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Global warming is shifting the thermal dynamics of lakes, with resulting climatic variability heavily affecting their mixing dynamics. We present a dual ensemble workflow coupling climate models with lake models. We used a large set of simulations across multiple domains, multi‐scenario, and multi GCM‐ RCM combinations from CORDEX data. We forced a set of multiple hydrodynamic lake models by these multiple climate simulations to explore climate change impacts on lakes. We also quantified the contributions from the different models to the overall uncertainty. We employed this workflow to investigate the effects of climate change on Lake Sevan (Armenia). We predicted for the end of the 21st century, under RCP 8.5, a sharp increase in surface temperature (4.3±0.7K) $(4.3\pm 0.7\,\mathrm{K})$ and substantial bottom warming (1.7±0.7K) $(1.7\pm 0.7\,\mathrm{K})$, longer stratification periods (+55 days) and disappearance of ice cover leading to a shift in mixing regime. Increased insufficient cooling during warmer winters points to the vulnerability of Lake Sevan to climate change. Our workflow leverages the strengths of multiple models at several levels of the model chain to provide a more robust projection and at the same time a better uncertainty estimate that accounts for the contributions of the different model levels to overall uncertainty. Although for specific variables, for example, summer bottom temperature, single lake models may perform better, the full ensemble provides a robust estimate of thermal dynamics that has a high transferability so that our workflow can be a blueprint for climate impact studies in other systems. Plain Language Summary: Lakes are threatened by climate change because of effects related to the increasing temperature, long stratification, and ice disappearance. One of the best tools to predict these effects on lakes is numerical modeling of lakes that benefit from climate modeling. Climate modeling is normally done globally or in the so‐called general circulation model (GCM) or more detailed simulations on regional levels (RCM) like the CORDEX data set. In this study, we used the CORDEX data, which employed several climate models from several regions (domains) for several climatic scenarios (emissions scenarios) to force multiple lake models. This approach gave us an extensive prediction about various possible outputs. We applied this approach to Lake Sevan (Armenia), a large mountain lake. Our study predicted for the worst‐case scenario, an increase of the surface temperature by almost 4.3 K by the end of the 21st century, 1.75 K for bottom temperature, a total disappearance of ice cover, and about 55 extra days of stratification, showing its vulnerability for climate change. This optimized workflow uses the strength of a wide variety of models on the climate and lake levels to better understand the impact of climate change and quantify the sources of uncertainty in the workflow. Key Points: Dual multi‐model ensemble of climate data and lake models is used for robust projections of climate change impactsVariance decomposition effectively identified the sources of uncertainty and contributions of different models to the overall uncertaintySignificant warming, longer stratification periods, and loss of ice cover are predicted for Lake Sevan by the end of the 21st century [ABSTRACT FROM AUTHOR]

Turbulent and radiative energy exchanges between lakes and the atmosphere play an important role in determining the process of lake‐mixing and stratification, including how lakes respond to climate and to climate change. Here we used a one‐dimensional hydrodynamic lake model to assess seasonal impacts of climate change on individual surface heat flux components in Lough Feeagh, Ireland, a deep, monomictic lake. We drove the lake model with an ensemble of outputs from four climate models under three future greenhouse gas scenarios from 1976 to 2099. In these experiments, the results showed significant increases in the radiative budget that were largely counteracted by significant increases in the turbulent fluxes. The combined change in the individual surface heat fluxes led to a change in the total surface heat flux that was small, but sufficient to lead to significant changes in the volume‐weighted average lake temperature. The largest projected changes in total surface heat fluxes were in spring and autumn. Both spring heating and autumnal cooling significantly decreased under future climate conditions, while changes to total surface heat fluxes in winter and summer were an order of magnitude lower. This led to counter‐intuitive results that, in a warming world, there would be less heat not more entering Lough Feeagh during the springtime, and little change in net heating over the summer or winter compared to natural climate conditions, projected increases in the volume‐weighted average lake temperature were found to be largely due to reduced heat loss during autumn. Plain Language Summary: The exchange of energy between the lake and the atmosphere is important to understand how atmospheric forcing affects the vertical thermal structure of lakes, especially in an era of climate change. Here, we perform a lake model experiment to better understand how surface heat fluxes in Lough Feeagh (Ireland) will respond to future greenhouse gas emissions. Our results suggest that surface heat fluxes will change substantially in the future as a result of the changes in the atmospheric forcing. Lake heating by net radiative fluxes will increase and will be nearly offset by lake heat loss trough turbulent fluxes increase. This small positive imbalance in surface heat fluxes will lead to an increase in lake water temperature. On a seasonal scale, spring and autumn will show the largest changes in net surface heat flux, both the spring heating and autumnal cooling will decrease, while summer and winter will show very little change in net surface heat flux. This leads to the counter‐intuitive results that in a warming world there will be less heat, not more, entering Lough Feeagh during the spring, and that decreased heat loss during autumn will be largely responsible for the long‐term changes in lake water temperature. Key Points: Future projections of surface heat fluxes in Lough Feeagh under different emission scenariosSignificant increases in the annual mean radiative balance were largely offset by significant increases in the annual mean turbulent fluxesBoth spring heating and autumnal cooling significantly decreased under future climate conditions [ABSTRACT FROM AUTHOR]

