Publications

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: Ongoing Hydrological Alterations Due To Climate Change And Anthropogenic Uses Of Water Have Major Implications For Freshwater Biodiversity. Quantifying The Relative Effects Of Environmental Variables On Macroinvertebrates Is Required To Predict Biological Responses To Hydrological Alterations. To Date, No Study Simultaneously Examined The Effects Of Physico-Chemistry, Hydraulics, And Hydrology On The Distribution Of Alpine Macroinvertebrate Communities And Taxa. In This Study, We Aimed To Quantify The Relative Correlation Between These Environmental Variables And Macroinvertebrate Community Composition And Structure. We Sampled Macroinvertebrates At 66 Stream Sites Located In Three Catchments In The French Alps. We Characterised The Proximate Habitat At Each Site Using 11 Variables Describing Measured Physico-Chemistry And Hydraulics, And Simulation-Based Hydrology. We Described Relationships Between Community Structure And The Environment Using A Co-Inertia Analysis And Modelled Individual Taxa Abundance With Generalised Linear Mixed Models. The Co-Inertia Revealed A Significant Co-Structure Between The Environmental And Macroinvertebrate Matrices. Glacier-Influenced Sites With High Turbidity And Summer Flow Exhibited Similar Community Composition With Low Total Abundance. Sources At High Altitude And Sites With Low Glacial Influence, Exhibiting High Summer Flow And Flow Velocity, Were Dominated By Diamesinae, Rhithrogena Spp., Dictyogenus Spp., And Baetis Alpinus. Streams Fed By Rainfall/Snowmelt And Valley Sources, Associated With Higher Temperature, Conductivity, And Monthly Discharge Variability Were Characterised By Higher Richness And Abundances. Models Indicated That The Three Types Of Proximate Habitat Variables Significantly Contributed To The Macroinvertebrate Distribution. Turbidity Was Strongly Negatively Associated With Macroinvertebrate Abundances. Increasing Flow Velocity And Summer Flow Had Significant (Mainly Negative) Effect In 43% Of Models. The Co-Structure Between Communities And Proximate Habitat Variables Was Shared By The Three Catchments. For Most Individual Taxa, Catchment Identity Did Not Influence Abundance Models And Cross-Validations Indicated Transferable Effects Of Proximate Habitat Variables Among Alpine Catchments. Our Results Can Be Used To Infer Responses Of Alpine Macroinvertebrates To Multivariate Environmental Changes. Understanding The Relationships Between Macroinvertebrates And Environmental Variables Help To Predict How Communities And Taxa Will Be Affected By Habitat Alterations Due To Ongoing Hydrological Changes And Resulting Physico-Chemical Conditions.

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: This Study Finds The Relationship Between Increases In Precipitable Water Vapor (Pwv), And Intense Rainfall Events In Four Different Climatological Regions Of South America'S Equatorial Northwest: The Coast, Andes Valley, High Mountains, And Amazon. First, The Pwv Was Derived From Tropospheric Zenith Delay Measured By Global Navigation Satellite System (Gnss) Instrumentation Located Near Meteorological Stations Within The Regions Of Interest Using Hourly Data From The Year 2014. A Harmonic Analysis Approach Through Continuous Wavelet Cross-Spectrum And Coherence, As Well As Discrete Wavelets, Was Used To Determine A Measure Of The Lags Found Between Pwv And Specific Heavy Rain Events And Then Compared With Satellite Ir Images And Meteorological Anomalies. The Link Between Pwv Peaks And Rainfall Was The Most Evident On The Coast, And Less Discernible In The Other Stations Possibly Due To Local Dynamic Factors. The Results Showed A Lag Of 11 H Between The Preceding Pwv Increase And An Intense Rainfall Event. This Was Apparent In All Of The Stations, Except In Amazon Where It Was 6 H, With The Highest Precision At The Coast And With The Largest Dispersion In The High Mountains. The Interpretation Of This Lag For Each Region Is Also Discussed.

