# Effect of Extreme Climate Events on Lake Ecosystems
###### Abstract  
The Earth is facing a major change in climate due to ongoing global warming [1], and as a result of this warming, the occurrence of more extreme weather is also expected to increase. Accordingly, the impacts of extreme climatic events on lakes have been receiving more and more attention in recent years. Furthermore, advances in real-time high-resolution monitoring, together with an increase in the use of in-situ monitoring platforms on many lakes across the globe, now make it possible to track even the short-term effects of such events in lakes with differing characteristics and local climates. Such high-resolution data can also be used to better validate dynamic models of lake processes, models which are essential if the projected effects of global warming on lake ecosystems are to be quantified. Extreme climatic events include heatwaves, storms, extreme calm periods, sudden and intense rainfall, and droughts. These changes in local weather have the potential to result in physical, chemical, and biological changes within lakes. In deep lakes, for example, heatwaves and calm periods lead to stronger stratification and, if the lakes are nutrient enriched, often to higher levels of cyanobacterial biomass [2, 3, 4, 5]. Similar conditions can lead to temporary stratification of shallow lakes and this, in turn, can result in higher internal loading of phosphorus and thus eutrophication [6]. Storms often deepen the mixed layer depth and, combined with rain, it may enhance the input of dissolved and particulate matter and ultimately increase eutrophication [7]. Extreme drought may result in reduced water level, higher salinity, and higher nutrient concentrations [8], and extreme rain may result in increases in the flux of dissolved organic carbon from catchments [9]. Such effects may be of short-term duration, but if severe, they may have long-lasting consequences, particularly in lakes with longer retention times [10]. There is no universally accepted approach to define extreme events for lake studies. Extremes in climatic and hydrological datasets are generally defined by the use of thresholds based on, for example, a top or bottom percentile of the observed data from the site [11]. This type of threshold approach does allow for a systematic identification and assessment of events but has the drawback that the absolute threshold values will differ depending on location and the local climate. Nevertheless, thresholds based on local meteorological data have been used to identify potential extreme events within lakes (e.g., [12]). Definitions based on within-like physical changes can, however, be more complex due to inconsistency in the metrics used to define such extremes [13]. Other commonly used and equally valid approaches focus on the effects of, for example, named storms (e.g., [14]) orstudies on extreme or episodic responses within the lakes, even though the meteorological conditions that trigger the response may not in itself be over any extreme threshold [10]. This Special Issue includes all of these approaches and addresses effects of extreme events based on field studies, controlled experiments, and modelling. While winter storms are generally common in western Europe, the rarer summer storms may have more pronounced impacts on lake physics. Using a 13-year high frequency dataset of weather and lake thermal structure from the west of Ireland, [PERSON] et al. [15] quantified the effects of storms (defined using local wind speeds) on the physical conditions in a monomitic, deep lake situated close to the Atlantic Ocean. In winter, changes were distributed over the entire water column, whereas in summer, when the lake was stratified, storms only impacted the smaller volume above the thermocline.