The CZOs are developing systems models that quantitatively combine coupled processes, typically at the watershed scale. These models typically track fluxes and storage of energy, water, carbon, sediments, and other materials.

For example, landscape and ecosystem responses to climate change and land use perturbations depend on a complex suite of coupled processes associated with water, energy and weathering cycles. More specifically, changes in temperature and precipitation may cause a non-linear and irreversible response in ecosystem structure and function (e.g., forest dieback, Breshears et al., 2005). Better prediction of threshold ecosystem response requires a clearer understanding of the physical and chemical landscapes that buffer climate forcings and shape the environment in which biota respond. Similarly, changes in ecosystem structure will influence ongoing Critical Zone structure and evolution and, therefore the provision of Critical Zone services.

Couplings between ecosystem function and water, energy and weathering cycles are measured at CZOs and will form the basis for the development of coupled systems models of interactions and feedbacks between biological, chemical and physical processes in the Critical Zone. The assimilation of hydrologic, meteorological and (bio)geochemical measurements within and across CZOs into such coupled systems models is a key component to providing the multi-scale/multi-process understanding that is currently lacking, but necessary to advance predictions of Critical Zone responses to land use and climate changes.