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: Modern hydrology relies on multiple sources of information combined with climatological, hydrological and glaciological data. These data can be collected through various sources such as private initiatives by companies, research programs, and both national and international organisms. They also vary by types, e.g., in situ measurements, satellite, reanalysis and simulated data. Recently the ANDEX research project, as a GEWEX regional program, was created to understand the processes related to the hydrological cycle and energy fluxes in the Andean region from Colombia to Patagonia. It is quite challenging to carry out this program given the complex orography and diversity of climates from tropical to sub-polar climates. This review article is a compilation of the various databases that are useful for hydrometeorological research in the South American Andes. The National Meteorological and Hydrological Services in Bolivia, Chile, Colombia, Ecuador, Peru, Venezuela and Argentina provide a large amount of data however the high-elevation areas are poorly instrumented and the number of stations varies greatly between the countries. National databases are only partially shared with the international bodies responsible for summarizing the existing data; this causes problems in term of data product assimilation. Across the entire continent, too few radiosondes are being used despite the fact that these data are crucial for validating and identifying problems in the atmospheric models. An increasing number of satellite data are available but it is difficult to assimilate them into the hydroclimatological models suited to the adjusted spatial and temporal resolutions. Specifically, for precipitation, we recommend merged products that account for the high spatial and temporal variability across the Andes. Finally, the international ANDEX program could be an excellent opportunity to increase the knowledge of the hydrological processes in the Andes.

Abstract: The respective impacts of Northern and Southern Hemispheric climatic changes on the Tropics during the last deglaciation remain poorly understood. In the High Tropical Andes, the Antarctic Cold Reversal (ACR, 14.3-12.9 ka BP) is better represented among morainic records than the Younger Dryas (12.9-11.7 ka BP). However, in the Altiplano basin (Bolivia), two cold periods of the Northern Hemisphere (Heinrich Stadial la, 16.5-14.5 ka BP, and the Younger Dryas) are synchronous with (i) major advances or standstills of paleoglaciers and (ii) the highstands of giant paleolakes Tauca and Coipasa. Here, we present new cosmic ray exposure (CRE) ages from glacial landforms of the Bolivian Andes that formed during the last deglaciation (Termination 1). We reconstruct the equilibrium line altitudes (ELA) associated with each moraine and use them in an inverse algorithm combining paleoglaciers and paleolake budgets to derive temperature and precipitation during the last deglaciation. Our temperature reconstruction (AT relative to present day) yields a consistent regional trend of progressive warming from Delta T = -5 to -2.5 degrees C during 17-14.5 ka BP, followed by a return to colder conditions around -4 degrees C during the ACR (14.5-12.9 ka BP). The Coipasa highstand (12.9-11.8 ka BP) is coeval with another warming trend followed by AT stabilization at the onset of the Holocene (ca. 10 ka BP), around -3 degrees C. Our results suggest that, during the last deglaciation (20-10 ka BP) atmospheric temperatures in the Tropical Andes mimicked Antarctic variability, whereas precipitation over the Altiplano was driven by changes in the Northern Hemisphere. (C) 2020 Elsevier Ltd. All rights reserved.

Abstract: Study region: Upper Madeira Basin (975,500 km(2)) in Southern Amazonia, which is suffering a biophysical transition, involving deforestation and changes in rainfall regime. Study focus: The evolution of the runoff coefficient (Rc: runoff/rainfall) is examined as an indicator of the environmental changes (1982-2017). New hydrological insights for the region: At an annual scale, the Rc at Porto Velho station declines while neither the basin-averaged rainfall nor the runoff change. During the low-water period Rc and runoff diminish while no changes are observed in rainfall. This cannot be explained by increase of evapotranspiration since the basin-averaged actual evapotranspiration decreases. To explain the decrease of Rc, a regional analysis is undertaken. While the characteristic rainfall-runoff time-lag (CT) at Porto Velho basin is estimated to 60 days, CT is higher (65-75 days) in the south and lower (50 days) over the Amazon-Andes transition regions. It is found that 1) the southern basin (south of 14 degrees S) best explains low-level Porto Velho runoff, 2) in the south, rainfall diminishes and the frequency of dry days increases. Both features explain the diminution of the runoff and the Rc in Porto Velho. Moreover, the increasing dryness in the south compensates for the rainfall and frequency of wet days (> 10 mm) increase north of 14 degrees S and explains the lack of basin-averaged rainfall trends of the upper Madeira basin.

