TY - JOUR T1 - Rainfall‐manipulation experiments as simulated by terrestrial biosphere models: where do we stand? JF - Global Change Biology Y1 - 2020 A1 - Paschalis, Athanasios A1 - Fatichi, Simone A1 - Zscheischler, Jakob A1 - Ciais, Philippe A1 - Michael Bahn A1 - Lena R. Boysen A1 - Chang, Jinfeng A1 - De Kauwe, Martin A1 - Estiarte, Marc A1 - Goll, Daniel A1 - Hanson, Paul J. A1 - Harper, Anna B. A1 - Hou, Enqing A1 - Kigel, Jaime A1 - Alan K. Knapp A1 - Larsen, Klaus Steenberg A1 - Li, Wei A1 - Lienert, Sebastian A1 - Luo, Yiqi A1 - Meir, Patrick A1 - Nabel, Julia E.M.S. A1 - Ogaya, Romà A1 - Parolari, Anthony J A1 - Peng, Changhui A1 - Peñuelas, Josep A1 - Pongratz, Julia A1 - Rambal, Serge A1 - Schmidt, Inger Kappel A1 - Shi, Hao A1 - Sternberg, Marcelo A1 - Tian, Hanqin A1 - Tschumi, Elisabeth A1 - Ukkola, Anna A1 - Vicca, Sara A1 - Viovy, Nicolas A1 - Wang, ‐Ping A1 - Wang, Zhuonan A1 - Williams, Karina A1 - Wu, Donghai A1 - Zhu, Qiuan AB -

Changes in rainfall amounts and patterns have been observed and are expected to continue in the near future with potentially significant ecological and societal consequences. Modelling vegetation responses to changes in rainfall is thus crucial to project water and carbon cycles in the future. In this study, we present the results of a new model‐data intercomparison project, where we tested the ability of ten terrestrial biosphere models to reproduce observed sensitivity of ecosystem productivity to rainfall changes at ten sites across the globe, in nine of which, rainfall exclusion and/or irrigation experiments had been performed.

The key results are:
(a) Inter‐model variation is generally large and model agreement varies with time scales. In severely water limited sites, models only agree on the interannual variability of evapotranspiration and to a smaller extent gross primary productivity. In more mesic sites model agreement for both water and carbon fluxes is typically higher on fine (daily‐monthly) time scales and reduces on longer (seasonal‐annual) scales.
(b) Models on average overestimate the relationship between ecosystem productivity and mean rainfall amounts across sites (in space) and have a low capacity in reproducing the temporal (interannual) sensitivity of vegetation productivity to annual rainfall at a given site, even though observation uncertainty is comparable to inter‐model variability.
(c) Most models reproduced the sign of the observed patterns in productivity changes in rainfall manipulation experiments but had a low capacity in reproducing the observed magnitude of productivity changes. Models better reproduced the observed productivity responses due to rainfall exclusion than addition.
(d) All models attribute ecosystem productivity changes to the intensity of vegetation stress and peak leaf area, whereas the impact of the change in growing season length is negligible. The relative contribution of the peak leaf area and vegetation stress intensity was highly variable among models.

VL - 26 UR - https://onlinelibrary.wiley.com/doi/abs/10.1111/gcb.15024 ER - TY - JOUR T1 - Asymmetric responses of primary productivity to altered precipitation simulated by ecosystem models across three long-term grassland sites JF - Biogeosciences Y1 - 2018 A1 - Wu, Donghai A1 - Ciais, Philippe A1 - Viovy, Nicolas A1 - Alan K. Knapp A1 - K.R. Wilcox A1 - Michael Bahn A1 - M.D. Smith A1 - Vicca, Sara A1 - Fatichi, Simone A1 - Zscheischler, Jakob A1 - He, Yue A1 - Li, Xiangyi A1 - Ito, Akihiko A1 - Arneth, Almut A1 - Harper, Anna A1 - Ukkola, Anna A1 - Paschalis, Athanasios A1 - Poulter, Benjamin A1 - Peng, Changhui A1 - Ricciuto, Daniel A1 - Reinthaler, David A1 - Chen, Guangsheng A1 - Tian, Hanqin A1 - Genet, élène A1 - Mao, Jiafu A1 - Ingrisch, Johannes A1 - Nabel, Julia E. S. M. A1 - Pongratz, Julia A1 - Lena R. Boysen A1 - Kautz, Markus A1 - Schmitt, Michael A1 - Meir, Patrick A1 - Zhu, Qiuan A1 - R. Hasibeder A1 - Sippel, Sebastian A1 - Dangal, Shree R. S. A1 - Sitch, Stephen A1 - Shi, Xiaoying A1 - Wang, Yingping A1 - Luo, Yiqi A1 - Liu, Yongwen A1 - Piao, Shilong AB -

Field measurements of aboveground net primary productivity (ANPP) in temperate grasslands suggest that both positive and negative asymmetric responses to changes in precipitation (P) may occur. Under normal range of precipitation variability, wet years typically result in ANPP gains being larger than ANPP declines in dry years (positive asymmetry), whereas increases in ANPP are lower in magnitude in extreme wet years compared to reductions during extreme drought (negative asymmetry). Whether the current generation of ecosystem models with a coupled carbon–water system in grasslands are capable of simulating these asymmetric ANPP responses is an unresolved question. In this study, we evaluated the simulated responses of temperate grassland primary productivity to scenarios of altered precipitation with 14 ecosystem models at three sites: Shortgrass steppe (SGS), Konza Prairie (KNZ) and Stubai Valley meadow (STU), spanning a rainfall gradient from dry to moist. We found that (1) the spatial slopes derived from modeled primary productivity and precipitation across sites were steeper than the temporal slopes obtained from inter-annual variations, which was consistent with empirical data; (2) the asymmetry of the responses of modeled primary productivity under normal inter-annual precipitation variability differed among models, and the mean of the model ensemble suggested a negative asymmetry across the three sites, which was contrary to empirical evidence based on filed observations; (3) the mean sensitivity of modeled productivity to rainfall suggested greater negative response with reduced precipitation than positive response to an increased precipitation under extreme conditions at the three sites; and (4) gross primary productivity (GPP), net primary productivity (NPP), aboveground NPP (ANPP) and belowground NPP (BNPP) all showed concave-down nonlinear responses to altered precipitation in all the models, but with different curvatures and mean values. Our results indicated that most models overestimate the negative drought effects and/or underestimate the positive effects of increased precipitation on primary productivity under normal climate conditions, highlighting the need for improving eco-hydrological processes in those models in the future.

VL - 15 UR - https://www.biogeosciences.net/15/3421/2018/ IS - 11 ER -