Hydrology and Earth System Sciences
www.hydrol-earth-syst-sci.net
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1
2008
10.5194/hess-12-303-2008
http://www.hydrol-earth-syst-sci.net/12/303/2008/
http://www.hydrol-earth-syst-sci.net/12/303/2008/hess-12-303-2008.html
http://www.hydrol-earth-syst-sci.net/12/303/2008/hess-12-303-2008.pdf
303
316
2008-02-27
Ecohydrology in Mediterranean areas: a numerical model to describe growing seasons out of phase with precipitations
D. Pumo
pumo@idra.unipa.it
F. Viola
L. V. Noto
Dipartimento di Ingegneria Idraulica ed Applicazioni Ambientali, Univ. of Palermo, Viale delle Scienze, 90128 Palermo, Italy
The probabilistic description of soil moisture dynamics is a relatively new
topic in hydrology. The most common ecohydrological models start from a
stochastic differential equation describing the soil water balance, where
the unknown quantity, the soil moisture, depends both on spaces and time.
Most of the solutions existing in literature are obtained in a probabilistic
framework and under steady-state condition; even if this last condition
allows the analytical handling of the problem, it has considerably
simplified the same problem by subtracting generalities from it.
<br><br>
The steady-state hypothesis, appears perfectly applicable in arid and
semiarid climatic areas like those of African's or middle American's
savannas, but it seems to be no more valid in areas with Mediterranean
climate, where, notoriously, the wet season foregoes the growing season,
recharging water into the soil. This moisture stored at the beginning of the
growing season (known as soil moisture initial condition) has a great
importance, especially for deep-rooted vegetation, by enabling survival in
absence of rainfalls during the growing season and, however, keeping the
water stress low during the first period of the same season.
<br><br>
The aim of this paper is to analyze the soil moisture dynamics using a
simple non-steady numerical ecohydrological model. The numerical model here
proposed is able to reproduce soil moisture probability density function,
obtained analytically in previous studies for different climates and soils
in steady-state conditions; consequently it can be used to compute both the
soil moisture time-profile and the vegetation static water stress
time-profile in non-steady conditions.
<br><br>
Here the differences between the steady-analytical and the non-steady
numerical probability density functions are analyzed, showing how the
proposed numerical model is able to capture the effects of winter recharge
on the soil moisture. The dynamic water stress is also numerically
evaluated, implicitly taking into account the soil moisture condition at the
beginning of the growing season. It is also shown the role of different
annual climatic parameterizations on the soil moisture probability density
function and on the vegetation water stress evaluation.
<br><br>
The proposed model is applied to a case study characteristic of
Mediterranean climate: the watershed of Eleuterio in Sicily (Italy).
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