Abstract: The melting of tropical glaciers provides water resources to millions of people, involving social, ecological and economic demands. At present, these water reservoirs are threatened by the accelerating rates of mass loss associated with modern climate changes related to greenhouse gas emissions and ultimately land use/cover change. Until now, the effects of land use/cover change on the tropical Andean glaciers of South America through biomass burning activities have not been investigated. In this study, we quantitatively examine the hypothesis that regional land use/cover change is a contributor to the observed glacier mass loss, taking into account the role of Amazonian biomass burning. We demonstrated here, for the first time, that for tropical Andean glaciers, a massive contribution of black carbon emitted from biomass burning in the Amazon Basin does exist. This is favorable due to its positioning with respect to Amazon Basin fire hot spots and the predominant wind direction during the transition from the dry to wet seasons (Aug-Sep-Oct), when most fire events occur. We investigated changes in Bolivian Zongo Glacier albedo due to impurities on snow, including black carbon surface deposition and its potential for increasing annual glacier melting. We showed that the magnitude of the impact of Amazonian biomass burning depends on the dust content in snow. When high concentration of dust is present (e.g. 100 ppm of dust), the dust absorbs most of the radiation that otherwise would be absorbed by the BC. Our estimations point to a melting factor of 3.3 +/- 0.8% for black carbon, and 5.0 +/- 1.0% for black carbon in the presence of low dust content (e.g. 10 ppm of dust). For the 2010 hydrological year, we reported an increase in runoff corresponding to 4.5% of the annual discharge during the seasonal peak fire season, which is consistent with our predictions.

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Abstract: The Ecuadorian Andes are characterized by a complex spatiotemporal variability of precipitation. Global circulation models do not have sufficient horizontal resolution to realistically simulate the complex Andean climate and in situ meteorological data are sparse; thus, a high-resolution gridded precipitation product is needed for hydrological purposes. The region of interest is situated in the center of Ecuador and covers three climatic influences: the Amazon basin, the Andes, and the Pacific coast. Therefore, regional climate models are essential tools to simulate the local climate with high spatiotemporal resolution; this study is based on simulations from the Weather Research and Forecasting (WRF) Model. The WRF Model is able to reproduce a realistic precipitation variability in terms of the diurnal cycle and seasonal cycle compared to observations and satellite products; however, it generated some nonnegligible bias in the region of interest. We propose two new methods for precipitation bias correction of the WRF precipitation simulations based on in situ observations. One method consists of modeling the precipitation bias with a Gaussian process metamodel. The other method is a spatial adaptation of the cumulative distribution function transform approach, called CDF-t, based on Voronoi diagrams. The methods are compared in terms of precipitation occurrence and intensity criteria using a cross-validation leave-one-out framework. In terms of both criteria, the Gaussian process metamodel approach yields better results. However, in the upper parts of the Andes (>2000 m), the spatial CDF-t method seems to better preserve the spatial WRF physical patterns.

