Ech2o (Maneta and Silverman, 2013) is a physically-based, distributed ecohydrologic model that solves the energy and water balance for the soil, vegetation, atmosphere column and calculates carbon uptake by vegetation. It also simulates vegetation dynamics and the later distribution of subsurface, overland, and channel flows. The model has been successfully to simulate hydrologic processes of watershed with a wide range of climates and environmental conditinos. Ech2o is research code developed in the Regional Hydrology Lab at the University of Montana and constantly evolving to accomodate the research needs of users.
Ech2o was designed as a watershed scale model that could be run externally with inputs from regional climate models. The conserves energy and water and is strongly based on the physics that describe the fluxes and stocks of water and energy in the landscape, but with simplifications that permit faster runs and fewer parameters.
The model has three major components: a vertical energy balance scheme that simulates soil-vegetation-atmosphere energy dynamics based on flux-gradient similarity approach; a hydrologic component based on the kinematic wave that provides lateral water transfer and ensures the hydrologic articulation of the landscape; and a forest growth component that includes carbon uptake, carbon allocation, leaf and root turnover and tree growth based on allometric relationships. The models are tightly coupled to ensure they capture the main feedbacks between vegetation, hydrology and climate.
Simulated feedbacks between the components include the effect of plant growth and phenology on the atmospheric boundary layer and on turbulent energy transfers. The leaf growth cycle impacts the transmission of shortwave radiation to the understory (shading), the emission of long wave radiation and the partition of sensible and latent heat fluxes. It also affects the interception of rain and snow by the canopy and the transpiration volumes. In turn, water and energy availability affect stomatal resistance, carbon uptake rates by vegetation, leaf and root turnover rates and carbon allocation ratios to leaves, stem and roots. Lateral redistribution of soil moisture affect the bulk heat capacity of soil and hence its temperature variation, it also affects the spatial pattern of water availability and the runoff generation areas.
The model domain is constructed and determined by a regularly gridded raster digital elevation model that defines the topography and the drainage network and establishes the finite-differences grid on which the governing equations are solved. Conservation of mass and energy are enforced at each time step and computational unit. Each grid cell in the model can have more than one vegetation type in addition to areas of bare soil. Vegetation types are differentiated in terms of its physiologic properties and structure rather than in terms of species.