Articles | Volume 20, issue 6
Hydrol. Earth Syst. Sci., 20, 2195–2205, 2016
Hydrol. Earth Syst. Sci., 20, 2195–2205, 2016

Research article 08 Jun 2016

Research article | 08 Jun 2016

A two-parameter Budyko function to represent conditions under which evapotranspiration exceeds precipitation

Peter Greve1,2, Lukas Gudmundsson1, Boris Orlowsky1, and Sonia I. Seneviratne1 Peter Greve et al.
  • 1Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland
  • 2Center for Climate Systems Modeling (C2SM), ETH Zurich, Zurich, Switzerland

Abstract. A comprehensive assessment of the partitioning of precipitation (P) into evapotranspiration (E) and runoff (Q) is of major importance for a wide range of socio-economic sectors. For climatological averages, the Budyko framework provides a simple first-order relationship to estimate water availability represented by the ratio E / P as a function of the aridity index (EpP, with Ep denoting potential evaporation). However, the Budyko framework is limited to steady-state conditions, being a result of assuming negligible storage change in the land–water balance. Processes leading to changes in the terrestrial water storage at any spatial and/or temporal scale are hence not represented. Here we propose an analytically derived modification of the Budyko framework including a new parameter explicitly representing additional water available to evapotranspiration besides instantaneous precipitation. The modified framework is comprehensively analyzed, showing that the additional parameter leads to a rotation of the original water supply limit. We further evaluate the new formulation in an example application at mean seasonal timescales, showing that the extended framework is able to represent conditions in which monthly to annual evapotranspiration exceeds monthly to annual precipitation.

Short summary
The widely used Budyko framework is by definition limited to steady-state conditions. In this study we analytically derive a new, two-parameter formulation of the Budyko framework that represents conditions under which evapotranspiration exceeds precipitation. This is technically achieved by rotating the water supply limit within the Budyko space. The new formulation is shown to be capable to represent first-order seasonal dynamics within the hydroclimatological system.