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Climate change and other anthropogenic stressors have led to long-term changes in the thermal structure, including surface temperatures, deepwater temperatures, and vertical thermal gradients, in many lakes around the world. Though many studies highlight warming of surface water temperatures in lakes worldwide, less is known about long-term trends in full vertical thermal structure and deepwater temperatures, which have been changing less consistently in both direction and magnitude. Here, we present a globally-expansive data set of summertime in-situ vertical temperature profiles from 153 lakes, with one time series beginning as early as 1894. We also compiled lake geographic, morphometric, and water quality variables that can influence vertical thermal structure through a variety of potential mechanisms in these lakes. These long-term time series of vertical temperature profiles and corresponding lake characteristics serve as valuable data to help understand changes and drivers of lake thermal structure in a time of rapid global and ecological change., Measurement(s) temperature of water • temperature profile Technology Type(s) digital curation Factor Type(s) lake location • temporal interval Sample Characteristic - Environment lake • reservoir Sample Characteristic - Location global Machine-accessible metadata file describing the reported data: 10.6084/m9.figshare.14619009

In water-limited regions worldwide, climate change and population growth threaten to desiccate lakes. As these lakes disappear, water managers have often implicated climate change-induced decreases in precipitation and higher temperature-driven evaporative demand-factors out of their control, while simultaneously constructing dams and drilling new wells into aquifers to permit agricultural expansion. One such shrinking lake is the Sea of Galilee (Lake Kinneret), whose decadal mean level has reached a record low, which has sparked heated debate regarding the causes of this shrinkage. However, the relative importance of climatic change, agricultural consumption, and increases in Lebanese water consumption, remain unknown. Here we show that the level of the Sea of Galilee would be stable, even in the face of decreasing precipitation in the Golan Heights. Climatic factors alone are inadequate to explain the record shrinkage of the Sea of Galilee. We found no decreasing trends in inflow from the headwaters of the Upper Jordan River located primarily in Lebanon. Rather, the decrease in discharge of the Upper Jordan River corresponded to a period of expanding irrigated agriculture, doubling of groundwater pumping rates within the basin, and increasing of the area of standing and impounded waters. While rising temperatures in the basin are statistically significant and may increase evapotranspiration, these temperature changes are too small to explain the magnitude of observed streamflow decreases. The results demonstrate that restoring the level of the Sea of Galilee will require reductions in groundwater pumping, surface water diversions, and water consumption by irrigated agriculture.

© The Author(s) 2020. Published by Nature Research. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons. org/licenses/by/4.0/. Globally, lake surface water temperatures have warmed rapidly relative to air temperatures, but changes in deepwater temperatures and vertical thermal structure are still largely unknown. We have compiled the most comprehensive data set to date of long-term (1970–2009) summertime vertical temperature profiles in lakes across the world to examine trends and drivers of whole-lake vertical thermal structure. We found significant increases in surface water temperatures across lakes at an average rate of + 0.37 °C decade−1, comparable to changes reported previously for other lakes, and similarly consistent trends of increasing water column stability (+ 0.08 kg m−3 decade−1). In contrast, however, deepwater temperature trends showed little change on average (+ 0.06 °C decade−1), but had high variability across lakes, with trends in individual lakes ranging from − 0.68 °C decade−1 to + 0.65 °C decade−1. The variability in deepwater temperature trends was not explained by trends in either surface water temperatures or thermal stability within lakes, and only 8.4% was explained by lake thermal region or local lake characteristics in a random forest analysis. These findings suggest that external drivers beyond our tested lake characteristics are important in explaining long-term trends in thermal structure, such as local to regional climate patterns or additional external anthropogenic influences. Funding in support of this work came from the following sources: Belarus Republican Foundation for Fundamental Research; IGB Long-Term Research; the European Commission within the MANTEL project; the DFG within the LimnoScenES project (AD 91/22-1); OLA-IS, AnaEE-France, INRAE of Thonon-les-Bains, CIPEL, SILA, CISALB; Universidad del Valle de Guatemala; Archbold Biological Station; the Oklahoma Department of Wildlife Conservation, the Oklahoma Water Resources Board, the Grand River Dam Authority, the US Army Corps of Engineers, and the City of Tulsa; the Ministry of Business, Innovation, and Employment (UOW X1503); the Natural Environment Research Council of the UK; the IGB’s International Postdoctoral Fellowship; NSERC, Canada Foundation for Innovation, Canada Research Chairs, Province of Saskatchewan; University of Regina; Queen’s University Belfast; Natural Environment Research Council; US-NSF, California Air Resources Board, NASA, and US National Park Service; the Ministry of Higher Education and Research (projects № FZZE-2020-0026; № FZZE-2020-0023) and RSCF 20-64-46003; US National Science Foundation Long Term Research in Environmental Biology program (DEB-1242626); the Environmental Agency of Verona; US National Science Foundation, the Gordon and Betty Moore Foundation, the Mellon Foundation, and the University of Washington; KMFRI, LVEMP, University of Innsbruck, OeAD, IFS, and LVFO-EU; Waikato Regional Council and Bay of Plenty Regional Council; Swedish Environmental Protection Agency and the Swedish Infrastructure for Ecosystem Sciences; US National Science Foundation grants DEB-1754276 and DEB-1950170. Faculty yes

Turbulent fluxes across the air-water interface are integral to determining lake heat budgets, evaporation, and carbon emissions from lakes. The stability of the atmospheric boundary layer (ABL) in ...

