RAIN EVENTS IN AN ARID ENVIRONMENT - THEIR DISTRIBUTION AND IONIC AND ISOTOPIC COMPOSITION PATTERNS - MAKHTESH RAMON BASIN, ISRAEL

Forty-six individual rain events and successive fractions of these events were studied with a network of instruments in the arid Makhtesh Ramon Basin, southern Israel, during 1981/1983. Annual rainfall varied from 47 to 107 mm, number of rain events varied from 8 to 20 per year, start of the rainy season varied from September to January, termination of the rainy season varied from March to May and length of the rainy season varied from 4 to 9 months. About 85% of the rain events were recorded at more than one station, indicating an aerial distribution exceeding 20 km. A cliff amount effect was observed - the rain on the cliff (800 m) was 73% more than the rain at the bottom of the Makhtesh (500 m). Soluble ionic compositions based on dust and rain samples are given in the paper. Two distinct sources of dissolved ions were inferred: dust, providing mainly Ca(HCO//3)//2, and cloud-borne sea spray, providing mainly Na** plus , Mg**2 ** plus , Cl** minus and SO//4**2** minus . A chemical and isotopic effect was observed and a chemical and isotopic front effect was observed. The observed rain distribution and chemical isotopic effects are discussed in terms of input sources, evaporation processes and altitude effects. The obtained data define rain and salt inputs into the hydrological systems.