Hidroclimatología del Oriente e hidrosedimentología de la Cuenca del Napo

En Ecuador, la hidroclimatología andina ha sido estudiada intensamente por el INAMHI desde la segunda mitad del siglo pasado. Sin embargo, los estudios hidrológicos en la planicie amazónica, empezaron recientemente con el proyecto HYBAM (convenio INAMHI/IRD), en una región que constituye la puerta oriental de acceso del Ecuador al resto del continente sudamericano.Los regímenes pluviométricos e hidrológicos así como los caudales anuales, presentan una gran variación espacial en relación a los importantes cambios fisiográficos de sus Cuencas (ej., relieve, clima). Las precipitaciones medias interanuales del orden de 400-900 mm.año-1 en la cordillera real, aumentan en dirección a la planicie amazónica donde alcanzan los 3 000 mm. año-1, pero con regímenes más regulares que en los Andes. La variación espacial de los escurrimientos se nota a través de los caudales específicos que varían de 6,6 hasta 110 l.s-1. km-2. En total son cerca de 150x109 m3 de agua que salen anualmente (promedio de los años 2001 y 2002) de las principales estaciones hidrológicas de las Cuencas del aguarico, Napo, Pastaza y Santiago. El Napo es el río oriental más caudaloso, seguido por los ríos Santiago y Pastaza, con 2 100, 1 400 y 650 m3.s-1 respectivamente.Existen también datos hidrosedimentológicos de los andes desde el año 1970, provenientes del INECEL y del INAMHI. Pero en la planicie amazónica, las primeras mediciones empezaron en el año 2001 con el mismo proyecto HYBAM. los primeros resultados nos permiten considerar a la Cuenca del Napo como la mayor Cuenca fluvial amazónica ecuatoriana, con una exportación anual de 63x109 m3 de flujo hídrico y 24x103 toneladas de flujo sólido. Casi la mitad de este flujo sólido proviene de la remoción de los sedimentos fluviales finos situados en las primeras llanuras del pie de monte. En este sector, el gradiente hidrológico del río Napo es relativamente alto (35 cm.km-1), superior en más de 10 veces a aquellos de la planicie amazónica central, lo que implica una velocidad y una fuerza suficiente para erosionar su propio cauce y mantener un curso relativamente rectilíneo

Heterogeneous distribution of rainfall and discharge regimes in the Ecuadorian Amazon basin

The hydrology of the Ecuadorian Amazon basin is still poorly documented. The research developed between the Institute for Research and Development (IRD) and the National Institute of Meteorology and Hydrology (INAMHI) of Ecuador takes advantage of a newly available rainfall and discharge dataset to explore spatial distribution and regimes in this region (135 600 km2). Forty-seven rainfall and 27 discharge stations were retained over a 30-yr period (1965-94). A new annual isoyets map is proposed for the Amazon basin of Ecuador. The most striking result is a high spatial regime variability, to the extent that out-of-phase regimes are found in nearby stations. Indeed, in high intra-Andean basins there is a marked bimodal rainfall regime, with maxima in March-April and in October and a minimum from June to August. On the contrary, as moisture transport reaches a maximum in June, a rainfall peak can also be observed at the same time on slopes to the east due to the moist easterlies. In the lowlands, a bimodal regime is observed as in the intra-Andean basin; as water vapor is abundant, seasonal variability is not as strong as in the Andes. Discharge regimes are related to rainfall regimes. However, even if no delay is observed between maximum rainfall and maximum discharge in the inner Andean basins, a delay varying from one to two months is observed in larger basins. Soil conditions also affect the discharge regime in the upper and inner Andes: paramo soils (a kind of tundra formation) release water, in particular after the March-April rainfall peak, and sustain the dry season runoff

