Junquas Clémentine

Abstract: The Last Few Decades Have Shown Evidence Of A Lengthening Dry Season In Southern Amazonia, Which Is Associated With A Delay In The Onset Of The South American Monsoon System (Sams). Using A Pattern Recognition Framework Of Atmospheric Circulation Patterns (Cps), Previous Studies Have Identified Specific Atmospheric Situations Related To The Onset Of The Sams. Here, We Analyze The Future Changes In The Cps That Largely Define The Main Hydro-Climatological States Of Tropical South America. We Evaluated The Cp Changes That Occurred Between Two Periods: Historical (1970-2000) And Future (2040-2070), Using Six General Circulation Models (Gcms) From The Coupled Model Intercomparison Project Phase 6. Future Gcm Projections Show Significant Spatio-Temporal Changes In The Cps Associated With The Dry Season In Southern Amazonia During The Mid-21St Century. These Changes Are Related To Both A Late Onset Of The Sams And An Early Demise Of The Sams. Particularly, The Cp Methodology Allowed For A Better Understanding Of The Behavior Of The Southern Amazon Dry Season Under Future Conditions, Showing An Increase In The Frequency Of The Cps Typically Observed During The Dry Season. The Occurrence Of Dry Days In The Amazon Basin During The Austral Winter Of The Mid-21St Century Increases By 19.4% On Average, With Respect To The Historical Period. This Methodology Also Identified A Future Increase In The Frequency Of Dry Cps, Both At The Beginning Of The Dry-To-Wet Transition Period (8%) And At The End Of The Wet-To-Dry Transition Season (11%).

Abstract: Andean Vegetation And Agriculture Depend On The Patterns Of Rainfall During The South American Monsoon. However, Our Understanding On The Importance Of Dynamic (Upper-Level Wind Circulation) As Compared To Thermodynamic (Amazon Basin Moisture) Drivers For Andes Rainfall Remains Limited. This Study Examines The Effect Of These Drivers On 3-7 Day Wet And Dry Spells Across The Tropical Andes And Assesses Resulting Impacts On Vegetation. Using Reanalysis And Remote Sensing Data From 1985-2018, We Find That Both Dynamic And Thermodynamic Drivers Play A Role In Determining The Rainfall Patterns. Notably, We Show That The Upper-Level Wind Is An Important Driver Of Rainfall Across The Entire Tropical Andes Mountain Range, But Not In The Amazon Lowlands, Suggesting A Crucial Role Of Topography In This Relationship. From Thermodynamic Perspective, We Find Wet Spell Conditions To Be Associated With Increased Moisture Along The Andes' Eastern Foothills Accompanied By A Strengthened South American Low-Level Jet, With Moisture Lifted Into The Andes Via Topography And Convection For All Considered Regions. Our Results Suggest That While Changes In Amazon Basin Moisture Dominate Rainfall Changes On Daily Time Scales Associated With Three Day Spells, Upper-Level Dynamics Play A More Important Role On The Synoptic Time Scale Of 5-7 Day Spells. Considering Impacts On The Ground, We Find That Only 5-7 Day Spells In The Semi-Arid Andes Have A Prolonged Effect On Vegetation. Our Study Emphasizes The Need To Consider Both Dynamic And Thermodynamic Drivers When Estimating Rainfall Changes In The Tropical Andes, Including In The Context Of Future Climate Projections.

Abstract: The Amazon Forest Has A Complex Interaction With Climate At Different Spatial And Temporal Scales. This Means That Alterations In Land Use Could Modify The Regional Water Cycle, Including The Surface And Atmospheric Water Budget. However, Little Is Known About How These Changes Occur Seasonally And In A Spatially Distributed Manner In The Most Vulnerable Regions, Such As The Southern Amazon. In This Study, The Local To Regional Effects Of Future Amazon Deforestation On The Surface And Atmospheric Water Budget Components Are Investigated By Twin Numerical Experiments Using The Regional Earth System Model Of The 'Institute Pierre Simone Laplace' (Regipsl) For 19 Yr (2001-2019). The Results Show That Significant Changes In Precipitation And Actual Evapotranspiration In The Southern Amazon (South Of 5 Degrees S) Are Associated With Surrounding Areas With A Deforested Ratio Higher Than 40%. During The Onset Of The Wet Season (September-November) The Largest Changes In Convective Processes Are Manifested By Opposite Atmospheric Dynamic In Adjacent Regions (Dipole), Associated With. This Dynamic Is Associated With Wind Orientation And The Different Sizes Of The Straight Corridors Of Continuous Deforestation (Pathways). The Dipole Manifests Itself As A Suppression Of Convection In The Upwind Sector, While Convection Increases In The Downwind Sector Of The Deforestation Pathway. For Medium-Sized Deforestation Pathways (-350 Km) Convection Changes Are Related To Dynamic Processes (Decrease In Surface Roughness). In Large-Sized Pathways (-500 Km) The Mechanisms Causing Convective Changes Are Combined, Dynamic And Thermal (Increase In Surface Temperature). In Deforested Regions There Is An Average Increase Of Terrestrial Water Storage Dynamics And Runoff -10 Times Higher Than In Non-Deforested Regions. Furthermore, The Atmosphere Becomes -8 Times Drier In Deforested Regions Than In Non-Deforested Regions. Our Findings Indicate A New Perspective Regarding A Comprehensive Modeling Approach To Understand Potential Changes In The Surface And Atmospheric Water Cycle In Different Regions Of Amazonia And In Different Seasons Due To Future Deforestation And Thus Provide New Insights Into Their Spatial And Temporal Variability At Sub-Regional Scales.

