2011

Isotopic And Hydrochemical Investigations Of Snowmelt-Groundwater Interaction In An Alpine Watershed, Colorado Front Range

Anonymous — Mon, 20 Aug 2018 21:26:03 +0000

Isotopic And Hydrochemical Investigations Of Snowmelt-Groundwater Interaction In An Alpine Watershed, Colorado Front Range Anonymous (not verified) Mon, 08/20/2018 - 15:26 Morgan Zeliff

Zeliff, Morgan M. ¹ ; Williams, Mark ²

¹ University of Colorado
² University of Colorado

Stable isotopes and hydrochemical constituents of water were used to evaluate the role of groundwater in two high-elevation, snowmelt dominated areas of the Colorado Front Range: The 8-ha Martinelli catchment at 3,440 m and the nearby Saddle site at 3,530 m. The Martinelli site has three shallow (1.5 m) and 3 deep (> 6 m) piezometers, while the Saddle site has 4 sets of deep and shallow piezometers. All wells were screened for their bottom 1.5 m. All shallow piezometers had water only during snowmelt. In contrast, all deep piezometers had water year-round, with water depths generally deeper than 4 m during the winter and water rising to the surface during snowmelt, followed by a long recession limb. Starting in 2006, water samples were collected weekly to monthly from all piezometers, and for precipitation, snow, and surface water and analyzed for stable isotopes and major solute chemistry. The snowpack had a mean δ18O value of -20.43 ‰ (n = 52), ranging from -22 ‰ to -18 ‰ during snowmelt. The 4 per mil difference in δ18O during snowmelt was from fractionation of meltwater as it infiltrated through the snowpack. The mean δ18O value of -19.14 ‰ (n =299) for the piezometers at the Martinelli site did not differ significantly between shallow and deep piezometers (p = 0.1684), nor between the piezometers and either the snowpack or stream. In contrast, shallow and deep piezometers at the Saddle site were significantly more enriched than Martinelli with a mean δ18O value of -16.95 ‰ (p < 0.001, n = 417). A plot of the δ18O versus δD values from all wells along with the Global Meteoric Water Line (GMWL) provides evidence of depletion of these isotopes in the well waters. Mean calcium concentrations at the Martinelli piezometers (89 μeq L-1) were more than an order of magnitude more dilute when compared to mean values from the Saddle piezometers (1684 μeq L-1). Mean silicon concentrations are also significantly (p<0.001) more dilute at the Martinelli piezometers (62 μeq L-1) than mean concentrations from the Saddle piezometers (200 μeq L-1). These results, combined with hydrogeological information, suggest that the Martinelli catchment is an unconfined aquifer with direct hydrologic connection between surface waters and groundwaters and has a groundwater system dominated by direct snowmelt recharge. In contrast, groundwater at the Saddle site appears to be in a confined aquifer with a relatively long residence time and with no direct connection between piezometers and overlying snowmelt.

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Groundwater Flow Of A Proposed Uranium In-Situ Recovery Mine Site And Surrounding Areas, Weld County, Colorado

Anonymous — Mon, 20 Aug 2018 21:25:15 +0000

Groundwater Flow Of A Proposed Uranium In-Situ Recovery Mine Site And Surrounding Areas, Weld County, Colorado Anonymous (not verified) Mon, 08/20/2018 - 15:25 Miori Yoshino

