Browsing by Author "Junquas, Clémentine"
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Item Restricted Climate variability and extreme drought in the upper Solimões River (western Amazon Basin): understanding the exceptional 2010 drought(American Geophysical Union (AGU), 2011-07) Espinoza, Jhan Carlo; Ronchail, Josyane; Guyot, Jean Loup; Junquas, Clémentine; Vauchel, Philippe; Lavado, Waldo; Drapeau, Guillaume; Pombosa, RodrigoThis 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.Item Open Access From drought to flooding: understanding the abrupt 2010-11 hydrological annual cycle in the Amazonas River and tributaries(IOP Publishing, 2012-04-19) Espinoza, Jhan Carlo; Ronchail, Josyane; Guyot, Jean-Loup; Junquas, Clémentine; Drapeau, Guillaume; Martínez, Jean-Michel; Santini, William; Vauchel, Philippe; Lavado, Waldo; Ordoñez, Julio; Espinoza Villar, Raúl ArnaldoIn 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 m³ s⁻¹) to one of the four highest discharges in April 2011 (49 500 m³ s⁻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 Niña-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 Niña event characterized the equatorial Pacific.Item Open Access Performance of Regional Climate Model Precipitation Simulations Over the Terrain-Complex Andes-Amazon Transition Region(American Geophysical Union, 2024-01-06) Gutierrez, Ricardo A.; Junquas, Clémentine; Armijos Cardenas, Elisa Natalia; Sörensson, Anna A.; Espinoza, Jhan-CarloRegional climate models (RCMs) are widely used to assess future impacts associated with climate change at regional and local scales. RCMs must represent relevant climate variables in the present-day climate to be considered fit-for-purpose for impact assessment. This condition is particularly difficult to meet over complex regions such as the Andes-Amazon transition region, where the Andean topography and abundance of tropical rainfall regimes remain a challenge for numerical climate models. In this study, we evaluate the ability of 30 regional climate simulations (6 RCMs driven by 10 global climate models) to reproduce historical (1981–2005) rainfall climatology and temporal variability over the Andes-Amazon transition region. We assess spatio-temporal features such as spatial distribution of rainfall, focusing on the orographic effects over the Andes-Amazon “rainfall hotspots” region, and seasonal and interannual precipitation variability. The Eta RCM exhibits the highest spatial correlation (up to 0.6) and accurately reproduces mean annual precipitation and orographic precipitation patterns across the region, while some other RCMs have good performances at specific locations. Most RCMs simulate a wet bias over the highlands, particularly at the eastern Andean summits, as evidenced by the 100%–2,500% overestimations of precipitation in these regions. Annual cycles are well represented by most RCMs, but peak seasons are exaggerated, especially at equatorial locations. No RCM is particularly skillful in reproducing the interannual variability patterns. Results highlight skills and weaknesses of the different regional climate simulations, and can assist in the selection of regional climate simulations for impact studies in the Andes-Amazon transition zone.Item Open Access Rainfall hotspots over the southern tropical Andes: spatial distribution, rainfall intensity, and relations with large‐scale atmospheric circulation(American Geophysical Union (AGU), 2015-05) Espinoza, Jhan Carlo; Chávez Jara, Steven Paul; Ronchail, Josyane; Junquas, Clémentine; Takahashi, Ken; Lavado, WaldoThe Andes/Amazon transition is among the rainiest regions of the world and the interactions between large‐scale circulation and the topography that determine its complex rainfall distribution remain poorly known. This work provides an in‐depth analysis of the spatial distribution, variability, and intensity of rainfall in the southern Andes/Amazon transition, at seasonal and intraseasonal time scales. The analysis is based on comprehensive daily rainfall data sets from meteorological stations in Peru and Bolivia. We compare our results with high‐resolution rainfall TRMM‐PR 2A25 estimations. Hotspot regions are identified at low elevations in the Andean foothills (400–700 masl) and in windward conditions at Quincemil and Chipiriri, where more than 4000 mm rainfall per year are recorded. Orographic effects