The dynamics of vertical mixing and the occurrence of basin-scale internal waves (internal seiches) in lakes and reservoirs are often classified and described based on the force balance of wind shear and horizontal pressure gradients resulting from wind-generated currents (the Wedderburn number). The classification schemes consider specific time scales that are derived based on a simplified vertical density distribution, a rectangular basin shape, and a constant water depth. Using field measurements and numerical simulations with a validated hydrodynamic model, we analyzed the transfer of energy from wind to the internal seiche field in a small reservoir. Our results demonstrate that the basin shape has a strong influence on the energy dissipation and on the transfer of energy to propagating high-frequency internal waves, thereby attenuating the generation of basin-scale internal seiches. Most of the energy loss of the internal seiche occurs at the sloping boundary, where the internal seiche is susceptible to shoaling and breaking. These findings suggest that the Wedderburn number can be used to predict the occurrence of internal seiche activity in continuously stratified systems. As the Wedderburn number and derived mixing classifications are widely applied also for the interpretation of observed ecological and biogeochemical processes, its application to basins with sloping bathymetry and complex shape should be critically scrutinized, and deviations from predicted dynamics, including the presence of hotspots of turbulent mixing, should be considered. Key points: The interaction of internal seiches with a sloping bottom is the primary mechanism in inhibiting the generation of internal seiches by promoting strong vertical mixing near the lakeshore Lake shape and its influence on the mean flow acts as a secondary mechanism to inhibit the generation of internal seiches by promoting the formation of high-frequency internal waves Sloping bottom and vertically distributed density gradients promote the generation of internal seiches of higher vertical modes [ABSTRACT FROM AUTHOR]

ABSTRACT Modeling catchment-lake interactions is computationally demanding, usually requiring coupled numerical models and parallel processing capabilities. However, models with these requirements are still rare. In this paper, we developed a coupled 2D-3D model for lake catchments using a parallel scheme that leverages processing power of GPU and multiple CPUs. The model allows for hydrodynamic simulation applications considering diffuse water flows at the interface between the catchment and the lake. We coupled the Environmental Fluid Dynamics Code (EFDC) with a two-dimensional shallow water model and test it on the Peri Lake Catchment in southern Brazil. The results revealed the ability of the model simulate lake water levels as well as the diffuse inputs of water and solutes, providing the possibility of its use in lake and reservoir water management.

Lakes Azuei (LA) and Enriquillo (LE) on Hispaniola Island started expanding in 2005 and continued to do so until 2016. After inundating large swaths of arable land, submerging a small community, and threatening to swallow a significant trade route between the Dominican Republic and Haiti; worries persisted at how far this seemingly unstoppable expansion would go. The paper outlines the approach to a look forward to answer this question vis-à-vis climate change scenarios developed by the Intergovernmental Panel on Climate Change (IPCC). It uses numerical representations of the two lakes, and it examines how the lakes might evolve, deploying three different forcing mechanisms: that of weather and drift due to climate change, that of extreme events, such as hurricanes, and that of anthropogenic impacts, such as unintended water transfers between adjacent watersheds. Runs are executed Monte Carlo style using 11 different forcing combinations, each with a thousand instances of results generated by varying the numerous parameters that define the numerical models. The results are necessarily not precise and vary significantly as the forecast horizon expands, creating expanding envelopes of outcomes. Although some outcomes suggest a continued rise of the lake levels, most scenarios yield a reduction and recession of the lake waters. [ABSTRACT FROM AUTHOR]

Water quality in tropical rivers is changing rapidly. The ongoing boom of dam construction for hydropower is one of the drivers for this change. In particular, the stratification in tropical reservoirs induces oxygen deficits in their deep waters and warmer surface water temperatures, which often translate into altered thermal and oxygen regimes of downstream river systems, with cascading consequences for the entire aquatic ecosystem. Operation rules of reservoirs, involving water intakes at different levels, could mitigate the consequences for downstream water quality. However, optimized water management of deep reservoirs relies on predictive models for water quality, but such predictive capability is often lacking for tropical dams. Here we focus on the Zambezi River Basin (southern Africa) to address this gap. Using the one‐dimensional General Lake Model, we reproduced the internal dynamics of the transboundary Lake Kariba, the world's largest artificial lake by volume, created by damming the Zambezi River at the border between Zambia and Zimbabwe. Through this modeling approach, we assessed and quantified the thermal and oxygen alteration in the Zambezi River downstream of the reservoir. Results suggest that these alterations depend directly on Kariba's stratification dynamics, its water level and the transboundary policies for water withdrawal from the reservoir. Scenario calculations indicate a large potential for mitigating downstream water quality alterations by implementing a hypothetical selective withdrawal technology. However, we show that a different and cooperative management of the existing infrastructure of Kariba Dam has the potential to mitigate most of the actual water quality alterations. Key Points: We reproduced water temperature and dissolved oxygen dynamics in the transboundary hydropower reservoir, Kariba, using a 1‐D modelHydropower operations and lake mixing behavior drive unnatural alterations to downstream river water temperature and dissolved oxygenPotential management strategies to improve downstream water quality include selective withdrawal technology and transboundary cooperation [ABSTRACT FROM AUTHOR]