Yoshino, Miori ¹ ; Ge, Shemin ²

¹ University of Colorado
² University of Colorado

Limited groundwater studies exist for aquifers in the Denver Basin north of the Greeley Arch. With continued proposals for uranium mining in this part of the basin, it is necessary to acquire a detailed understanding of groundwater flow in order to estimate impacts, if any, of in-situ mining processes. This study focuses on discerning groundwater flow at the proposed Centennial Project site and its surrounding areas in west-central Weld County, Colorado, by using a steady state, regional scale groundwater flow model and a local scale model in the proposed mining zone. Generalized stratigraphy of the Pierre Shale, the Fox Hills Formation, and Laramie Formation was simulated. Data from public well records of the Colorado Department of Water Resources were used for hydraulic head contour mapping and calibration. In the study area, recharge to groundwater is low, typical for non-irrigated or natural grasslands. The depth of the groundwater table varies between 3 m and 9 m below the surface. MODFLOW, a finite-difference numerical model, was used to simulate the background steady state groundwater conditions. Model calibration achieved a correlation coefficient of 0.891 between model hydraulic head and observed water level data. Groundwater in the study area flows mainly to the south and slightly east, although there are local exceptions to this general flow direction. Slug and bail tests conducted in low sandstones of the Laramie Formation yielded hydraulic conductivity between 9.2 x 10-7 m/s to 1.8 x 10-6 m/s. A multi-well aquifer pumping test in the Fox Hills Formation yielded hydraulic conductivity of 7.2 x 10-6 m/s. The Pierre Shale was assumed in the model to be equal to or less than 1.0 x 10-8 m/s. Results suggest the potential impact of uranium mining in the Fox Hills Formation on groundwater in areas overlying, underlying and downgradient of the proposed mining zone within the Laramie-Fox Hills aquifer is limited to the proposed mining zone boundaries during in-situ recovery.

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Impact Of Climate Change And Human Interference On The Evolution Of The Ebro Delta, Spain In The Last 2000 Year

Anonymous — Mon, 20 Aug 2018 21:24:29 +0000

Impact Of Climate Change And Human Interference On The Evolution Of The Ebro Delta, Spain In The Last 2000 Year Anonymous (not verified) Mon, 08/20/2018 - 15:24 Fei Xing

Xing, Fei ¹ ; Kettner, Albert J. ² ; Hannon, Mark T. ³

¹ CSDMS Integration Facility, INSTAAR, University of Colorado, Boulder
² CSDMS Integration Facility, INSTAAR, University of Colorado, Boulder
³ CSDMS Integration Facility, INSTAAR, University of Colorado, Boulder

The Ebro Delta, one of the largest wetland areas (320 km²) in the western Mediterranean region, has undergone a series of complicated stages since its formation about 6000 years ago, due to changes in climate and human impacts. For example, an intensification of precipitation leads often to an increase in fluvial sediment load that gets transported to a deltaic area and visa versa. The Ebro Delta is no exception in this as climate varied over the last 2000 years. On the other hand, human impact on the drainage basin started as early as the Roman times by deforestation of large areas. Most likely this human interference in the form of deforestation increased the delta progression rate as well, that together with changes in climate led to the current shape of the Ebro Delta (Canicio, A. and Ibanez, C., 1999). In the last 50 to 60 years dams and reservoir construction for energy and irrigation purposes, are trapping more than 99% of fluvial sediment (Tena et al., 2010), which might result in the recession of the Ebro delta in the nearby future.

In order to explore the extent of climate change and human impact on the evolution of the delta, two models were applied to simulate the Ebro Basin and delta for the last 2000 years. HydroTrend, a climate-driven hydrological transport model is used to reproduce the freshwater and sediment flux to the delta, and subsequently a coastline evolution model (CEM) is applied to simulate the according changes in delta and coastal line morphology. A model-coupling tool CMT, is used to join the two models for this study. Validation of the HydroTrend model for the last 50 years indicates that the hydrological model is able to mimic the observed water discharge and sediment loads. Confident that the hydrological model can reproduce the water and sediment flux to the deltaic area, historical climate data and human impact information is applied to simulate the fluvial signal to the delta for the last 2000 years. Preliminary results indicate that given our model input assumptions, the sediment flux to the ocean follows the trend of climate change, but is increasingly influenced by human interference over time, by an order of magnitude. Human interference is first noticeable by devastating deforestation rates that significantly increased the sediment flux to the deltaic area and thereafter by the construction of dams and reservoirs that consequently let to a dramatic decrease of sediment flux to the ocean (Fig.1). At the same time, climate sensitive analysis shows that river discharge is defined by precipitation, while the sediment flux seems to express a larger correlation with temperature change, however humans due have the most significant impact on changes in sediment flux.

Tena,A., Batalla,R.J.,Vericat,D.,López-Tarazón,J.A.,2010. Suspended sediment dynamics in a large regulated river over a 10-year period (the lower Ebro, NE Iberian Peninsula): Geomorphology, v.125,p.73-84.
Canicio,A.and Ibanez,C.,1999.The Holocene Evolution of the Ebro Delta,Catalonia,Spain:Acta Geographica Sinica,v.54,p.462-469.