and exposure to easterly winds produce a strong annual rainfall gradient between the lowlands and the Andes that can reach 190 mm/km. Although TRMM‐PR reproduces the spatial distribution satisfactorily, it underestimates rainfall by 35% in the hotspot regions. In the Peruvian hotspot, exceptional rainfall occurs during the austral dry season (around 1000 mm in June–July–August; JJA), but not in the Bolivian hotspot. The direction of the low‐level winds over the Andean foothills partly explains this difference in the seasonal rainfall cycle. At intraseasonal scales in JJA, we found that, during northerly wind regimes, positive rainfall anomalies predominate over the lowland and the eastern flank of the Andes, whereas less rain falls at higher altitudes. On the other hand, during southerly regimes, rainfall anomalies are negative in the hotspot regions. The influence of cross‐equatorial winds is particularly clear below 2000 masl.Item Open Access Simulaciones de la precipitación de verano por modelos climáticos regionales de CORDEX en la zona de transición Andes-Amazonía(Instituto Geofísico del Perú, 2023-02) Gutiérrez, Ricardo A.; Junquas, Clémentine; Armijos Cardenas, Elisa Natalia; Sörensson, A. A.; Espinoza, Jhan-CarloEl presente avance de investigación evalúa el realismo de la climatología histórica (1981-2005) de la precipitación de verano en la zona de transición Andes-Amazonía a partir de las simulaciones del experimento regional coordinado de reducción de escala (CORDEX, por sus siglas en inglés) para Sudamérica. Los resultados preliminares muestran que no habría una relación aparente entre la performance del modelo y la resolución espacial en cuanto a la reproducción de las climatologías de precipitación, cuando se esperaría que los modelos tengan un mejor rendimiento, es decir, reproduzcan mejor las precipitaciones al tener una resolución espacial más alta o más fina. En conclusión, será necesaria la aplicación de modelos regionales de resolución espacial más fina y realizar experimentos de sensibilidad con diferentes parametrizaciones físicas para lograr mejorar el realismo de los patrones espaciales de la precipitación orográfica sobre la región de estudio.Item Open Access Spatio-temporal assessment of WRF, TRMM and in situ precipitation data in a tropical mountain environment (Cordillera Blanca, Peru)(European Geosciences Union (EGU), 2016-01-18) Mourre, L.; Condom, T.; Junquas, Clémentine; Lebel, T.; Sicart, J. E.; Figueroa, R.; Cochachin, A.The estimation of precipitation over the broad range of scales of interest for climatologists, meteorologists and hydrologists is challenging at high altitudes of tropical regions, where the spatial variability of precipitation is important while in situ measurements remain scarce largely due to operational constraints. Three different types of rainfall products – ground based (kriging interpolation), satellite derived (TRMM3B42), and atmospheric model outputs (WRF – Weather Research and Forecasting) – are compared for 1 hydrological year in order to retrieve rainfall patterns at timescales ranging from sub-daily to annual over a watershed of approximately 10 000 km² in Peru. An ensemble of three different spatial resolutions is considered for the comparison (27, 9 and 3 km), as long as well as a range of timescales (annual totals, daily rainfall patterns, diurnal cycle). WRF simulations largely overestimate the annual totals, especially at low spatial resolution, while reproducing correctly the diurnal cycle and locating the spots of heavy rainfall more realistically than either the ground-based KED or the Tropical Rainfall Measuring Mission (TRMM) products. The main weakness of kriged products is the production of annual rainfall maxima over the summit rather than on the slopes, mainly due to a lack of in situ data above 3800 m a. s. l. This study also confirms that one limitation of TRMM is its poor performance over ice-covered areas because ice on the ground behaves in a similar way as rain or ice drops in the atmosphere in terms of scattering the microwave energy. While all three products are able to correctly represent the spatial rainfall patterns at the annual scale, it not surprisingly turns out that none of them meets the challenge of representing both accumulated quantities of precipitation and frequency of occurrence at the short timescales (sub-daily