The hydrologic responses of two similar in size watersheds in the Lake Kinneret basin are examined: Karstic Hermon watershed and basaltic Meshushim watershed. The streamflow properties at these watersheds are different in their surface flow to baseflow ratio, runoff coefficients and response to extreme rainfall events. The HYdrological Model for Karst Environment (HYMKE) model, developed to simulate daily flow in karst formation, was modified to address the basaltic formation at the Meshushim watershed. Water fluxes simulations were used to compare the hydrologic processes between the watersheds. The twice-higher annual precipitation in the Hermon watershed, generates annual streamflow that is five times more than in the Meshushim. This amplification of the rainfall-streamflow ratio between the watersheds is because larger fraction of the rainfall is lost to evapotranspiration at the basaltic Meshushim watershed and larger portion of the rainfall percolates to the karstic aquifer through preferential flow and appear as baseflow at the Hermon watershed. During large rainfall events when soil water content is near saturation, lower rainfall amount over the Meshushim watershed generates larger peak flow than the Hermon watershed. In both watersheds, surface flow was generated only when the soil water content is at or near saturation conditions. The streamflow dependency on soil water content, suggests high sensitivity of streamflow generation to the intra-annual variability of precipitation. Understanding the hydrologic response of the different sources of Lake Kinneret improves the ability to forecast its inflow.

Summary The relationships between the evaporation from a medium size (168.7 km 2 ) Lake Kinneret (Northern Israel), and its governing synoptic factors are well demonstrated during the summer of 2010. During July–August the daily temperature of the air and water surface were ∼2–4 °C higher, the daily wind over the lake was ∼80% weaker, and the evaporation from the lake was ∼5% lower than the long-term July–August mean. In this study, we explore the impact of the regional and local synoptic-scale atmospheric conditions on the evaporation from the lake during exceptionally hot days in the mid-summer months (July–August). The factors that were found to be correlated with the lake evaporation are the temperatures at 850 hPa (negative) and 500 hPa (positive), the sea level pressure difference between Northern Egypt and Armenia (positive), and the height of the marine inversion (positive). Synoptic analysis indicates that two conditions are responsible for the reduction of the Mediterranean Sea Breeze (MSB) during exceptionally hot days, and consequently to the reduction of evaporation from the lake. First, the weakening of the permanent synoptic Etesian winds, which otherwise supports the inland penetration of the MSB; and second, the descent of the marine inversion to a height below the topographic ridge of the Galilee Mountains upwind of the study area, which blocks the Marine Sea Breeze from reaching Lake Kinneret.

Climate change is affecting lake stratification with consequences for water quality and the benefits that lakes provide to society. Here we use long-term temperature data (1970–2010) from 26 lakes around the world to show that climate change has altered lake stratification globally and that the magnitudes of lake stratification changes are primarily controlled by lake morphometry (mean depth, surface area, and volume) and mean lake temperature. Deep lakes and lakes with high average temperatures have experienced the largest changes in lake stratification even though their surface temperatures tend to be warming more slowly. These results confirm that the nonlinear relationship between water density and water temperature and the strong dependence of lake stratification on lake morphometry makes lake temperature trends relatively poor predictors of lake stratification trends.

The measured temperature of the hypolimnion of Lake Kinneret, Israel, reveals an average rise of ∼0.6 ± 0.3°C between April and December. Three mechanisms are suggested as the cause of this rise: (i) direct radiation; (ii) an entire-lake vertical diffused heat transfer; and (iii) a mechanism of “indirect warming,” which is investigated here for the first time. The indirect warming mechanism prevails in the sublittoral zones, which are affected by internal seiche activity, including Poincare and Kelvin waves with cycle periods of ∼12 h and ∼24 h, respectively. During part of the seiche's time span, the warm epilimnetic water comes into contact with the underlying bottom sediments and heats them. During the rest of the seich's cycle, part of the sublittoral bed sediments become overlain by cold hypolimnetic water and cause the previously heated sediments to emit most of their heat, slightly warming the hypolimnion. The daily cycle of this indirect warming mechanism is superimposed on the seasonal cycle of the sublittoral bed sediments, which are cold in the winter and warm in the summer, in accordance with the seasonal pattern of the epilimnion's temperature. Empirical evidence that suggests that indirect warming actually takes place in response to well-documented seiche water motions is presented in this article. For example, according to the proposed analysis of sediment temperature changes, in the month of June a daily heat flux of 7.88 W m−2 (0.68 MJ m−2 d−1) was estimated. It was found that during the first 5 months of stratification this mechanism contributes ∼41% of the thermal energy needed for the 0.6°C temperature increase. This mechanism is expected to occur at any thermally stratified lake that is significantly affected by internal seiche activity.

Summary In warm temperate mountain regions where water is often scarce vapor losses from the snow-surface can substantially limit snowmelt. Therefore, understanding the key snow dynamic processes that affect water availability in these mountains is essential. We studied the snowpack energy and mass balance in Mt. Hermon, Israel using a comprehensive field campaign during 2010/11. We analyzed the snowpack energy and mass balance during the winter of 2010/11 in a Deep Snow Patch (DSP), and in the Bulan valley experiment area (BVEA), where both windswept locations and lee-side (deep snowpack) locations were examined. We applied for this analysis an energy and mass balance snow model that was forced by input from two meteorological stations. The calibration of the model for the DSP and BVEA was based on surveyed snow water equivalent data, and melting cycles that were measured with time-lapse cameras, respectively. Using a step function to describe wind speed over the DSP we showed that the turbulent fluxes were influenced by changes in snowpack height. The turbulent fluxes were found as the dominant energy fluxes at the snow-surface. During winter, vapor losses varied between 46% and 82% of the total ablation. Consequently, latent heat flux consumed much of the available energy at the snow-surface, greatly limiting melting rate to 1 mm day−1. During spring, vapor flux was positive which enhanced condensation, resulting in an average melting flux of 86 mm day−1. The spatial variation in the vapor flux at the BVEA due to terrain orientation yield variation in space of the available water at the bottom of the snowpack.

