Spatial analysis of urban stormwater quality: Ramallah district as a case study, Palestine Ziad Mimi Water and Environmental Studies Institute, Birzeit University, Birzeit, Palestine Keywords land use; Palestine; pollutants; spatial analysis; stormwater. Correspondence Ziad Mimi, Water and Environmental Studies Institute, Birzeit University, Birzeit, Palestine. Email: zmimi@birzeit.edu doi:10.1111/j.1747-6593.2008.00118.x Abstract Urban runoff pollution sources are formidable obstacles to achieving water source goals in numerous municipalities. Ramallah district currently holds one of the highest rates of urbanization in Palestine causing a significant increase in surface runoff. Consequently, this causes increased flooding and a significant decrease in water quality due primarily to the accumulation of pollutants. To date, most research has focused on specifying temporal variations of storm- water quality parameters that include high uncertainties and also increase the risk of pollution control structures’ failure. Spatial variations of the runoff quality are the key factor in nonpoint source pollution studies. This research investigates the spatial variability of urban runoff quality parameters in relation to land use of urban catchments. The research estimated pollutant concentra- tion for improved and efficient design of pollution control structures for each land use. Introduction Land development and intensive land use lead directly to many of the pollution problems associated with urban runoff. These problems can be divided into two basic categories: urban runoff pollution and hydrologic impact of urbanization. Urban runoff pollution results from numerous sources, the most common of which is rainfall that becomes contaminated as it travels through the atmosphere, along the land surface and makes its way to a water body. Because urban runoff, which enters water bodies from diffuse or unidentifiable locations and sources, can cause significant water quality degradation, it must be addressed as part of a municipality’s overall urban runoff pollution prevention and control pro- gramme. The hydrologic impact of urbanization may cause the following changes to the hydrology of a devel- oping watershed: increased peak discharges, increased volume of storm runoff, decreased travel time or time of concentration and increased frequency and severity of flooding. To date, most investigations conducted on runoff quality have focused on the estimation of point-source pollu- tants. Little attention has been paid to different land uses such as residential, commercial, industrial and rural areas as sources of pollution. This kind of pollution is called nonpoint source or diffused pollution, which has been acknowledged as a major source of pollution to receiving waters (Goonetilleke et al. 2005). Despite considerable stormwater volume being gener- ated from urban catchments, pollutant concentrations and loads vary in relation to either land use or type of activity, which make their estimation for design of pollu- tant control structures very difficult. Complexity in the estimation of the diffused pollutants concentration and load is a serious impediment in the design of efficient pollutant treatment structures and also in planning reuse schemes of stormwater (Ghafouri & Swain 2004). Without field measurements, the direct assessment of detrimental effects from urban storm drainage remains uncertain, even when state-of-the-art modelling techni- ques are used. A number of urban hydrological models contain routines to simulate water quality (Donigian et al. 1995). Still, most of them are quite incapable of providing answers in the wider environmental context associated with the urbanization process. Questions such as rising groundwater levels beneath urban areas (George 1990), changes in groundwater quality in such locales, effects on aquatic systems and on fluvial processes (Graf 1975) have been accorded insufficient attention. Hall (1984) compared the loads of different pollutants in urban stormwaters and discovered an extreme varia- bility between different urban areas [e.g. biochemical oxygen demand (BOD) varying between 4.6 and 172 kg/ Water and Environment Journal 23 (2009) 128–133 c  2008 The Author. Journal compilation c  2008 CIWEM. 128 Water and Environment Journal. Print ISSN 1747-6585