Abstract: Heinrich events are characterized by worldwide climate modifications. Over the Altiplano endorheic basin (high tropical Andes), the second half of Heinrich Stadial 1 (HS1a) was coeval with the highstand of the giant paleolake Tauca. However, the atmospheric mechanisms underlying this wet event are still unknown at the regional to global scale. We use cosmic-ray exposure ages of glacial landforms to reconstruct the spatial variability in the equilibrium line altitude of the HS1 a Altiplano glaciers. By combining glacier and lake modeling, we reconstruct a precipitation map for the HS1a period. Our results show that paleoprecipitation mainly increased along the Eastern Cordillera, whereas the southwestern region of the basin remained relatively dry. This pattern indicates a southward expansion of the easterlies, which is interpreted as being a consequence of a southward shift of the Bolivian High. The results provide a new understanding of atmospheric teleconnections during HS1 and of rainfall redistribution in a changing climate.

Abstract: We present the glacier-wide summer surface mass balances determined by a detailed hydrological balance (sSMBhydro) and the quantification of the uncertainties of the calculations on the Argentiere and Mer de Glace-Leschaux drainage basins, located in the upper Arve watershed (French Alps), over the period 1996-2004. The spatial distribution of precipitation within the study area was adjusted using in situ winter mass-balance measurements. The sSMBhydro performance was assessed via a comparison with the summer surface mass balances based on in situ glaciological observations (sSMBglacio). Our results show that the sSMBhydro has an uncertainty of +/- 0.67 m w.e.a(-1) at Argentiere and +/- 0.66 m w.e.a(-1) at Mer de Glace-Leschaux. Estimates of the Argentiere sSMBhydro values are in good agreement with the sSMBglacio values. These time series show almost the same interannual variability. From the marked difference between the sSMBhydro and sSMBglacio values for the Mer de Glace-Leschaux glacier, we suspect a significant role of groundwater fluxes in the hydrological balance. This study underlines the importance of taking into account the groundwater transfers to represent and predict the hydro-glaciological behaviour of a catchment.

Abstract: In this study, we investigate changes in the glaciated surface and the formation of lakes in the headwater of the Querococha watershed in Cordillera Blanca (Peru) using 24 Landsat images from 1975 to 2014. Information of glacier retreat was integrated with available climate data, the first survey of recent depositional dynamics in proglacial Yanamarey Lake (4600 m a.s.l.), and a relatively short hydrological record (2002-2014) at the outlet of Yanamarey Lake. A statistically significant temperature warming (0.21 degrees C decade(-1) for mean annual temperature) has been detected in the region, and it caused a reduction of the glacierized area since 1975 from 3.5 to 1.4 km(-2). New small lakes formed in the deglaciated areas, increasing the flooded area from 1.8 ha in 1976 to 2.8 ha in 2014. A positive correlation between annual rates of glacier recession and runoff was found. Sediment cores revealed a high sedimentation rate (>1 cm yr(-1)) and two contrasted facies, suggesting a shift toward a reduction of meltwater inputs and higher hydrological variability likely due to an increasing role of precipitation on runoff during the last decades. Despite the age control uncertainties, the main transition likely occurred around 19982000, correlating with the end of the phase with maximum warming rates and glacier retreat during the 1980s and 1990s, and the slowing down of expansion of surface lake-covered surface. With this hydrological – paleolimnological approach we have documented the association between recent climate variability and glacier recession and the rapid transfer of hydroclimate signal to depositional and geochemical processes in high elevation Andean environments. This, study also alerts about water quality risks as proglacial lakes act as secondary reservoirs that trap trace and minor elements in high altitude basins. (C) 2016 Elsevier B.V. All rights reserved.

Abstract: The strong socio-economic growth of Quito has led to significant projects of inter-basin transfers, intensifying high-altitude resources mobilization in environmentally sensitive areas and with accelerated melting of glaciers. In order to study various future scenarios, we propose modelling of the climate/glacier/hydrology/water resources management continuum, applied to Andean basins. Using the tool Water Evaluation and Planning (WEAP21), we developed: (1) semi-distributed hydro-climate modelling with monthly data using regional homogenization (vector method); (2) glacier modelling of water production and inter-annual evolution; (3) modelling in hydrological units depending on land cover; and (4) water management modelling distinguishing water rights, allocation and use. In this paper, we mainly present results of monthly hydrological calibrations (1963-2006), studying, in particular, the equifinality of various parameter settings. We show flexibility, robustness and limits of the proposed modelling, contributing to identification of uncertainties for evaluation of future scenarios.

