[1] The Dead Sea is a hypersaline terminal lake experiencing a water level drop of about 1 m/yr over the last decade. The existing estimations for the water balance of the lake are widely variable, reflecting the unknown subsurface water inflow, the rate of evaporation, and the rate of salt accumulation at the lake bottom. To estimate these we calculate the energy and mass balances for the Dead Sea utilizing measured meteorological and hydrographical data from 1996 to 2001, taking into account the impact of lowered surface water activity on the evaporation rate. Salt precipitation during this period was about 0.1 m/yr. The average annual inflow is 265–325 × 106 m3/yr, corresponding to an evaporation rate of 1.1–1.2 m/yr. Higher inflows, suggested in previous studies, call for increased evaporation rate and are therefore not in line with the energy balance.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2005WR004084

Water, salt, and energy balances of the Dead Sea

The ability of both the ECMWF-TOGA analyses and regional model RegCM2 to simulate the climate of the Middle East is examined. The climate of the region displays high spatial, seasonal and interannual variability, providing a strong test of a climate model’s abilities. The higher resolution of RegCM2, compared with the ECMWF analyses, allows it to capture the spatial variability of temperature and precipitation better despite model biases being present. Both RegCM2 and the analyses have a cold bias, exacerbated in RegCM2 by a bias present in the prescribed sea-surface-temperature forcing. RegCM2 does not capture the annual cycle of precipitation on the Black and Caspian Sea coasts, where very steep topography exists, nor on the eastern Mediterranean coast, where the coastal mountains are not resolved. RegCM2 does capture the seasonal cycle in the Fertile Crescent and Zagros Mountains, where it is strongly influenced by a plateau circulation above the Iranian plateau. It is shown that accurate simulation of precipitation in these regions requires the correct simulation of storm tracks, topographic interactions and atmospheric stability. RegCM2 is better able to simulate the interannual variability averaged over the entire domain compared with the ECMWF analyses; however, they both have difficulty reproducing the interannual variability in particular subregions. It is also shown that processes controlling the seasonality of precipitation differ in different subregions and are often different from the processes controlling interannual variability. This suggests that, in order to model precipitation successfully, a horizontal scale that allows differentiation of precipitation zones dominated by different precipitation processes, both seasonally and interannually, is required. Copyright  2004 Royal Meteorological Society.

Middle east climate simulation and dominant precipitation processes

Dust deposition over the Dead Sea

In this study, the ability of a regional climate model, based on MM5, to simulate the climate of the Middle East at the beginning of the twenty-first century is assessed. The model is then used to simulate the changes due to global warming over the twenty-first century. The regional climate model displays a negative bias in temperature throughout the year and over most of the domain. It does a good job of simulating the precipitation for most of the domain, though it performs relatively poorly over the southeast Black Sea and southwest Caspian Sea. Using boundary conditions obtained from CCSM3, the model was run for the first and last 5 years of the twenty-first century. The results show widespread warming, with a maximum of ~10 K in interior Iran during summer. It also found some cooling in the southeast Black Sea region during spring and summer that is related to increases in snowfall in the region, a longer snowmelt season, and generally higher soil moisture and latent heating through the summer. The results also show widespread decreases in precipitation over the eastern Mediterranean and Turkey. Precipitation increases were found over the southeast Black Sea, southwest Caspian Sea, and Zagros mountain regions during all seasons except summer, while the Saudi desert region receives increases during summer and autumn. Changes in the dominant precipitation-triggering mechanisms were also investigated. The general trend in the dominant mechanism reflects a change away from the direct dependence on storm tracks and towards greater precipitation triggering by upslope flow of moist air masses. The increase in precipitation in the Saudi desert region is triggered by changes in atmospheric stability brought about by the intrusion of the intertropical convergence zone into the southernmost portion of the domain.

Global warming impact on the dominant precipitation processes in the Middle East

Atmospheric measurements were performed during a 1 month period in early summer of 1997 at the Dead Sea in Israel in an attempt to identify bromine monoxide BrO, and evaluate its effect on ozone chemistry. The differential optical absorption spectroscopy (DOAS) technique was utilized to identify and measure BrO present in the air masses. Concurrent to the DOAS measurements, continuous monitoring of SO2, NO/NOx, O3, and CO was performed. Filter samples for aerosol analysis and whole air canister samples for bromocarbon analysis were also collected. The present paper reports the complete comprehensive data set of the measurements at the Dead Sea site and is a continuation to our preliminary communication [Heberstreit et al., 1999]. The more complete data now available enable a more detailed examination of the sources and mechanisms of the reactive halogen species and the presentation of new conclusions. The results showed a diurnal repeating cycle of O3 and BrO variations, correlated with solar radiation and wind direction. During the elevated BrO events, where bromine oxide rose to daily maximum values often exceeding 100 ppt, a clear negative correlation with O3 was observed. During these episodes, the O3 regularly decreased from noontime levels of 50–80 ppb or higher down to 10–30 ppb and occasionally to levels below the detection limit of 2 ppb. The enhanced BrO levels were associated with southerly winds that are typical for the location during midday hours. This suggests that a possible source for the reactive bromine species is the interaction of atmospheric oxidants with bromide at the surface of the large salt pans located at the southern end of the Dead Sea. Research flights flown over the area showed that ozone destruction to levels well below the background values were observed over large areas of the Dead Sea Valley.

/pdf/bromine-oxide-ozone-interaction-over-the-dead-sea-37v5k0cho2.pdf

Bromine oxide—ozone interaction over the Dead Sea

In the last decade pan evaporation measured at the Southern Dead Sea has significantly increased. Wind, temperature and humidity measurements at the Dead Sea starting in the 1930s as well as 3-D model simulations all seem to indicate a statistically significant change in the local climate of the Dead Sea region. The potential contribution to this climatic change through the weakening of the local land-sea breeze circulation caused by the reduction in the Dead Sea surface area in 1979–1981, is examined. It is suggested that since the breeze tempers the Dead Sea climate, its weakening has caused the air temperature to increase, the relative humidity to decrease and thus increased the pan evaporation. The climatic changes as implied by the MM4 Mesoscale PSU/NCAR model simulations, seem to fit the observed changes and to suggest a local tendency to the more arid climate that now prevails to the south of the study region.

H. Shafir

Papers

Recent changes in the climate at the dead sea - a preliminary study