Hydrograph separation (HS) using recursive digital filter approaches focuses on trying to distinguish between the rapidly occurring discharge components like surface runoff, and the slowly changing discharge originating from interflow and groundwater. Filter approaches are mathematical procedures, which perform the HS using a set of separation parameters. The first goal of this study is to minimize the subjective influence that a user of the filter technique exerts on the results by the choice of such filter parameters. A simple optimal HS (OHS) technique for the estimation of the separation parameters was introduced, relying on measured stream hydrochemistry. The second goal is to use the OHS parameters to benchmark the performance of process-based hydro-geochemical (HG) models. The new HG routine can be used to quantify the degree of knowledge that the stream flow time series itself contributes to the HG analysis, using newly developed benchmark geochemistry efficiency (BGE). Results of the OHS show that the two HS fractions (“rapid” and “slow”) differ according to the HG substances which were selected. The BFImax parameter (long-term ratio of baseflow to total streamflow) ranged from 0.26 to 0.94 for SO4−2 and total suspended solids, TSS, respectively. Then, predictions of SO4−2 transport from a process-based hydrological model were benchmarked with the proposed HG routine, in order to evaluate the significance of the HG routines in the process-based model. This comparison provides valuable quality test that would not be obvious when using the traditional measures like r2 or the NSE (Nash–Sutcliffe efficiency). The process-based model resulted in r2 = 0.65 and NSE = 0.65, while the benchmark routine results were slightly lower with r2 = 0.61 and NSE = 0.58. However, the comparison between the two model resulted in obvious advantage for the process-based model with BGE = 0.15.

A high-resolution 3-D orographic precipitation model (OPM) forced by Climate Forecast System (CFS) reanalysis fields was developed for the Lake Kinneret watershed (Israel-Syria-Lebanon territories). The OPM was tuned to represent the interaction between the advected and stratiform rainfall, and the local orographic enhancement. The OPM evaluation was focused on the densely instrumented lower part of the watershed. To evaluate the ungauged upper-elevation, bias-adjusted precipitation estimates from the Global-Hydro-Estimator were used. The OPM simulates higher rainfall amounts in the upper-elevation watershed compared to currently used rainfall estimates from an elevation dependent regression. The larger differences are during rain events with southwesterly wind flow and high moisture flux. These conditions, according to the OPM, are conducive to enhanced orographic lifting in the Hermon Mountain. A sensitivity analysis indicated that the higher wind speeds for southwesterly–northwesterly trajectories generate significant orographic lifting and increase the precipitation differences between the lower and upper elevations.

[1] Many hydrological systems exhibit complex subsurface flow and storage behavior. Runoff observations often only provide insufficient information for unique process identification. Quantitative modeling of water and solute fluxes presents a potentially more powerful avenue to explore whether hypotheses about system functioning can be rejected or conditionally accepted. In this study we developed and tested four hydrological model structures, based on different hypotheses about subsurface flow and storage behavior, to identify the functioning of a large Mediterranean karst system. Using eight different system signatures, i.e., indicators of particular hydrodynamic and hydrochemical characteristics of the karst system, we applied a novel model evaluation strategy to identify the best conceptual model representation of the karst system within our set of possible system representations. Our approach to test model realism consists of three stages: (1) evaluation of model performance with respect to system signatures using automatic calibration, (2) evaluation of parameter identifiability using Sobol's sensitivity analysis, and (3) evaluation of model plausibility by combining the results of stages (1) and (2). These evaluation stages eliminated three out of four model structures and lead to a unique hypothesis about the functioning of the studied karst system. We used the estimated parameter values to further quantify subsurface processes. The chosen model is able to simultaneously provide high performances for eight system signatures with realistic parameter values. Our approach demonstrates the benefits of interpreting different tracers in a hydrologically meaningful way during model evaluation and identification.

Erosion modeling has been generally scaling up from plot scale but not based on landscape topographic position, which is a main variable in saturation excess runoff. In addition, predicting sediment loss in Africa has been hampered by using models developed in western countries and do not perform as well in the monsoon climate prevailing in most of the continent. The objective of this paper is to develop a simple erosion model that can be used in the Ethiopian Highlands in Africa. We base our sediment prediction on a simple distributed saturated excess hydrology model that predicts surface runoff from severely degraded lands and from bottom lands that become saturated during the rainy season and estimates interflow and baseflow from the remaining portions of the landscape. By developing an equation that relates surface runoff to sediment concentration generated from runoff source areas, assuming that baseflow and interflow are sediment-free, we were able to predict daily sediment concentrations from the Anjeni watershed with a Nash–Sutcliffe efficiency ranging from 0.64 to 0.78 using only two calibrated sediment parameters. Anjeni is a 113 ha watershed in the 17.4 million ha Blue Nile Basin in the Ethiopian Highlands. The discharge of the two watersheds was predicted with Nash–Sutcliffe efficiency values ranging from 0.80 to 0.93. The calibrated values in Anjeni for degraded (14%) and saturated (2%) runoff source area were in agreement with field evidence. The analysis suggests that identifying the runoff source areas and predicting the surface runoff correctly is an important step in predicting the sediment concentration.

