The Water Isotopic Version of the Land-Surface Model ORCHIDEE: Implementation, Evaluation, Sensitivity to Hydrological Parameters

Camille Risi,Philippe Peylin,Nina Buchmann,Sandrine Bony,Francesca Guglielmo,Cathy Kurz Besson,Marie Hronkova,Lisa Wingate,Jerome Ogee,Monique Leclerc,Alexander Knohl,Naama Raz Yaseef,Jiri Santrucek,Thierry Bariac,Teresa David,Jeffrey Welker,Gengsheng Zhang

doi:10.4172/2157-7587.1000258

Abstract

Land-Surface Models (LSMs) exhibit large spread and uncertainties in the way they partition precipitation into surface runoff, drainage, transpiration and bare soil evaporation. To explore to what extent water isotope measurements could help evaluate the simulation of the soil water budget in LSMs, water stable isotopes have been implemented in the ORCHIDEE (ORganizing Carbon and Hydrology In Dynamic EcosystEms: the land-surface model) LSM. This article presents this implementation and the evaluation of simulations both in a stand-alone mode and coupled with an atmospheric general circulation model. ORCHIDEE simulates reasonably well the isotopic composition of soil, stem and leaf water compared to local observations at ten measurement sites. When coupled to LMDZ (Laboratoire de Meteorologie Dynamique-Zoom: the atmospheric model), it simulates well the isotopic composition of precipitation and river water compared to global observations. Sensitivity tests to LSM (Land-Surface Model) parameters are performed to identify processes whose representation by LSMs could be better evaluated using water isotopic measurements. We find that measured vertical variations in soil water isotopes could help evaluate the representation of infiltration pathways by multi-layer soil models. Measured water isotopes in rivers could help calibrate the partitioning of total runoff into surface runoff and drainage and the residence time scales in underground reservoirs. Finally, co-located isotope measurements in precipitation, vapor and soil water could help estimate the partitioning of infiltrating precipitation into bare soil evaporation.

Highlights

Land-surface models (LSMs) used in climate models exhibit a large spread in the way they partition radiative energy into sensible and latent heat [1,2] precipitation into evapo-transpiration and runoff [3,4,5], evapo-transpiration into transpiration and bare soil evaporation [6,7], and runoff into surface runoff and drainage [8,9,10]
Even when restricting the analysis to continental regions, the spatial correlations between the ctrl and nofrac simulations are 0.999 and 0.95 for δ18Op and dp respectively, and the root mean square differences are 0.27‰ and 1.1‰ for δ18Op and dp respectively. This confirms that fractionation at the land surface has a second-order effect on precipitation isotopic composition compared to the strong impact of atmospheric processes
The ORCHIDEE Land-Surface Models (LSMs), in which we have implemented water stable isotopes, reproduces the isotopic compositions of the different water pools of the land surface reasonably well compared to local data from MIBA and Carbo-Europe and to global observations from the GNIP and GNIR networks

Summary

Introduction

Land-surface models (LSMs) used in climate models exhibit a large spread in the way they partition radiative energy into sensible and latent heat [1,2] precipitation into evapo-transpiration and runoff [3,4,5], evapo-transpiration into transpiration and bare soil evaporation [6,7], and runoff into surface runoff and drainage [8,9,10].

Objectives

Results

Conclusion