Effect of Air Relative Humidity Harvest on Soil Moisture Content under Moroccan Climatic Conditions

El Khadir Lakhal Int. Journal of Engineering Research and Applications www.ijera.com
ISSN : 2248-9622, Vol. 5, Issue 4, ( Part -1) April 2015, pp.74-82
www.ijera.com 74 | P a g e
Effect of Air Relative Humidity Harvest on Soil Moisture Content
under Moroccan Climatic Conditions
El Khadir Lakhal*
and Abdellatif Ayyoub**
*
Cadi Ayyad University, Faculty of Sciences Semlalia, Physics Department. Laboratoire d’Automatique de
l’Environnement et Procédés de Transferts, B.P. 2390, Marrakesh, Morocco
**
Faculté des Sciences et Techniques de Beni Mellal, Université Sultan My Slimane, Beni Mellal, Morocco,
Abstract
In this work, we aim to analyse the effect of the harvest of air relative humidity on soil water content. Some
experiments were conducted on hilly areas with various hypsographic and microclimatic conditions greatly
affecting daily fluctuations of air relative humidity. The metrological data’s were obtained by using a Campbell
Scientific equipments station recorder on data loggers every half hour. Time Domain Reflectometers (TDR) is
used for calculating water content at different soil layers. The effect of many parameters such as: minimal and
maximal air atmospheric humidity, potential of soil water and minimal temperature of air on harvesting air
relative humidity is also discussed. The experimental results indicate that soil moisture content in the upper soil
layer fluctuates with the same manner to diurnal fluctuation of relative air humidity. These fluctuations due to the
harvest of relative air humidity decreased with increasing soil depth and daily amplitude of relative air humidity.
The water adsorbed according to this phenomenon increased with increasing maximal relative and decreasing
minimal temperature. The contribution of this soil water collected is about 40% of losses due to evaporation
process. The correlation between principal climatic data and soil water adsorption by harvest relative air
humidity is presented in this paper in order to incorporate it in the total water balance during water infiltration.
Keywords - Harvest, relative air humidity, soil water content, water vapor adsorption, evaporation.
I. INTRODUCTION
In Mediterranean regions, the development of
agriculture is strongly depending on climatic
conditions and their economical and social situations
are usually unstable. Controlling the consequences of
the interaction between human and climatic activities
in arid and semi-arid areas is very important and
based on the understanding of different processes
above all those that are determinant in the hydric
balance. The objectives of reducing unbalances in
water requirements vs water availability in most arid
and semi-arid areas of the Mediterranean region,
since by capturing atmospheric moisture a potential
enhancement in water available to crops can be
achieved without subtracting water to domestic and
industrial uses, thus soothing social strains.
Finally, the major advantages of exploitation of
atmospheric humidity are that it can be captured at
zero cost and that a reduction in energy input can be
obtained (no water lifting from deep wells, no
pressurization are required) as well as the good
quality of captured water. In conclusion, the study has
such social, economical and environmental
advantages. A review in literature indicates that two
major’s uses in collection of water vapour are
dominated.
1. Water drink application
Most countries have been conducted some
largest atmospheric humidity (i.e. fog) project in
order to ensure the village water use. The principal
application of fog collection was conducted by [1].
They propose as fog collector an apparatus
constructed of sample and low cost materials
available in all countries. The fog collector is a flat
rectangular and arranged perpendicular to the
direction of the prevailing wind. The surface
collecting is made from nylon fine-mesh and at
bottom of the panel a trough gutter collects the water
droplets falling under gravity. The result indicates
that 3 litres of water per day and that per square meter
of collecting surface were obtained. For
polypropylene mesh, the fog collector produces 3360
litters of water/day in the Sultanate of Oman over a
period of two and a half years, [2].
2. Agricultural application
In this study we were interested to the
atmospheric humidity harvest for agricultural uses.
The existing systems for collection were the same in
all Mediterranean regions. The importance of this
study results on important contribution of harvest
relative humidity for stopping desertification
especially for our country. In last decade, an
important support of works was developed by many
RESEARCH ARTICLE OPEN ACCESS