Lakes Azuei (LA) and Enriquillo (LE) on Hispaniola Island started expanding in 2005 and continued to do so until 2016. After inundating large swaths of arable land, submerging a small community, and threatening to swallow a significant trade route between the Dominican Republic and Haiti; worries persisted at how far this seemingly unstoppable expansion would go. The paper outlines the approach to a look forward to answer this question vis-à-vis climate change scenarios developed by the Intergovernmental Panel on Climate Change (IPCC). It uses numerical representations of the two lakes, and it examines how the lakes might evolve, deploying three different forcing mechanisms: that of weather and drift due to climate change, that of extreme events, such as hurricanes, and that of anthropogenic impacts, such as unintended water transfers between adjacent watersheds. Runs are executed Monte Carlo style using 11 different forcing combinations, each with a thousand instances of results generated by varying the numerous parameters that define the numerical models. The results are necessarily not precise and vary significantly as the forecast horizon expands, creating expanding envelopes of outcomes. Although some outcomes suggest a continued rise of the lake levels, most scenarios yield a reduction and recession of the lake waters.

Abstract: Climate change may have notable impacts on carbon cycling in freshwater ecosystems, especially in the boreal zone. Higher atmospheric temperature and changes in annual discharge patterns and carbon loading from the catchment affect the thermal and biogeochemical conditions in a lake. We developed an extension of a one‐dimensional process‐based lake model MyLake for simulating carbon dioxide (CO2) dynamics of a boreal lake. We calibrated the model for Lake Kuivajärvi, a small humic boreal lake, for the years 2013–2014, using the extensive data available on carbon inflow and concentrations of water column CO2 and dissolved organic carbon. The lake is a constant source of CO2 to the atmosphere in the present climate. We studied the potential effects of climate change‐induced warming on lake CO2 concentration and air‐water flux using downscaled air temperature data from three recent‐generation global climate models with two alternative representative concentration pathway forcing scenarios. Literature estimates were used for climate change impacts on the lake inflow. The scenario simulations showed a 20–35% increase in the CO2 flux from the lake to the atmosphere in the scenario period 2070–2099 compared to the control period 1980–2009. In addition, we estimated possible implications of different changes in terrestrial inorganic and organic carbon loadings to the lake. The scenarios with plausible increases of 10% and 20% in CO2 and dissolved organic carbon loadings, respectively, produced increases of 2.1–2.5% and 2.2–2.3% in the annual CO2 flux. [ABSTRACT FROM AUTHOR]

We evaluate the performance of the regional climate model (RCM) RegCM4 coupled to a one dimensional lake model for Lake Malawi (also known as Lake Nyasa in Tanzania and Lago Niassa in Mozambique) in simulating the main characteristics of rainfall and near surface air temperature patterns over the region. We further investigate the impact of the lake on the simulated regional climate. Two RCM simulations, one with and one without Lake Malawi, are performed for the period 1992-2008 at a grid spacing of 10 km by nesting the model within a corresponding 25 km resolution run (“mother domain”) encompassing all Southern Africa. The performance of the model in simulating the mean seasonal patterns of near surface air temperature and precipitation is good compared with previous applications of this model. The temperature biases are generally less than 2.5 °C, while the seasonal cycle of precipitation over the region matches observations well. Moreover, the one-dimensional lake model reproduces fairly well the geographical pattern of observed (from satellite measurements) lake surface temperature as well as its mean month-to-month evolution. The Malawi Lake-effects on the moisture and atmospheric circulation of the surrounding region result in an increase of water vapor mixing ratio due to increased evaporation in the presence of the lake, which combines with enhanced rising motions and low-level moisture convergence to yield a significant precipitation increase over the lake and neighboring areas during the whole austral summer rainy season. [ABSTRACT FROM AUTHOR]

Summary Climate change and intense land use practices are the main threats to ecosystem structure and services of Mediterranean lakes. Therefore, it is essential to predict the future changes and develop mitigation measures to combat such pressures. In this study, Lake Beyşehir, the largest freshwater lake in the Mediterranean basin, was selected to study the impacts of climate change and various land use scenarios on the ecosystem dynamics of Mediterranean freshwater ecosystems and the services that they provide. For this purpose, we linked catchment model outputs to the two different processed-based lake models: PCLake and GLM-AED, and tested the scenarios of five General Circulation Models, two Representation Concentration Pathways and three different land use scenarios, which enable us to consider the various sources of uncertainty. Climate change and land use scenarios generally predicted strong future decreases in hydraulic and nutrient loads from the catchment to the lake. These changes in loads translated into alterations in water level as well as minor changes in chlorophyll a (Chl- a ) concentrations. We also observed an increased abundance of cyanobacteria in both lake models. Total phosphorus, temperature and hydraulic loading were found to be the most important variables determining cyanobacteria biomass. As the future scenarios revealed only minor changes in Chl- a due to the significant decrease in nutrient loads, our results highlight that reduced nutrient loading in a warming world may play a crucial role in offsetting the effects of temperature on phytoplankton growth. However, our results also showed increased abundance of cyanobacteria in the future may threaten ecosystem integrity and may limit drinking water ecosystem services. In addition, extended periods of decreased hydraulic loads from the catchment and increased evaporation may lead to water level reductions and may diminish the ecosystem services of the lake as a water supply for irrigation and drinking water. [ABSTRACT FROM AUTHOR]

