Abstract

The Budyko curve is a widely used framework for predicting the steady-state water balance –solely based on the hydro-climatic setting of river basins. While this framework has been tested and verified across a wide range of climates and settings around the globe, numerous catchments have been reported to considerably deviate from the predicted behavior. Here, we hypothesize that storage capacity and field capacity of the root zone are important controls of the water limitation of evapotranspiration and thus deviations of the mean annual water balance from the Budyko curve. For testing our hypothesis, we selected 16 catchments of different climatic settings and varied the corresponding parameters of a simple water balance model that was previously calibrated against long-term data and investigated the corresponding variations of the simulated water balance in the Budyko space. We found that total soil storage capacity –by controlling water availability and limitation of evapotranspiration– explains deviations of the evaporation ratio (EVR) from the Budyko curve. Similarly, however to a lesser extent, the evaporation ratio showed sensitivity to alterations of the field capacity. In most cases, the parameter variations generated evaporation ratios enveloping the Budyko curve. The distinct soil storage volumes that matched the Budyko curve clustered at a normalized storage capacity equivalent to 5–15 % of mean annual precipitation. The second, capillarity-related soil parameter clustered at around 0.6–0.8, which is in line with its hydropedological interpretation. A simultaneous variation of both parameters provided additional insights into the interrelation of both parameters and their joint control on offsets from the Budyko curve. Here we found three different sensitivity patterns and we conclude the study with a reflection relating these offsets to the concept of catchment coevolution. The results of this study could also be useful to facilitate evaluation of the water balance in data-scarce regions, as they help constrain parameterizations for hydrological models a priori using the Budyko curve as a predictor.

Highlights

  • Reliable a priori estimates of the catchment water balance based on minimum data requirements still represents the holy grail 30 for many hydrologists (Sivapalan, 2003)

  • We found that total soil storage capacity –by controlling water availability and limitation of evapotranspiration– explains deviations of the evaporation ratio (EVR) from the Budyko curve

  • We interpret our results in terms of catchment coevolution in the Budyko framework, concentrating on patterns that emerged during the simultaneous parameter variations. 375 4.1 Water balance modeling 4.1.1 Model performance and hydrologic processes representation The hydrological model, despite its simplicity, proved capable of reproducing monthly discharge dynamics as well as the catchments’ annual and interannual water balance in the 30 years of simulation period

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Summary

Introduction

Reliable a priori estimates of the catchment water balance based on minimum data requirements still represents the holy grail 30 for many hydrologists (Sivapalan, 2003). The Budyko framework has been successfully used for catchment classification studies at continental scale (Berghuijs et al, 2014; Wagener 35 et al, 2007), for reducing equifinality in conceptual models by constraining the catchment water balance (Gharari et al, 2014), or for verifying uncalibrated predictions of the catchment water balance using thermodynamic optimality approaches (Porada et al, 2011) Due to this widely reported success and its theoretical underpinning (Wang et al, 2015; Westhoff et al, 2016), it appeared straightforward to us to use the Budyko framework to constrain the mean water balance of data-scarce Peruvian catchments (subcatchments of Chillón and Lurín river), which contribute to the fresh water supply of the city of Lima.

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