Abstract: 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 km(2) 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 ma.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.

Abstract: In many partially glacierized watersheds glacier recession driven by a warming climate could lead to complex patterns of streamflow response over time, often marked with rapid increases followed by sharp declines, depending on initial glacier ice cover and rate of climate change. Capturing such "phases'' of hydrologic response is critical in regions where communities rely on glacier meltwater, particularly during low flows. In this paper, we investigate glacio-hydrologic response in the headwaters of the Zongo River, Bolivia, under climate change using a distributed glacio-hydrological model over the period of 1987-2100. Model predictions are evaluated through comparisons with satellite-derived glacier extent estimates, glacier surface velocity, in situ glacier mass balance, surface energy flux, and stream discharge measurements. Historically (1987-2010) modeled glacier melt accounts for 27% of annual runoff, and 61% of dry season (JJA) runoff on average. During this period the relative glacier cover was observed to decline from 35 to 21% of the watershed. In the future, annual and dry season discharge is projected to decrease by 4% and 27% by midcentury and 25% and 57% by the end of the century, respectively, following the loss of 81% of the ice in the watershed. Modeled runoff patterns evolve through the interplay of positive and negative trends in glacier melt and increased evapotranspiration as the climate warms. Sensitivity analyses demonstrate that the selection of model surface energy balance parameters greatly influences the trajectory of hydrological change projected during the first half of the 21st century. These model results underscore the importance of coupled glacio-hydrology modeling.

Abstract: Continental climate change during the late glacial period has now been widely documented thanks to Cosmic-Ray Exposure (CRE) dating of glacial features. The accuracy of these CRE ages mainly relies on a priori knowledge of the production rate of the cosmogenic nuclide that has accumulated in a specific mineral. To produce unequivocal and accurate chronologies of glacier fluctuations during the late glacial period, it is crucial that the cosmogenic nuclide production rates are better constrained, particularly in the high tropics where existing spatial and temporal scaling models show significant discrepancies. Here we report a new production rate established at low latitude (19 degrees S) and high elevation (3800 alas on the Challapata fan-delta, at the edge of the Paleolake Tauca, on the flank of Cerro Azanaques (Bolivia). Sedimentological evidence for synchronicity with the Tauca Lake highstand along with U-Th and C-14 measurements established that the fan-delta is 16.07 +/- 0.64 kyr BP old. In situ-produced Be-10 concentrations measured in 15 boulders lying on the fan-delta yield a mean Be-10 concentration of 4.92 +/- 0.05 x 10(5) at g(-1). A local in situ Be-10 production rate of 30.8 +/- 1.3 at g(-1) yr(-1) is thus obtained at 3800 masl and 19 degrees S. Application of the “Lal-modified” scaling scheme to this Azanaques production rate, using a standard atmosphere and the Muscheler et al. (2005) geomagnetic reconstruction, leads to a Sea Level High Latitude (SLHL) in situ Be-10 production rate of 3.76 +/- 0.15 at g(-1) yr(-1) (1 a uncertainty). In addition, we propose a reference in situ Be-10 calibration dataset for the region that combines the production rates of this study with those of Blard et al. (2013b) and Kelly et al. (2015). This dataset of three calibration sites shows a good consistency and yields a regional in situ Be-10 production rate of 3.74 +/- 0.09 at g(-1) yr(-1) using the same scaling. (C) 2015 Elsevier B.V. All rights reserved.

