Surface water storage is an essential component of the hydrological cycle. Remote sensing offers valuable tools for monitoring both surface water extent from satellite images and water levels from radar altimetry. Combining both information, we were able to estimate the variations of surface water extent and storage in the Lower Mekong Basin from 2000 to 2020. Signatures of the extreme climatic events - floods from 2000 to 2002, of 2011, drought of 2015 clearly appear on both extent and storage. The mean amplitude of these variables shows a strong decrease when comparing the periods of 2000–2010 and 2011–2020. Between these two periods, a large reduction of the annual average number of days with the presence of floods can be observed in most of the Lower Mekong Basin, except around the Tonle Sap (Cambodia) and in some parts of the delta.

Lakes and reservoirs have been identified as sentinels of climate change. Tonle Sap is the largest lake in both the Mekong Basin and Southeast Asia and because of the importance of its ecosystem, it is has been described as the "heart of the lower Mekong". Its seasonal cycle depends on the annual flood pulse governed by the flow of the Mekong River. This study provides an impact analysis of recent climatic events from El Niño 1997/1998 to El Niño 2015/2016 on surface storage variations in the Tonle Sap watershed determined by combining remotely sensed observations, multispectral images and radar altimetry from 1993 to 2017. The Lake's surface water volume variations are highly correlated with rainy season rainfall in the whole Mekong River Basin (R = 0.84) at interannual time-scale. Extreme droughts and floods can be observed when precipitation deficit and excess is recorded in both the Tonle Sap watershed and the Mekong River Basin during moderate to very strong El Niño/La Niña events (R = -0.70) enhanced by the Pacific Decadal Oscillation (R = -0.68). Indian and Western North Pacific Monsoons were identified as having almost equal influence. Below normal vegetation activity was observed during the first semester of 2016 due to the extreme drought in 2015.

La Amazonia Boliviana se r4racteriza por una gran llanura central regularmente inundada mas de 4 meses al ano. La superficie afectada puede abarcar 100 000 a 150 000 km segun la variabilidad meteorologica inter anuaL Las inundaciones provocan generalmente perdidas de muchas cabezas de ganado y afectan numerosas poblaciones. Sin embargo, la intensidad y la duracion de la inundacion condiciona directamente la diversidad biologica y la produccion piscicola. En 1997, el 1RO ha iniciado, con sus socios bolivianos de SENAMHI, ABTEMA y SEMENA un programa de investigaciones (BIOCAB: Biodiversidad acuatica en la Cuenca Amazonica Boliviana) que incluye un estudio de la dinamica de las inundaciones en la llanura central del rio Mamore. El conocimiento hidrologico aportado permitira entender el funcionamiento ecologico de esta zona y aprovechar, con un manejo sostenible, el producto de la inundacion. En epoca de lluvias, esta region presenta una persistente cobertura nubosa y amplias zonas de dificil acceso, por esta razon, el estudio hidrologico, utiliza la percepcion remota radar (banda C con polarizaciones HH del satelite ERS, y VV de RADARSAT) para comprenderla distribucion espacio-temporal de las inundaciones. Se presenta los primeros resultados obtenidos en los dos ultimos anos, en los alrededores de la ciudad de Trinidad. Los datos incluyen imagenes ascendientes ERS-SAR y RADARSAT-SAR en epoca seca e inundada, datos de terreno y de sobrevuelos adquiridos simultaneamente, y datos hidrometereologicos (precipitaciones, temperaturas y niveles diarios de agua) obtenidos en la cuenca alta y en la ilanura del rio Mamore. Despues de la caracterizacion del ciclo hidrometeorologico anual de las inundaciones estudiadas, se presenta compuestas coloreadas y clasificacion de imagenes opticas Landsat TM para mapear las principales unidades de ve getacion, e imagenes SAR-TM compuestas a color para evaluar las respectivas contribuciones de los datos radar en el ma peo de la extension de las inundaciones. Palabras clave: Inundaciones, Cuenca Amazonica, Bolivia, Radar, Mapeo ABSTRACT The Bolivian Amazon is characterized by a large floodplain which is flooded more than 4 months a year. The surface flooded annualy fluctuates between 100 000 and 150 000 km depending on inter-annual meteorological variations. The floods often provoke loss of cattle and affect a high number of human settlements. Qn the other hand, the intensity and the duration of the floods condition directly biological diversity and fish production. In 1997, 1RO together with bolivian institutes SENAMHI, ABTEMA and SEMENA set up a research programme (BIOCAB: Aquatic biodiversity in the Bolivian Amazon basin) that includes a study of the flood dynamics in the central floodplain of River Mamore. The hydrological knowledge is supposed to increase insight in the ecologi cal functioning of this area. During the raining season, the study area presents a persistent cloud cover and the accessibility is reduced: for f this reason, the hidrological study was carried out through radar remote sensing in order to understand the spa tial and temporal flooding patterns. In this report the first results obtained in the surroundings of the town of Trinidad are presented. The data include ima ges ERS-SAR and RADARSAT-SAR during fhe dry and during the flooding season, field and aereal data taken simultaneously, and hidro-meteorogical data (precipitations, temperatures, daily water level) obtained in the high basin and in the floodplain of the River Mamore. Besides the caracterization of the hidro-meteorological annual flooding cycle, colored maps and classified satellite images Landsat TM showing the main vegetation units are presented, as well as images SAR-TM integrating the respective contributions of the radar data to the final map of the flooded area. Key words: Floods, Amazon Basin, Bolivia, radar, mappings