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Groundwater And Groundwater Recharge In Mountain Hydrology

Anonymous — Mon, 20 Aug 2018 21:23:12 +0000

Groundwater And Groundwater Recharge In Mountain Hydrology Anonymous (not verified) Mon, 08/20/2018 - 15:23 John L Wilson

Wilson, John L ¹

¹ New Mexico Institute of Mining and Technology

The traditional hydrologic view of western mountains was constrained by the notion that the only significant natural water storage in mountains is snowpack, giving less attention to soil water storage, and essentially ignoring the role of groundwater. The only significant pathway for transmitting water through mountains was considered to be stream flow. Groundwater’s only role was as a contributor to stream base flow, which was empirically characterized through base flow separation calculations. Bedrock constitutes the bulk of a mountains mass, and this traditional view was conditioned by bedrock’s apparent imperviousness. That view has changed over the last fifteen years, and a much larger role for groundwater has emerged, both of processes within the mountain itself, and of mountains as a source of water to adjacent basins. A full view of the mountain system includes the entire mountain block, not just the thin veneer of soil and vegetation covering the bedrock. It includes the focused flow of mountain stream channels, but also the diffuse and focused movement of groundwater through fractured and faulted bedrock and, in sedimentary and certain volcanic rocks, through the rock matrix itself. This paper discusses this emerging view by reference to studies throughout the western states, with many of those studies aimed at the source of mountain groundwater, that is deep percolation into the bedrock from the shallow soil mantle, and a few aimed at how the recharge from deep percolation moves through the mountain block to eventually discharge at lower mountain streams or even the mountain front.

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Simulating The Effect Of Matrix Diffusion In Fractured Porous Media With Dual Domain Mass Transfer: A Modeling Comparison

Anonymous — Mon, 20 Aug 2018 21:20:50 +0000

Simulating The Effect Of Matrix Diffusion In Fractured Porous Media With Dual Domain Mass Transfer: A Modeling Comparison Anonymous (not verified) Mon, 08/20/2018 - 15:20 Matthew Weingarten

Weingarten, Matthew ¹ ; Hsieh, Paul ²

¹ University of Colorado at Boulder, Boulder, CO, USA
² U.S. Geological Survey, Menlo Park, CA, USA

Solute transport through fractured porous rocks can be described by advective-dispersive transport through the fractures and diffusive transport through the unfractured matrix. The effect of matrix diffusion is to reduce the effective solute velocity in the fracture until the matrix storage capacity has been reached. A model comparison between (1) fully simulating advection-dispersion in fractures and diffusive transport in the matrix and (2) the dual-domain mass transfer (DDMT) approach is presented. Numerous case studies of contaminant transport in highly fractured or heterogeneous media have shown that the DDMT model may improve model calibration at the field scale. The simulations are compared for a simple case involving solute transport through a single fracture and the matrix diffusion associated with this transport. Solute injection to the domain is varied to study the model responses to continuous injection and pulse injection under a variety of matrix porosities and dispersivities. This study finds the best-fit mass transfer rate coefficients under these various aquifer conditions at the very near field scale.

Grisak, G. E., J. F. Pickens, 1980, Solute transport through fractured media, 1, The effect of matrix diffusion: Water Resources Research, v. 16(4), pp. 719-730.
Zheng, C., and P.P. Wang, 1999, MT3DMS: A modular three-dimensional multispecies model for simulation of advection, dispersion and chemical reactions of contaminants in groundwater systems: Documentation and user's guide: Contract Rep. SERDP-99-1, U.S. Army Eng. Res. and Dev. Cent., Vicksburg, Miss.