Abstract: The supply of glacier water to La Paz city, Bolivia, between 1963 and 2006 was assessed at annual and seasonal timescales based on the mass-balance quantification of 70 glaciers located within the drainage basins of La Paz. Glaciers contributed similar to 15% of water resources at an annual scale (14% in the wet season, 27% in the dry season). Uncertainties in our estimation are related to the assumed constant precipitation (similar to 0.5% for ice-free areas and up to 6.5% for glaciated areas), the constant runoff coefficient (similar to 1%), the surface areas of the glaciers and catchments (similar to 5%) and the mean mass-balance uncertainty of the 21 glaciers used to obtain the mass balance of the 70 glaciers (12% of the total discharge). Despite the loss of 50% of the glacierized area during the study period, runoff at La Paz did not change significantly, showing that increase in ice melt rates compensated for reduction in the surface area of the glaciers. In the future, assuming complete disappearance of the glaciers and no change in precipitation, runoff should diminish by similar to 12% at an annual scale, 9% during the wet season and 24% during the dry season.

Abstract: To improve both precision and accuracy of cosmic-ray exposure dating methods, there is a crucial need of calibration sites constraining the production rate of cosmogenic isotopes. This is particularly true in the high tropical area, where existing scaling models present significant discrepancies. This study presents a new calibration site for cosmogenic He-3, located at 3800 m in the tropical Altiplano (19.9 degrees S, 67.6 degrees W), on the southern flank of the Tunupa volcano, in the vicinity of the Salar de Uyuni. It consists in a fluvio-glacial outwash that is stratigraphically bracketed by two successive lacustrine shorelines. These shorelines are well-dated by C-14 and U-series dating (n = 57), allowing determination of the age of the boulder field at the surface of the delta, at 15.3 +/- 0.5 ka (let). Eleven andesitic boulders were sampled on this fluvio-glacial surface and the cosmogenic He-3 contents of their pyroxene phenocrysts and amphiboles was analyzed. The nucleogenic contribution from Li-6 capture is well-constrained by determining the (U-Th-Sm)/He-4 age of these rocks. This correction is minimal (<2%) and does not represent a significant source of uncertainty. Cosmogenic He-3 (He-c) concentrations are characterized by a very high reproducibility: 10 samples overlap within 10- analytical error. This suggests that pre- or post-deposition processes have minimal impact on the 3Hec data. Furthermore, there is no correlation between the Li and the He-3(c) content of the mineral, indicating that He-3(c) production from cosmogenic thermal neutron is here negligible. Combined with the absolute dating of the delta, these He-3(c) data yield a local production rate of 999 +/- 38 (1 sigma) at g(-1) yr(-1), at 3800 m and 19.89 S. After scaling with the time dependent scaling scheme of (Stone, 2000), this result yields a rate of 121 +/- 5 (1 sigma) at g(-1) yr(-1) at high latitude and sea level. This new calibration is the highest among the existing global dataset It will thus permit the establishment of new robust glacial chronologies in the high Tropics, with an uncertainty lower than 5% at 1 sigma. Such precision may have important implications in paleoclimatology, notably because it will allow comparison with other well-dated paleoclimatic archives. Including this new data, the updated global He-3(c) production rate is 122 +/- 15 at g(-1) yr(-1), using the time-dependent scaling of Stone (2000). The new site-specific He-3(c) production rate is used here to refine glacier fluctuations on Cerro Tunupa, confirming that the local last glacial maximum was synchronous with the Lake Tauca highstand (15.5 ka). Data also suggest that a dramatic glacial retreat occurred at about 15 ka, few hundred years before the Lake Tauca regression, synchronously with the onset of the Bolling-Allerod. (C) 2013 Elsevier B.V. All rights reserved.