Abstract: A multi-experiment ensemble is performed using the WRF (Weather Research and Forecasting) model at high spatial resolution (1 km) over the Antisana glacier region (Ecuador), during the year 2005. Our goal is to identify the best model configurations to simulate atmospheric processes at diurnal and seasonal scales. The model is able to reproduce the complex zonal gradient of precipitation between the wet Amazon and the drier inter-Andean region. The main precipitation biases are (i) an overestimation in the afternoon (up to 6 mm/day) in the Antisana region related to local surface circulation patterns and (ii) a nighttime overestimation (up to 20 mm/day) in the Andes-Amazon transition zone associated with the regional circulation. Changing the microphysics scheme and/or the cumulus scheme primarily affect nighttime processes, while changing the topography forcing and activating slope radiation and shading options mostly affects afternoon processes. An adequate choice of the model configuration allows a correct representation of the diurnal cycle of precipitation, and in particular: (i) the mid-level easterly regional flow, (ii) the local moisture transport along and across the valleys, and (iii) the orographic mountain waves on the Antisana summit. For this specific area and year, the best configuration retained defined as “dSRTM_LRad” shows nighttime (daytime) precipitation biases smaller than 2 mm/day (3 mm/day); it is based on non-smoothed SRTM digital elevation model (dSRTM), Lin Purdue microphysics (L), and slope and shading radiation options (Rad). This 1-km resolution configuration requires the activation of the cumulus scheme, that improves the regional nighttime convection induced by the easterly regional flow on the Amazon-Andes transition region. It allows also a realistic strengthening of the daytime upward moisture transport. This study demonstrates that in the Antisana region, 1 km is a resolution still too coarse to deactivate cumulus schemes for a correct representation of cloud convection.

Abstract: The Cordillera Blanca (central Andes of Peru) represents the largest concentration of tropical glaciers in the world. The atmospheric processes related to precipitations are still scarcely studied in this region. The main objective of this study is to understand the atmospheric processes of interaction between local and regional scales controlling the diurnal cycle of precipitation over the Santa River basin located between the Cordillera Blanca and the Cordillera Negra. The rainy season (December-March) of 2012-2013 is chosen to perform simulations with the WRF (Weather Research and Forecasting) model, with two domains at 6 km (WRF-6 km) and 2 km (WRF-2 km) horizontal resolutions, forced by ERA5. WRF-2 km precipitation shows a clear improvement over WRF-6 km in terms of the daily mean and diurnal cycle, compared to in situ observations. WRF-2 km shows that the moisture from the Pacific Ocean is a key process modulating the diurnal cycle of precipitation over the Santa River basin in interaction with moisture fluxes from the Amazon basin. In particular, a channeling thermally orographic flow is described as controlling the afternoon precipitation along the Santa valley. In addition, in the highest parts of the Santa River basin (in both cordilleras) and the southern part, maximum precipitation occurs earlier than the lowest parts and the bottom of the valley in the central part of the basin, associated with the intensification of the channeling flow by upslope cross-valley winds during mid-afternoon and its decrease during late afternoon/early night.

Abstract: Study region: The upper part of the Guayllabamba and Napo basins (78.2 degrees W, 0.3 degrees S; 18,500 km(2)) in the equatorial Andes, which are vulnerable to stress on the ecosystem services. Study focus: This paper analyses the diurnal cycle of precipitation over a transect from the Andes to the Amazon. The diurnal cycle is estimated as the diurnal distribution of precipitation for 2014-2019 using records from 80 stations. Cluster analysis performed on the diurnal cycle estimates depicts the spatial association between the diurnal and seasonal cycles of precipitation. New hydrological insights: A northwest-southeast spatial variation in the diurnal and seasonal cycles is identified with four groups of stations. In the western part, the seasonal cycles of Groups 1 and 2 are bimodal with precipitation maxima in the March-April and October-November seasons and a short drier season in July-August. In the eastern part, Group 3 also presents bimodality, but a weaker seasonal cycle. Conversely, Group 4 is unimodal with a peak in June. Distinct diurnal cycles are observed in both drier and wetter seasons of Groups 1-3; no marked diurnal cycle is observed in Group 4. Groups 3 and 4 are the most spatially heterogeneous, with an exceptional horizontal variation of 330 mm/yr/km. The analysis of these variations provides insight into the atmospheric dynamics driving precipitation in this zone, and may help to better optimize the water supply system.