Climate disrupts aquatic ecosystems directly through changes in temperature, wind, and precipitation, and indirectly through watershed effects. Climate-induced changes in northern lakes include longer ice-free season, stronger stratification, browning, shifts in algae, and more cyanobacterial blooms. We compared retrospective temperature-depth relationships modeled using MINLAKE2012 with biogeochemical changes recorded in sediment cores. Four lakes in Voyageurs National Park (VOYA) and four lakes in Isle Royale National Park (ISRO) were studied. Meteorological data from International Falls and Duluth, Minnesota, were used for VOYA and ISRO, respectively. Model output was processed to analyze epilimnetic and hypolimnetic water temperatures and thermal gradients between two periods (1962-1986, 1987-2011). Common trends were increased summer epilimnion temperatures and, for deep lakes, increased frequency and duration of thermoclines. Changes in diatom communities differed between shallow and deep lakes and the parks. Based on changes in benthic and tychoplanktonic communities, shallow lake diatoms respond to temperature, mixing events, pH, and habitat. Changes in deep lakes are evident in the deep chlorophyll layer community of Cyclotella and Discostella species, mirroring modeled changes in thermocline depth and stability, and in Asterionella and Fragilaria species, reflecting the indirect effects of in-lake and watershed nutrient cycling and spring mixing. [ABSTRACT FROM AUTHOR]

The GLEON Research And PRAGMA Lake Expedition-GRAPLE-is a collaborative effort between computer science and lake ecology researchers. It aims to improve our understanding and predictive capacity of the threats to the water quality of our freshwater resources, including climate change. This paper presents GRAPLEr, a distributed computing system used to address the modeling needs of GRAPLE researchers. GRAPLEr integrates and applies overlay virtual network, high-throughput computing, and WEB service technologies in a novel way. First, its user-level IP-over-P2P overlay network allows compute and storage resources distributed across independently administered institutions (including private and public clouds) to be aggregated into a common virtual network, despite the presence of firewalls and network address translators. Second, resources aggregated by the IP-over-P2P virtual network run unmodified high-throughput-computing middleware to enable large numbers of model simulations to be executed concurrently across the distributed computing resources. Third, a WEB service interface allows end users to submit job requests to the system using client libraries that integrate with the R statistical computing environment. The paper presents the GRAPLEr architecture, describes its implementation and reports on its performance for batches of general lake model simulations across 3 cloud infrastructures (University of Florida, CloudLab, and Microsoft Azure). [ABSTRACT FROM AUTHOR]

Obtaining accurate and timely lake surface water temperature (LSWT) analyses from satellite remains difficult. Data gaps, cloud contamination, variations in atmospheric profiles of temperature and moisture, and a lack of in situ observations provide challenges for satellite-derived LSWT for climatological analysis or input into geophysical models. In this study, the Multi-scale Ultra-high Resolution (MUR) analysis of LSWT is evaluated between 2007 and 2015 over a small (Lake Oneida), medium (Lake Okeechobee), and large (Lake Michigan) lake. The advantages of the MUR LSWT analyses include daily consistency, high-resolution (~1 km), near-real time production, and multi-platform data synthesis. The MUR LSWT versus in situ measurements for Lake Michigan (Lake Okeechobee) have an overall bias (MUR LSWT-in situ) of --0.20 °C (0.31 °C) and a RMSE of 0.86 °C (0.91 °C). The MUR LSWT versus in situ measurements for Lake Oneida have overall large biases (--1.74 °C) and RMSE (3.42°C) due to a lack of available satellite imagery over the lake, but performs better during the less cloudy 15 July-30 September period. The results of this study highlight the importance of calculating validation statistics on a seasonal and annual basis for evaluating satellite-derived LSWT. [ABSTRACT FROM AUTHOR]

Hutchinson and Löffler's (1956) classification of lakes based on the seasonal thermal mixing regime has become a cornerstone of any analysis of lakes as elements of the earth surface. Until now however the lake classification has lacked a physically sound quantitative criterion distinguishing between two fundamental lake types: thermally stratified during a large portion of the year (mono- and dimictic) and predominantly mixed to the bottom (polymictic). Using the mechanistic balance between potential and kinetic energy we review the different formulations of the Richardson number to derive a generalized scaling for seasonal stratification in a closed lake basin. The scaling parameter is the critical mean basin depth, H crit , that delineates lakes that mix regularly from those that stratify seasonally based on lake water transparency, lake length, and an annual mean estimate for the Monin-Obukhov length. We validate the scaling on available data of lakes worldwide using logistic regression. The scaling criterion consistently described the mixing regime significantly better than either the conventional unbounded basin scaling or a simple depth threshold. Thus, the generalized scaling is universal for freshwater lakes and allows the seasonal mixing regime to be estimated without numerically solving the heat transport equations. [ABSTRACT FROM AUTHOR]