institutions research. Generally, the soil is considered
as a porous medium with capillaries of various sizes
that helping the condensed water to infiltrate by
capillarity, [3].
An intensive work was presented to enrich
literature in this field. The authors attempt to
approach and simulate the above described
complicated phenomena of capillary condensation by
using either fractal, [4]. Many approaches were
conducted in order to simulate the transport
condensable vapors in porous structures, [5] and [6].
By referring to [7], the authors have indicated
that soil is considered as a porous medium with
capillaries of various diameters. These capillaries
condensed water to infiltrate by capillarity but in the
same time in the capillaries occurs also condensation
of water vapor depending on the air relative humidity.
In this work, the authors tried out to qualify water
vapor adsorption by soil by using weighing
Lysimeters (WL) and Time Domain Reflectometers
(TDR) for obtaining data under semi arid climatic
conditions. The result shows that the soil moisture
content in the upper soil layer fluctuates in
correspondence with the diurnal fluctuations of the
relative air humidity.
In more recent work, [8] have studied the
parameters affecting water vapor adsorption by the
soil under semi-arid climatic conditions. The authors
indicate that under such climatic conditions, soil
physical characteristics such as texture, surface
mulching, and density of the growing plants greatly
affect water vapor adsorption and soil water
conservation. Also, they indicate that the process of
water vapor adsorption by the sol appears to be more
important for areas in which the geomorphological
conditions and the proximity to the surface water,
such as lakes or sea, favors high diurnal fluctuations
in relative air humidity.
II. MATERIALS AND METHODS
1. Description of sites
In order to evaluate the importance of harvest
relative air humidity effect on soil water content
under different land characteristics, four sites (S1, S2
and S3) were chosen. All sites are characterized by
intensive agricultural activities and the irrigation
covered only 20% of the agricultural areas.
The sites of (S1 and S2) are located in
Marrakech Tensift Alhaouz region. The sites (S1) and
(S2) are respectively located about 60 and 20km from
Marrakech city at an average elevation of 600m
above see level. The relief of this region is
characterized by a great diversity: the interior flats
and plates that contain good arable lands; the old
solid masses, the littoral plates and high mountains of
the Atlas. The climates are warm and dry with
relativity cold period during the winter. Precipitations
are weak and irregular (in Marrakech 240 mm/year).
The summery temperatures are very high (37.7°C at
maximum) and the winter ones are low (4.9°C at
minimum). The evaporation is important (2300mm/
year) and the rainfall is variable: 50% of the territory
has an averaged-300 mm-rainfall per year and almost
30% has a rainfall ranging from 300 to 400mm per
year (Toufliht station). We noticed that the averaged
rainfalls increase from the North to the South. It’s
completely normal because the south is characterized
by heights (High Mountains). Agriculture constitutes
the principal activity for 60% of regional population.
The principal productions are annual cultures
(cereals, alfalfa, tobacco, etc…) and plantations of
olive –trees, citrus fruits and fruit trees.
The site of (S3) is located in Doukkala region
and about 40Km from ELJadida city. The soil is
essentially dominated by Sand, Tirs and Hamri. The
climate is of a Mediterranean type, semi-arid in
winter with a soft temperature, and was generally hot
and dry. It was characterised by an index irregularity
and intra-annual. The annual average pluvial is about
317 to 592mm, registered in 40 and 60 days between
October and April. The relative air humidity data
indicate a dramatically variation between each month
and between maximum and minimum values. The air
temperature is moderate and its value varies between
10°C and 36°C. The existing vegetation in these areas
is exclusively growing by occurring available rain and
the water adsorbed by the soil from the atmosphere.
2. Man characteristics of the study soils
Table 1 show the principal characteristics of the
soils considered in this study are presented as : the
constitution of (S1 and S2) soils is dominated clay
constitution (47% and 39%) and lemon (34% and
40%). However the constitution of (S3) is principally
dominated by sand (52%) and lemon (34.5%). For
This study, the relation-ships between soil water
content and soil water potential, and between
hydraulic conductivity and water content are given
respectively by [9] and [10] formulas :
1 (2/n)n
s g
θ ψ
1
θ h

  
        
and
η
s
s
θ
K K
θ
 
  
 
