Temperature of the surface layer of temperate lakes is reconstructed by means of a simplified model on the basis of air temperature alone. The comparison between calculated and observed data shows a remarkable agreement (Nash-Sutcliffe efficiency indices always larger than 0.87, mean absolute errors of approximately 1uC) for all 14 lakes investigated (Mara, Sparkling, Superior, Michigan, Huron, Erie, Ontario, Biel, Zurich, Constance, Garda, Neusiedl, Balaton, and Baikal, in west-to-east order), which present a wide range of morphological and hydrological characteristics. Differently from a pure heat flux balance approach, where the different fluxes are determined on the basis of independent relationships, the input data directly inform parameters of a simple model that, in turn, provides meaningful information about the properties of the real system. The dependence of the model parameters on the main morphological indicators is presented, which allows for a quantitative description of the strong influence of the mean depth of the lake on the thermal inertia and the hysteresis pattern between air and lake surface temperatures.The temperature of the surface layer is a crucial factor for the hydrodynamics and ecology of lakes. Water temperature changes may have important direct and indirect ecological effects via their influence on the lifehistory processes of organisms (metabolism, growth, reproduction) and the properties of the habitats (Winder and Sommer 2012). Temperature variations affect foodweb structures and the availability of nutrients for the biological systems in a lake. The effects of temperature on physical and chemical characteristics of lakes may also modify the distribution of individual taxa from the microbiological to the top predator scale (Eggermont and Heiri 2012;Wojtal-Frankiewicz 2012;De Senerpont Domis et al. 2013).Surface temperature is the result of heat fluxes at the lake surface (short-wave solar radiation, long-wave radiation from and to the lake, sensible and latent heat exchange) and at the boundaries (inflows and outflows, groundwater exchange, precipitation, etc.), and of heat transport due to mixing within the lake. All these fluxes depend on several variables (solar radiation, air temperature, wind speed and direction, cloudiness, relative humidity, etc.), some of which may be difficult or expensive to measure reliably and with sufficient precision. Moreover, some of the variables can change significantly over the lake surface and in time (e.g., wind), and reconstructing their spatial variation can be a particularly hard task. Predicting water temperature is nonetheless a desired goal and models of different types and of different complexity have been proposed, ranging from simple regression models (Livingstone and Lotter 1998;Sharma et al. 2008) to more complex process-based numerical one-dimensional Perroud et al. 2009;Thiery et al. 2014) and three-dimensional models (Wahl and Peeters 2014).In this work, we aim at obtaining results that are accurate enough to reliably p...

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Ice cover of the two Central European steppe lakes, Lake Balaton (Hungary) and Lake Neusiedl (Austria/Hungary), is characterized by high interannual variability (mean ice duration ± s.d.: 44±26 days and 73±28 days, respectively). For both lakes, a trend towards shorter ice duration and earlier ice-off can be observed in the 86 and 81 year data records, respectively. For Lake Neusiedl, significant trends for ice-on (+2.3 days decade −1 ), ice-off ( −1.8 days decade −1 ) and ice duration ( −3.1 day decade −1 ) are detected. At Lake Balaton, however, trends for ice-on (0 day decade −1 ), ice-off ( −0.7 days decade −1 ) and ice duration ( −1.2 days decade −1 ) are not significant. The temporal trends have accelerated for Lake Neusiedl in the past 60 years (ice duration −5.6 days decade −1 ). The variability of the ice parameters has increased during the 80 year observation period for Lake Neusiedl, but not for Lake Balaton. The number of melt-refreeze cycles at Lake Balaton increased at first, but then decreased during the last 20 years at both lakes.Warming trends in mean surface water temperatures for all seasons are more distinct than temporal trends of mean air temperatures. Increases of winter air temperature by 1°C are related to an ice-on delay, a decrease in ice duration (Lake Balaton: −12 days°C −1 , R 2 =0.72; Lake Neusiedl: −11 day°C −1 , R 2 =0.54) and an earlier ice-off. Snow cover, wind speed, and solar radiation are also related to ice dates.Mediterranean Oscillation and the North Atlantic Oscillation show significant relationships with ice phenology at both lakes whereas the East Atlantic teleconnection pattern only is related to ice characteristics of Lake Neusiedl.