Lakes are key indicators of a region's hydrological cycle, directly reflecting the basin-wide balance between precipitation and evaporation. Lake-level records are therefore valuable repositories of climate history. However, the interpretation of such records is not necessarily straightforward. Lakes act as integrators of the year-to-year fluctuations in precipitation and evaporation that occur even in a constant climate. Therefore lake levels can exhibit natural, unforced fluctuations that persist on timescales of decades or more. This behavior is important to account for when distinguishing between true climate change and interannual variability as the cause of past lake-level fluctuations. We demonstrate the operation of this general principle for the particular case-study of the Great Salt Lake, which has long historical lake-level and climatological records. We employ both full water-balance and linear models. Both models capture the timing and size of the lake's historical variations. We then model the lake's response to much longer synthetic time series of precipitation and evaporation calibrated to the observations, and compare the magnitude and frequency of the modeled response to the Great Salt Lake's historical record. We find that interannual climate variability alone can explain much of the decadal-to-centennial variations in the lake-level record. Further, analytic solutions to the linear model capture much of the full model's behavior, but fail to predict the most extreme lake-level variations. We then apply the models to other lake geometries, and evaluate how the timing and amplitude of a lake-level response differs with climatic and geometric setting. A lake's response to a true climatic shift can only be understood in the context of these expected persistent lake-level variations. On the basis of these results, we speculate that lake response to interannual climate variability may play an important part in explaining much of Holocene lake-level fluctuations. [ABSTRACT FROM AUTHOR]

Obtaining accurate and timely lake surface water temperature (LSWT) analyses from satellite remains difficult. Data gaps, cloud contamination, variations in atmospheric profiles of temperature and moisture, and a lack of in situ observations provide challenges for satellite-derived LSWT for climatological analysis or input into geophysical models. In this study, the Multi-scale Ultra-high Resolution (MUR) analysis of LSWT is evaluated between 2007 and 2015 over a small (Lake Oneida), medium (Lake Okeechobee), and large (Lake Michigan) lake. The advantages of the MUR LSWT analyses include daily consistency, high-resolution (~1 km), near-real time production, and multi-platform data synthesis. The MUR LSWT versus in situ measurements for Lake Michigan (Lake Okeechobee) have an overall bias (MUR LSWT-in situ) of −0.20 °C (0.31 °C) and a RMSE of 0.86 °C (0.91 °C). The MUR LSWT versus in situ measurements for Lake Oneida have overall large biases (−1.74 °C) and RMSE (3.42°C) due to a lack of available satellite imagery over the lake, but performs better during the less cloudy 15 July–30 September period. The results of this study highlight the importance of calculating validation statistics on a seasonal and annual basis for evaluating satellite-derived LSWT.

Several modified versions of the Monod model have been proposed to simulate algal dynamics in lakes by keeping the parent model's advantages of simplicity and low data requirement. This study evaluated the performance of a widely-used modified Monod model in predicting algal dynamics at various time scales in Lake Tai, a typical shallow lake in east China, using multiple time series. Chlorophyll-a (Chl-a) concentration was used as a surrogate for algal (CyanoHABs: cyanobacterial harmful algal blooms) growth and the independent variables were total nitrogen (TN), total phosphorus (TP), and either water temperature or air temperature. The evaluation indicated that the model parameters could have distinctly different values, depending on whether or not constraints are imposed, time scales, and types of nutrients. The model performance varied in terms of time scales as well as magnitudes and fluctuations of Chl-a and TN or TP concentrations, achieving a relative better performance for the monthly rather than three-day time scale and for the central part rather than bays of the study lake. The model with TP as the independent variable had a better performance than the model with TN as the independent variable, regardless of the time scale used. The temperature-nutrient interactions were important for algal growth when the temporal fluctuations of these two factors were large but the interactions could become minimal otherwise. [ABSTRACT FROM AUTHOR]

Lakes can influence regional climate, yet most general circulation models have, at best, simple and largely untested representations of lakes. We developed the Lake, Ice, Snow, and Sediment Simulator(LISSS) for inclusion in the land-surface component (CLM4) of an earth system model (CESM1). The existing CLM4 lake modelperformed poorly at all sites tested; for temperate lakes, summer surface water temperature predictions were 10–25uC lower than observations. CLM4-LISSS modifies the existing model by including (1) a treatment of snow; (2) freezing, melting, and ice physics; (3) a sediment thermal submodel; (4) spatially variable prescribed lakedepth; (5) improved parameterizations of lake surface properties; (6) increased mixing under ice and in deep lakes; and (7) correction of previous errors. We evaluated the lake model predictions of water temperature and surface fluxes at three small temperate and boreal lakes where extensive observational data was available. We alsoevaluated the predicted water temperature and/or ice and snow thicknesses for ten other lakes where less comprehensive forcing observations were available. CLM4-LISSS performed very well compared to observations for shallow to medium-depth small lakes. For large, deep lakes, the under-prediction of mixing was improved by increasing the lake eddy diffusivity by a factor of 10, consistent with previouspublished analyses. Surface temperature and surface flux predictions were improved when the aerodynamic roughness lengths were calculated as a function of friction velocity, rather than using a constant value of 1 mm or greater. We evaluated the sensitivity of surface energy fluxes to modeled lake processes and parameters. Largechanges in monthly-averaged surface fluxes (up to 30 W m22) were found when excluding snow insulation or phase change physics and when varying the opacity, depth, albedo of melting lake ice, and mixing strength across ranges commonly found in real lakes. Typical variation among model parameterization choices can therefore cause persistent local surface flux changes much larger than expected changes in greenhouse forcing. We conclude that CLM4-LISSS adequately simulates lake water temperature and surface energy fluxes, with errors comparable in magnitude to those resulting from uncertainty in global lake properties, and is suitable for inclusion inglobal and regional climate studies.