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Middle Holocene Natural Variability Of Temperature And Salinity In The North Atlantic Ocean, Southwest Of Iceland

Anonymous — Mon, 20 Aug 2018 21:19:04 +0000

Middle Holocene Natural Variability Of Temperature And Salinity In The North Atlantic Ocean, Southwest Of Iceland Anonymous (not verified) Mon, 08/20/2018 - 15:19 Vivian R Underhill

Underhill, Vivian R ¹

¹ University of Colorado

With rising global temperatures, a major concern is that fresh water from melting glaciers and the Greenland ice sheet will slow down global oceanic circulation patterns, in particular the North Atlantic Current (NAC). The NAC, an extension of the Gulf Stream, carries warm, saline Atlantic waters north to mix with cold, fresh Arctic water. It then cools and sinks, forming the North Atlantic Deep Waters and the deep limb of thermohaline circulation (Broecker et al, 1985).

I investigated a marine sediment core collected off the southwest coast of Iceland (see Fig. 1) to reconstruct conditions during the mid-Holocene (4,000-8,000 years ago). This epoch is important because it is the only time when the North Atlantic oceanic circulation was not being influenced by freshwater melting from nearby ice sheets, which inhibits deep water formation (Broecker et al, 1985). This allows me to research the natural variability of NAC water-mass characteristics, such as temperature and salinity, in the absence of addition of external freshwater. Knowing more about North Atlantic circulation without additional fresh water will help predict the effects of increased freshwater forcing.

To do this, I am using the oxygen isotopic composition and magnesium/calcium ratios in the calcium carbonate shells of a benthic foraminiferal species, Cassidulina laevigata, a single-celled organism that lives in the upper few centimeters of ocean sediments. When precipitating their shells, foraminifera preferentially take up the isotope Oxygen-16, but can also use the heavier Oxygen-18. The ratio of Oxygen-16 and Oxygen-18 incorporated into the shells is correlated with both water temperature and salinity (Katz et al, 2010). The Mg/Ca ratio is a function only of temperature, with a higher ratio correlated with higher temperatures. I use this ratio, a relatively new development in the field (Katz et al, 2010), to separate temperature and salinity components of the δ18O signal and obtain far more accurate results than were possible in the past. (See Fig. 2). Preliminary results of these analyses will be ready to be presented by mid-March.

Broecker, W.S., Peteet, D.M., Rind, D, 1985, Does the ocean-atmosphere system have more than one stable mode of operation?: Nature, v. 315, p. 21-26.
Jennings, A.E., Hald, M., Smith, M., & Andrews, J.T, 2006, Freshwater forcing from the Greenland ice sheet during the Younger Dryas: evidence from Southeastern Greenland shelf cores: Quaternary Science Review, v. 25, p. 282-298.
Katz, M.E., Cramer, B.S., Franzese, A., Honisch, B., Miller, K.G., Rosenthal, Y., Wright, J.D, 2010, Traditional and Emerging Geochemical Proxies in Foraminifera: Journal of Foraminiferal Research, v. 40, p. 165-192.

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Variations In Summertime Sea Ice Along The Chukchi Coast Since 1849

Anonymous — Mon, 20 Aug 2018 21:17:50 +0000

Variations In Summertime Sea Ice Along The Chukchi Coast Since 1849 Anonymous (not verified) Mon, 08/20/2018 - 15:17 Vivian R Underhill

Underhill, Vivian R ¹ ; Wood, Kevin R ² ; Mahoney, Andy ³

¹ University of Colorado, Environmental Sciences Department
² Joint Institute for the Study of the Atmosphere and Ocean
³ University of Alaska, Geophysical Institute

The amount of sea ice remaining in the Chukchi Sea by the September summer minimum has shrunk dramatically over the last ten years. This decrease is even more striking when compared to historical reports describing heavy sea ice along the Siberian coast and extending into the western Bering Strait through September. We reconstructed a simple index of sea ice presence along the Chukchi coast based on historical observations. This index shows that late-summer sea ice has appeared along the coast with some frequency since 1849 but has not been present since 1998. Its appearance is linked to northwesterly winds and varies on synoptic to decadal time scales. Its recent disappearance is probably due to decreases in the multi-year sea ice fraction in the vicinity of Wrangell Island. Since both the coastal ice belt and the intermittent Siberian Coastal Current (SCC) can be related to similar wind fields, it is possible that our index may be a proxy for the SCC. Documenting longer-term variations in sea ice distribution allows us to show how unusual current ecosystem changes may be.

