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| Titel |
Modeling spatial and seasonal soil moisture in a semi arid hillslope: The impact of integrating soil surface seal parameters |
| VerfasserIn |
Shai Sela, Tal Svoray, Shmuel Assouline |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250032677
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| Zusammenfassung |
| Modeling hillslope hydrology and the complex and coupled reaction of runoff processes to
rainfall, lies in the focus of a growing number of research studies. The ability to characterize
and understand the mechanisms underlying the complex hillslope soil moisture patterns,
which trigger spatially variable non linear runoff initiation, still remains a current
hydrological challenge especially in ungauged catchments. In humid climates, connectivity of
transient moisture patches was suggested as a unifying concept for studying thresholds
for subsurface flow and redistribution of soil moisture at the hillslope scale. In
semiarid areas, however, transient moisture patches control also the differentiation
between evaporation and surface runoff and the ability to identify a unifying concept
controlling the large variability of soil moisture at the hillslope scale remains an
open research gap. At the LTER Lehavim site in the center of Israel (31020’ N,
34045’ E) a typical hillslope (0.115 km2) was chosen offering different aspects and a
classic geomorphologic banding. The annual rainfall is 290 mm, the soils are brown
lithosols and arid brown loess and the dominant rock formations are Eocenean
limestone and chalk with patches of calcrete. The vegetation is characterised by
scattered dwarf shrubs (dominant species Sarcopoterium spinosum) and patches
of herbaceous vegetation, mostly annuals, are spread between rocks and dwarf
shrubs. An extensive spatial database of soil hydraulic and environmental parameters
(e.g. slope, radiation, bulk density) was measured in the field and interpolated to
continuous maps using geostatistical techniques and physically based modelling. To
explore the effect of soil surface sealing, Mualem and Assouline (1989) equations
describing the change in hydraulic parameters resulting from soil seal formation
were applied. Two simple indices were developed to describe local evaporation
values and contribution of water from rock outcrops to the soil down slope. This
spatio-temporal database was used to characterise 1187 spatial cells serving as an input to a
numeric model (Hydrus 1D) solving the flow equations to predict soil water content
at the single storm and seasonal scales. The model was verified by sampling soil
moisture at 63 random locations at the research site, during three consecutive storms
in the 2008-09 rainy season. The results show that incorporating a seal layer in
the model reduces significantly the variability of soil moisture and improves the
correlation between simulated and observed values (R2 = 0.84). The emerging soil
moisture patterns have clear structural nature, shaped by the following factors as found
by applying a stepwise regression analysis: 1) soil porosity; 2) profile depth; 3)
radiation and 4) rock outcrops. We suggest that seal layers, as a cross scale phenomena,
decrease the variability in the soil hydrological parameters and allow the variability in
environmental factors to dominate spatial water content patterns. This approach allows
investigations of the different factors affecting hillslope soil moisture patterns and
functional role of different geomorphic units on water relocation at the hillslope scale. |
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