Régionalisation de l’influence du El Niño sur les précipitations de l’Équateur

Regionalization of El Niño influence on rainfall in Ecuador Homogenization analysis of rainfall series of 210 rainfall stations from the coast, the highlands, and the eastern part of Ecuador allows to study for the first time, over a period of 30 years, the influence of El Niño on the annual precipitation in Ecuador. This influence is analysed and quantified using several statistical and numerical techniques that point out the relation between annual precipitation and El Niño. Synthesis of the results obtained using the different methods allows the division of Ecuador into three regions. The first region where the influence of El Niño over the annual precipitation is very high, the second region where this influence is not significant and an intermediate zone where its influence varies from one event to the other.L’homogénéisation des séries pluviométriques de 210 stations réparties entre les régions côtières, la cordillère des Andes et le versant amazonien de l’Équateur permet d’étudier pour la première fois, sur une période de 30 ans, l’influence du Niño sur les précipitations annuelles. Cette influence est analysée et quantifiée à l’aide de plusieurs méthodes statistiques et numériques qui mettent en évidence le lien entre les précipitations annuelles et le Niño. La comparaison et la synthèse des résultats obtenus avec ces différentes analyses nous permettent de diviser l’Équateur en trois régions. La première, où l’influence du Niño sur les totaux pluviométriques annuels est forte, la seconde où elle n’est pas significative, et une zone intermédiaire où l’influence varie selon les événements El Niño.Regionalización de la influencia de El Niño sobre las precipitaciones en el Ecuador La homogeneización de las series pluviométricas de 210 estaciones de la Costa, de la Sierra y del Oriente permite estudiar por primera vez, sobre un periodo de 30 años, la influencia de El Niño sobre las precipitaciones anuales del Ecuador. Ésta influencia está analizada y cuantificada gracias a varios métodos estadísticos y numéricos que hacen resaltar las relaciones entre las precipitaciones anuales y el Niño. La síntesis de los resultados obtenidos con los diferentes métodos permite dividir el Ecuador en tres regiones. La primera, donde la influencia del fenómeno El Niño sobre los totales pluviométricos anuales es elevada, la secunda donde esta influencia no es significativa, y una zona intermedia en donde la influencia fluctúa de un evento al otro.Rossel Frédéric, Mejía Raúl, Ontaneda Gonzalo, Pombosa Rodrigo, Roura Javier, Le Goulven Patrick, Cadier Éric, Calvez Roger. Régionalisation de l’influence du El Niño sur les précipitations de l’Équateur. In: Bulletin de l'Institut Français d'Études Andines, tome 27, N°3, 1998. Variations climatiques et ressources en eau en Amérique du Sud. Importance et conséquences des événements El Niño. pp. 643-654

Variations climatiques et ressources en eau en Amérique du Sud : importance et conséquences des évènements El Niño

La homogeneización de las series pluviométricas de 210 estaciones de la Costa, de la Sierra y del Oriente permite estudiar por primera vez, en un periodo de 30 años, la influencia de El Niño sobre las precipitaciones anuales del Ecuador. Esta influencia está analizada y cuantificada gracias a varios métodos estadísticos y numéricos que hacen resaltar las relaciones entre las precipitaciones anuales y El Niño. La síntesis de los resultados obtenidos con los diferentes métodos permite dividir al Ecuador en tres regiones. La primera, donde la influencia del fenómeno El Niño sobre los totales pluviométricos anuales es elevada, la segunda donde esta influencia no es significativa, y una zona intermedia en donde la influencia fluctúa de un evento al otro. (Résumé d'auteur

Climate variability and extreme drought in the upper Solimões River (western Amazon Basin): Understanding the exceptional 2010 drought

International audienceThis work provides an initial overview of climate features and their related hydrological impacts during the recent extreme droughts (1995, 1998, 2005 and 2010) in the upper Solimões River (western Amazon), using comprehensive in situ discharge and rainfall datasets. The droughts are generally associated with positive SST anomalies in the tropical North Atlantic and weak trade winds and water vapor transport toward the upper Solimões, which, in association with increased subsidence over central and southern Amazon, explain the lack of rainfall and very low discharge values. But in 1998, toward the end of the 1997-98 El Niño event, the drought is more likely related to an anomalous divergence of water vapor in the western Amazon that is characteristic of a warm event in the Pacific. During the austral spring and winter of 2010, the most severe drought since the seventies has been registered in the upper Solimões. Its intensity and its length, when compared to the 2005 drought, can be explained by the addition of an El Niño in austral summer and a very warm episode in the Atlantic in boreal spring and summer. As in 2005, the lack of water in 2010 was more important in the southern tropical tributaries of the upper Solimões than in the northern ones

Comparison between Silicate Weathering and Physical Erosion Rates in Andean Basins of the Amazon River ?

