World’s Soil Resources

extremes several weeks in advance (e.g. Koster et al., 2010a; Mueller and Seneviratne, 2010). Such early soil
moisture information can be either provided by an offline land surface model driven with observation-based
forcing (e.g. Dirmeyer et al., 2006), by remote sensing products (e.g. Wagner et al., 2007; De Jeu et al., 2008),
or by the assimilation of remote sensing products in land surface models (e.g. Reichle, 2008). However, the
scarcity of precipitation and soil moisture observations still limits the derivation of reliable soil moisture
estimates and the evaluation of satellite approaches on most continents (e.g. Koster et al., 2010b; Dorigo et
al., 2013).
Figure 7.8 Estimation of evapotranspiration drivers (moisture and radiation) based on observation-driven land surface model
simulation. Source: Seneviratne et al., 2010.
The figure displays yearly correlations of evapotranspiration with global radiation Rg and precipitation P in simulations from the 2nd
phase of the Global Soil Wetness Project (GSWP, Dirmeyer et al., 2006) using a two-dimensional color map, based on Teuling et al.
2009, redrawn for the whole globe. (Seneviratne et al., 2010)
Climate models project that several regions will be affected by more frequent drought conditions in the
future as a consequence of enhanced greenhouse gas concentrations (e.g. Wang, 2005; Sheffield and Wood,
2007; Seneviratne et al., 2012). This implies shifts in climate and soil moisture regimes, with important impacts
on temperature projections (e.g. Seneviratne et al., 2006; Dirmeyer et al., 2012), in particular for temperature
extremes (Seneviratne et al., 2013).
Another feedback of soil moisture on climate is the possible impact of droughts on plant carbon uptake
and a resulting decreased sink for CO 2
emissions (Ciais et al., 2005; Friedlingstein et al., 2006; Sitch et al.,
2008; Reichstein et al., 2013). One particularly important region for this feedback is the Amazon rainforest,
which is projected in some models to dry substantially (e.g. Mahli et al., 2008). However, these projections
are associated with high uncertainty in current climate models (Orlowsky and Seneviratne, 2013), and the
resulting effects on carbon uptake could also be affected by the representation of plant physiology in the land
surface schemes (Huntingford et al., 2012).
Finally, the combined effects of soil moisture on near-surface humidity and temperature are also relevant
for boundary layer development and precipitation occurrence (e.g. Betts, 2004; Koster et al., 2004; Taylor et
al., 2012). More details on these feedbacks are provided in Sections 7.5 and 7.6 below.
Status of the World’s Soil Resources | Main Report The impact of soil change on ecosystem services
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