Multiple paleoclimate proxies are required for robust assessment of past hydroclimatic conditions. Currently, estimates of drought variability over the past several thousand years are based largely on tree-ring records. We produced a 1,500-y record of winter precipitation in the Pacific Northwest using a physical model-based analysis of lake sediment oxygen Isotope data. Our results indicate that during the Medieval Climate Anomaly (MCA) (900-1300 AD) the Pacific Northwest experienced exceptional wetness in winter and that during the Little Ice Age (LIA) (1450-1850 AD) conditions were drier, contrasting with hydroclimatic anomalies in the desert Southwest and consistent with climate dynamics related to the El Niño Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO). These findings are somewhat discordant with drought records from tree rings, suggesting that differences in seasonal sensitivity between the two proxies allow a more compete understanding of the climate system and likely explain disparities in inferred climate trends over centennial timescales. [ABSTRACT FROM AUTHOR]

Lakes can influence regional climate, yet most general circulation models have, at best, simple and largely untested representations of lakes. We developed the Lake, Ice, Snow, and Sediment Simulator (LISSS) for inclusion in the land-surface component (CLM4) of an earth system model (CESM1). The existing CLM4 lake model performed poorly at all sites tested; for temperate lakes, summer surface water temperature predictions were 10-25°C lower than observations. CLM4-LISSS modifies the existing model by including (1) a treatment of snow; (2) freezing, melting, and ice physics; (3) a sediment thermal submodel; (4) spatially variable prescribed lake depth; (5) improved parameterizations of lake surface properties; (6) increased mixing under ice and in deep lakes; and (7) correction of previous errors. We evaluated the lake model predictions of water temperature and surface fluxes at three small temperate and boreal lakes where extensive observational data was available. We also evaluated the predicted water temperature and/or ice and snow thicknesses for ten other lakes where less comprehensive forcing observations were available. CLM4-LISSS performed very well compared to observations for shallow to medium-depth small lakes. For large, deep lakes, the under-prediction of mixing was improved by increasing the lake eddy diffusivity by a factor of 10, consistent with previous published analyses. Surface temperature and surface flux predictions were improved when the aerodynamic roughness lengths were calculated as a function of friction velocity, rather than using a constant value of 1 mm or greater. We evaluated the sensitivity of surface energy fluxes to modeled lake processes and parameters. Large changes in monthly-averaged surface fluxes (up to 30 W m−2) were found when excluding snow insulation or phase change physics and when varying the opacity, depth, albedo of melting lake ice, and mixing strength across ranges commonly found in real lakes. Typical variation among model parameterization choices can therefore cause persistent local surface flux changes much larger than expected changes in greenhouse forcing. We conclude that CLM4-LISSS adequately simulates lake water temperature and surface energy fluxes, with errors comparable in magnitude to those resulting from uncertainty in global lake properties, and is suitable for inclusion in global and regional climate studies. [ABSTRACT FROM AUTHOR]

A model is developed to quantify the wind sheltering of a lake by a tree canopy or a bluff. The experiment-based model predicts the wind-sheltering coefficient a priori, without calibration, and is useful for one-dimensional (1-D) lake hydrodynamic and water quality modeling. The model is derived from velocity measurements in a boundary layer wind tunnel, by investigating mean velocity profiles and surface shear stress development downwind of two canopies and a bluff. The wind tunnel experiments are validated with field measurements over an ice-covered lake. Both wind tunnel and field experiments show that reduced surface shear stress extends approximately 50 canopy heights downwind from the transition. The reduction in total shear force on the water surface is parameterized by a wind-sheltering coefficient that is related to the reduction of wind-affected lake area. While all measurements are made on solid surfaces, the wind-sheltering coefficient is shown to be applicable to the lake surface. Although several canopy characteristics, such as its height, aerodynamic roughness, and its porosity affect the transition of velocity profiles and surface shear stress onto a lake, a relationship based on canopy height alone provides a sufficiently realistic estimate of the wind-sheltering coefficient. The results compare well with wind-sheltering coefficients estimated by calibration of lake water temperature profile simulations for eight lakes. [ABSTRACT FROM AUTHOR]

