Global review of hydrological response time: analysis and synthesis across diverse climates

Accurate estimation of time of concentration (TC) or lag time (TL) is essential for understanding watershed hydrological response and for flood forecasting, infrastructure design, and watershed management. However, the wide variety of TC and TL estimation methods, often developed for specific regional conditions, limits their transferability across watersheds with different sizes and climatic regimes. This study reviews 100 published articles on empirical TC/TL methods and evaluates their performance across climate zones ranging from hyper-arid to humid and across watershed scales from micro to large. Methods that incorporate flow-resistance factors, such as curve number and Manning’s coefficient, perform best in humid regions, whereas slope- and length-based channel methods are more suitable in arid environments. TC estimates show little variation in micro-watersheds but diverge markedly in larger basins due to complex drainage networks and spatial rainfall variability. Ranking analysis identifies the SCS Velocity (1986), NRCS Lag (1972), and Pasini (1914) equations overall.