Paragraphs Environmental Design

Rainwater Harvesting Potential of Residential Roofs in Selected Tropical Cities: A Secondary Data Assessment

Original Research · Environmental Design · 2024, Volume 2, Issue 2: 59–76

DOI: 10.5281/zenodo.24159353

Sarlono Sarwi Bochar*

Department of Architecture, Universitas Diponegoro

*Correspondence: sarloniserwib467@hotmail.com

Received: June 2024 | Accepted: August 2024 | Published: September 2024

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Abstract

Residential rooftop rainwater harvesting is frequently assessed from annual rainfall, although water arrives unevenly and must meet a defined demand. This study compares Singapore, Mumbai, and Chennai using published 1981–2010 monthly rainfall normals and literature released before 1 May 2023. Original calculations distinguish effective roof inflow, a monthly pooling benchmark without intermonth carryover, and an idealized seasonal carryover requirement. A standardized 100-square-metre connected roof, collection fraction of 0.80, four occupants, and illustrative target of 50 litres per person per day produce annual inflows of 173.27, 189.86, and 110.63 cubic metres, respectively, against annual demand of 73 cubic metres. All three are annually adequate, but monthly pooling matches 100.0 percent of demand in Singapore, 44.5 percent in Mumbai, and 65.4 percent in Chennai. Ideal seasonal carryover quantities are zero, 40.51, and 25.22 cubic metres; these are mean-month diagnostics, not recommended tank capacities. Rescaling each rainfall profile to 2,000 mm annually preserves the contrast, demonstrating the importance of seasonal distribution independently of annual amount. Sensitivity analysis across 81 roof, efficiency, and demand combinations shows that additional catchment has limited effect on dry-season matching where rainfall is nearly absent. At the higher demand scenario, Chennai becomes annually insufficient, which storage alone cannot remedy. The findings support differentiated service objectives and evaluation of roof area per resident. Daily rainfall sequences, building inventories, usable-water quality, local costs, and operating responsibilities remain necessary before claiming dependable household supply or citywide benefit. The assessment provides a reproducible screening basis while defining the limits of inference from monthly secondary data.

Keywords: rooftop rainwater harvesting; tropical cities; secondary data; rainfall seasonality; residential water demand; seasonal storage; water security

Citation

Bochar S. S. (2024). Rainwater Harvesting Potential of Residential Roofs in Selected Tropical Cities: A Secondary Data Assessment. Paragraphs Environmental Design, 2(2), 59–76. DOI: 10.5281/zenodo.24159353

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