Assessing runoff harvesting potential through water budgeting: a comparative study of three Indian secondary cities

• Significant annual runoff potential was quantified, offering a key local resource: 134,275 ML for Bhopal, 69,646 ML for Kozhikode, and a critical 6,586 ML for Bhuj. • Despite climatic differences, all three cities show major water deficits and depend heavily on external sources for 55% to 74% of their municipal supply. • Seasonal analysis reveals a concerning, long-term rise in evapotranspiration across all cities, highlighting the escalating impact of climate change on urban water security. • Tailored runoff harvesting can leverage each city's unique climate to reduce external dependency, close supply gaps, and build urban water resilience. Rapid urbanization in India presents significant challenges to water management, particularly in the context of climate change. This study investigates the potential of water budgeting as a tool for achieving water-sensitive urban design in three Indian secondary cities of Bhopal, Bhuj, and Kozhikode having diverse climatic zones, by using the Soil and Water Assessment Tool (SWAT). Daily precipitation and temperature records from 1951 to 2019, are sourced from the India Meteorological Department (IMD). The models for each city are successfully calibrated and validated against remotely sensed MODIS evapotranspiration data. The results reveal substantial variations in water budget ratios for the test cases. Bhopal, predominantly having urban and agricultural area, exhibits higher evapotranspiration and surface runoff, yielding an estimated runoff potential of 134,275.01 ± 12,061.49 ML/year. Bhuj, characterized by a larger urban footprint, faces severe water scarcity, yielding an estimated runoff potential of 6586.23 ± 2542.76 ML/year. Kozhikode, shows lower evapotranspiration, struggles with frequent flooding having an estimated runoff potential of 69646.21 ± 15693.15 ML/year. In addition, a seasonal analysis highlights the dominance of the monsoon in generating runoff, while revealing a consistent increasing trend in evapotranspiration across all three cities. The study identifies water deficits in all three cities when comparing population-based water supply requirements to the existing municipal supply. Bhopal relies heavily on external water sources (74%), while Bhuj (55%) and Kozhikode (58%) also depend significantly on external and groundwater sources. It is proposed that tailored runoff harvesting strategies can help all these cities leverage their unique climate and land use characteristics to promote water self-sufficiency.