The El Niño and La Niña impacts on the hydrology of Peru were assessed based on discharge data (1968–2006) of 20 river catchments distributed over three drainage regions in Peru: 14 in the Pacific Coast (PC), 3 in the Lake Titicaca (TL) region, and 3 in the Amazonas (AM). To classify the El Niño and La Niña events, we used the Southern Oscillation Index (SOI) based on hydrological years (September to August). Using the SOI values, the events were re-classified as strong El Niño (SEN), moderate El Niño (MEN), normal years (N), moderate La Niña (MLN) and strong La Niña (SLN). On average during the SEN years, sharp increases occurred in the discharges in the north central area of the PC and decreases in the remaining discharge stations that were analyzed, while in the years of MEN events, these changes show different responses than those of the SEN. During the years classified as La Niña, positive changes are mostly observed in the majority of the stations in the rivers located in the center of Peru's Pacific Coast. Another important result of this work is that the Ilave River (south of the Titicaca watershed) shows higher positive (negative) impacts during La Niña (El Niño) years, a fact that is not clearly seen in the rivers of the northern part of the Titicaca watershed (Ramis and Huancane rivers).

The Upstream-downstream sediment budget along the Napo River (100520 kill 2, 6300 m(3) s(-1)) was studied in the Andean foothills of Ecuador, at the west of the Amazon basin. A comparative study was made during four hydrological cycles (2001-2005) for three hydrological stations located upstream, and during one hydrological cycle (2004-2005) for the Fourth one located near the mouth of the Napo River (region of Iquitos in Peru). This analysis showed an unusual increase in the concentration of suspended sediment recorded for the western part of the Amazon plain. Like the runoff (81 l s(-1) km(2)), which is a world's maximum, the erosion rate (1160 t km(-2) year(-1), i.e. 47% of total suspended solid (TSS) export at the exit of Ecuador), one of the highest for a floodplain basin is the result of a stepper slope than in the rest of the Andean foothills, where typically sedimentation phenomena are predominant, and can be explained in part by a greater tectonic activity. Similar phenomenes were evidenced in small mountainous rivers in New Guinea (Milliman and Syvitski, 1992; Milliman, 1995).On the headwaters of the Napo River drainage basin, the tectonic uplift causes the Pastaza Megafan's existence. This progressively diverts the Course of Napo River towards north and also provokes the remobilization of fine fluvial deposits. Moreover, this geodynamic trend is completed by the impact of volcanic eruption, earthquakes and landslides. The combination of these phenomena, so common in the region, has provided a large sediment transfer, not only at present but also in the past, as can be confirmed by the presence of incised terraces, mainly formed by volcanic materials.Then, these results were compared with a similar Study carried out further south in the Madeira basin at the Bolivian foothills. These studies show the spatio-temporal variability of the relation between sediment transfer and geodynamic processes at the Andean Piedmont. Copyright (C) 2009 John Wiley & Sons, Ltd.

