On the uncertainty induced by pedotransfer functions in terrestrial biosphere modeling

Hydrological, ecohydrological, and terrestrial biosphere models depend on pedotransferfunctions for computing soil hydraulic parameters based on easily measurable variables, such as soil texturaland physical properties. Several pedotransfer functions have been derived in the last few decades, providingdivergent estimates of soil hydraulic parameters. In this study, we quantify how uncertainties embedded inusing different pedotransfer functions propagate to ecosystem dynamics, including simulated hydrologicalfluxes and vegetation response to water availability. Using a state-of-the-art ecohydrological model applied at79 sites worldwide, we show that uncertainties related to pedotransfer functions can affect both hydrologicaland vegetation dynamics. Uncertainties in evapotranspiration, plant productivity, and vegetation structure,quantified as leaf area, are in the order of ∼10% at annual time scales. Runoff and groundwater rechargeuncertainties are one order of magnitude larger. All uncertainties are largely amplified when small-scaletopography is taken into account in a distributed domain, especially for water-limited ecosystems with lowpermeability soils. Overall, pedotransfer function related uncertainties for a given soil type are higher thanuncertainties across soil types in both hydrological and ecosystem dynamics. The magnitude of uncertainties isclimate-dependent but not soil type-dependent. Evapotranspiration, vegetation structure, and plant productivityuncertainties are higher in water-limited semiarid climates, whereas groundwater recharge uncertainties arehigher in climates where potential evapotranspiration is comparable to precipitation.