Heatwaves in the hypersaline Dead Sea and freshwater Lake Kinneret caused by severe dust intrusion

We investigate lake heatwaves (LHWs) in the Eastern Mediterranean region, where desert dust intrusions are frequently observed. The role of dust intrusions in the formation of lake heatwaves has not been investigated in previous studies. In our study we focused on this point using both satellite and in-situ observations. In-situ buoy measurements showed that, in the two lakes located in the Eastern Mediterranean, in Israel: freshwater Lake Kinneret and the hypersaline Dead Sea, - a severe dust intrusion (AOD of over 2.5 and surface dust concentration of over 4000 µg/m³) caused the formation of lake heatwaves (LHWs), as appeared in September 2015. This was due to the two factors contributing to water heating at the lake surface: (a) the arrival of warm air from the desert and (b) the absorption of both shortwave solar radiation and longwave terrestrial radiation by large amounts of dust particles. In the two lakes, the lake heatwaves were represented by abnormally high daily maximal and minimal surface water temperature (SWT) in comparison with their seasonally varied 90^th percentile thresholds during the 10-day period (7 – 17 September 2015). The intensity of the observed LHWs was as high as 3 ^oC. We compared satellite (METEOSAT and MODIS-Terra) SWT data with in-situ SWT based on buoy measurements. First, spatial distribution of satellite (METEOSAT and MODIS-Terra) SWT showed that, over any part of the Dead Sea, satellite SWT on dusty days was lower than satellite SWT on clear-sky September 6. This contradicted the increase in in-situ SWT in the presence of the dust intrusion. Next, in the hypersaline Dead Sea and freshwater Lake Kinneret, we conducted a quantitative comparison between satellite SWT data and in-situ SWT. Our quantitative comparison showed that, in the presence of the dust intrusion, both orbital (MODIS-Terra) and geostationary (METEOSAT) satellites did not detect the observed LHWs. Instead of an increase in SWT, both satellites showed a decrease underestimating the in-situ SWT by up to 10 °C. The obtained significant difference between the satellite-derived SWT and in-situ SWT can be explained by the impact of the dust-caused infrared (IR) perturbations on satellite IR measurements. This should be considered when using satellite data to analyze heatwaves in the presence of dust pollution.

Reference: Kishcha et al., Remote Sensing 2024, https://doi.org/10.3390/rs16132314