In 1997, a study was initiated by IRD, Bolivia to analyse the dynamics of floods in the Bolivian Amazon, which commonly affect an area of 100 000 to 150 000 km2 for about 4 months of the year. This region is characterized by vast isolated areas with difficult access and is continuously covered by clouds in the wet season. For these reasons, this hydrological study depends heavily on the use of remote sensing, and particularly radar data, for flood monitoring and the identification of areas at risk of inundation. This article presents preliminary results obtained in the Trinidad area, around the Mamoré River, using LANDSAT, ERS and RADARSAT radar data from dry, wet and flood seasons (collected between 1996 and 1998), and water level and, hydrometeorological data obtained from the upper and lower parts of the Mamoré basin. After characterizing the annual flood cycle within the study area, a TM colour composite (to map the vegetation) and a radar colour composite (multi‐temporal), are used to evaluate the potential contribution of microwave data (RADARSAT and ERS) for mapping the extent of flooding at both the regional (all the flood plain) and the local scale (around the city of Trinidad). Copyright © 2009 John Wiley & Sons, Ltd.

Extensive inundations have been observed in the Llanos de Mojos (Mamore basin, south western Amazon) causing social and economic disasters. Since the beginning of the seventies precipitations have increased in the Bolivian lowlands (Llanos) and in the over-rainy eastern Cordillera and Andean foothills (Yungas) and inundations have become more frequent.As a result inundations have been investigated in relation to rainfall over the Mamore basin in Trinidad-Puerto Varador and, in order to determine whether they are predictable, in relation to Sea Surface Temperature (SST) in the Atlantic and the Equatorial Pacific Oceans. The methods are correlation and composite techniques.As expected, during the 1945-1946/1998-1999 period, inundations have been associated with abundant rainfall in the Mamore basin, mainly in the Llanos and Yungas. The role of rainfall in the inner dry Andes and downstream from Trinidad is more limited. When consecutive floods are observed, the ground water storage contributes to the occurrence of the second or third inundation event and rainfall anomaly is generally weaker.Rainfall in the Mamore basin is hardly associated with Sea Surface Temperature Anomalies (SSTA) in the Pacific and Atlantic Oceans during the 1952-1953/1998-1999 period. However, during the nineties the southern Atlantic SSTA account for 50 percent of rainfall variability. Inundations are also related to negative SSTA differences between the tropical and subtropical southern Atlantic. Two thirds of the 22 inundation events occurred in association with this oceanic anomaly that features a weak SSTA gradient in the southern Atlantic. During the 1988-1989/1998-1999 period, a particularly significant relation can be observed between SSTA and inundations events. Despite being associated with major El Nino events (1982-1983, 1991-1992), inundations are not significantly related to the equatorial Pacific SSTA. (C) 2004 Elsevier B.V. All rights reserved.

The Andean Cordillera and piedmont significantly influence river system and dynamics, being the source of many of the important rivers of the Amazon basin. The Beni River, whose upper sub-catchments drain the Andean and sub-Andean ranges, is a major tributary of the Madeira River. This study examines the river in the south-western Amazonian lowlands of Bolivia, where it develops mobile meanders. Channel migration, meander-bend morphology and ox-bow lakes are analysed at different temporal and spatial scales. The first part of this study was undertaken with the aim to link the erosion-deposition processes in the active channel with hydrological events. The quantification of annual erosion and deposition areas shows high inter-annual and spatial variability. In this study, we investigate the conditions of sediment exportation in the river in relation to three hydrological parameters (flood intensity, date of discharge peak and duration of the bank-full stage level). The second part of this study, focusing on the abandoned meanders, analyses the cutoff processes and the post-abandonment evolution during 1967-2001. This approach shows the influence of the active channel behaviour on the sediment diffusion and sequestration of the abandoned meanders and allows us to build a first model of the contemporary floodplain evolution. Copyright (c) 2006 John Wiley & Sons, Ltd.