Biotic and abiotic interactions between the riparian zone and the river determine relevant hydrological processes and wield control on riparian and bordering upland vegetation types; plants respond and adapt to environmental conditions; likewise they control the hydrological cycle of the ecosystems. Vegetation growth and development are mainly controlled by water availability on semiarid regions, thus root depths and soil water content fluctuations are fundamental at the soil–plant–atmosphere continuum. Under this condition the closeness to the river yields a moisture gradient which clearly determines the boundaries between exuberant riparian zone and semiarid upland. 

To emphasize semiarid conditions and ecohydrological processes, a mathematical model called riparian water and vegetation RibAV has been designed and applied to simulate riparian vegetation and hydrological river regime interactions, based on the main worldwide ecosystem modeling approaches and field expertise. This technological tool is useful on the determination of vegetation growth and responses to fluctuations on saturated and unsaturated water availability, originated in a daily basis water balance controlled by the river and the plant type own adaptation mechanisms.

In this riparian model the hydrological regime determines the water-table fluctuations on the riparian zone by a simple approach. The hydrology of the riparian zone is simulated by a conceptual water balance which takes into account the soil water storage, the main water fluxes (precipitation, infiltration, evapotranspiration, surplus, and upward flux from the water table) and also the hydraulic lift by roots as an innovation on riparian scale modeling.

The theory of plant functional types proposed for semiarid riparian zone was applied and strengthening by including taxonomical vegetation ordination. After establishing zones to be modeled, characteristic biophysical parameters were determined at the level of undisturbed riparian forest and deciduous dry forest of the upland in the semiarid Motagua Valley, Guatemala. The implementation of the RibAV model has allowed to evaluate riparian vegetation responses to permanent rivers of basins draining from the UNESCO Biosphere Reserve Sierra de las Minas (Teculután and Uyús) which hydrology has been obtained with distributed hydrological modeling.

The rates of evapotranspiration of the vegetation types are generated by RibAV from their different response and adaptation mechanisms to the available water at the saturated and unsaturated zone; through values comparison, a categorical scale from the RibAV evapotranspiration indexes ETindex is established to predict riparian plant absence / presence.

By using the so called vegetation ecological index Kappa the model has been calibrated, validated and evaluated, to know its efficiency on predictive plant distribution. Thus the RibAV outstanding performance to establish vegetation riparian types and the limit between this zone and the bordering upland has been proved; the strength of ETindex before other commonly used indexes to classify plant communities in riparian semiarid environment has also been proved.