Contemporary Climate Change in the Jordan Valley

Abstract

This study examines the climate changes that have occurred in the 40 years since the publication of Jehuda Neumann's classic climatological studies of the energy and water balance of the natural water bodies of the Jordan Valley. The measurements analyzed in this paper were those made during the last half century at three rural sites in the Israel Meteorological Service's climate station network. They consist of 45?60 years of continuous records of daily minimum and maximum temperature, and rainfall and shorter, intermittent pairs of early and recent measurement series of global irradiance, which were available from nearby sites. Annual averages of minimum and maximum temperatures showed statistically significant decreases in mean annual maximum temperatures. These were ?0.035°C per year at Kfar Blum (north of the former Hula swamp), ?0.024°C per year at Degania A (on the southern show of Lake Kinneret) and ?0.018°C per year at Sedom (near the southern shore of the Dead Sea). Minimum temperatures showed no significant change at Kfar Blum, decreased significantly at Degania by 0.011°C per year and increased significantly by 0.024°C per year at Sedom. The temperature trends showed a complex seasonal pattern. No significant changes in total annual rainfall or its interannual variance were found. Although much of the interannual variance in the temperature records could be explained by the large variations in annual rainfall, annual temperature trends remain unchanged after removal of the rainfall influence. Comparison of the three pairs of global irradiance measurement series made in the Jordan Valley during the 1960s and the 1980s indicates that a marked decrease in irradiance has accompanied the decreases in maximum temperatures, the decrease in irradiance being greatest at the cloudier sites and seasons. Cloud cover observations at Kfar Blum showed that this decrease in irradiance could not be explained by an increase in cloud cover. The results indicate that a significant reduction in atmospheric transmissivity has occurred in this region, possibly caused by the increased emissions of anthropogenic aerosols from the upwind industrialized coastal region of Israel and of Europe. Finally the consequences of the above changes for the agriculture and hydrology of the region are briefly discussed.