Observing trends and extreme events impacts on lakes using ESA CCI Satellite Data Package

Lakes are already responding rapidly to climate change and in coming decades it is projected that global warming will have a more persistent and stronger effects on hydrology, nutrient cycling, and biodiversity (Cardoso et al. 2009; Carpenter et al. 2011). Recent projections estimate that lakes will get warmer for longer periods, with heatwaves potentially spreading across multiple seasons (Woolway et al. 2021). In some regions, heatwaves can add to existing pressure from drought which can lower lake levels and areal extent resulting from reduced inflows, increased evaporation and extraction for anthropogenic purposes (M?ynski et al. 2021; Zhao et al. 2022). The double heatwave event that occurred in the summer of 2019 in Europe was one of the top five warmest summers since 1500 (Sousa et al. 2020). In lakes, intense phytoplankton blooms might be the result of consecutive heatwave (e.g., Søndergaard et al. 2003; Free et al. 2021). When high temperatures are combined with low humidity, low rainfall, dry vegetation there is an increased risk of wildfire in case there is a source of ignition. Wildfires can have a significant hydro-geomorphological impact on watersheds in relation to post-fire rainfall events that can trigger erosion and transport processes leading to potential alteration of water quality (Smith et al., 2011). Despite the increased concern on the impact of wildfires on lake water quality, an uneven coverage of their geographical distribution has been observed (Shakesby and Doerr, 2006). Moreover, the topic has mainly been addressed at small scales while there remains a poor understanding at larger scales. The European Space Agency (ESA) Climate Change Initiative (cci) products could fill these gaps by providing long term, global coverage of both fire and water quality satellite-derived data also for the remote regions. The Lakes_cci project develops products covering Lake Water Level (LWL), Lake Water Extent (LWE), Lake Surface Water Temperature (LSWT), Lake Ice Cover (LIC) and Lake Water-Leaving Reflectance (LWLR) with the overarching objective to produce and validate a consistent long term dataset. The first phase of the project has recently been completed with the release of the last version (v2.0.2) of the dataset, including about 2000 lakes for the period 1992-2020. The dataset (netCDF file format) is hosted at the Centre for Environmental Data Analysis (https://catalogue.ceda.ac.uk/uuid/a07deacaffb8453e93d57ee214676304). A third user survey was conducted to collect user feedback on the data exploitation (https://climate.esa.int/en/projects/lakes/news-and-events/news/a-new-survey-for-users/). Phase 2 of the project started in July 2022. One scope of the project is the integration of different satellite-derived products across ESA CCI projects. For this reason, a study on wildfire and lakes is ongoing aiming to investigate the relationship between fires and lakes water quality over a wide range of geographical regions and fire regimes. The Fire_cci project, already at phase 2, focuses on several issues relating to fire disturbance including analysing and specifying scientific requirements relating to climate, production of burned area datasets, and product validation and product assessment. In this study potential of the CCI dataset is explored in three different case studies in the Eurasian region. I.Long-term trends in the ECV "Lakes" The dataset was explored for two Italian lakes and one Swedish lake of different depth and trophic state. The lakes are part of the Long-Term Ecosystem Research (LTER) network. In situ data from the LTER dataset were used to compare and integrate satellite products. Time-series of satellite data were then explored to examine trends in the context of key meteo-climatic variables.