In recent decades, many perialpine lakes have been affected by oligotrophication due to efficient sewage treatment and by altered water turbidity due to upstream hydropower operations. Such simultaneous environmental changes often lead to public debate on the actual causes of observed productivity reductions. We evaluate the effects of those two changes by a combined approach of modeling and data interpretation for a case study on Lake Brienz (Switzerland), a typical oligotrophic perialpine lake, located downstream of several hydropower reservoirs. A physical k- scheme and a biogeochemical advection-diffusion-reaction model were implemented and applied for several hypothetical scenarios with different nutrient loads and different particle input dynamics. The simulation results are compared to long-term biotic data collected from 1999 to 2004. The analysis shows that enhanced nutrient supply increases the nutritious value of algae, stimulating zooplankton growth, while phytoplankton growth is limited by stronger top-down control. Annually integrated productivity is only slightly influenced by altered turbidity, as phosphorous limitation prevails. Simulations indicate that the spring production peak is delayed because of increased turbidity in winter caused by upstream hydropower operation. As a consequence, the entire nutrient cycle is seasonally delayed, creating an additional stress for zooplankton and fish in the downstream lake. [ABSTRACT FROM AUTHOR]

Degradation of water quality is the major health concern for lakes and reservoirs in the central regions of the United States as a result of heavily devoted agricultural production. A vital key to the development of a reservoir management strategy is to identify nutrient loading that describes associated water quality conditions in reservoirs. This study integrated AnnAGNPS watershed and BATHTUB lake models to simulate actual lake water quality conditions of Cheney Reservoir, KS, and demonstrated the use of the coupled model for simulating lake response to changes in different watershed land use and management scenarios. The calibrated current-conditions model simulated in-lake reductions as much as 52% for TN, 48% for TP, and 70% for chlorophyll a due to conversion to native grass, and increases as much as 4% for TN, 9% for TP and 6% for chlorophyll a due to conversion of land from the Conservation Reserve Program (CRP) to cropland (15.5% of watershed). This model also demonstrated an increase in chlorophyll a (19%) as the lake sediment capacity was reached over the next century. [ABSTRACT FROM AUTHOR]

A statistical analysis of water quality data from Lake Vänern spanning three decades has been performed in order to establish an appropriate level of complexity for a water quality model. The analysis consists of paired t-tests for differences in the vertical direction and multiple comparison tests (Tukey's honestly significant difference criterion) for differences in the horizontal direction. The analysis indicates significant differences between the epi- and hypolimnion during stratified periods, but no significant differences in mixed periods. The two distinct basins are only marginally different. Furthermore, each basin can be considered well-mixed horizontally, except for parts located close to point emissions, or the particularly shallow regions. [ABSTRACT FROM AUTHOR]

The characteristic feature of the physical structure of Lac Pavin is a distinct and permanent chemically induced density increase between about 60 and 70 m depth. This chemocline separates the seasonally mixed mixolimnion from the monimolimnion, which is characterized by elevated temperature and salinity as well as complete anoxia. Previously published box-models of the lake postulated substantial groundwater input at the lake bottom, and consequently a short water residence time in the monimolimnion and high fluxes of dissolved constituents across the chemocline. We present a new view of the physical structure and dynamics of Lac Pavin, which is based on the results of high-resolution CTD profiles, transient and geochemical tracers (tritium, CFCs, helium), and numerical modeling. The CTD profiles indicate the existence of a sublacustrine spring above rather than below the chemocline. A stability analysis of the water column suggests that vertical turbulent mixing in the chemocline is very weak. A numerical one-dimensional lake model is used to reconstruct the evolution of transient tracer distributions over the past 50 years. Model parameters such as vertical diffusivity and size of sublacustrine springs are constrained by comparison with observed tracer data. Whereas the presence of a significant water input to the monimolimnion can clearly be excluded, the input to the mixolimnion - both at the surface and from the indicated sublacustrine spring - cannot be accurately determined. The vertical turbulent diffusivity in the chemocline is well constrained to K ≈ 5 × 10-8 m² s-1, about a factor of three below the molecular diffusivity for heat. Assuming thus purely molecular heat transport, the heat flow through the chemocline can be estimated to between 30 and 40 mW m-2. With respect to dissolved constituents, the very weak turbulent diffusive exchange is equivalent to a stagnant monimolimnion with a residence time of nearly 100 years. Based on these results and vertical concentration profiles of dissolved species, diffusive fluxes between monimolimnion and mixolimnion can be calculated. A large excess of helium with a ³He/4He ratio of (9.09 ± 0.01) × 10-6 (6.57 Ra) is present in the monimolimnion, clearly indicating a flux of magmatic gases into the monimolimnion. We calculate a flux of 1.0 × 10-12 mol m-2 s-1 for mantle helium and infer a flux of 1 .2 × 10-7 mol m-2 s-1 (72 t year-1) for magmatic CO2. The monimolimnion appears to be in steady state with respect to these fluxes. [ABSTRACT FROM AUTHOR]

