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This work was supported by grant 234-2015-FONDECYT (Master Program) from Cienciactiva of the National Council for Science,Technology and Technological Innovation (CONCYTEC-PERU).

We thank Professor Santiago Mas Coma for suggestions to improve this contribution. This work was supported by grants to JRE from CONCYTEC (Consejo Nacional de Ciencia y Tecnolog?´a-PERU), Proyecto VIGIA-USAID 2003, The International Foundation for Science contract B/2856-1, Sweden and INCAGRO-PERU /Contract 007-2003.

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 sum...

Este trabajo ofrece un panorama inicial de las características climáticas y los impactos hidrológicos afines durante las recientes sequías extremas (1995, 1998, 2005 y 2010) en el río Amazonas peruano. Para ello se empleó una base de datos in situ de caudales y precipitaciones. Las sequías generalmente se asocian a anomalías positivas de temperatura superficial del mar (TSM) en el Atlántico tropical norte, vientos alisios y transporte de vapor de agua débiles hacia el oeste de la cuenca amazónica, que acompañados de un aumento en la subsidencia sobre la parte central y sur de la cuenca, explican la falta de lluvias y los muy bajos valores de caudales. Sin embargo, en 1998 hacia el final del evento El Niño de 1997/1998 la sequía estuvo más relacionada con una divergencia anómala de vapor de agua en el oeste de la amazonia, que es característica de un evento cálido en el ...

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 preci...

The Andes/Amazon transition is among the rainiest regions of the world and the interactionsbetween large-scale circulation and the topography that determine its complex rainfall distribution remainpoorly known. This work provides an in-depth analysis of the spatial distribution, variability, and intensity ofrainfall in the southern Andes/Amazon transition, at seasonal and intraseasonal time scales. The analysis isbased on comprehensive daily rainfall data sets from meteorological stations in Peru and Bolivia. We com-pare our results with high-resolution rainfall TRMM-PR 2A25 estimations. Hotspot regions are identified atlow elevations in the Andean foothills (400–700 masl) and in windward conditions at Quincemil and Chipir-iri, where more than 4000 mm rainfall per year are recorded. Orographic effects and exposure to easterlywinds produce a strong annual rainfall gradient between the ...

This study investigates the spatial and temporal characteristics of cold surges that propagates northward along the eastern flank of the Andes from subtropical to tropical South America analysing wintertime in situ daily minimum temperature observations from Argentina, Bolivia and Peru and ERA-40 reanalysis over the 1975–2001 period. Cold surges usually last 2 or 3 days but are generally less persistent in the southern La Plata basin compared to tropical regions. On average, three to four cold surges are reported each year. Our analysis reveals that 52 % of cold episodes registered in the south of La Plata basin propagate northward to the northern Peruvian Amazon at a speed of around 20 m s−1. In comparison to cold surges that do not reach the tropical region, we demonstrate that these cold surges are characterized, before they reach the tropical region, by a higher occurrence of a s...

Previos estudios describen de manera general la variabilidad anual de los caudales en el curso principal del Amazonas en Brasil, el cual sólo representa el estado general del sistema hidrológico de la cuenca. Por ello, este estudio utiliza una nueva serie de datos que incluye la descarga diaria de 18 subcuencas, con la finalidad de analizar la variabilidad de los extremos regionales en la cuenca del Amazonas. Luego de describir la diversidad de los ciclos hidrológicos anuales, diferentes pruebas estadísticas son aplicadas para detectar tendencias y rupturas de las series temporales. Este estudio muestra que durante el período 1974-2004, la estabilidad de caudales del río principal en Óbidos, se explica por cambios regionales opuestos que involucran principalmente a ríos Andinos: una disminución de la escorrentía en el periodo de estiage, particularmente importante en las region...

