A long-term dataset of simulated epilimnion and hypolimnion temperatures in 401 French lakes (1959–2020)

Abstract. Understanding the thermal behavior of lakes is crucial for water quality management. Under climate change, lakes are warming and undergoing alterations in their thermal structure, including surface and deep-water temperatures. These changes require continuous monitoring due to the possible major ecological implications on water quality and lake processes. With the scarcity of long-term in situ water temperature datasets, we present a regional long-term water temperature dataset (LakeTSim: Lake Temperature Simulations) produced over 401 French lakes by combining numerical modelling and satellite thermal data. The dataset consists of daily epilimnion and hypolimnion temperatures for the period 1959–2020 simulated with the semi-empirical OKPLM (Ottosson-Kettle-Prats Lake Model). We also describe this model and its performance. We present the uncertainty analysis of simulations with default (parametrized with satellite thermal data over all lakes and in situ measurements) and calibrated (with in situ temperature measurements for each lake) model parameters as well as the sensitivity analysis of the latter. Overall, the 90 % confidence uncertainty range is largest for hypolimnion temperature simulations with a median of 8.5 ºC and 2.32 ºC respectively with default and calibrated parameter values. There is less uncertainty associated with epilimnion temperature simulations with a median of 5.42 ºC and 1.85 ºC before and after parameter calibration. This dataset will help provide insight into the thermal functioning of French lakes. It provides over six decades of epilimnion and hypolimnion temperature data, crucial for climate change studies at a regional scale. The dataset will also be of great advantage for decision making by stakeholders.