This research presents a new method to verify the measurements of surface fluxes and the heat balance at a lake surface, by means of Distributed Temperature Sensing (DTS) measurements from 0.5 m above to 1.5 m below the surface. Using a polyvinyl chloride hyperboloid construction, a floating standalone measuring device was developed. Being an open construction, it is almost insensitive to direct radiation. With this construction, a spiral-shaped fiberoptic cable setup was created that obtained temperature measurements with a vertical spatial resolution of 0.0002 m and a temporal resolution of 1 min. DTS measured the detailed variations in air and surface water temperature. The new method was tested in the deep Lake Kinneret (Israel) from 6 to 9 Oct 2011 and in the shallow Lake Binaba (Ghana) from 24 to 28 Oct 2011. With the developed method, it is possible to capture the heat storage change in the top water layer, and therefore verify the water surface heat balance on a time scale of several minutes. Furthermore, a comparison was made between the measured temperature profiles of the airwater interface in Lake Kinneret and Lake Binaba. It was shown that the usage of DTS measurements for the verification of surface energy balance was applicable for Lake Kinneret, but probably not suitable for the conditions in the shallow Lake Binaba. In the latter, heat storage changes near the lake surface were not only caused by surface energy fluxes, but by internal heat waves and currents that bring cooler water to the upper layer.

Peer-reviewed. Copyright: © 2016 Woolway et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.PLoS ONE 11(3): e0152466. doi:10.1371/journal.pone.0152466, Ecological and biogeochemical processes in lakes are strongly dependent upon water temperature. Long-term surface warming of many lakes is unequivocal, but little is known about the comparative magnitude of temperature variation at diel timescales, due to a lack of appropriately resolved data. Here we quantify the pattern and magnitude of diel temperature variability of surface waters using high-frequency data from 100 lakes. We show that the near-surface diel temperature range can be substantial in summer relative to long-term change and, for lakes smaller than 3 km2, increases sharply and predictably with decreasing lake area. Most small lakes included in this study experience average summer diel ranges in their near-surface temperatures of between 4 and 7°C. Large diel temperature fluctuations in the majority of lakes undoubtedly influence their structure, function and role in biogeochemical cycles, but the full implications remain largely unexplored., This project was funded by OTT Hydrometry Ltd and a University College London impact award awarded to RIW and is part of the Natural Environment Research Council (NERC) Sensor Network project United Kingdom Lake Ecological Observatory Network (UKLEON;NE/I007407/1). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Sustainability of fresh water ecosystems and human activities in Mediterranean watersheds under future climate change can be supported with integrated hydrological modeling. The Lake Kinneret Watershed (LKW), which spans over 2730 km2, is divided between three Mediterranean countries, Israel, Lebanon, and Syria; and incorporates four different hydrogeological units: Mt. Hermon in the north, the Golan Heights in the east, the eastern Galilee Mountains in the west, and the Hula Valley in the central part of the watershed. In this study, we used several modeling tools together with a detailed observed database to assemble, test, calibrate and predict simultaneously the water availability within the entire LKW. The hydrological tools that we used compounded of two built-in catchment modules in the Water Evaluation and Planning (WEAP) tool, a model of karst hydrology (HYMKE), lake water balance calculations and artificial rain series based on a stochastic rainfall generation tool. With this setup we defined the “coverage” parameter for water availability and identified vulnerable partial areas inside the watershed, which are more sensitive to extreme draught conditions. The heterogeneity of the LKW water system and the tools we operated enabled the separation of the watershed into regions affected by “climate change” scenarios (mainly reduced amounts of annual rainfall) compared to regions impacted mainly by operational decisions.

State-of-the-art reviews on the dynamics of climate and hydrology inMediterranean mountain regions show that this is a subject that receives little attention compared to mountain studies in other, more popular mountain ranges such as the Alps, Rockies and Himalayas (Messerli and Ives, 1997; Bohm et al., 2001; Viviroli et al., 2003; Corripio and de Jong, 2005; de Jong et al., 2005a,b,c; Bales et al., 2006). However, in the context of the significance and contributing potential of the world’s mountains as water towers to the forelands, Mediterranean mountains are classified as having a high contributing potential to dry lowlands (Viviroli et al., 2007). Climatological and hydrological literature on the mountainous catchments of the Mediterranean Basin itself is much sparser than that of other regions of the world with a Mediterranean climate, such as California. The Mediterranean Basin has unique geographical and climatological characteristics, since its periphery is almost entirely surrounded by mountains at a short distance from the sea (Figure 5.1). Therefore the dominant climate and hydrology around the Mediterranean, although essentially determined by latitude, is strongly influenced by the mountainous relief (Rhanem, 2008). Topographical gradients from sea level up to 2000–4000m altitude are not uncommon.Mediterranean mountains zones, whether consisting of chains or individual peaks, act locally as cold islands with strong climatic gradients (Ozenda, 1975). Typical for such extremes is, for example, the High Atlas in Morocco, which can experience temperatures of −18◦C yet is surrounded by the Sahara within less than 200 km distance. Mediterranean climatology is complex, and basically unites three different zones: the sub-Saharan climate, the dry continental climate to the east and the more continental climate to the north. It forms the boundary between the mid-altitude and tropical climate, between vegetated and non-vegetated, and between highly and poorly developed regions. The climate, together with the distribution and altitudinal range of mountain ranges (Table 5.1), strongly influences water availability and ensuing

Caballero, Luis A., Alon Rimmer, Zachary M. Easton, and Tammo S. Steenhuis, 2012. Rainfall Runoff Relationships for a Cloud Forest Watershed in Central America: Implications for Water Resource Engineering. Journal of the American Water Resources Association (JAWRA) 48(5): 1022-1031. DOI: 10.1111/j.1752-1688.2012.00668.x Abstract: Understanding the basic relationships between rainfall and runoff is vital for effective management and utilization of scarce water resources. Especially, this is important in Central America with widespread potable water shortage during the dry months of the monsoon. Potential good water sources are cloud forests, but little information concerning its potential is available to water supply engineers. Our objective is to define rainfall-runoff-base flow relationships for a cloud forest catchment. Flumes were installed for measuring river flow in four subwatersheds in La Tigra National Park, Honduras. One of the four watersheds was a 636-ha subwatershed (WS1) with 60% cloud forest coverage. Precipitation averaged 1,130 mm/yr over the entire basin. About half of the total rainfall became runoff for the cloud forest watershed whereas, for the adjacent undisturbed forested watershed, the total discharge was

