A warning system plays a crucial role in disaster management, and rainfall–runoff modeling is highly effective in representing real-world hydrological conditions using historical meteorological data. This study employed HEC-HMS, a freely available hydrological modeling software, to develop a flash flood model for the Sylhet region of Bangladesh. The model was set up for the Upper Meghna River Basin (also known as the Barak Basin), covering approximately 25,000 km². Discharge data from the Sheola station (SW173A) were simulated using 0.25°×0.25° gridded rainfall and 2-meter temperature data from the ERA5 database. The SCS Curve Number (CN) method, a loss method in HEC-HMS, was used to estimate runoff volume. The model was calibrated for 2019 and validated for 2020–2021, yielding R² values of 0.87 and 0.81, respectively, indicating satisfactory performance. The Nash–Sutcliffe Efficiency (NSE) index further confirmed model reliability, with values of 0.82 for calibration and 0.86 for validation. Finally, the model was applied to simulate flash flood events for 2019 and 2022, providing valuable insights for event-based hydrological simulations in the region.
Nitrous oxide (N2O) has gained increasing attention as a potent greenhouse gas, and its catalytic decomposition offers a promising mitigation strategy. In this study, single-atom Ru embedded in a rod-shaped CeO2 catalyst was synthesized via a H2O2 chemical etching strategy. The single-atom Ru catalyst demonstrated an exceptional N2O decomposition performance with only 0.48 wt % Ru loading, exhibiting a 34-fold increase in the turnover frequency compared to Ru nanoparticle catalysts. Under simulated exhaust conditions (NO, CO, and N2O), Ru1/CeO2 enabled complete conversion of all three pollutants at 280 °C. Mechanistic studies revealed that N2O decomposition over Ru1/CeO2 and Run/CeO2 followed the Mars-van Krevelen (MvK) and Langmuir-Hinshelwood (L-H) mechanisms, respectively. The exceptional N2O decomposition activity of the single-atom catalyst stems from enhanced O2 desorption through the recombination of oxygen atoms that dissociate from N2O with adjacent lattice oxygen. Notably, Ru1/CeO2 exhibits remarkable O2 tolerance due to the selective adsorption: N2O binds to single Ru atoms, whereas O2 occupies oxygen vacancies. In contrast, the high energy barrier associated with O2 combination and desorption in Run/CeO2 hindered N2O decomposition, and the competitive adsorption of O2 on its surface led to poor O2 resistance. This study demonstrates Ru1/CeO2 as an efficient catalyst for abating N2O and multipollutant removal.