(1)
Where: s: maximal soil water content (%) ;
Ks : Hydraulic conductivity at saturation (m/s) ;
hg : Hygrometric pressure (m) ;
n and  : Regression parameters of Equation (1).
Table 1. Main characteristics of the study soils.
Site Clay
(%)
Sand
(%)
Lemon
(%)
Ks
(m/s)
hg
(m)
n 
(S1) 46 17.2 34.3 0.810-6
-0.14 2.3 11
(S2) 39 19 40 0.910-6
-0.13 2.2 10.7
(S3) 10 52.4 34.5 1.210-6
-0.08 2.1 9.5

3. Climate data
The climatic forcing needed was averaged over a
30 min time step. Global radiation, atmospheric
humidity, speed of wind, temperature (max and min)
and rainfall were measured at the follow sites
described above. In table 2, we present the results
given by many meteorological stations placed at the
studied sites for ten years in term of average annual
relative air humidity, air temperature, evaporation and
wind speed. The result indicates that the average
annual relative air humidity varies from 58 to 85%.
The average annual air temperature (T) varies from
11°C for coastal site (S3) to 21°C to mountainous site
(S2). The wind speeds indicate that all locations are
favourable to harvest of relative air humidity because
the average values of WS were situated from 1.8 to
3.4m/s. The average total evaporation is very
important for all study sites especially for interior
region.
Table 2. Main climatic data calculated for ten
years.
Study
site
Average
humidity
%
Temperature
°C
Total
evaporation
mm
Wind
speed
m/s
S1 64 19.2 2383 2.2
S2 58 21 1804 2.0
S3 85 11 1410 3.4
The results presented in Figure 1 shows a very
important daily variation of relative air humidity for
(S1) during the period of end December 2003 to May
2004. These high undulations were favourable to
harvesting of relative air humidity by the soil
especially in dry period.
Figure 1. Variation of relative air humidity for the
site of S1 during end December 2003 to May 2004.
Figure 2 indicate that soil temperature calculated
at different depth varies between 3 (hiver) to 30°C
(spring) for all section. The soil temperature varies
with the agreement of relative air humidity variation
depending on soil characteristics, climatic conditions,
soil surface conditions and rainfall. The result shows
that the values of soil temperature for Z=5cm are
higher than Z=10cm and 20cm values because the
climatic conditions were an important effect on the
upper layers of soil. In the period situated between
20th
to 30th
Julian days, we assist to a decreasing soil
temperature due to rainfall.
Figure 2. Variation of soil temperature at
different depth for the site of S1 during end
December 2003 to May 2004.
4. Determination of soil water potential
In order to calculate the water potential ()
corresponding to a given air relative humidity, we use
the equation given by [11]:
)
100
RHln(
M
RTψ (2)
Where: R is the gas constant (8.31J mol-1
K-1
) ; T is
the temperature (K) and M is the partial molar mass
of water (0.018kg mol-1
). By referring to [12] work,
when soil suction varies between 0 and 100 bars, the
vapour pressure changes only by 1.6 mbar. This
variation induces automatically some variation in
temperature profiles in soil especially at 5cm depth
that fluctuating between 8 and 25°C, [7].
In Table 3, we present the monthly variation of
soil water potential maximum max and minimum min
with reel data for the (S1) site. The results indicate
that the amplitude of the difference of RHmax- RHmin
is very important and varies during January to
December from 75 to 88%. This amplitude is very
important that when air and soil temperatures are
weak, the harvesting water by soil becomes very
important. These variations are also an important
effect on soil water potential. This potential varies
between diurnal and nocturne period for July from
21.3kPa to 331.3kPa. In diurnal period, the
evaporation increases and the stress become
important, so, the vegetation grows only by using
irrigation or rainfall. However, in nocturne period, the
phenomenon of soil water adsorption becomes
important that can assure the part of water need for
vegetation. The result indicates that both air
temperature and relative air humidity have an
important effect on soil water potential and root