Abstract: Hydro-sedimentology development is a great challenge in Peru due to limited data as well as sparse and confidential information. This study aimed to quantify and to understand the suspended sediment yield from the west-central Andes Mountains and to identify the main erosion-control factors and their relevance. The Tablachaca River (3132 km(2)) and the Santa River (6815 km(2)), located in two adjacent Andes catchments, showed similar statistical daily rainfall and discharge variability but large differences in specific suspended-sediment yield (SSY). In order to investigate the main erosion factors, daily water discharge and suspended sediment concentration (SSC) datasets of the Santa and Tablachaca rivers were analysed. Mining activity in specific lithologies was identified as the major factor that controls the high SSY of the Tablachaca (2204 t km(2) yr(-1)), which is four times greater than the Santa's SSY. These results show that the analysis of control factors of regional SSY at the Andes scale should be done carefully. Indeed, spatial data at kilometric scale and also daily water discharge and SSC time series are needed to define the main erosion factors along the entire Andean range.

Abstract: Understanding the climate dynamics in mountainous areas still remains a challenge. For Peruvian areas situated above 3000 m three aspects concerning the temperatures are developed with in-situ and NCEP NCAR Reanalysis from National Center for Environmental Prediction and National Center for Atmospheric Research (NNR) data: a) Based on in-situ temperature records of about 30 years for 27 stations, no trend was identified at 99% of confidence level in the Northern Andes (Cordillera Blanca y Negra) of Peru, contrary to regions in the south of Central Andes of Peru where it was identified local trends in the Andean valleys near to Vilcanota node with maximum values of 0.03 degrees C/year. b) Taking into account the importance of temperature and data scarcity in mountainous regions, in-situ records were compared with other data source such as NNR. The comparison was made according to the geographical location, the common periods of the records and grid coverage. We conclude that NNR at 700 hPa level (similar to 3000 m asl) and 600 hPa level (similar to 4000 m asl) offer an approximation to terrain elevation of stations, however that comparison has variations from 10 degrees C in Northern Andes to 0.4 degrees C in Central Andes. c) Considering the differences between in-situ and NNR data, a correction of NNR data is proposed with monthly regional lapse rate. The methodology considers the use of one base in-situ station into a NNR grid with an altitudinal gradient, thus we generate mean monthly temperatures records in other areas into the NNR grid. The reliability of corrections are evaluated is terms of the correlation coefficient and the root mean squared error and the results offer very acceptable results in Northern and Central Andes.

Abstract: This study provides new geochronological and stable isotope constraints on Late Pleistocene fluctuations in lake level that occurred in the closed-watershed of the Central Altiplano between similar to 25 and similar to 12 ka. U-series isochrons and C-14 ages from carbonates are used to confirm and refine the previous chronology published (Placzek et al., 2006b). Our new data support three successive lake highstands during the Late Pleistocene: (i) the lake Sajsi cycle, from similar to 25 to 19 ka, that culminated at 3670 m at about 22 ka, almost synchronously with the global last glacial maximum, (ii) the Lake Tauca cycle, that lasted from 18 to 14.5 ka and was characterized by the highest water level, reached at least 3770 m from 16.5 to 15 ka, (iii) the Lake Coipasa cycle, from 12.5 to 11.9 ka, that reached an elevation of similar to 3700 m, 42 m above the elevation of the Salar de Uyuni (3658 m). These high amplitude lake level fluctuations are in phase with the cold-warm oscillations that occurred in the North Atlantic and Greenland during the Late Pleistocene (Heinrich 1, Bolling-Allerod, Younger Dryas). Such temporal coincidence supports the hypothesis that wet events recorded in the Central Altiplano are controlled by the north-south displacement of the Inter Tropical Convergence Zone resulting from changes in the meridional temperature gradient. Finally, the oxygen isotope ratios measured in these lacustrine carbonates allows for calculation of the delta O-18 value of paleolake waters. Estimates of water delta O-18 (V-SMOW) are -2.8 +/- 0.7 parts per thousand for Lake Tauca and -1.6 +/- 0.9 parts per thousand, for Lake Coipasa. These data are used to constrain changes in lake hydrology and can be interpreted to indicate that the proportion of precipitation arising from local water recycling was less than 50%. (C) 2011 Elsevier Ltd. All rights reserved.