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The Hard Rock Café: Nutrient And Energy Sources Supporting The Deep Terrestrial Biosphere In Colorado

Anonymous — Mon, 20 Aug 2018 21:16:14 +0000

The Hard Rock Café: Nutrient And Energy Sources Supporting The Deep Terrestrial Biosphere In Colorado Anonymous (not verified) Mon, 08/20/2018 - 15:16 Elizabeth D Swanner

Swanner, Elizabeth D ¹ ; Templeton, Alexis S ²

¹ University of Colorado
² University of Colorado

It is now established that microbial life inhabits pore spaces and fractures deep within the solid rock of our continents. However, the nutrient and energy sources that support the deep terrestrial biosphere remain largely unconstrained. The Henderson Molybdenum Mine near Empire, CO is a hard rock laboratory for the study of life in granite. We used a geochemical approach to quantify the inorganic energy sources available to microbes in Henderson subsurface fluids and to predict which reactions should support life. Culturing campaigns revealed that as predicted, metal-oxidizing metabolisms are common. Detailed study of an Fe-oxidizing isolate delineated biological and geochemical controls over the formation of Fe minerals that sequester nutrients and metals, and may serve as electron donors for Fe-reducing bacteria in situ.

Our geochemical dataset led us to question the origin of certain nutrients, particularly nitrogen. The presence of nitrogen in multiple oxidation states (NO₃-, NO₂-, NH₄+) in subsurface fluids further suggested that nitrogen was not only a nutrient but an energy source. Due to the higher abundance of NH₄+ in the most metal-rich fluids, we hypothesized NH₄+ was sourced from water-rock interaction with NH₄+-bearing biotite. However, FTIR analyses of biotites from drill cores did not detect NH₄+. Concomitantly, we amplified N₂-fixing genes (nifH) from a metal-rich fluid DNA sample. Further amplification of archaeal ammonium-oxidation genes (amoA) from the sample confirmed that biologically-fixed nitrogen likely drives the subsurface nitrogen cycle that was predicted from our geochemical calculations. These genes were only detected in the metal-rich fluid samples, suggesting the abundance of Mo, V and other metals required for nitrogen cycling enzymes may select the microbial community.

Our findings demonstrate the utility of paired geochemical, microbiological and molecular methods for unraveling the nutrient and energy sources supporting this biosphere. At Henderson, metal oxidation appears to be a major energy source, and the mineral products can in turn supply oxidants to metal-reducing organisms. Metals may also select for N₂-fixing organisms that support the nutritional and energetic demands of the biosphere. This is the first demonstrated example of Fe-oxidation supporting deep subsurface life, and the first investigation of the origin of nitrogen to the subsurface biosphere.

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Compressing The Cotton Glacier Project: Attempting To Explain Two-Years Of Complex Multi-Disciplinary Research To Just �鶹��Ƶ Anyone, In Less Than Two Minutes.

Anonymous — Mon, 20 Aug 2018 21:14:54 +0000

Compressing The Cotton Glacier Project: Attempting To Explain Two-Years Of Complex Multi-Disciplinary Research To Just �鶹��Ƶ Anyone, In Less Than Two Minutes. Anonymous (not verified) Mon, 08/20/2018 - 15:14 Michael D SanClements

SanClements, Michael D ¹ ; McKnight, Diane M ² ; Foreman, Christine M ³

¹ INSTAAR, University of Colorado at Boulder
² INSTAAR, University of Colorado at Boulder
³ Montana State University

While in Antarctica this year I was afforded the opportunity to create a two minute audio postcard for The New York Times website explaining our research and life in Antarctica. This turned out to be very difficult. How do you summarize two years of research and life in Antarctica for a general audience in two minutes? Here is a summary of the project:

Antarctica provides a unique natural environment for the study of dissolved organic matter (DOM). The absence of vascular plants results in an organic carbon pool derived from microbial sources (McKnight et al., 2001). While terrestrial waters in the dry valleys of Antarctica provide valuable insight into the composition of autochthonous organic matter, the Cotton Glacier is a unique system for studying the origins of DOM (Aiken et al., 1996; Foreman et al., In review). The Cotton Glacier fluvial system is extremely dynamic, resulting in little or no accumulation of recalcitrant and humic carbon on a yearly basis, making it ideal for the study of autochthonous DOM precursors.

