Comment on the paper : “ Basin hydrologic response relations to distributed physiographic descriptors and climate ” by Karen Plaut

A basic problem relating to the long-term water balance involves splitting precipitation P, into runoff R, and actual evapotranspiration E. Berger and Entekhabi (2001) showed that the evapotranspiration efficiency E/Ep (Ep denotes potential evapotranspiration) and the runoff ratio R/P, are related to physiographic basin features and regional climate information. Berger and Entekhabi (2001) estimated actual watershed evapotranspiration E, and runoff R, at 10 basins across the US, using an equilibrium distributed hydrologic model. They argue that their results are preliminary because they are only based on modeled values of E and R. They suggest that the next step is to assemble observed evapotranspiration and runoff data for a number of basins to test their modeled results. We describe the results of such experiments here. We develop basin hydrologic response relations using observed (instead of modeled) fluxes of runoff from 1305 basins in the continental US. Analogous to their study which employed six basin descriptors, this study uses the following four basin characteristics: wetness ratio P/Ep, relative infiltration capacity ir/Ks, average slope S, and drainage density Dd. A linear regression model is developed which relates the runoff ratio to those basin descriptors, and our model is compared with an analogous model developed by Berger and Entekhabi.