International audienceFrom published data based on the HYBAM observatory database, we explore the relationship between silicate weathering rates and physical erosion rates over the Andean basins of the Amazon River. No homogenous relationship between erosion rates and chemical weathering rate is observed over this area. Only the volcanic basins respond to the global relationship defined by Millot et al1. For remaining areas, two hypotheses can explain the absence of coherence with this global empiric law: 1) The relationship between weathering and physical erosion rates need to be defined for each lithological class, and 2) For erosion rates higher than around 1000t.km-2.yr-1 the system is "weathering limited"

Monitoring of the Spatio-Temporal Dynamics of the Floods in the Guayas Watershed (Ecuadorian Pacific Coast) Using Global Monitoring ENVISAT ASAR Images and Rainfall Data

The floods are an annual phenomenon on the Pacific Coast of Ecuador and can become devastating during El Niño years, especially in the Guayas watershed (32,300 km2), the largest drainage basin of the South American western side of the Andes. As limited information on flood extent in this basin is available, this study presents a monitoring of the spatio-temporal dynamics of floods in the Guayas Basin, between 2005 and 2008, using a change detection method applied to ENVISAT ASAR Global Monitoring SAR images acquired at a spatial resolution of 1 km. The method is composed of three steps. First, a supervised classification was performed to identify pixels of open water present in the Guayas Basin. Then, the separability of their radar signature from signatures of other classes was determined during the four dry seasons from 2005 to 2008. In the end, standardized anomalies of backscattering coefficient were computed during the four wet seasons of the study period to detect changes between dry and wet seasons. Different thresholds were tested to identify the flooded areas in the watershed using external information from the Dartmouth Flood Observatory. A value of −2.30 ± 0.05 was found suitable to estimate the number of inundated pixels and limit the number of false detection (below 10%). Using this threshold, monthly maps of inundation were estimated during the wet season (December to May) from 2004 to 2008. The most frequently inundated areas were found to be located along the Babahoyo River, a tributary in the east of the basin. Large interannual variability in the flood extent is observed at the flood peak (from 50 to 580 km2), consistent with the rainfall in the Guayas watershed during the study period

Apports de matiéres en suspension et de solides dissous des les bassins andins de l'Equateur

Water discharge and suspended and dissolved sediment data from three rivers (Napo, Pastaza and Santiago) in the Ecuadorian Amazon basin and a river in the Pacific basin (Esmeraldas) over a 9-year period, are presented. This data set allows us to present: (a) the chemical weathering rates; (b) the erosion rates, calculated from the suspended sediment from the Andean basin; (c) the spatio-temporal variability of the two regions; and (d) the relationship between this variability and the precipitation, topography, lithology and seismic activity of the area. The dissolved solids load from the Esmeraldas basin was 2 × 106 t year-1, whereas for the Napo, Pastaza and Santiago basins, it was 4, 2 and 3 × 106 t year-1, respectively. For stations in the Andean piedmont of Ecuador, the relationship between surface sediment and the total sediment concentration was found to be close to one. This is due to minimal stratification of the suspended sediment in the vertical profile, which is attributed to turbulence and high vertical water speeds. However, during the dry season, when the water speed decreases, sediment stratification appears, but this effect can be neglected in the sediment flux calculations due to low concentration rates. The suspended sediment load in the Pacific basin was 6 × 106 t year-1, and the total for the three Amazon basins was 47 × 106 t year-1. The difference between these contributions of the suspended sediment load is likely due to the tectonic uplift and the seismic and volcanic dynamics that occur on the Amazon side. © 2013 © IAHS Press