• We developed a workflow to produce seasonal forecasts to support water management. • The workflow is demonstrated in four contrasting study catchments. • Discharge and lake water temperature forecasts have potential to inform management. Seasonal climate forecasts produce probabilistic predictions of meteorological variables for subsequent months. This provides a potential resource to predict the influence of seasonal climate anomalies on surface water balance in catchments and hydro-thermodynamics in related water bodies (e.g., lakes or reservoirs). Obtaining seasonal forecasts for impact variables (e.g., discharge and water temperature) requires a link between seasonal climate forecasts and impact models simulating hydrology and lake hydrodynamics and thermal regimes. However, this link remains challenging for stakeholders and the water scientific community, mainly due to the probabilistic nature of these predictions. In this paper, we introduce a feasible, robust, and open-source workflow integrating seasonal climate forecasts with hydrologic and lake models to generate seasonal forecasts of discharge and water temperature profiles. The workflow has been designed to be applicable to any catchment and associated lake or reservoir, and is optimized in this study for four catchment-lake systems to help in their proactive management. We assessed the performance of the resulting seasonal forecasts of discharge and water temperature by comparing them with hydrologic and lake (pseudo)observations (reanalysis). Precisely, we analysed the historical performance using a data sample of past forecasts and reanalysis to obtain information about the skill (performance or quality) of the seasonal forecast system to predict particular events. We used the current seasonal climate forecast system (SEAS5) and reanalysis (ERA5) of the European Centre for Medium Range Weather Forecasts (ECMWF). We found that due to the limited predictability at seasonal time-scales over the locations of the four case studies (Europe and South of Australia), seasonal forecasts exhibited none to low performance (skill) for the atmospheric variables considered. Nevertheless, seasonal forecasts for discharge present some skill in all but one case study. Moreover, seasonal forecasts for water temperature had higher performance in natural lakes than in reservoirs, which means human water control is a relevant factor affecting predictability, and the performance increases with water depth in all four case studies. Further investigation into the skillful water temperature predictions should aim to identify the extent to which performance is a consequence of thermal inertia (i.e., lead-in conditions). [ABSTRACT FROM AUTHOR]

• The winter diatom bloom is studied in a temperate shallow lake fed by groundwater. • High frequency data and lake physical and ecological modeling are employed. • Water temperature and light both regulate diatom growth before the bloom. • Indirect effect of temperature on ice thaw and light condition triggers the bloom. • Silicon limitation and sedimentation terminate the bloom before stratification. In temperate lakes, it is generally assumed that light rather than temperature constrains phytoplankton growth in winter. Rapid winter warming and increasing observations of winter blooms warrant more investigation of these controls. We investigated the mechanisms regulating a massive winter diatom bloom in a temperate lake. High frequency data and process-based lake modeling demonstrated that phytoplankton growth in winter was dually controlled by light and temperature, rather than by light alone. Water temperature played a further indirect role in initiating the bloom through ice-thaw, which increased light exposure. The bloom was ultimately terminated by silicon limitation and sedimentation. These mechanisms differ from those typically responsible for spring diatom blooms and contributed to the high peak biomass. Our findings show that phytoplankton growth in winter is more sensitive to temperature, and consequently to climate change, than previously assumed. This has implications for nutrient cycling and seasonal succession of lake phytoplankton communities. The present study exemplifies the strength in integrating data analysis with different temporal resolutions and lake modeling. The new lake ecological model serves as an effective tool in analyzing and predicting winter phytoplankton dynamics for temperate lakes. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Interwave Analyzer is an open source software that provides detailed characterization of the dynamics of internal waves in lakes and reservoirs. It is based on well-established theories and empirical knowledge on internal waves and lake mixing and facilitates a general physical classification of lakes and reservoirs. As input data, the program requires time series of water temperature from various depths and meteorological data, which can be obtained from measurements or numerical models. Interwave Analyzer performs an in-depth analysis of periodic motion by spectral analysis to identify predominant internal wave periods. To facilitate the identification of wave modes, the software is coupled with a multi-layer model. Interwave Analyzer is a powerful, easily accessible, and universal tool, which can be used for obtaining detailed understanding lake hydrodynamics not only in physical sciences, but also in the context of water quality, ecological interactions and biogeochemical fluxes in aquatic ecosystems. [ABSTRACT FROM AUTHOR]

Lake Auburn, Maine, USA, is a historically unproductive lake that has experienced multiple algal blooms since 2011. The lake is the water supply source for a population of ~60,000. We modeled past temperature, and concentrations of dissolved oxygen (DO) and phosphorus (P) in Lake Auburn by considering the catchment and internal contributions of P as well as atmospheric factors, and predicted the change in lake water quality in response to future climate and land-use changes. A stream hydrology and P-loading model (SimplyP) was used to generate input from two major tributaries into a lake model (MyLake-Sediment) to simulate physical mixing, chemical dynamics, and sediment geochemistry in Lake Auburn from 2013 to 2017. Simulations of future lake water quality were conducted using meteorological boundary conditions derived from recent historical data and climate model projections for high greenhouse-gas emission cases. The effects of future land development on lake water quality for the 2046 to 2055 time period under different land-use and climate change scenarios were also simulated. Our results indicate that lake P enrichment is more responsive to extreme storm events than increasing air temperatures, mean precipitation, or windstorms; loss of fish habitat is driven by windstorms, and to a lesser extent an increasing water temperature; and catchment development further leads to water quality decline. All simulations also show that the lake is susceptible to both internal and external P loadings. Simulation of temperature, DO, and P proved to be an effective means for predicting the loss of water quality under changing land-use and climate scenarios. Unlabelled Image • Linked models can be applied to assessing future lake water quality. • Climate change and watershed development stimulate water quality decline. • Lake phosphorus enrichment is most responsive to extreme storm events. • Lakes are susceptible to external and internal phosphorus loadings. [ABSTRACT FROM AUTHOR]