Summary Identifying and quantifying future climate effects on water resources has major economic and societal implications, rendering such studies extremely important for water planners. Here we integrate output from one high resolution global (Japan Meteorological Agency) and three regional (ECHAM-RegCM, Hadley-MM5, ECHAM-MM5) climate models into three hydrological tools (1. annual incoming water volumes; 2. evaporation from the lake; and 3. lake salinity) to provide first approximations of climate change impacts on water quantity and quality in Lake Kinneret (also known as Sea of Galilee), the major freshwater resource in Israel. Meteorological data extracted from the climate models were used as input data into the models. Results were calculated for the historical 1979–2009 and the future 2015–2060 periods. The modeled historical period was verified against observed data, first by each model alone, and then by the combined model structure. Predicted results varied between the climate models. The ECHAM-RegCM predicted decreased precipitation in an average rate of ∼7 mm year −1 (−0.8% annually) while the trends of precipitation predicted by the other models were less obvious. According to the combination of ECHAM-RegCM, ECHAM-MM5 and Hadley-MM5 with the lake evaporation model, the evaporation will increase by 0.2–0.6 Mm 3 (0.10–0.25%) annually while according to the JMA no trend was found. The lake salinity is mostly impacted by changes in inflows and therefore only the ECHAM-RegCM predicted significant increase of salinity (from 280 ppm Cl today to ∼450 ppm Cl in 2060), while the trends of salinity according to other models were mild.

summary Snow surface temperature (SST) is a key component in the calculation of snow-surface energy balance. Common snow models have adapted a specific linearized SST equation that accounts for the energy fluxes at the snow–atmosphere interface. An inspection of this widely used equation reveals that the areal units for three of the energy fluxes disregard the effect of sloped terrain and as a result presents a unit inconsistency in the equation. The objectives of this paper are to: (1) introduce a corrected SST equation; (2) discuss the role of the SST in snow models; and (3) assess the impact of this unit inconsistency on the simulation of snow variables in various climatic conditions. Meteorological observations were used to compare results that were obtained by implementation of the original and the corrected SST equations in a point energy and mass balance snow model. The calculated SST values in the original equation tend to be higher than the calculated value in the corrected equation. As a result when the original equation is used the SST-dependent energy fluxes (i.e. sensible heat, latent heat and net long-wave radiation) into the snow are lower, which yield lower melting rates. In conclusion, while the original SST equation might be applicable in snow models for gentle terrain, it introduces substantial biases in steep terrain. Therefore, it is conservatively recommended to consider the implementation of the corrected SST equation for snow model applications in mountainous terrain that are steeper than 15.

Analysis of a 39-yr record (1969-2008) of temperature profiles from Lake Kinneret, Israel, revealed that average epilimnion thickness decreased by - 1.2 m (∼ 3 cm yr ―1 ), metalimnion thickness decreased by between ∼ 1.0 m (December) and ∼ 2.0 m (April), and average temperature of the epilimnion increased by ∼ 1°C (∼ 0.028°C yr ―1 ). Average hypolimnetic temperature remained constant (∼ 15°C), so that the thermal gradient across the metalimnion increased. The average duration of the stratification period (∼ 286 d) remained unchanged. We show that the stratification changes were the result of a decrease in lake level, a slight increase in air temperature during the spring and summer, and a reduction of inflows to the lake. These changes in time affected the stratification pattern in the same direction, i.e., an increase in the lake epilimnetic temperature and an increase in the thermal gradient across the metalimnion. Analysis of the data indicates that the effect of overpumping, which leads to a reduction in lake level, is larger than the effect of changes due to air-temperature increase and the reduction in inflow volumes.

High resolution chemical data collected during summer 2003 indicate that the lower water mass (LWM) of the thermally stratified Lake Kinneret (LK) can be subdivided into three layers: a benthic boundary layer (BBL), overlain by the hypolimnion (HYP), and on top, the lower part of the metalimnion (ME-L). After onset of thermal stratification, the BBL is the first layer that turns anoxic, followed shortly afterward by the ME-L, while the HYP remains oxic and has relatively higher pH until later in summer. Thus, during the early summer, the HYP forms an oxygen-containing layer in-between two DO-deficient layers. Somewhat later, the HYP is characterized by still having significant levels of nitrate NO3, while in both adjacent layers nitrate is already removed through denitrification. The mechanisms controlling the gradual decline of dissolved oxygen (DO) in the HYP during the summer were studied. The seasonal mean lake-wide vertical eddy diffusion coefficient in this layer, evaluated from heat flux measurements, is approximately 4 × 10−6 m2 s−1. The vertical oxygen flux due to diffusion from within the HYP toward its oxygen-deficient upper and lower boundaries accounts for most of the slow summer decline in DO in this layer. A smaller portion of this decline can be attributed to in-layer respiratory processes. The low turbidity, relatively high pH, and slow accumulation rate of NH4 in the HYP support the notion that the slower mineralization processes occurring in this layer result from relatively low ambient concentrations of biodegradable organic matter, most probably due to the short residence time of the particles settling through this layer.