extraction, and illustrates that the function min
(RHmax) has the same variation of annual temperature
Tmax because the maximum is shown during June to
August month and the minimum values of min are
detected from November to February. The variation
of min passes from 1.3kPa observed in January to
21.3kPa observed in July. For max (RHmin)
function, the maximum is shown in July and the
minimum is detected in January. The value of soil
water potential passes from 228 to 331.3kPa. These
variations between maximum and minimum value of
soil water potential are responsible on soil water
adsorption phenomenon. This behaviour is shown in
the soil water content variation especially for the first
depth of soil. The showing undulations observed in
the experimental data for soil water content between
night and diurnal period explain this comportment
because in diurnal time the evaporation and
transpiration rate are equal zero. So, the soil water
adsorption is considered as an important parameter
that must be considered in the balance of soil water
and in control of water storage process.
Table 3. Calculation of min and max of (S1).
Month RHmax- RHmin
(%)
min
(bars)
max
(bars)
January
February
March
April
May
June
July
August
September
October
November
December
82.4
88.2
85.7
85.2
80.4
81
75.5
74.7
78.7
78.3
79.5
78.7
1.3
1.4
2.1
2.7
4.8
12.2
21.3
15.2
9.9
3.5
1.6
1.8
228
250
292.5
223.9
296.4
312.1
331.3
297.3
260.8
215.4
207.7
200.6
III. MEASUREMENT OF SOIL
MOISTURE CONTENT
In each site, five Time Domain Reflectometers
(TDR) (Campbell Scientific, type CS615), were
installed in order to measure the volumetric soil
moisture content at different soil depths. The probe of
each reflectometer was installed horizontally into the
soil to detect the passing of wetting fronts. The
reflectometers were calibrated by taking measurement
at several knows water content by using theta probe
equipment and gravimetric methods. The soil
moisture was registered on a data logger at half
hourly intervals. The volumetric soil water content
was measured using a third degree polynomial
equation, [13]. In this paper we present only the data
relative to volumetric soil water content for (S1) and
(S3).
In Figure 3a, we present the change in volumetric
soil moisture content at the depths of 5, 10 and 70cm
for (S1) soils. In the same figure we present the
rainfall and water irrigation rates applied during the
experimental period in order to evaluate their effect
on soil moisture content distribution. The result
indicates that soil moisture content measured by the
TDR electrodes showed an important diurnal
fluctuation, analogue to the air relative humidity
fluctuations. For all data, the amplitude of diurnal
fluctuations of the volumetric soil moisture content
becomes very important for first soil depths situated
between 5 cm to 20 cm. This is confirmed by the
result obtained in term of the measured soil moisture
content at TDR 70cm. The result shows weak
amplitude variations in term of soil water content
when depth is more than 25 cm. These undulations
observed in the first depths were disappeared for
TDR 70cm because the climate conditions have a
negligible effect on variations of soil moisture content
at this depth.
As shown in Figure 3a, the soil moisture content
increase quickly for all depths and we assist on very
important amplitude of the observed undulations
especially for the first depths when the water
irrigation is applied. The diurnal change in soil
moisture content phenomenon is a result from the
water adsorbed by harvesting relative air humidity.
These fluctuations depend on many factors as soil
constitutions, crops occupation, climate conditions
(temperature and air relative humidity and initial soil
humidity).
In Figure 3b, we present the variation of soil
water content during end December 2003 to May
2004 for TDR 5, 10 and 20cm. The result shows
increasing undulations of soil water content for the
first depth especially when irrigation or rainfall is
applied. These undulations become weak when the
depth of soil is higher than Z=20 cm. By comparing
the results presented in Figures 3a and 3b, the effect
of climatic conditions is evident. The amount water
by rainfall or irrigation has a very important effect on
the undulations amplitude.
For this period, the harvest water is observed
only on the upper layers Z≤25cm. While in (S3), this
phenomenon is more pronounced and it is observed
for the profound layers Z≤40cm. This is due to the
soil characteristics and the climatic conditions, (Fig.
3c). It is also mentioned that in this year (2005) the
amount water by rainfall is very weak and the harvest
water is only observed in the humid period but in dry
period the phenomenon is totally absent.

