Climate and the hydrological cycle are strongly coupled with land surface and ecosystem processes, both in the sense that modifications of the water cycle significantly affect land surface properties and ecosystem functioning, and because vegetation and land surface changes can lead to important effects on the whole hydrological cycle and on climate. This is represented in the concept of temporal and spatial cross-scale interactions.
A crucial problem is the scale mismatch between climatic variability, usually resolved at rather large spatial scales, and the much smaller scales of land surface processes.
This research task intends to address the following open questions:
Upscaling of small-scale ecosystem and land surface changes and how to incorporate them into climate models and downscaling of climate information to properly drive land surface and ecosystem responses (Figure 2, see below).
Assessing the impact of small-scale heterogeneities on climate variability. Here, one can ask up to which scale variations in the small-scale surface processes (e.g. evapotranspiration) affect climate dynamics, or what effect land surface heterogeneities can have on the statistics of extreme events.
Whether changes in vegetation properties (such as vegetation patterning) and ecosystem transitions can trigger regional or global changes in climate dynamics.
The methods used to address these issues include conceptual approaches, intermediate complexity models, fully coupled, scale-crossing climate and land surface models, global and regional climate models, statistical and stochastic downscaling methods, besides the analysis of available data and the development and use of metrics to compare models and observations.
Figure 2. Linking of regional- to continental-scale land-atmosphere feedbacks with local vegetation-environment feedbacks by using a model hierarchy. (a) Current climate models account for large-scale land-atmosphere feedbacks, but do not account for local ecosystem feedbacks. (b) Linking large-scale land-atmosphere feedbacks with local vegetation-environment feedbacks by downscaling the climate model to the local feedback model. Up-scaling is based on model outcomes of the local feedback model, through parameterization of the large-scale vegetation model, leading to improved fluxes to the atmosphere model. From Rietkerk et al., Local ecosystem feedbacks and critical transitions in the climate, Ecological Complexity, 8, 223–228 (2011).