The Weather Research and Forecasting (WRF) model was employed to provide precipitation forecasts during the 2008/09 and 2009/10 winters (wet season) for Israel and the surrounding region where complex terrain dominates. The WRF precipitation prediction has been coupled with the Hydrological Model for Karst Environment (HYMKE) to forecast the upper Jordan River streamflow. The daily WRF precipitation forecasts were verified against the measurements from a dense network of rain gauges in northern and central Israel, and the simulation results using the high-resolution WRF indicated good agreement with the actual measurements. The daily precipitation amount calculated by WRF at rain gauges located in the upper parts of the Jordan River basin showed good agreement with the actual measurements. Numerical experiments were carried out to test the impact of the WRF model resolution and WRF microphysical schemes, to determine an optimal model configuration for this application. Because of orographic forcing in the region, it is necessary to run WRF with a 4–1.3-km grid increment and with sophisticated microphysical schemes that consider liquid water, ice, snow, and graupel to produce quality precipitation predictions. The hydrological modeling system that ingests the high-resolution WRF forecast precipitation produced good results and improved upon the operational streamflow forecast method for the Jordan River that is now in use. The modeling tools presented in this study are used to support the water-resource-assessment process and studies of seasonal hydroclimatic forecasting in this region.

The integration of climate change projections into hydrological and other response models used for water resource planning and management is challenging given the varying spatial resolutions of the different models. In general, climate models are generated at spatial ranges of hundreds of kilometers, while hydrological models are generally watershed specific and based on input at the station or local level. This paper focuses on techniques applied to downscale large-scale climate model simulations to the spatial scale required by local response models (hydrological, agricultural, soil). Specifically, results were extracted from a regional climate model (RegCM) simulation focused on the Middle East, which was downscaled to a scale appropriate for input into a local watershed model [the Hydrological Model for Karst Environment (HYMKE)] calibrated for the upper Jordan River catchment. With this application, the authors evaluated the effect of future climate change on the amount and form of precipitation (rain or snow) and its effect on streamflow in the Jordan River and its tributaries—the major water resources in the region. They found that the expected changes in the form of precipitation are nearly insignificant in terms of changing the timing of streamflow. Additionally, the results suggest a future increase in evaporation and decrease in average annual rainfall, supporting expected changes based on global models in this region.

Summary Estimation of surface fluxes in general, and evaporation rates over lake surfaces in particular, is a difficult task. While previous studies of Lake Kinneret, Israel, have looked at evaporation rate using a single timescale or single measurement method, this is the first comprehensive study to reconcile and explain the differences between a variety of measurement and calculation methods (pan evaporation, water and heat balance, aerodynamic methods and Penman simplified methods) across a multitude of temporal scales (10 min, 1 h, daily, monthly). The cross validation of the methods suggests that the hourly calculation with the aerodynamic methods may result in a better estimation of the monthly Bowen Ratio for the energy balance methods, and therefore may increase its reliability. We also show that comprehensive measurements and calculations of monthly heat storage change in the lake can be used to verify the hourly results of the hydrodynamic method, and the daily calculations of the Penman’s equation method. Moreover, using the Penman’s equation it is suggested that daily Pan A evaporation measurements are nearly similar to the evaporation from the deep water lake when the heat storage change is not taken into account. It is suggested that subject to data availability, the cross validation of multiple methods increases the reliability and confidence of the measured and calculated surface fluxes.

As a response to climate change, shifting rainfall trends including increased multi-year droughts and an escalation in extreme rainfall events are expected in the Middle East. The purpose of this study is to evaluate the potential impact of these shifting trends on stream flow in the Jordan River and its tributaries. We use a non-homogeneous hidden Markov model to generate artificial daily rainfall simulations which capture independently shifting trends of increased droughts and escalated extreme. These simulations are then used as input into a hydrological model calibrated for the upper catchments of the Jordan River to compare the impact on stream flow and water resources between the different rainfall scenarios. We compare the predicted baseflow and surface flow components of the tested watersheds, and find that while an increase in extreme rainfall events increases the intensity and frequency of surface flow, the over all flow to the Jordan River, and the characteristics of the baseflow in the Jordan River system is not largely impacted. In addition, though it has been suggested that in the case of a multi-year drought the karstic nature of the aquifer might lead to more intense, non-linear reductions in stream flow, here we quantify and show the conditions when annual stream flow reduce linearly with rainfall, and when these relations will become non-linear.

The association of topographic waves with wind action has been documented in several natural lakes throughout the world. However, the influence of the wind’s spatial variability (wind stress curl) on the frequency of topographic waves has only been partially investigated. Here the role of wind stress curl on the frequency of topographic waves in an idealized elliptic paraboloid basin has been studied both analytically and numerically. It is shown that the analytical solution is the sum of an elliptic rotation determined by the wind stress curl and two counterrotating circulation cells, which propagate cyclonically after the wind ceases. Furthermore, it is shown that cyclonic elliptical rotation (associated with positive wind stress curl) increases the rotation frequency of the double-gyre pattern while anticyclonic elliptical rotation (associated with negative wind stress curl) decreases the oscillatory mode frequency. It is also shown that bottom friction has some effect on the structure of the double-gyre pattern but hardly affects the oscillatory frequency. Numerical solutions of the depth-integrated nonlinear shallow-water equations confirmed that the frequency of the topographic wave increases (decreases) when forcing the model with cyclonic (anticyclonic) wind curl.

The green sulfur bacterium Chlorobium phaeobacteroides forms a dense population in the oxygen-devoid layers of Lake Kinneret, Israel, from July throughout November. The typical vertical distribution of the species is characterized by a prominent peak at the center of the metalimnion, but the light available at that depth in Lake Kinneret is far below the values that enable maximal photosynthetic activity of C. phaeobacteroides. In this paper, we report on our findings regarding the characteristics of C. phaeobacteroides development in Lake Kinneret, both in space and time. We further quantified the available light in the metalinmion and suggest a model for the development of C. phaeobacteroides in the lake. Spatial analysis of C. phaeobacteroides suggest that a combination of diurnal north-west wind, diurnal oscillations of the metalimnion and the hours of sunlight result in a situation in which the metalimnion in some parts of the lake is exposed to slightly higher light intensities than the other parts of the lake, and therefore allows higher concentrations of C. phaeobacteroides to develop. The analysis of C. phaeobacteroides with time suggests that it can be described fairly well by the logistic growth model.

