Papers by Josyane Ronchail
Hydrological Sciences Journal, 2002
Effectuées dans le cadre du Projet Hidrologia e geoquímica na Bacia Amazônica (HiBAm), les nouvel... more Effectuées dans le cadre du Projet Hidrologia e geoquímica na Bacia Amazônica (HiBAm), les nouvelles mesures de débit à Óbidos ont amélioré la connaissance des caractéristiques hydrologiques de l'Amazone à cette station qui contrôle les plus forts débits du monde. Une nouvelle méthode de correction détermine les débits journaliers avec une précision de ±3.0%. La reconstitution des périodes manquantes, avec les observations faites à Manaus, permet de disposer d'une chronologie de près d'un siècle. Avec cet échantillon commençant en 1902, le module interannuel de l'Amazone à Óbidos est de 163 000 m 3 s -1 , avec un coefficient d'irrégularité extrêmement faible ( K3 = 1.28). L'étiage décennal (78 000 m 3 s -1 ) est de même grandeur que la crue centenaire du Congo à Brazzaville. La crue décennale est estimée à 260 000 m 3 s -1 . Le Bilan hydrologique indique un déficit d'écoulement de 1193 mm, qui peut être assimilé à l'évapotranspiration réelle. En conclusion, l'Amazone est bien le fleuve le plus puissant et le plus régulier de la planète.
Rainfall variability in the Andes and in the lowlands of Bolivia is great during the two phases o... more Rainfall variability in the Andes and in the lowlands of Bolivia is great during the two phases of the Pacific Southern Oscillation (SO). We show that very strong or weak seasonal rainfalls are independant of the SO Index, except in a few cases. In the Andes, negative rainfall anomalies occur during seven ENSO events above 8 (with a mean of
Extensive inundations have been observed in the Llanos de Mojos (Mamoré basin, south western Amaz... more Extensive inundations have been observed in the Llanos de Mojos (Mamoré 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.
The hydroclimatology of the Peruvian Amazon-Andes basin (PAB) which surface corresponding to 7% o... more 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 (T mean ), maximum temperature (T max ) and minimum temperature (T min ) time series over two PABs (Huallaga and Ucayali) over the last 40 years. 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 T mean positive trends are located over the Andes region. Finally, changes in the mean values occurred earlier in T max (during the 1970s) than in T min (during the 1980s). In the PAB, there is neither trend nor mean change in rainfall during the 1965-2007 period. However, annual, summer and autumn rainfall in the southern Andes presents an important interannual variability that is associated with the sea surface temperature in the tropical Atlantic Ocean while there are limited relationships between rainfall and El Niño-Southern Oscillation (ENSO) events. On the contrary, the interannual temperature variability is mainly related to ENSO events.
Hydrological Sciences Journal-journal Des Sciences Hydrologiques, 2012
According to the Peruvian agricultural ministry, the Pacific watersheds where the great cities an... more According to the Peruvian agricultural ministry, the Pacific watersheds where the great cities and intense farming are located only benefit from 1% of the available freshwater in Peru. Hence a thorough knowledge of the hydrology of this region is of particular importance. In the paper, analysis of this region and of the two other main Peruvian drainages, the Titicaca and
Environmental Research Letters, 2012
In this work we document and analyze the hydrological annual cycles characterized by a rapid tran... more 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
Journal of Hydrology, 2011
With the objective of understanding the potential and limitations of available precipitation prod... more With the objective of understanding the potential and limitations of available precipitation products for hydrological studies, this paper compares six daily and sub-daily precipitation datasets and their impacts on the water balance of the Negro River basin in the Amazon basin. The precipitation datasets contain gauge-based data [data derived from the Hybam Observatory Precipitation (HOP) dataset and provided by the Climate Prediction Center (CPC)], satellite-based data [the Global Precipitation Climatology Project (GPCP) one-degree daily and TRMM Multisatellite Precipitation Analysis (TMPA) datasets] and model-based data [the NCEP-DOE AMIP-II re-analysis (NCEP-2) and 40-year ECMWF Re-Analysis (ERA-40) datasets]. Each dataset has a common set of meteorological forcing data which are used to run the MGB-IPH hydrological model for the period from January 1998 to August 2002.The average precipitation of all the datasets is 2542 mm for the Negro River basin, with a standard deviation of 317 mm. TMPA and NCEP-2 have the lowest (2216 mm/year) and the highest (3065 mm/year) precipitation rates, respectively. The HOP and CPC datasets agree best with observed discharge. GPCP gives the best results among the ungauged datasets, followed by ERA-40. TMPA and NCEP-2 are found to be the least accurate. TMPA can reproduce the water cycles reasonably well, but underestimates the precipitation fields and discharges over the basin, while NCEP-2 is unable to represent the rainfall quantity and cycles, and the water discharge. Results suggest that gauge-based data are still the most representative of the actual precipitation in the northern Amazon basin. However, some satellite and model-based can reproduce fairly well the water cycle at the basin scale and monthly time step.► The spatio-temporal heterogeneities of six precipitation at the daily time step over the Negro River basin were compared. ► The effects of the datasets on the simulated water cycle of the Negro River basin were analyzed by using the MGB-IPH model. ►The rainfall datasets were compared at different temporal scales and also at the basin-wide and catchment scales. ► Mean rainfall over the basin varied substantially from a dataset to another but the evapotranspiration is in good agreement. ► This reveals an energy limited evapotranspiration in most parts of the basin.