In this work, the authors analyze the origin of the extreme floods in the Peruvian Amazonas River during the 1970-2012 period, focusing on the recent April 2012 flooding (55400m3 s-1). Several hydrological variables, such as rainfall, terrestrial water storage, and discharge, point out that the unprecedented 2012 flood is mainly related to an early and abundant wet season over the north of the basin. Thus, the peak of the Marañón River, the northern contributor of the Amazonas, occurred sooner than usual (in April instead of May), coinciding with the peak of the Ucayali River, the southern contributor. This concomitance caused a dramatic flood downstream in the Peruvian Amazonas. These results are compared to the amplitude and timing of the three most severe extreme floods (1970-2011). The analysis of the climatic features related to the most important floods (1986, 1993, 1999, and 201...

This 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 Solimes 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 Solimes, 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 Nio 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 ...

The impacts of El Niño (EN) and La Niña (LN) in rainfall in Peru are evaluated using monthly data (1965-2007) of 155 stations distributed over the three hydrographic drainages of Peru: 85 in the Pacific (VP), 21 in the Lake Titicaca (VT) and 49 in the Amazon (VA). To classify El Niño and La Niña is used the Index Troup Southern Oscillation (SOI) based on hydrological years (September to August). Using these values was reclassified as strong El Niño (ENF) moderate El Niño (ENM), moderate La Niña (LNM) and strong La Niña (LNF). The results show that only during ENF and LNF events exhibit a high percentage of stations with significant anomalies of precipitation and mainly located in the VP and VT during the December to May period. Our analysis confirms that the northern part of the VP has an increased rainfall during ENF, while the southern Andean region of the VP has decreased (inc...

grant no. 0114-02-93-01

2 Páginas

Satellites are an alternative source of rainfall data used as input to hydrological models in poorly gauged or ungauged regions. They are also useful in regions with highly heterogeneous precipitation, such as the tropical Andes. This paper evaluates three satellite precipitation datasets (TMPA, CMORPH, PERSIANN), as well as a dataset based only on rain gauge data (HYBAM), and their impacts on the water balance of the Western Amazon basin, a region where hydrological modeling and hydrological forecasting are poorly developed. These datasets were used as inputs in the MGB-IPH hydrological model to simulate streamflows for the 2003-2009 period. The impacts of precipitation on model parameterization and outputs were evaluated in two calibration experiments. In Experiment 1, parameter sets were separately defined for each catchment; in Experiment 2, a single parameter set was defined for the...

Poster presented at the 2023 SWOL Workshop, Ushuaia, Argentina, October 2-6.

Study region: The Amazonas River and its tributaries (Peru), where riparian farmers face hydrological events that put their lowland crops at high risk of production loss during the flood recession period. Study focus: This paper analyzes the hydro-meteorological mechanisms over the Andes-Amazon basins that produce “repiquetes”, which are sudden reversals of the river stage. They are defined and characterized for the period 1996–2018 by using river stage data from three hydrological gauging stations for the Amazonas, Marañón and Ucayali Rivers. Daily rainfall and low-level winds depict the large-scale atmospheric patterns associated with repiquetes. New hydrological insights: Among 73 significant repiquetes (reversal ? 20 cm) observed in the Amazonas River, 64 % were preceded by repiquetes only in the Marañón River, 5 % by repiquetes only in the Ucayali River, 21 % by repiquetes...

The hydroclimatology of the Peruvian Amazon-Andes basin (PAB) which surface corresponding to 7% of the Amazon basin is still poorly documented. We propose here an extended and original analysis of the temporal evolution of monthly rainfall, mean temperature (Tmean), maximum temperature (Tmax) and minimum temperature (Tmin) time series over two PABs (Huallaga and Ucayali) over the last 40years. This analysis is based on a new and more complete database that includes 77 weather stations over the 1965-2007 period, and we focus our attention on both annual and seasonal meteorological time series. A positive significant trend in mean temperature of 0.09°C per decade is detected over the region with similar values in the Andes and rainforest when considering average data. However, a high percentage of stations with significant Tmean positive trends are located over the Andes region. Finally, ...