On the importance of including vegetation dynamics in Budyko’s hydrological model

Abstract. The Budyko curve describes the relationship between climate, evapotranspiration and run-off and can be used to model catchment energy and water balances. The curve’s underlying framework assumes catchments are at steady-state, a condition dependent on the scales of application, such that its reliability is greatest when applied to large catchments (>10 000 km2) and using long-term averages (≫1 year). At these scales previous experience has shown that the hydrological role of vegetation does not need to be explicitly considered within the framework. By demonstrating how dynamics in the leaf area, photosynthetic capacity and rooting depth of vegetation affect not only annual and seasonal vegetation water use, but also steady-state conditions, we argue that it is necessary to explicitly include vegetation dynamics into the Budyko framework before it is applied at small scales. Such adaptations would extend the framework not only to applications at small timescales and to small catchments but to operational activities relating to vegetation and water management.