Abstract: In the last four decades, the Southern Amazon (south of 8 degrees S) has shown changes in the spatial and temporal patterns of its hydro-climatic components, leading to drier conditions. Due to climate and land-use changes, this region is considered as a zone under biophysical transition processes. Previous studies have documented a complex interaction between climate and deforestation either on a large-scale or based on limited in situ data, typically covering the Brazilian Amazon. In this study, we analyse the relationships between hydro-climate, the surface water-energy partitioning and an index of regional forest cover change for the period 1981-2018. Additionally, we discretized three regions covering the Bolivian Amazon and the southern portions of the Peruvian and Brazilian Amazon due to their differences in the evolution of land use. In the Bolivian region, a high ratio of forest cover change, exceeding 40-50%, is related to a significant tendency to become water-limited. This change is associated with decreased rainfall, increased potential evapotranspiration and decreased actual evapotranspiration. Regardless of the region analysed, those that are characterized by a high ratio of forest cover change (>40-50%) show growing imbalance between increasing potential and decreasing actual evapotranspiration. However, in the Peruvian and Brazilian regions, hydro-climatic conditions remain energy-limited due to minor rainfall changes. The observed differences in surface water-energy partitioning behaviour evidence a complex dependence of both sub-regional (i.e., land cover changes) and large-scale (i.e., strengthening of the Walker and Hadley circulations) conditions. Our findings indicate a clear link between hydro-climatic changes and deforestation, providing a new perspective on their spatial variability on a sub-regional scale.

Abstract: Analyzing December-February (DJF) precipitation in the southern tropical Andes-STA (12 circle S}; > 3000 m.a.s.l) allows revisiting regional atmospheric circulation features accounting for its interannual variability over the past 35 years (1982-2018). In a region where in-situ rainfall stations are sparse, the CHIRPS precipitation product is used to identify the first mode of interannual DJF precipitation variability (PC1-Andes). A network of 98 rain-gauge stations further allows verifying that PC1-Andes properly represents the spatio-temporal rainfall distribution over the region; in particular a significant increase in DJF precipitation over the period of study is evident in both in-situ data and PC1-Andes. Using the ERA-Interim data set, we found that aside from the well-known relationship between precipitation and upper-level easterlies over the STA, PC1-Andes is also associated with upward motion over the western Amazon (WA), a link that has not been reported before. The ascent over the WA is a component of the meridional circulation between the tropical North Atlantic and western tropical South America-WTSA (80 circle W). Indeed, the precipitation increase over the last 2 decades is concomitant with the strengthening of this meridional circulation. An intensified upward motion over the WA has moistened the mid-troposphere over WTSA, and as a consequence, a decreased atmospheric stability between the mid- and the upper troposphere is observed over this region, including the STA. We further show that, over the last 15 years or so, the year-to-year variability of STA precipitation (periodicity < 8 years) has been significantly associated with upward motion over the WA, while upper-level easterlies are no longer significantly correlated with precipitation. These observations suggests that the STA have experienced a transition from a dry to a wet state in association with a change in the dominant mode of atmospheric circulation. In the former dominant state, zonal advection of momentum and moisture from the central Amazon, associated with upper-level easterlies, is necessary to develop convection over the STA. Since the beginning of the 21st century, DJF precipitation over the STA seems to respond directly and primarily to upward motion over the WA. Beyond improving our understanding of the factors influencing STA precipitation nowadays, these results point to the need of exploring their possible implications for the long-term evolution of precipitation in a context of global warming.

Abstract: The original version of the article contained errors in Fig.

Abstract: In 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 (0.25A degrees x 0.25A degrees) and swath data from the TRMM-2A25 precipitation radar product (5 km x 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.

Abstract: In this study we identified a significant low frequency variability (8 to 20 years) that characterizes the hydroclimatology over the Central Andes. Decadal-interdecadal variability is related to the central-western Pacific Ocean (R-2 = 0.50) and the zonal wind at 200 hPa above the Central Andes (R-2 = 0.66). These two oceanic-atmospheric variables have a dominant decadal-interdecadal variability, and there is a strong relationship between them at a low frequency time scale (R-2 = 0.66). During warming decades in the central-western Pacific Ocean, westerlies are intensified at 200 hPa above the Central Andes, which produce decadal periods of hydrological deficit over this region. In contrast, when the central- western Pacific Ocean is cooler than usual, easterly anomalies prevail over the Central Andes, which are associated with decades of positive hydrological anomalies over this region. Our results indicate that impacts of El Nino on hydrology over the Central Andes could be influenced by the low frequency variability documented in this study.

Abstract: The 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 35A degrees S (at 30A degrees S-35A degrees 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.