Surface runoff and pollutant load response to urbanization, climate variability, and low impact developments – a case study Mohammad Nazari-Sharabian, Masoud Taheriyoun and Moses Karakouzian ABSTRACT Using the Storm Water Management Model (SWMM), this study evaluated the impacts of (a) 20% and 50% urbanization at the mountainous Mahabad Dam watershed in Iran, as probable future land developments, (b) the urbanization location (near the outlet, in the middle, and at the far end of the watershed), (c) climate variability (increase in evaporation and rainfall intensity), and (d) implementing vegetative swales as low impact developments (LIDs), on watershed-generated runoff and pollutant loads (total suspended solids (TSS), total nitrogen (TN), and total phosphorus (TP)). Combination of the above-mentioned factors resulted in 17 scenarios, and each scenario was run for a 12-hour simulation in the model. The results indicated that based on land developments, areas with more dominant agricultural land generated more TN and TP, areas with more undeveloped lands generated more TSS, and more urbanized areas generated more runoff. Moreover, the 50% urbanization scenario resulted in more runoff and pollutant loads, compared with the 20% urbanization scenario. Under scenarios with climate variability, runoff and pollutant load peaks occurred earlier in time, due to the higher intensity rainfall events. Furthermore, LIDs decreased pollutant loads up to 25%, indicating their effectiveness in decreasing the impact of urbanization on receiving water bodies. Mohammad Nazari-Sharabian (corresponding author) Moses Karakouzian Department of Civil and Environmental Engineering and Construction, University of Nevada Las Vegas, Las Vegas, NV 89154, USA E-mail: nazarish@unlv.nevada.edu Masoud Taheriyoun Department of Civil Engineering, Isfahan University of Technology, Isfahan 8415683111, Iran Key words | climate variability, low impact development (LID), surface runoff, SWMM, vegetative swales INTRODUCTION Due to ongoing climate change, population growth, and high rates of urbanization during the late 20th and early 21st centuries, more cities have become exposed to the occurrence and impacts of pluvial flooding (Kalra et al. ). Land development is strongly related to impervious- ness, which is a critical property for determining surface runoff in an area. Therefore, unplanned urbanization can cause excessive runoff and higher pollutant loads, which can deteriorate water quality in receiving water bodies (Thakali et al. ). Moreover, climate change will affect the hydrological cycle and change atmospheric and meteorological properties, such as precipitation patterns, atmospheric water vapor, and evaporation (IPCC ; Thakali et al. ). In this situation, cities that lack drainage facilities are more vulnerable to flood inundations, especially from increased rainfall intensities and flash- floods, as a consequence of the change in climatic con- ditions (IPCC ). Understanding how pollutants travel in an environment requires an analysis of the underlying hydrological processes (Nazari-Sharabian et al. ). 2410 © IWA Publishing 2019 Water Supply | 19.8 | 2019 doi: 10.2166/ws.2019.123 Downloaded from http://iwaponline.com/ws/article-pdf/19/8/2410/662352/ws019082410.pdf by guest on 22 February 2023