Figure 3a. Changes in soil water moisture content
with time due to Irrigation, Rainfall and Harvest
of Relative air Humidity at TDR 5cm, TDR 10cm
and TDR 70cm depths under various climatic
conditions (February 2003 to May 2003) for (S1)
site.
Figure 3b. Changes in soil water moisture content
with time due to Irrigation, Rainfall and Harvest
of Relative Air Humidity at TDR 5cm, TDR 10cm
and TDR 20cm depths under various climatic
conditions (end December 2003 to May 2004) for
(S1) site.
Figure 3c. Changes in soil water moisture content
with time due to Rainfall and Harvest of Relative
Air Humidity at TDR 5, 10, 20, 50, 90 cm depths
under various climatic conditions (December 2004
to February 2005) for (S3) site.
In Figure 4, we presented the observed
undulations of soil water moisture content with time
due to water vapour adsorption at TDR 5cm, TDR
10cm and TDR 20cm depths under various climatic
conditions (February 2003 to March 2003) for (S1).
A supplied water of irrigation at 51st
Julian day is also
shown in order to explain the rapid increases of soil
moisture content at different depths. The moisture
increases about 150, 120 and 80 respectively for Z=5,
10 and 20cm of depths. Undulations variations were
reached for all depths (especially for 5 and 10cm)
after and toward irrigation. In this period, the applied
water by rainfall has a reduced effect on the changes
in soil water content because its intensity is very weak
and the redistribution of water with time is realised
slowly.
Figure 4. Observed undulations of soil water
moisture content with time at TDR 5cm, TDR
10cm and TDR 20cm depths under various
climatic conditions (February 2003 to March
2003) for (S1) site. The effect irrigation is also
presented.
IV. CALCULATION OF SOIL WATER
ADSORBED (WG) AND SOIL
WATER LOSSES (WL)
The soil water captured by harvesting relative air
humidity (WG) and the soil water lost by evaporation
(WL) for each soil layer are calculated by using the
differences between maximal and minimal volumetric
water moisture content occurred at night for each
section of soil and multiplied by the section of soil Z
(in mm) as demonstrated in the following
expressions:
).Zθ(θWG j
min
j
max  (3)
).Zθ(θWL 1j
min
j
max

 (4)
Where (j+1) is the following Julian day.
The result shows that WL is greater than WG for
all days and all layers excepted when irrigation are
rainfall is applied. WG increases when irrigation or
rainfall is applied and fluctuated as the same variation
of air relative humidity. However, WL is a decreasing

function with humid period. For the 121th day, the
harvest atmosphere humidity contribution in water
movement decreases with depth. This contribution is
about 56.5, 10.8 and 6.4% respectively for Z=5, 10
and 20cm. The total water adsorbed by soil is 8.27,
10.3 and 5.06mm respectively for Z=5, 10 and 20cm.
The total water losses in this period are 13.8, 19.3
and 26.5mm respectively for Z=5, 10 and 20cm. The
contribution of harvest of relative air humidity in
water balance is about 60, 53 and 19% respectively
for Z=5, 10 and 20cm. These results indicate that in
each time, the contribution of soil water adsorbed by
harvesting relative air humidity can replace the losses
quantities by evaporation and root extraction. These
results were observed at 130th Julian day when
RHmax (92%) was very important and Tmin was very
weak (about 8°C). This phenomenon can explain the
growing of agriculture in arid climate without
irrigation.
1. Irrigation effect on cumulative soil water
adsorption (CWG)
In order to explain the contribution of soil water
adsorption in total soil water movement, we present
the variation of cumulative soil water adsorption,
CWA, with time for all soil depth. The result
indicates that CWA is an increasing function of time
for the studied depths. The maximum of cumulative
soil water adsorption is observed when Z varies from
Z=0 to 10cm. When Z20cm the soil water
adsorption is a decreasing function of depth. These
decreases are due to the reduced of amplitude of
undulation of soil moisture content. The effect of
water irrigation on cumulative soil water adsorption is
clearly shown by the following curves presented in
Figure 5a and 5b respectively for (S1) and (S3). The
results indicated that when water irrigation is applied,
the curves corresponding to cumulative water content
increase rapidly especially for the first soil layers
(Fig. 5a). This increases is very important for
Z=20cm because the majority of water applied by
irrigation affect considerably the global distribution
of moisture content profiles especially for the
profound section of soil. The result shows two
tendencies of cumulative soil water adsorption. The
first behaviour indicates the same tendency of
increases in CWG and weak differences between the
corresponding values of CWG for all depth when
water irrigation isn’t applied. The second behaviour
indicates the visible effect of irrigation on tendency
and values of CWG. The differences become very
important between the studied depths. When water
irrigation is applied, the increases observed in term of
CWG at 49th
day are 25, 15 and 30mm respectively
for Z=5, 10 and 20cm that indicated an inverse sense
of variation that is shown in Fig. 5. The same
phenomenon increased after a rainfall event and
become significantly high especially during 3 or 4
day after a rainfall. The amount water by rainfall has
a weak effect on cumulative soil water adsorption
(Figure 5b).
a)
b)
Figure 5. Effect of water irrigation on variation
with time of cumulative soil water adsorption by
harvest or relative air humidity, a) site (1) and b)
site (S3).
2. Effect of climate on harvest of relative air
humidity
In order to evaluate the effect of climate
conditions on harvest of relative air humidity, we
present in Table 3 the amount of water adsorbed by
the upper 10cm soil layer in (S1, S2 and S3) sites for
the period of May. The result indicates that this
amount was important ranging from 24.8 to 31.7 mm.
In this period, the average maximum relative air
humidity is ranged from 87.6 to 95.5%, while the
average minimum humidity is ranged from 38.5 to
65.4%. These high daily fluctuations favour the
formation of a high vapour pressure gradient from the
atmosphere to the soil that responsible of soil water
adsorption, [8]. Air at a relative air humidity (RH) of
98.2% which is a maximum measured value in the

