The roles of water vapour, rainfall and solar radiation in determining air temperature change measured at Bet Dagan, Israel between 1964 and 2010

Abstract

Monthly mean values of climate at Bet Dagan in the central coastal plain of Israel, downwind of Tel Aviv, were analysed to yield seasonal and annual values of long- and short-wave irradiance which were then related to changes in air temperature measured between 1964 and 2010. Over half the large interannual variation and significant increase in atmospheric long-wave radiation, which averaged 0.7 W m⁻² per decade, was associated with concurrent changes measured in specific humidity. The remaining changes were attributed to increases in concentrations of carbon dioxide and other anthropogenic radiatively active gases. Large decadal variations and a significant overall reduction in short-wave solar radiation were measured averaging 3.6 W m⁻² per decade which were, in part, attributed to urban pollution. Changes in downwelling long- and short-wave irradiances together accounted for 58% of interannual variation in the mean annual temperature. Climate sensitivity to short-wave radiation forcing was very low compared with that of long-wave forcing resolving the paradox of the sharp rise in temperature accompanying negative all-wave radiative forcing (RF). Possible physical mechanisms explaining the decoupling between annual values of solar irradiance and air temperature are discussed. A significant, inverse correlation between temperature and the annual number of rain days was found, accounting for 21% of the interannual variation in air temperature unexplained by surface RF. During the last 45 years, changes in annual temperature at Bet Dagan, a near-coastal site with a strong urban influence situated in the semi-arid Mediterranean climate, were associated, in the following order of importance, with changes in water vapour, rainfall and solar radiation. Copyright © 2012 Royal Meteorological Society