Summary Spatiotemporal changes in the hydrogeology of the Hula altered wetland may influence the water quality of Lake Kinneret, which provides up to 30% of the potable water for the state of Israel. The main objectives of this work were to study the groundwater-flow characteristics in this wetland and assess the potential impact on downstream water quality. We constructed variograms of hydraulic heads, computed decision-tree models of major ions, and determined the hydraulic conductivity ( K ) and δ 2 H/δ 18 O ratios, to ascertain the spatial and vertical distribution of hydrogeological parameters. We also performed large-scale field experiments (⩾1 km 2 ) to assess the connectivity between the waterways and the wetland’s aquifer. The aquifer is fragmented by three parent materials: deep peat, shallow peat/marl complex and marl. The decision-tree-based model, the isotopic ratios and K determinations suggest that the deep peat subaquifer is composed of one homogeneous layer characterized by low K (0.001 m d −1 ). The two other subaquifers consist of three hydrostratigraphic layers: (i) the vadose zone, (ii) a layer with well-developed macropores at a depth of 1.5–4 m and (iii) an aquitard layer at a depth of 4–15 m. The temporal head fluctuations, the high K values of the second layer (>170 m d −1 ), and the large volume of water flowing into and out of the two subaquifers during large-scale field experiments all attest to excellent connectivity with the waterways. These results support the concept of critical source area which claims that most of the P loss in a catchment derives from small areas in which specific P release and transport mechanisms coincide with high connectivity. We conclude that the high connectivity of this Mediterranean altered wetland to waterways, coupled with the high P release that has occurred in recent years following soil flooding, provides the loading mechanism that partially explains the observed P increase in the Jordan River.

Rimmer, A. Systems hydrology models for the Upper Catchments of the Jordan River and Lake Kinneret, Israel. Isr. J. Earth Sci. 56: 1–17. In this paper we investigate three hydrological systems in the Upper Catchments of the Jordan River (UCJR) and Lake Kinneret (LK), Israel, for the explicit purpose of establishing an input–output relationship that can be used for reconstructing past events or predicting future events. By application of the system modeling approach to each problem we ascertained the nature of each system and the major physical laws that govern its operation. The studies focused on: (1) Identification of the hydrological system (precipitation–stream flow relations) of the Jordan River sources that originate from the karstic region of Mt. Hermon; (2) Detection of three unknown components—evaporation, saline springs discharge, and salinity—of the monthly water–solute–heat balances of Lake Kinneret; and (3) Long-term predictions of Lake Kinneret salinity, in response to operational changes such as reduced water and solute inflows. Each of the three hydrological problems that we show here will exemplify one of these three categories, applied for practical purposes to the water system of the UCJR and LK. Each system is presented from the description of the problem, through the mathematical justifications and equations, to the results and the attributed conclusions.

Global environmental change has influenced lake surface temperatures, a key driver of ecosystem structure and function. Recent studies have suggested significant warming of water temperatures in individual lakes across many different regions around the world. However, the spatial and temporal coherence associated with the magnitude of these trends remains unclear. Thus, a global data set of water temperature is required to understand and synthesize global, long-term trends in surface water temperatures of inland bodies of water. We assembled a database of summer lake surface temperatures for 291 lakes collected in situ and/or by satellites for the period 1985–2009. In addition, corresponding climatic drivers (air temperatures, solar radiation, and cloud cover) and geomorphometric characteristics (latitude, longitude, elevation, lake surface area, maximum depth, mean depth, and volume) that influence lake surface temperatures were compiled for each lake. This unique dataset offers an invaluable baseline perspective on global-scale lake thermal conditions as environmental change continues.

Peer reviewed. ©2015. The Authors.This is an open access article under theterms of the Creative CommonsAttribution-NonCommercial-N oDerivsLicense, which permits use and distri-bution in any medium, provided theoriginal work is properly cited, the use isnon-commerc ial and no modificationsor adaptations are made., In this first worldwide synthesis of in situ and satellite-derived lake data, we find that lake summer surface water temperatures rose rapidly (global mean = 0.34°C decade 1) between 1985 and 2009. Our analyses show that surface water warming rates are dependent on combinations of climate and local characteristics, rather than just lake location, leading to the counterintuitive result that regional consistency in lake warming is the exception, rather than the rule. The most rapidly warming lakes are widely geographically distributed, and their warming is associated with interactions among different climatic factors —from seasonally ice-covered lakes in areas where temperature and solar radiation are increasing while cloud cover is diminishing (0.72°C decade 1) to ice-free lakes experiencing increases in air temperature and solar radiation (0.53°C decade 1). The pervasive and rapid warming observed here signals the urgent need to incorporate climate impacts into vulnerability assessments and adaptation efforts for lakes.

Summary A system approach, daily precipitation-streamflow model was developed for both the base and the surface flow components, of large-scale karst basins. Long-term streamflow data were separated to baseflow and surface flow using the “recursive digital filter” method, which provides time series for model calibration. The HYdrological Model for Karst Environment (HYMKE) includes attributes to large-scale preferential flow that recharge the groundwater and solve the problem of uncorrelated baseflow and surface flow in a karst environment. HYMKE was applied simultaneously to the three major tributaries of the Upper Catchment of the Jordan River, which originate in the karstic region of the Hermon Mountain (Northern Israel). It was verified by comparing the calculated surface flow and baseflow with the daily time series of the baseflow separation procedure, and demonstrated good agreement of both the surface (r2 > 0.6) and baseflow (r2 > 0.77) components of each stream.

