Observations of positive sea surface temperature trends in the steadily shrinking Dead Sea

Abstract

Increasing warming of steadily shrinking Dead Sea surface water compensates for surface water cooling (due to increasing evaporation) and even causes observed positive Dead Sea sea surface temperature trends. This warming is caused by two factors: increasing daytime heat flow from land to sea (as a result of the steady shrinking) and regional atmospheric warming. Using observations from the Moderate Resolution Imaging Spectroradiometer (MODIS), positive trends were detected in both daytime and nighttime Dead Sea sea surface temperature (SST) over the period of 2000-2016. These positive SST trends were observed in the absence of positive trends in surface solar radiation, measured by the Dead Sea buoy pyranometer. We also show that long-term changes in water mixing in the uppermost layer of the Dead Sea under strong winds could not explain the observed SST trends. There is a positive feedback loop between the positive SST trends and the steady shrinking of the Dead Sea, which contributes to the accelerating decrease in Dead Sea water levels during the period under study. Satellitebased SST measurements showed that maximal SST trends of over 0.8 • C decade −1 were observed over the northwestern and southern sides of the Dead Sea, where shrinking of the Dead Sea water area was pronounced. No noticeable SST trends were observed over the eastern side of the lake, where shrinking of the Dead Sea water area was insignificant. This finding demonstrates correspondence between the positive SST trends and the shrinking of the Dead Sea indicating a causal link between them. There are two opposite processes taking place in the Dead Sea: sea surface warming and cooling. On the one hand, the positive feedback loop leading to sea surface warming every year accompanied by long-term increase in SST; on the other hand, the measured acceleration of the Dead Sea water-level drop suggests a long-term increase in Dead Sea evaporation accompanied by a long-term decrease in SST. During the period under investigation, the total result of these two opposite processes is the statistically significant positive sea surface temperature trends in both daytime (0.6 • C decade −1 ) and nighttime (0.4 • C decade −1 ), observed by the MODIS instrument. Our findings of the existence of a positive feedback loop between the positive SST trends and the shrinking of the Dead Sea imply the following significant point: any meteorological, hydrological or geophysical process causing the steady shrinking of the Dead Sea will contribute to positive trends in SST. Our results shed light on continuing hazards to the Dead Sea.

Spatial Non-Uniformity of Surface Temperature of the Dead Sea and Adjacent Land Areas

“…Based on both MODIS/Terra data ( Figure 6a) and MODIS/Aqua data (Figure 6b), positive SST trends over the pixels covering the west part of the lake are higher than those over the pixels covering the middle and east parts. The obtained positive trends in Dead Sea SST were observed in the absence of any positive trend in surface solar radiation [7].…”

“…Nehorai et al [3] discussed that the SST field is heterogeneous in the daytime and homogeneous in the nighttime. Kishcha et al [7] showed that, in the summer months, the spatial distribution of daytime Dead Sea surface temperature was non-uniform with maximal SST observed near the coastline, while minimal SST was observed in the middle of the Dead Sea. Further investigation of spatial non-uniformity of SST will advance the general understanding of SST-related atmospheric processes not only over the Dead Sea but also over other hypersaline lakes.Buoy measurements of temperature vertical profiles in the Dead Sea provide information about water temperature at different depths [3,[8][9][10][11].…”

“…Further investigation of spatial non-uniformity of SST will advance the general understanding of SST-related atmospheric processes not only over the Dead Sea but also over other hypersaline lakes.Buoy measurements of temperature vertical profiles in the Dead Sea provide information about water temperature at different depths [3,[8][9][10][11]. There are several studies on the Dead Sea SST [3,7,[12][13][14]. Kishcha et al [7] showed that increasing warming of steadily shrinking Dead Sea surface water was observed during the period of 2000-2016.…”

“…Kishcha et al [7] showed that increasing warming of steadily shrinking Dead Sea surface water was observed during the period of 2000-2016. They found that a positive feedback loop between steady shrinking of the Dead Sea and positive sea surface temperature trends causes the acceleration of Dead Sea evaporation and water level drop [7].Available remote sensing observations of skin surface temperature from MODIS on board the two satellites-Terra and Aqua [15,16]-provided us with an opportunity to monitor specific features of sea surface temperature of the Dead Sea and of land surface temperature (LST) over areas adjacent to the lake at the times when the two satellites cover the Dead Sea. Our study is aimed at investigating the patterns of spatial non-uniformity of SST/LST using the 17-year period of MODIS/Terra records (2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016) and the 15-year period of MODIS/Aqua records (2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016).…”

“…Kishcha et al [7] showed that increasing warming of steadily shrinking Dead Sea surface water was observed during the period of 2000-2016. They found that a positive feedback loop between steady shrinking of the Dead Sea and positive sea surface temperature trends causes the acceleration of Dead Sea evaporation and water level drop [7].…”