study areas during the night and air temperature
T=293K will be in equilibrium with soil at a water
potential of about 2.5 bars (Equation (2)). Air at a RH
of 37.1% which is an average minimum value for the
study areas during day time and air temperature
T=308K, the water potential will be 140.5 bars. As
stated a change in matric suction between 0 to 100
bars is accompanied by vapour pressure change of
only 1.6mbar, [12]. Under such conditions soil air is
nearly vapour saturated at almost all times and water
vapour adsorption is limited. The diurnal amplitude
of soil temperature measured at 5cm soil depth
fluctuated between 6.5 to 27°C depending on time of
the year, soil characteristics and soil surface
conditions. Under such climatic conditions, the soil
surface layers become very dry allowing the water to
be adsorbed by the soil during night time.
Table 3. Effect of climate conditions on relative
air humidity harvest.
Site R
(mm)
RHm
ax
(%)
RHmin
(%)
CWL
(mm)
CWG
(mm)
S1
S2
S3
56.8
50.8
86.5
90.1
87.6
98.2
37.1
38.5
63.4
163
185
135
25.2
24.8
31.7
In this period, the amount of rainfall in this
period is ranged from 50.8 to 86.5mm, while the total
evaporation is ranged from 135 to 185mm. According
to this result, the amount of water adsorbed by soil
might be of the great importance for the soil water
balance under the existing climatic conditions of the
study areas. As Table 3 shows, the amount of
cumulative soil water absorbed during May by
harvesting relative air humidity satisfies a great
portion of cumulative soil water losses by total
evaporation root extraction. Soil water 13 to 23% of
the total evaporated water was recovered by CWG
under the existing climatic conditions of the study
site. In total soil water balance, the amount of both
rainfall and CWG measured during the study period
varies between 40% for the dry site to 87% for the
humid site.
V.EFFECT OF RELATIVE AIR
HUMIDITY AND SOIL WATER
POTENTIAL
Figure 6 shows the effect of relative air humidity
on the absorbed soil water which is calculated for Site
(S3) during January and February 2004. The results
shown in this figure indicate that water adsorbed by
soil according to harvest air relative humidity
increased as the daily fluctuation in relative air
humidity (measured at the difference between
maximum and minimum daily values) increased for
the soil potential lower than 320KPa. The soil water
adsorption WG was inversely and proportionally
related to the minimum value of relative humidity.
This is because when humidity is decreased, the
potential of soil is higher and the soil becomes dry
and the adsorption phenomenon is also important.
The following linear relations were found to predict
the water harvested by the study soil of (S3) as a
function of the minimum daily relative humidity
(RHmin, %) and the daily amplitude of relative
humidity (RHmax-RHmin, %) of the upper 5cm soil
layer :
b)RH(RHaWG minmax  (5)
bRHaWG min  (6)
b
WG a (h)  (7)
As shown in figure 6, the above empirical
equations adopted are satisfactorily for describing the
soil water adsorption by harvest of relative air
humidity soil for all depths considered in this study.
The correlation coefficient varies between R=0.78 to
0.92 under the existing climatic conditions.
(a)
b)