(2006). Empirical classification of stratification patterns in warm monomictic lakes. SIL Proceedings, 1922-2010: Vol. 29, No. 4, pp. 1773-1776.

The major hydrological variables that may cause long-term salinity changes in fresh water lakes are the volume of the lake, stream and/or groundwater inflows and outflows, direct rainfall, stream, groundwater, and rainfall salinity and evaporation. Measurements of these variables are usually subject to natural fluctuations and unavoidable errors of the measured data. Therefore, evaluation of the contribution of each component to the long-term salinity trends is difficult. In this work, it is shown that since salinization processes are linear, lakes are able to retain a 'solute influx memory', which records information about their lake-watershed-climate relationship in the past. Our objective was to test and verify a system approach method, which evaluates this 'memory', i.e. investigates the causes of long-term salinization processes in fresh water lakes. With this approach, a general expression is developed that represents the lake as a natural integrator of linear processes in space and time. The long-term change of the chloride concentration in the lake (representing salinity) reflects the long-term changes in each of the various past hydrological variables. The general theory of the lake as a natural integrator was tested by examination of the long-term salinity changes in Lake Kinneret, Israel, and Lake Biwa, Japan. The hydrology and salinity of both lakes are well monitored for several decades. In the analysis of Lake Kinneret, the long-term measurements of inflows, outflows and lake salinity were used to verify that the salinization mechanism follows the theory of complete mixing (system identification). In Lake Biwa the same approach was used, however, we assumed that the salinization mechanism was 'complete mixing', and the long-term measurements of the lake hydrology were used to investigate the reasons for increasing salinity (system detection). Since the system analysis is affected by uncertainties of the measured variables, a stochastic component was added, in order to take these uncertainties into account.

In thermally stratified lakes, nutrient-enriched hypolimnion and a nutrient-depleted epilimnion is a common feature. Vertical mixing between these layers affects geochemical and biological processes. We used chloride ion as an inert tracer to model the main factors controlling the chemical stratification and to identify lake-wide mixing processes. The stratified lake is treated as two completely mixed reservoirs separated by the thermocline. Based on the long-term records of temperature, hydrochemical, and hydrological data from Lake Kinneret (Israel) and Lake Biwa (Japan), monthly hypolimnetic and epilimnetic chloride concentrations were predicted and tested against measured chloride concentration profiles. Water-volume exchange between the layers during the thermocline deepening was calculated using mass balance. We found that changes in the epilimnetic and hypolimnetic inventories of an inert tracer (chloride) correspond quantitatively to the calculated water mass exchange, and as such, reflect mixing. Our inert-tracer-approach provides a basis for an operational means of quantifying the vertical mixing process in thermally stratified lakes independently from the heat budget.

Stream ordering is a useful property of every river network, having a wide range of applications. A method for determining stream orders that quickly and easily addresses various network topologies and magnitudes is therefore needed. This paper introduces a general recursive stream ordering framework for vector hydrography. It also presents a linear, O(n), stream ordering procedure for braided river networks, which is a major improvement to the existing quadratic, O(n2), procedure. The discussion includes results and interpretations, and the appendices present procedure pseudocodes and thorough line by line explanations.

Increased lake salinity is a growing problem in arid and semi-arid regions. Operational management, which is based on a reliable hydrological understanding, has the potential to reduce the lake salinity. This is the case of the salinity in Lake Kinneret (Sea of Galilee), where saline water flows into the lake through on-shore and off-shore springs. Here, we present a time-dependent flow and transport numerical model that successfully reproduces the monitored groundwater level, discharge, and salinity of the lake springs. The model utilizes a continuum approach and describes the flow through a confined saline carbonate aquifer, which interacts with the discharge lake through fractures and faults. In particular, the model investigates the hydrology around two groups of springs, Fuliya and Tabgha, along the western shore of the lake. Based on seasonal characteristics of the springs and measured boundary conditions, the two springs groups were defined as Lake Dominated Springs (LDS, Fuliya) and Aquifer Dominated Springs (ADS, Tabgha). The models of the two groups differ from each other in the distribution of fractured regions that link between the lake and the underlying aquifers. The numerical solution shows how the fractured regions affect groundwater head, spring discharge, and spring salinity. The different behavior of the LDS and ADS was reproduced with an excellent agreement between measured and calculated patterns. Differences in salinity within a group of springs are shown to be dependent on the depth of the fractured region. It was revealed that in addition to the appropriate distribution of fractured regions some adjustment in the up-stream boundary conditions is necessary to fully reproduce the system hydrology. The model has improved our understanding and provides a prediction tool for future management strategies.

The relatively high salinity of Lake Kinneret, Israel (190–350 ppm Cl−) is a result of the activity of saline springs located at the bottom of the lake. Their subsurface location inhibits direct monitoring of their fluxes. The objective of this work is to characterize the monthly ground water flow and salinity of the unmonitored saline springs over a long-term period, and to find a functional relationship between deriving variables and these monthly discharges. Results of the long-term evaluation of the unmonitored saline springs activity, are intended to help distinguish between two competing models (‘gravity driven flow’ (GFM) and ‘self potential’ models), which were proposed as the mechanism of the Lake Kinneret saline springs. The monthly solute and water balance of 32 consecutive years (1968–2001) was calculated, in which the contribution of the saline springs was considered as the residual. Error analyses were conducted for both the water and the solute residuals, and constraints were used to calculate a better, physically based time series representing the unmonitored saline springs activity. The calculated time-series of water and solute discharge from the springs were used to find the functional relationship with the lake level. It was found that there was an increase of water and solute fluxes to the lake at periods of high lake level. We concluded that the results are in agreement with the proposed GFM: high fluxes of ground water to the lake, and high leaching of solute are the result of rainy seasons, which usually cause high lake levels as well.