Universität zu Köln

Post, Hanna, Franssen, Harrie-Jan Hendricks, Han, Xujun, Baatz, Roland, Montzka, Carsten ORCID: 0000-0003-0812-8570, Schmidt, Marius ORCID: 0000-0001-5292-7092 and Vereecken, Harry (2018). Evaluation and uncertainty analysis of regional-scale CLM4.5 net carbon flux estimates. Biogeosciences, 15 (1). S. 187 - 209. GOTTINGEN: COPERNICUS GESELLSCHAFT MBH. ISSN 1726-4189

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Abstract

Modeling net ecosystem exchange (NEE) at the regional scale with land surface models (LSMs) is relevant for the estimation of regional carbon balances, but studies on it are very limited. Furthermore, it is essential to better understand and quantify the uncertainty of LSMs in order to improve them. An important key variable in this respect is the prognostic leaf area index (LAI), which is very sensitive to forcing data and strongly affects the modeled NEE. We applied the Community Land Model (CLM4.5-BGC) to the Rur catchment in western Germany and compared estimated and default ecological key parameters for modeling carbon fluxes and LAI. The parameter estimates were previously estimated with the Markov chain Monte Carlo (MCMC) approach DREAM((zs)) for four of the most widespread plant functional types in the catchment. It was found that the catchment-scale annual NEE was strongly positive with default parameter values but negative (and closer to observations) with the estimated values. Thus, the estimation of CLM parameters with local NEE observations can be highly relevant when determining regional carbon balances. To obtain a more comprehensive picture of model uncertainty, CLM ensembles were set up with perturbed meteorological input and uncertain initial states in addition to uncertain parameters. C-3 grass and C-3 crops were particularly sensitive to the perturbed meteorological input, which resulted in a strong increase in the standard deviation of the annual NEE sum (sigma(Sigma NEE)) for the different ensemble members from similar to 2 to 3 gCm(-2) yr(-1) (with uncertain parameters) to similar to 45 gCm(-2) yr(-1) (C-3 grass) and similar to 75 gCm(-2) yr(-1) (C-3 crops) with perturbed forcings. This increase in uncertainty is related to the impact of the meteorological forcings on leaf onset and senescence, and enhanced/reduced drought stress related to perturbation of precipitation. The NEE uncertainty for the forest plant functional type (PFT) was considerably lower (sigma(Sigma NEE) similar to 4.0-13.5 gCm(-2) yr(-1) with perturbed parameters, meteorological forcings and initial states). We conclude that LAI and NEE uncertainty with CLM is clearly underestimated if uncertain meteorological forcings and initial states are not taken into account.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Post, Hanna UNSPECIFIED UNSPECIFIED UNSPECIFIED Franssen, Harrie-Jan Hendricks UNSPECIFIED UNSPECIFIED UNSPECIFIED Han, Xujun UNSPECIFIED UNSPECIFIED UNSPECIFIED Baatz, Roland UNSPECIFIED UNSPECIFIED UNSPECIFIED Montzka, Carsten UNSPECIFIED orcid.org/0000-0003-0812-8570 UNSPECIFIED Schmidt, Marius UNSPECIFIED orcid.org/0000-0001-5292-7092 UNSPECIFIED Vereecken, Harry UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-198940
DOI:	10.5194/bg-15-187-2018
Journal or Publication Title:	Biogeosciences
Volume:	15
Number:	1
Page Range:	S. 187 - 209
Date:	2018
Publisher:	COPERNICUS GESELLSCHAFT MBH
Place of Publication:	GOTTINGEN
ISSN:	1726-4189
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language LEAF-AREA INDEX; COMMUNITY LAND MODEL; EARTH SYSTEM MODELS; EDDY-COVARIANCE; DATA ASSIMILATION; SENSITIVITY-ANALYSIS; SOIL-MOISTURE; SURFACE MODEL; WINTER-WHEAT; SPIN-UP Multiple languages Ecology; Geosciences, Multidisciplinary Multiple languages
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/19894