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We present a bio-economic model by combining a process-based grassland simulation model with an economic decision model that accounts for income risks and yield quality. The model is used to examine optimal nitrogen (N) application rates in a grass–clover system in Switzerland under current and future climatic conditions. Results for present-day climatic conditions suggest that an increase in N inputs has positive effects on yields but also leads to higher yield variability, yield distributions more skewed to the left and therefore higher downside risks. As a result, accounting for farmers’ risk aversion in solving the optimisation problem leads to lower optimal N inputs. Simulations with a climate change scenario that predicts higher temperatures throughout the year and lower rainfall amounts during the growing season indicate higher yields, increasing yield variability, and changes in yield quality. By allowing herbage prices to vary as a function of yield quality, we find overall lower optimal N inputs and more marked effects of risk aversion on optimal N levels under climate change than under present conditions. However, disregarding yield quality in solving the optimisation problem gives higher optimal N inputs under future conditions.

Abstract: The Mesoscale Alpine Programme’s Riviera project investigated the turbulence structure and related exchange processes in an Alpine valley by combining a detailed experimental campaign with high-resolution numerical modelling. The present contribution reviews published material on the Riviera Valley’s boundary layer structure and discusses new material on the near-surface turbulence structure. The general conclusion of the project is that despite the large spatial variability of turbulence characteristics and the crucial influence of topography at all scales, the physical processes can accurately be understood and modelled. Nevertheless, many of the “text book characteristics” like the interaction between the valley and slope wind systems or the erosion of the nocturnal valley inversion need reconsideration, at least for small non-ideal valleys like the Riviera Valley. The project has identified new areas of research such as post-processing methods for turbulence variables in complex terrain and new approaches for the surface energy balance when advection is non-negligible. The exchange of moisture and heat between the valley atmosphere and the free troposphere is dominated by local “secondary” circulations due to the curvature of the valley axis. Because many curved valleys exist, and operational models still have rather poor resolution, parameterization of these processes may be required.

We improved a process‐oriented biogeochemical model of carbon and nitrogen cycling in grasslands and tested it against in situ measurements of biomass and CO2and CH4fluxes at five European grassland sites. The new version of the model (PASIM) calculates the growth and senescence of aboveground vegetation biomass accounting for sporadic removals when the grassland is cut and for continuous removals when it is grazed. Limitations induced by high leaf area index (LAI), soil water deficits and aging of leaves are also included. We added to this a simple empirical formulation to account for the detrimental impact on vegetation of trampling and excreta by grazing animals. Finally, a more realistic methane emission module than is currently used was introduced on the basis of the quality of the animals' diet. Evaluation of this improved version of PASIM is performed at (1) Laqueuille, France, on grassland continuously grazed by cattle with two plots of intensive and extensive grazing intensities, (2) Oensingen, Switzerland, on cut grassland with two fertilized and nonfertilized plots, and (3) Carlow, Ireland, on grassland that is both cut and grazed by cattle during the growing season. In addition, we compared the modeled animal CH4emissions with in situ measurements on cattle for two grazing intensities at the grazed grassland site of Laqueuille. Altogether, when all improvements to the PASIM model are included, we found that the new parameterizations resulted into a better fit to the observed seasonal cycle of biomass and of measured CO2and CH4fluxes. However, the large uncertainties in measurements of biomass and LAI make simulation of biomass dynamics difficult to make. Also simulations for cut grassland are better than for grazed swards. This work paves the way for simulating greenhouse gas fluxes over grasslands in a spatially explicit manner, in order to quantify and understand the past, present and future role of grasslands in the greenhouse gas budget of the European continent.

We apply a simulation model in order to quantify the patterns of carbon and nitrogen cycling within European grasslands. We map the fluxes of CO2, N2O and CH4exchanged with the atmosphere as controlled by climate and management conditions. We distinguish between grazing and cutting practice. Because geo‐referenced management information for grasslands does not exist at the scale of Europe, we develop a new and robust set of rules defining some management variables. We then perform realistic simulations in term of N fertilization using a national level data set. The model results at European scale are compared with agricultural statistics (yield, animal stocks), which shows that our very simple management calculation is reasonably realistic. We also compare the simulated seasonal cycle of grassland phenology as calculated by PASIM with remote sensing observations from the EOS‐TERRA‐MODIS satellite, which shows a good general agreement. Emission factors for soil N2O and grazing animals CH4emissions are diagnosed from the model runs and shown to be comparable to those of previous experimental surveys. We investigate impact of N fertilization on NPP and C storage potential, N2O emissions by soils and CH4emissions by ruminants. We conclude that, for different time horizon, CH4and N2O sources are lower than the potential sink of CO2, on a carbon equivalent basis. This result is independent of fertilization intensity but assumes that the current soil C stocks are below the long‐term equilibrium values.