Offer rozenstein was supported by the Tim casgrain water management fund from McGill university several individuals from Ben-gurion university of the Negev are acknowledged noaohana-Levi is thinked for her advice on Geo-statistial analysis and comment on an early version of manuscript professor Amon karnieli is acknowledged for photographs in fig.5 and thanked for helpful discussion about the research area we thank Rachel been-stein for her field assistance yehoshua ratzon and roman joffe foy their technical assistance and joffe foy their technical assistance and Dr.shimrit maman for her techni-cal and administrative support asar data was provided by the European space agency