Throughout the 2009-2010 and 2010-2011 austral summers we sampled the Cotton Glacier Stream ten times. As a comparison, Canada Stream, a terrestrial stream in the McMurdo Dry Valleys was also sampled. Waters from both sites were analyzed for dissolved organic carbon (DOC), base cations, anions, and number of microbiological measurements. Reverse osmosis (RO) was employed to concentrate and isolate DOM from stream waters. UV-VIS and excitation-emission fluorescence spectroscopy were used to infer the composition of DOM in whole waters and RO concentrates.

During the 2010-2011 field season we used a combination of methods to collect data on the hydrology of the supraglacial Cotton Stream. These methods included deployment of a meteorological station, time-lapse photography, satellite imagery, and flow and depth monitoring.

Results from the two field seasons reveal systems with low DOC concentrations, generally ~1 mg L-1 in both Cotton and Canada streams. UV-VIS and fluorescence spectroscopy indicate a unique and transient DOM signature in waters of the Cotton Glacier, while DOM from Canada Stream revealed a more stable refractory organic matter pool. Cotton Glacier waters lacked a humic signature but over time (days) changes in the fluorescence signature demonstrated a shift toward characteristics more commonly found in DOM of other natural waters (i.e., the formation of humic peaks).

Temperature and solar radiation appear to exert significant influence on the daily flow regime but were not the dominant factor in driving extreme changes in hydrology during the summer. Data suggests the flow regimes of supraglacial streams are controlled by a complex relationship between geomorphology and meteorology which may result in a decoupling of flow, temperature, and radiation.

McKnight, D. M., E. W. Boyer, P. K. Westerhoff, P. T. Doran, T. Kulbe, and D. T. Andersen. Limnology and Oceanography, 2001; 46:38-48.
Foreman, C. M., C. E. Morris, R. M. Cory, J. T. Lisle, P. L. Miller, Y.-P. Chin, and D. M. McKnight. Journal of Geophysical Research, In review.
Aiken, G., D. McKnight, R. Harnish, and R. Wershaw. Biogeochemistry, 1996; 34:157-188.

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21st Century Precipitation Trend For Swiss River Basins

Anonymous — Mon, 20 Aug 2018 21:13:40 +0000

21st Century Precipitation Trend For Swiss River Basins Anonymous (not verified) Mon, 08/20/2018 - 15:13 James V Rudolph

Rudolph, James V ¹ ; Friedrich, Katja ²

¹ University of Colorado, Dept. of Atmospheric and Oceanic Sciences (ATOC)
² University of Colorado, Dept. of Atmospheric and Oceanic Sciences (ATOC)

A 21st century precipitation forecast for seven Swiss river basins is generated by linking high resolution (2 x 2 km2) radar-estimated precipitation observations to a global climate model (GCM) via synoptic weather patterns. The use of synoptic patterns characterizes the effect of changes in large scale circulation, or dynamic effects, on expected precipitation. In each basin observed total daily precipitation received during advective synoptic patterns is shown to be dependent on the basin’s general topographic aspect. Across all basins convective synoptic patterns follow the same trend in total daily precipitation with cyclonic patterns consistently producing a larger amount of precipitation than anticyclonic patterns. Identification of synoptic patterns from a GCM for the 21st century (Community Climate System Model Version 3.0, CCSM3) shows increasing frequency of anticyclonic synoptic patterns, decreasing frequency of cyclonic patterns, and constant frequency of advective patterns over Switzerland. When coupled with observed radar-estimated precipitation for each synoptic pattern, the changes in synoptic pattern frequencies result in an approximately 10-15% decrease in decadal precipitation over the course of the 21st century for seven Swiss river basins. The study results also show an insignificant change in the future (21st century) probability of exceeding the current (2000-2008) 95th quantile of total precipitation. The lack of a trend in exceeding the 95th quantile of precipitation in combination with a decreasing trend in total precipitation provides evidence that dynamic effects will not result in increased frequency of heavy precipitation events, but that heavy precipitation will account for a greater proportion of total precipitation in Swiss river basins by the end of the 21st century.

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