Abstract:Runoff generation in a Mediterranean carbonate rock environment-the Judaean Mountains, West Bank and Israel-was studied by a 2 day sprinkling experiment on an 18 ð 10 m 2 plot. During the first day, three spells of 24Ð1 mm h 1 (12Ð3 mm), 27Ð8 mm h 1 (12Ð3 mm) and 14Ð4 mm h 1 (12Ð5 mm) were applied, almost saturating the runoff plot. On the second day, 20 h later, two spells of 18Ð7 mm h 1 (34Ð3 mm) and 35Ð2 mm h 1 (25Ð4 mm) followed. Surface runoff was a combination of infiltration excess runoff from rocky portions of the plot and saturation excess runoff from areas covered by soil. Soil saturation was accelerated by lateral runoff from adjacent rocky areas. Once the plot was saturated, 80-90% of the applied rainfall became surface runoff. Significantly different concentrations of chloride, sulphate, and nitrate ions in the sprinkled water on two successive days served as tracers. During the second day a two-component hydrograph separation pointed to the importance of shallow reservoirs playing active parts in runoff generation. About 14% of the flow collected during the second day originated from water applied during the first day. During the second day of sprinkling, both water sources obviously mixed in saturated soil reservoirs and contributed in variable percentages to surface flow. It is hypothesized that, at least during high-magnitude rainfall, the steep rocky slopes investigated might be regarded as flood-generating zones rather than areas of pronounced recharge into the underlying Yarkon-Taninim aquifer.

Abstract. The Mediterranean climate together with the type of urban setting found in mountainous Middle Eastern cities generate much lower runoff yields than previously reported and than usually estimated for urban design. In fact, a close analysis shows that most of the rainwater remains within the cities as a possible source for urban groundwater recharge. The present study examined two locales -Ramallah, an old traditional Palestinian Arab town, and Modiin, a new township in Israel -both situated on the karstic Yarkon Taninim aquifer. This aquifer supplies the only high-quality drinking water in the region (one quarter of the Israeli-Palestinian water demand), which is characterized by dense populations and limited water resources.This paper provides the first measured information on the hydrological effects of urbanization in the area. It was found that the shift of the mountainous natural steep slopes into a series of closed-terraces with homes and gardens create areas that are disconnected from the urban runoff response. Roofs drained into the attached gardens create favorable recharge units. Mainly low-gradient roads became the principal source for urban runoff already following 1-4 mm of rainfall. Parallel roads converted single peak hydrographs towards multi-peak runoff responses, increasing flow duration and reducing peak discharges. The remaining urban area (public parks, natural areas, etc.) generated runoff only as a result of high-magnitude rainstorms. All of the above conditions limited urban runoff coefficients to an upper boundary of only 35% and 30% (Ramallah and Modiin, respectively). During extreme rainstorms (above 100 mm) similar runoff coefficients were measured in urban and natural catchments as a result of the limited areas contributing to runoff in the urban areas, while natural terrain does not have these artificial limits. Hence, the effects of urbanization decrease with Correspondence to: T. Grodek (tamir.grodek@huji.ac.il) event magnitude and there is significant potential for urban groundwater recharge. However, frequent low-magnitude rainstorms often generate highly polluted stormwater in urban sewer systems and this water should only be used with great caution.

Abstract. In the Middle East, water is scarce and population growth causes a rapid rise of urban centers. Since many towns of the Palestinian Authority (PA) suffer from water shortage, the use of rainwater harvesting (RWH) as an alternative to conventional water supply has gained increasing interest among water resources planners. This study quantifies actual volumes of urban RWH to be expected from highly variable Mediterranean rainfall. A one-parameter model uses measured potential evaporation and high resolution rainfall data as input to calculate RWH volumes from rooftops inside Ramallah, a traditional Arab town. While during average seasons a 87 % runoff harvest (480 from 550 mm of rainfall) can be expected, this value decreases to about 75 % (190 from 250 mm of rainfall) during drought seasons. A survey comprising more than 500 questionnaires suggests that approximately 40 % of the houses are equipped with RWH systems from which one third are out of use. Although water quality is perceived to be favourable, only 3 % of the active RWH systems are actually used for drinking and only 18 % for domestic purposes. All active RWH systems investigated may harvest approximately 16 × 10 3 m 3 of rooftop runoff during an average season and 6 × 10 3 m 3 during droughts. When these numbers are extrapolated to all houses in Ramallah, theoretical maximum potentials increase to approximately 298 × 10 3 m 3 during average seasons and 118 × 10 3 m 3 during droughts. A part of this potential can easily be exhausted by rehabilitation of installed RWH systems. The use of RWH for emergency water supply should be advocated, although care is needed because of hygienic risks. Regional estimates for the entire Lower Jordan River Basin yielded RWH potentials of 20 × 10 6 m 3 during the average season 2002/2003 but only 3 × 10 6 m 3 during the drought season 1998/1999. Thus, urban RWH is a relatively small contribution to overcome water scarcity in the region and decreases significantly during droughts. Yet it is a sustainable water resource, which is available on spot for everybody. Due to population growth and ongoing urbanization it will be more important in future.

In the Middle East, water is scarce and population growth causes a rapid rise of urban centers. Since many towns of the Palestinian Authority (PA) suffer from water shortage, the use of rainwater harvesting (RWH) as an alternative to conventional water supply has gained increasing interest among water resources planners. This study quantifies actual volumes of urban RWH to be expected from highly variable Mediterranean rainfall. A one-parameter model uses measured potential evaporation and high resolution rainfall data as input to calculate RWH volumes from rooftops inside Ramallah, a traditional Arab town. While during average seasons a 87% runoff harvest (480 from 550 mm of rainfall) can be expected, this value decreases to about 75% (190 from 250 mm of rainfall) during drought seasons. A survey comprising more than 500 questionnaires suggests that approximately 40% of the houses are equipped with RWH systems from which one third are out of use. Although water quality is perceived to be favourable, only 3% of the active RWH systems are actually used for drinking and only 18% for domestic purposes. All active RWH systems investigated may harvest approximately 16 × 10³ m³ of rooftop runoff during an average season and 6 × 10³ m³ during droughts. When these numbers are extrapolated to all houses in Ramallah, theoretical maximum potentials increase to approximately 298 × 10³ m³ during average seasons and 118 × 10³ m³ during droughts. A part of this potential can easily be exhausted by rehabilitation of installed RWH systems. Also, the use of collected water for drinking should be advocated. This should go along with regular checks of water quality and regulations concerning adequate water storage and treatment/disinfection procedures where necessary. Regional estimates for the entire Lower Jordan River Basin yielded RWH potentials of 20 × 10⁶ m³ during the average season 2002/2003 but only 3 × 10⁶ m³ during the drought season 1998/1999. Thus, urban RWH is a relatively small contribution to overcome water scarcity in the region and decreases significantly during droughts. Yet it is a sustainable water resource, which is available on spot for everybody. Due to population growth and ongoing urbanization it will be more important in future

Box 1 Sanitary inspec tion form for household latrines (single pit VIP)