and daily) required for glacio-hydrological studies in this region. It is concluded that new methods should be used to merge various rainfall products so as to make the most of their respective strengths.Item Restricted Understanding the influence of orography on the precipitation diurnal cycle and the associated atmospheric processes in the central Andes(Springer, 2018-06) Junquas, Clémentine; Takahashi, Ken; Condom, Thomas; Espinoza, Jhan Carlo; Chávez Jara, Steven Paul; Sicart, J. E.; Lebel, ThierryIn the tropical Andes, the identification of the present synoptic mechanisms associated with the diurnal cycle of precipitation and its interaction with orography is a key step to understand how the atmospheric circulation influences the patterns of precipitation variability on longer time-scales. In particular we aim to better understand the combination of the local and regional mechanisms controlling the diurnal cycle of summertime (DJF) precipitation in the Northern Central Andes (NCA) region of Southern Peru. A climatology of the diurnal cycle is obtained from 15 wet seasons (2000–2014) of 3-hourly TRMM-3B42 data (0.25° × 0.25°) and swath data from the TRMM-2A25 precipitation radar product (5 km × 5 km). The main findings are: (1) in the NCA region, the diurnal cycle shows a maximum precipitation occurring during the day (night) in the western (eastern) side of the Andes highlands, (2) in the valleys of the Cuzco region and in the Amazon slope of the Andes the maximum (minimum) precipitation occurs during the night (day). The WRF (Weather Research and Forecasting) regional atmospheric model is used to simulate the mean diurnal cycle in the NCA region for the same period at 27 km and 9 km horizontal grid spacing and 3-hourly output, and at 3 km only for the month of January 2010 in the Cuzco valleys. Sensitivity experiments were also performed to investigate the effect of the topography on the observed rainfall patterns. The model reproduces the main diurnal precipitation features. The main atmospheric processes identified are: (1) the presence of a regional-scale cyclonic circulation strengthening during the afternoon, (2) diurnal thermally driven circulations at local scale, including upslope (downslope) wind and moisture transport during the day (night), (3) channelization of the upslope moisture transport from the Amazon along the Apurimac valleys toward the western part of the cordillera.Item Restricted What dynamics drive future wind scenarios for coastal upwelling off Peru and Chile?(Springer, 2014) Belmadani, Ali; Echevin, Vincent; Codron, Francis; Takahashi, Ken; Junquas, ClémentineThe dynamics of the Peru–Chile upwelling system (PCUS) are primarily driven by alongshore wind stress and curl, like in other eastern boundary upwelling systems. Previous studies have suggested that upwelling-favorable winds would increase under climate change, due to an enhancement of the thermally-driven cross-shore pressure gradient. Using an atmospheric model on a stretched grid with increased horizontal resolution in the PCUS, a dynamical downscaling of climate scenarios from a global coupled general circulation model (CGCM) is performed to investigate the processes leading to sea-surface wind changes. Downscaled winds associated with present climate show reasonably good agreement with climatological observations. Downscaled winds under climate change show a strengthening off central Chile south of 35°S (at 30°S–35°S) in austral summer (winter) and a weakening elsewhere. An alongshore momentum balance shows that the wind slowdown (strengthening) off Peru and northern Chile (off central Chile) is associated with a decrease (an increase) in the alongshore pressure gradient. Whereas the strengthening off Chile is likely due to the poleward displacement and intensification of the South Pacific Anticyclone, the slowdown off Peru may be associated with increased precipitation over the tropics and associated convective anomalies, as suggested by a vorticity budget analysis. On the other hand, an increase in the land–sea temperature difference is not found to drive similar changes in the cross-shore pressure gradient. Results from another atmospheric model with distinct CGCM forcing and climate scenarios suggest that projected wind changes off Peru are sensitive to concurrent changes in sea surface temperature and rainfall.