Quaternary International, 2005
Three stalagmites were collected in the ''Perolas'' cave, 150 km NW of Cuiaba`, Mato Grosso, Braz... more Three stalagmites were collected in the ''Perolas'' cave, 150 km NW of Cuiaba`, Mato Grosso, Brazil, in order to reconstruct the climate history of the surrounding region. These stalagmites were similarly formed by stacking of thousands of calcitic pairs of laminae. Microphotographs of polished thin sections were used to count the laminae pairs and measure their width. A reasonable fit was found between the counting results and U/Th and 14 C geochronological data, proving that these pairs are annually deposited; and correlations were also found between the annual growth rate of the stalagmites and the annual water excess in the Perolas region, proving that the former parameter could be used as a climatic proxy. Three files of climatic proxy data covering 256 years were thus obtained and statistically treated to restore the historical fluctuations of the climate. Apart from well-documented periodicities, a still poorly known but very strong half-century climatic oscillation appeared in the results. r
Journal of Hydrometeorology, 2007
The hydrology of the Ecuadorian Amazon basin is still poorly documented. The research developed b... more 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 km 2 ). Forty-seven rainfall and 27 discharge stations were retained over a 30-yr period . 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.
Journal of Hydrometeorology, 2013
In this work, the authors analyze the origin of the extreme floods in the Peruvian Amazonas River... more 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 (55 400 m 3 s 21 ). 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 Marañ on 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 . The analysis of the climatic features related to the most important floods (1986, 1993, 1999, and 2012) suggests that they are characterized by a La Niña event, which originates a geopotential height wave train near the ground, with positive anomalies over the subtropical South and North Pacific and Atlantic and over southeastern South America. These patterns contribute to 1) the origin of an abundant humidity transport flux from the tropical North Atlantic and the Caribbean Sea toward the northwestern Amazon and 2) the maintenance of the monsoon flux over this region. They both favor a strong convergence of humidity in the northern Amazonas basin. Finally, the authors suggest that the intensity of floods is more likely related to an early La Niña event (as observed during the 2011/12 season), early rainfall, and simultaneous peaks of both tributaries of the Amazonas River.
Journal of Hydrology, 2009
Amazon basin Discharge trend Rainfall and runoff variability Brazil Peru Bolivia s u m m a r y Fo... more Amazon basin Discharge trend Rainfall and runoff variability Brazil Peru Bolivia s u m m a r y Former hydrological studies in the Amazon Basin generally describe annual discharge variability on the main stem. However, the downstream Amazon River only represents the mean state of the Amazonian hydrological system. This study therefore uses a new data set including daily discharge in 18 sub-basins to analyze the variability of regional extremes in the Amazon basin, after recalling the diversity of the hydrological annual cycles within the Amazon basin. Several statistical tests are applied in order to detect trends and breaks in the time series. We show that during the 1974-2004 period, the stability of the mean discharge on the main stem in Óbidos is explained by opposite regional features that principally involve Andean rivers: a decrease in the low stage runoff, particularly important in the southern regions, and an increase in the high stage runoff in the northwestern region. Both features are observed from the beginning of the nineties. These features are also observed in smaller meridian sub-basins in Peru and Bolivia. Moreover we show that the changes in discharge extremes are related to the regional pluriannual rainfall variability and the associated atmospheric circulation as well as to tropical large-scale climatic indicators.
Journal of Hydrology, 2005
This paper is devoted to illustrating new wavelet analysis methods in the field of hydrology. New... more This paper is devoted to illustrating new wavelet analysis methods in the field of hydrology. New wavelet indicators are applied to long-term hydrological and climatologic proxies. They are first applied to four Atlantic large river monthly discharges (Amazon, Parana, Orinoco and Congo) and then applied to two well-known long-term climatologic indexes: the Southern Oscillation and the North Atlantic Oscillation. This approach makes it possible to suggest physical explanations for time-scale dependant relationships.
Journal of Hydrology, 2005
Extensive inundations have been observed in the Llanos de Mojos (Mamoré basin, south western Amaz... more Extensive inundations have been observed in the Llanos de Mojos (Mamoré 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.
