The uncertainties and sources of variation in projected impacts of climate change on agriculture and terrestrial ecosystems depend not only on the emission scenarios and climate models used for projecting future climates, but also on the impact models used, and the local soil and climatic conditions of the managed or unmanaged ecosystems under study. We addressed these uncertainties by applying different impact models at site, regional and continental scales, and by separating the variation in simulated relative changes in ecosystem performance into the different sources of uncertainty and variation using analyses of variance. The crop and ecosystem models used output from a range of global and regional climate models (GCMs and RCMs) projecting climate change over Europe between 1961–1990 and 2071–2100 under the IPCC SRES scenarios. The projected impacts on productivity of crops and ecosystems included the direct effects of increased CO2 concentration on photosynthesis. The variation in simulated results attributed to differences between the climate models were, in all cases, smaller than the variation attributed to either emission scenarios or local conditions. The methods used for applying the climate model outputs played a larger role than the choice of the GCM or RCM. The thermal suitability for grain maize cultivation in Europe was estimated to expand by 30–50% across all SRES emissions scenarios. Strong increases in net primary productivity (NPP) (35–54%) were projected in northern European ecosystems as a result of a longer growing season and higher CO2 concentrations. Changing water balance dominated the projected responses of southern European ecosystems, with NPP declining or increasing only slightly relative to present-day conditions. Both site and continental scale models showed large increases in yield of rain-fed winter wheat for northern Europe, with smaller increases or even decreases in southern Europe. Site-based, regional and continental scale models showed large spatial variations in the response of nitrate leaching from winter wheat cultivation to projected climate change due to strong interactions with soils and climate. The variation in simulated impacts was smaller between scenarios based on RCMs nested within the same GCM than between scenarios based on different GCMs or between emission scenarios

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Abstract. The complexity of coupled transport of heat and moisture at the soil surface necessitates a combination of field and numerical experiments to evaluate the interactions between liquid and vapor phase flow. The near-surface moisture and temperature conditions of a bare soil were investigated experimentally and by using the SOIL model to assess the importance of water vapor flow. During a 1-month period in early fall, intensive measurements of water content, water tension, and temperature were made in a bare soil plot. Soil thermal conductivity, measured on soil cores extracted for laboratory analysis, was found to agree with estimates based on the Kersten equation. Simulated water content and soil temperature agreed well with observations. Modeled soil vapor flow was significant compared to liquid flow only during the initial dry days when the inclusion of vapor flow improved the predicted diurnal variation in water tension. Model predictions were sensitive to an accurate representation of the soil surface energy balance, including the consideration of steep gradients in tension near the soil surface, and to the enhancement of vapor flow. IntroductionThe unsaturated soil layers near the surface play an important role in several environmental phenomena: The soil surface conditions control the partitioning of precipitation into surface runoff and infiltration and the partitioning of radiant energy into latent and sensible heat losses. Soil microbial activity, seed germination, and plant development depend on the moisture content and temperature of the topsoil.The moisture and energy balance at the surface are influenced by liquid as well as vapor phase flow, and both processes are important for an accurate representation of the surface energy balance. The model soil hydraulic properties can be specified using either the Brooks and Cer• [1964] expression or the van Genuchten [1980] expression. In our study we found that the soil properties were adequately described using the Brooks and Corey parameterization. Field MeasurementsThe continuous field measurements were initiated on September 12 and continued until October 10, 1991. During this period, soil temperature, soil water tension, and soil water content were logged with a time resolution of 30 min.Soil temperature was measured using thermistor-based probes at the soil surface and at depths of 2.5, 5, 7.5, 10, 12.5, 15, 20, and 25 cm, with two replicates at the three uppermost depths.Soil water tension was measured at depths of 5, 10, 15, 20, and 25 cm, using small tensiometers (2100 F) and pressure transducers (5301) The model was initialized by specifying a uniform temperature (13øC) profile and a nonuniform water tension profile estimated from observations at the start of the experiment.Because of the diurnal heat flow in the soil, the simulated temperature profile rapidly changed from its initial uniform value to match the observed profile (see Figure 6).The saturated soil hydraulic conductivity, Ks, was initially estimated from laboratory measu...

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