Trends in daily rainfall intensity over Israel 1950/1-2003/4.

Abstract

The study focuses on long-term trends of daily rainfall in Israel as a function of their intensity in order to identify potential trends in rainfall extremity. The study period is the rainy season, October-May between 1950/1 and 2003/4. For the total rainfall, an increased trend is shown across Israel, especially for the central and southern regions, though non-significant. Daily rainfall intensity showed non-significant trends of increase in the heavy rainfall at the center and south and decrease at the north. The light to moderate rainfall trends increased in the north while they decreased at the center and south. Trends are significantly correlated with known teleconnection patterns, especially the East Atlantic- Western Russia and the North Sea-Caspian Sea patterns. Positive trends toward heavier rainfall are noted in Israel, which are significant in several specific locations. This finding has to be carefully followed since the region is a climatic border subjected to severe water shortage and is predicted to dry-up in most global warming scenarios. During the last decades there is an increasing evidence for more extreme rainfall at different places around the globe. Global warming was suggested to be linked with an increase in heavy rainfall due to an increase in atmospheric vapor and the warmer air. This trend is shown in the 4 th Assessment Report of the IPCC (1). In general, the Mediterranean Basin shows decreasing trends in the precipitation amount (2-4). The EM shows mixed rainfall trends but almost all stations show a decreasing trend in the precipitation which is especially large and significant during winter in the Greek, Cypriot and Turkish stations (5). Precipitation reduction over most Greek stations, combined with enhanced anticyclonic activity over almost the whole Mediterranean was found during the late 1980s and the early 1990s, a period characterized by high North Atlantic oscillation index values (6). Time series of extreme precipitation cases in Greece for the period 1970-2002, did not reveal significant positive or negative trend (7). Alpert et al. (8) showed the paradoxical increase of Mediterranean extreme daily rainfall in spite of the decrease in the total rainfall. They showed an increase in the torrential rainfall in Italy and Spain, heavy rainfall in Israel and heavy- torrential rainfall over Cyprus for the period 1951-1995. These trends were significant only in Italy and Spain. Kostopoulou and Jones (5) analyzed seasonal and annual trends over the central and Eastern Mediterranean (EM, 1958-2000). They showed statistically significant positive trends toward intense rainfall events and greater amount of precipitation for stations around the Italian Peninsula. For the EM, i.e., the Balkan Peninsula, western Turkey and