Contemporary Climate Change in the Jordan Valley

Lee Teras


Cohen and Stanhill's study examines the climate changes that have occurred in the Jordan Valley since the publication of work by Jehuda Neumann (former director of research and training at the Israel Meteorological Service) forty years ago. Their work uses data gathered in Neumann's original study as well as more recent data from three sites in the Jordan Valley, on the border of Israel and Jordan. They compared records of daily minimum and maximum temperature, rainfall, and shorter, intermittent pairs of early and recent measurement series of global irradiance. Cohen and Stanhill used data gathered at three weather stations in the area. These sites were chosen based on the following criteria: unchanged location, continuous measurement of data over at least 45 years, absence of significant urbanization in the surrounding area, and proximity to the sites of the three major water bodies of the Valley. The chosen sites were Kfar Blum in the northern Hula Valley, Dagania Alef at the southern shore of Lake Kinneret, and Setom Pans to the south of the Dead Sea. In examining the data thus collected, Cohen and Stanhill reported climatologically significant changes in several parameters. First, they noticed a large decrease in global irradiance. Second, there was a 0.5 C decrease in average annual air temperature in the north and central regions of the valley, and a similar increase in the south. Finally, they noted a large decrease in estimated surface evaporation from both Lake Kinneret and the Dead Sea. Accompanying these changes were significant changes in land use of the surrounding vicinities. Lake Hula was drained in the 1950's. The Dead Sea's northern basin has shrunk significantly in area and its waters are now salt saturated. The sea's southern basin is now used as evaporation pans for mineral production. None of the data showed significant changes in rainfall at any of the sites. Neither has there been any change in interannual variability of rainfall. As mentioned, significant changes in temperature were noted. Particularly, maximum air temperatures and diurnal temperature ranges decreased significantly at all three stations. The seasonal course of the trends in temperature was complex and varied at the different sites. For the global irradiance data, only a few sets of intermittent data were available for the 1960's and 1980's. However, all three sites show a large and consistent reduction in irradiance. An attempt was made to correlate irradiance and other data with cloud cover data available for the Kfar Blum station, but no significant trends were found. In their discussion of the data trends, Cohen and Stanhill suggest that reductions in atmospheric transmissivity in the region may account for the decreases in global irradiance and in diurnal temperature ranges. They cite work by Bristow and Campbell (1984) that showed a strong correlation between diurnal temperature range and atmospheric transmissivity at two North American sites. Increases in the emissions of air pollutants from upwind, industrialized areas on the coastal plain of Israel may be responsible for the decrease in transmissivity. The decrease in irradiance can also be expected to contribute to the observed decrease in evaporation. Since the changes in land use in the Jordan Valley are still relatively recent, the effects are as yet largely unknown. Cohen and Stanhill suggest continued observation to document any effects.

The reduction in atmospheric transmissivity postulated in the Jordan Valley region is a good example of the cooling effect that anthropogenic emissions of aerosols may have. As discussed in several lectures and class readings, the effects of atmospheric pollutants is not always to increase global warming. The total effect depends on the relative amounts of greenhouse gases like carbon dioxide and other pollutants like aerosols or sulfur compounds that act to increase the reflectivity of clouds and thus produce a localized cooling effect, such as that demonstrated in the Jordan Valley. This study by Cohen and Stanhill demonstrates the importance of continued observations of weather patterns across the globe, so that the total effect of land use changes and atmospheric emissions can be documented. In this way, possible solutions to anthropogenic environmental damage can be formed based on the best available information.

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