What are distributed hydrological models and when are they used?

Distributed models represent spatial variation in catchment properties using grid cells or sub-catchments, unlike lumped models treating catchment as single unit. Types: physically-based (solve Richards equation, energy balance - MIKE SHE, GSSHA), conceptual distributed (HEC-HMS gridded, SWAT for water quality). Each cell has soil, land use, and topography parameters. Input includes spatial rainfall (radar, satellite). Advantages: capture spatial patterns, model ungauged basins, assess land use change impacts. Require extensive data and calibration. Appropriate for large, heterogeneous catchments.