spatio-temporal variability of rainfall is set parallel to the hydrological variability in major basins of the Amazon region