International Journal of Remote Sensing, 2004
This work presents results which help to understand the behaviour of the Normalized Difference Ve... more This work presents results which help to understand the behaviour of the Normalized Difference Vegetation Index (NDVI) anomalies over the South America continent during the two strongest El Niñ o events of the last century (1982-1983 and 1997-1998). The data used are parts of a long-term series (July 1981 to December 1999) of calibrated NDVI data derived from National Oceanic and Atmospheric Administration Advanced Very High Resolution Radiometer (NOAA AVHRR) datasets. Special emphasis has been given to the analysis of the response of the major Brazilian vegetation types. This paper introduces an approach that enhances NDVI anomalies relative to the long-term climatology of the region. We find a negative NDVI anomaly for most of the region during the 1982-1983 event, whereas for the 1997-1998 event positive NDVI anomalies were observed over most regions. Only the 'Nordeste' region showed a similar vegetation response for both events. We identify three possible International Journal of Remote Sensing
International Journal of Climatology, 2013
ABSTRACT Assessing the impact/adaptation of human activities on/to climate change is a key issue,... more ABSTRACT Assessing the impact/adaptation of human activities on/to climate change is a key issue, especially in the tropics that concentrate major anthropogenic dynamics such as deforestation and nearly two-thirds of the planetary rainfall. However, this task is often made tough because human activities such as agricultural dynamics are usually analysed at local or regional scale whereas climate related studies are led at large to global scales due to a lack of reliable data, especially in the tropics. In this article we argue that the increased spatial resolution of remote sensing-based rainfall estimates enables assessing the spatiotemporal variability of rainfall regimes at regional and local scales, thus allowing fine analysis of the interactions with human activities. We processed Tropical Rainfall Measuring Mission (TRMM) 3B42 daily rainfall estimates over the state of Mato Grosso (southern Brazilian Amazon) for the 1998–2012 study period in order to compute rainfall metrics such as annual rainfall and duration, onset and end dates of the rainy season based on the Anomalous Accumulation methodology (at a 0.25° spatial resolution). We then crossed these metrics with agricultural maps (produced at a 250 m spatial resolution) and proved that the adoption of intensive agricultural practices such as double cropping systems is partly the result of a strategy to adapt practices to local climatic conditions. Finally, we discuss how such results raise important issues regarding the sustainability of the agricultural development model in the Southern Amazon.
International Journal of Climatology, 2002
Rainfall variability in the Amazon basin is studied in relation to sea-surface temperatures (SSTs... more Rainfall variability in the Amazon basin is studied in relation to sea-surface temperatures (SSTs) in the equatorial Pacific and the northern and southern tropical Atlantic during the 1977-99 period, using the HiBAm original rainfall data set and complementary cluster and composite analyses.
International Journal of Climatology, 2006
The location of eight rainfall stations in the Zongo valley (Eastern Cordillera -Bolivia) between... more The location of eight rainfall stations in the Zongo valley (Eastern Cordillera -Bolivia) between 1195 and 4750 meters above sea level (masl) gives a unique opportunity to study the time-space rainfall variability between two regions, i.e. the Altiplano and the Amazonian lowlands of Bolivia, that are differently related to El Niño-Southern Oscillation (ENSO)
International Journal of Climatology, 2009
Rainfall variability in the Amazon basin (AB) is analysed for the 1964-2003 period. It is based o... more Rainfall variability in the Amazon basin (AB) is analysed for the 1964-2003 period. It is based on 756 pluviometric stations distributed throughout the AB countries. For the first time it includes 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. The impact of mountain ranges on rainfall is pointed out. The highest rainfall in the AB is observed in low windward regions, and low rainfall is measured in leeward and elevated stations. Additionally, rainfall regimes are more diversified in the Andean regions than in the lowlands. Rainfall spatio-temporal variability is studied based on a varimax-rotated principal component analysis (PCA). Long-term variability with a decreasing rainfall since the 1980s prevails in June-July-August (JJA) and September-October-November (SON). During the rainiest seasons, i.e. December-January-February (DJF) and March-April-May (MAM), the main variability is at decadal and interannual time scales. Interdecadal variability is related to long-term changes in the Pacific Ocean, whereas decadal variability, opposing the northwest and the south of the AB, is associated with changes in the strength of the low-level jet (LLJ) along the Andes. Interannual variability characterizes more specifically the northeast of the basin and the southern tropical Andes. It is related to El Niño-Southern Oscillation (ENSO) and to the sea surface temperature (SST) gradient over the tropical Atlantic. Mean rainfall in the basin decreases during the 1975-2003 period at an annual rate estimated to be −0.32%. Break tests show that this decrease has been particularly important since 1982. Further insights into this phenomenon will permit to identify the impact of climate on the hydrology of the AB.
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Papers by Josyane Ronchail