c)
Figure 6. Relation between soil water adsorbed by
harvest relative air humidity and a) daily
amplitude of relative air humidity (RHmax-
RHmin, %), b) minimum air humidity (RHmin,
%) and soil water potential (h, KPa). Z=5cm.
VI. CORRELATION OF WATER
ADSORPTION WITH CLIMATIC
DATA
The finding result shows that water adsorption by
soil increased as the daily function of the daily
fluctuations in relative air humidity (RHmax-RHmin)
and increased with increased of soil water potential
(hsoil). The daily fluctuations in minimum air humidity
have an inverse effect on soil water adsorption by
harvest of air relative humidity. The amount of water
vapor adsorbed by the soil could replace about 20-
25% of water lost by evaporation during dry periods
under arid or semi arid climatic conditions. This
contribution is about 30-45% in coastal region when
the phenomenon is important and covers a large
period of year, [8]. This contribution of water
adsorption is very important to take it in the total
balance of moving water in soil- vegetation -
atmosphere system. In order to take it, we propose a
correlation of soil water adsorption WG as a multiple
linear relation with minimal air relative humidity
RHmin, daily amplitude of air relative humidity
(RHmax-RHmin) and soil water potential hsoil (KPa).
The proposed correlation equation is given by the
following equation and in Table 4, we present the
correlation coefficient.
soilminmamin hd)RH(RHcRHbaWG  (8)
Table 4. Parameter for the proposed correlation.
depth a b c d R
Z=5cm 1.36 -0.003 0.0014 0.211 0.78
Z=10cm 0.316 -0.016 0.0019 -0.27 0.74
Z=15cm 0.137 -0.019 0.0003 -0.33 0.76
VII. VII. CONCLUSION
In this paper we have study the effect of many
important parameters on humidity harvesting such:
maximal and minimal air relative humidity, the soil
potential of water, the average temperature of air and
we have present some correlation laws. Also, we have
noted that the state of soil has an important effect on
humidity harvesting, because when the soil is humid,
the soil temperature decreases and the condensation
becomes more important than a dry soil.
We have presented some new results in order to
estimate the real contribution of harvesting humidity
in the total water balance. These results concern the
period of April 2005 to February 2006.
Evapotranspiration ET has been estimated and it is
demonstrated that for such climatic We have
presented some new results in order to estimate the
real contribution of harvesting humidity in the total
water balance. These results concern the period of
April 2005 to February 2006. Evapotranspiration ET
has been estimated and it is demonstrated that for
such climatic conditions and soil characteristics,
water captured from air relative humidity contribute
about 30% of the total water balance.
The results obtained by meteorological station,
time domain reflectometers and theta Probe indicate
that soil water content is greatly affected by the
harvest of relative air humidity. Four sites were
selected with different climatic data and various soil
characteristics. The Experimental data obtained by
time domain reflectometers indicate that soil moisture
content in the upper soil layer fluctuates with the
same manner to diurnal fluctuation of relative air
humidity. These fluctuations due to water vapour
adsorption decreased with increasing soil depth and
daily amplitude of air relative humidity. The
contribution of water adsorption is considered
important that must be introduced in the soil water
balance. Its contribution is about 50% of losses due to
evaporation (and root extraction) process. The
applied water irrigation has a strongly effect of
cumulative soil water adsorption because the values
of CWG becomes important for Z=20cm and
disappear completely when Z30 cm. The water
adsorbed by harvest of relative air humidity
contributes to the soil a significant amount of water
which may positively affect the water needed of
vegetation. It is demonstrated that:
1. RHmin has an inversely effect on harvesting of
relative humidity by the soils. When RHmin
increases, the soil water adsorbed by harvest
relative air humidity is scientifically reduced ;
2. The variation of amplitude between maximal and
minimal daily of relative air humidity,
A=(RHmax-RHmin), has an important effect on soil
water adsorption. WG is an increasing function
with A ;

