Correspondence: Space-time asymmetry undermines water yield assessment

Understanding the effects of climate and land-cover changes on water yield is a challenging component in assessments of future water resources. Zhou et al. use Fuh’s equation, based on the widely used Budyko framework, to quantify the spatial differences of mean water yield normalized by precipitation (R/P) as a function of the climate wetness index (precipitation/potential evaporation P/PET) and watershed characteristics (m). Similar to what has been done before, Zhou et al. subsequently derive the sensitivity of R/P to both wetness (∂R/P/∂P/PET) and watershed characteristics (∂R/P/∂m) to expose the role of climatic and land-use changes on water yield. However, Zhou et al. ignore several crucial assumptions that undermine their use of the framework.