Hybrid Radiative–Evaporative Water‑Wall Integrating Persian Qanat, Badgir Wind‑Towers, and Modern Radiative Films/ Hydro‑Active Gels for Passive Cooling and Water Harvesting in Semi‑Arid Cities

Urban heat and water scarcity intensify in Mediterranean and semi‑arid regions. We propose a hybrid“Water‑Wall” concept that revisits ancient qanat galleries, badgir wind‑catch towers and step‑well cisterns,upgrading them with a SiO₂‑PVDF daylight‑radiative film (ε₈‑13 µm ≈ 0.97) and hydro‑active PVA–chitosangel panels¹ (latent heat ≈ 2250 kJ kg⁻¹). Coupled CFD–WRF simulations for a 1 m² prototype predict anaverage skin‑temperature reduction of ≈ 11 °C under 1 Sun and a nightly water yield of ≈ 12 L m⁻².Energy‑plus modelling suggests up to 25 % HVAC savings for a 100 m² classroom. If confirmed in field trials,the system could upgrade heritage water infrastructures toward SDG 6 & 13 with low‑cost (~45 USD m⁻²)materials.