Observational diagnostics of soil moisture-climate interactions as constraints to IPCC climate projections

Recent investigations suggest that land-climate interactions will play a major role for projected climate change, in particular with regard to changes in climate variability and extreme events (e.g. Seneviratne et al. 2006, 2010). Soil moisture is a key player in such interactions, and is expected to impact changes in temperature and the occurrence of heat waves, extreme precipitation events, as well as carbon uptake by vegetation (e.g. Ciais et al. 2005, Reichstein et al. 2007, Seneviratne et al. 2010). There is, however, significant uncertainty in the representation of the relevant processes in climate models (e.g. Koster et al. 2004, Orlowsky and Seneviratne 2010), in particular because long-term observations of soil moisture and surface fluxes have been lacking in the past. This is gradually changing thanks to the development of ground-based and remote sensing measurements of land states and fluxes, in particular from the FLUXNET network (e.g. Baldocchi 2008, Teuling et al. 2009).

In the present study, we investigate diagnostics that can be derived both from observations and model data in order to evaluate the accuracy of soil moisture-climate interactions in current models. The derived diagnostics are applied to IPCC AR4 simulations and used to constrain the related climate-change projections with regard to changes in climate mean and variability. Possible impacts for biogeochemical exchanges and land carbon uptake are also addressed.

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