SCHRIFTENREIHE Institut für Pflanzenernährung und Bodenkunde ...

Chapter 3 Spatio-temporal variability of soil moisture in grazed steppe areas investigated by geostatistics
measurement scales ranging from meters to kilometres (Hills and Reynolds,
1969; Famiglietti et al., 1998; Qiu et al., 2001; Western et al., 2004), and
temporal scales ranging from days to years (Entin et al., 2000; Cantόn et al.,
2004; Parent et al., 2006). However, the results appear to be influenced by the
specific study area examined and the sampling time.
The spatio-temporal variability of soil moisture has been shown to be
associated with many controlling factors such as soil, vegetation, topography
and weather (Francis et al., 1986; Crave and Gascuel-Odoux, 1997; Bádossy et
al., 1998; Famiglietti et al., 1998). However, disentangling the influence of each
controlling factor is marred by complexity, as some properties are
interdependent and many have site specific spatio-temporal variations
(Famiglietti et al., 1998; Western et al., 1999). In particular, the correlation length
of soil moisture may be related to different processes that operate at particular
scales or moisture conditions. Soil moisture patterns at small scale will be
regulated by local factors (i.e. soil, vegetation, and surface topographical factors),
whereas at larger scale processes such as subsurface flow and weather will
have a greater impact. The weight of factors also depends on the antecedent
moisture conditions at the time of sampling. In wet conditions, subsurface lateral
flow may be important, whereas dry conditions will be influenced more by
surface vertical flow at the onset of precipitation (Grayson et al., 1997;
Gómez-Plaza et al., 2001). However, there is still great uncertainty about the
scale-dependent relationship between soil moisture and its controlling factors
(Zeleke and Si, 2006).
Geostastitical techniques allow for complicated spatio-temporal soil
moisture patterns to be characterized (Western et al., 1998; Entin et al., 2000;
Webster and Oliver, 2001; Anctil et al., 2002). Using multivariate geostatistics,
the interrelation of soil properties can be evaluated, e.g. soil moisture, in the
presence of multivariate spatial data of regionalized variables (Castrignano et al.,
2000; Buttafuoco et al., 2005; Casa and Castrignanò, 2007). However, as
Famiglietti et al. (1998) noted, research using geostatistics to link soil moisture
variability to its controlling factors, may be limited by low sampling frequency in
41