3. When soil water potential increases, the
capitation of water by soil according to the
relative air humidity harvesting increases. This
increase becomes very important when the soil is
dry and the soil potential is higher ;
4. When the proportion of sandy and lemon
increase, the soil water adsorption phenomenon
becomes important especially for the first layers
and its also observed for the profound layers.
The present study includes some environmental
considerations such as:
1. Developing the non-irrigated crops in arid
regions contributes to stop the progress of
desertification especially for the south countries
of Mediterranean basin. In these regions the
water resources are very weak and growing crops
is done only by rainfall (about 100-150mm/year)
and the humidity capture can contribute
positively to regulate a fraction of the water
balance ;
2. The use of water captured from air relative
humidity in other regions (example, Agadir,
Elwalidia, Lâarach, Chaouia and Doukkala)
contributes to preserve water resources and the
quality of soil ;
3. The collection of fog water and the harvest of air
relative humidity by forests constitute an
important support of research in order to
preserve the ecology system especially in the arid
regions.
Acknowledgements
This work was carried out as of INCO-MED
Contract N°: ICA3-CT2002-10032, Project untitled:
HUPHAT. The financial support by European Union
and Moroccan CNRST, URAC28 are greatly
acknowledged.
REFERENCES
[1] S. Mukerji, S. Fahmy, D., Weeb, O. Fuentes,
W. Canto, R. Schemenauer, P. Cereceda, P.
Hirsch-Reishagen, C. Masson, L. Venero
and J. Cerda. ‘’Fogwater collection System’’.
http://www.idcr.ca/library, 1993.
[2] B. Rosensweig. ‘’Harvesting water from
fog’’. http: // exn.ca /Storie/ 1989/07/21/52
asp , 1998.
[3] A. Frangoudakis and S. Kyritsis.
‘’Atmospheric Humidity Harvest Review’’.
First Meeting HUPHAT Project, Marrakesh
Morocco, 8-9, December 2003.
[4] G.A. Niklasson. ‘’Adsorption on fractal
structures: applications to cement
materials’’. Cement and Concrete Research.
Vol. 23 N° 5, pp. 1153-1158. 1993.
[5] M.E. Kainourgiakis, A.K. Stubos, N.D.
Konstantinou, N.K. Kanellopoulos, V.
Milisic. ‘’Network model for the
permeability of ‘condensable vapours
through mesoporous media’’. Journal of
Membrane Science. Vol. 114 N°2, 215-225.
1996.
[6] P. Rajniak, R. T. Yang. ‘’Unified network
model for diffusion of condensable vapors in
porous media’’, AIChE Journal. Vol. 42 N°
2, pp. 319-331. 1996.
[7] C. Kosmas, N.G. Danalatos, J. Poesen, and
B. Van Wesemael, ‘’The effect of water
vapour adsorption on soil moisture content
under Mediterranean climatic conditions’’.
Agriculture Water Management. Vol. 36,
pp. 157-168. 1998.
[8] C. Kosmas, M. Marathianou, St. Gerontidis,
V. Detsis, M. Tsara and J. Poesen.
‘’Prameters affecting water vapour
adsorption by the soil under semi-arid
climatic conditions’’. Agriculture Water
Management. Vol. 48, pp. 61-78. 2001.
[9] M. Th. Van Genuchten. ‘’A closed form
equation for predicting the hydraulic
conductivity of unsaturated soils’’. Soil Sci.
Soc. J., Vol. 44, pp. 892-898. 1980.
[10] R.H. Brooks and C.T. Correy. ‘’Hydraulic
properties of porous media’’, Hydrology.
Paper 3. Colorado State University, Fort
Collins. 1964.
[11] A.W. Adamson. ‘’Physical Chemestry of
urfaces’’, 5th
ed. Wiley, New York. 1990.
[12] D. Hillel. ‘’Introduction to soil physics,
Academic Press. New York. pp. 124-126’’.
1982.
[13] G.C. Topp, J.I. Davis and A.P. Annan.
‘’Electromagnetic determination of soil
water content, Measurement in coaxial
transitional lines’’. Water Resources
Research, Vol. 16, pp. 574-582. 1980.

Effect of Air Relative Humidity Harvest on Soil Moisture Content under Moroccan Climatic Conditions

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Effect of Air Relative Humidity Harvest on Soil Moisture Content under Moroccan Climatic Conditions