Climate forcing and engineering design controls on household rainwater harvesting system reliability in Peri-urban Dar es Salaam, Tanzania

Study region: Kizito Huonjwa Street in Kimbiji Ward, Kigamboni Municipality, is a peri-urban coastal settlement in Dar es Salaam, Tanzania. Study focus: This study evaluated how seasonal rainfall structure, moderate extremes, projected climate forcing, and engineering design were associated with simulated household rooftop rainwater harvesting system (RWHS) reliability. Gridded rainfall and gauge observations were combined with six scenario-complete regional climate model chains under RCP4.5 and RCP8.5. Seasonal diagnostics, peak-over-threshold (POT) analysis, empirical quantile mapping (EQM), deterministic daily water balance simulation, and Type II analysis of variance were used to distinguish local design responses from formal variance attribution. Different roof catchment areas, RWHS storage capacities, and household demands were evaluated. New hydrological insights for the region: Across the 864 scenario simulations, engineering design terms accounted for 75.7% of simulated reliability variance, compared with 18.9% for the included climate forcing terms. Storage capacity had the largest individual contribution within the fitted design, followed by household demand, climate model identity, and roof area. For the climate model-based stress testing results, the rainfall scenario median differences were smaller than the corresponding inter-modal spread. These results are conditional on the evaluated factor ranges, six-model ensemble, daily rainfall forcing, deterministic RWHS formulation, and the absence of validation against observed household tank operation.