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Water Evaporation rate in Ras-Al-Khaimah_ UAE

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					                                                                 United Arab Emirates




Water Evaporation Rate at Ras-Al-Khaimah, UAE
Introduction
United Arab Emirates has an arid climate with less than 100 mm/yr average
rainfall. The low percentage of cloudy days and the high solar radiation over
the region result in high evaporation rates. The total annual potential
evaporation ranges from 2.5 m in the coastal areas to more than 4.5 m inland.
Estimation of evaporation losses is very important in this region in particular
where water ponds or pools are used for industrial, domestic or agricultural
purpose. In order to evaluate water evaporation losses in a water pond at
Solar Island site of CSEM-uae, a brief study has been carried out which
provides estimation of evaporation rates in the Emirate of Ras-Al-Khaimah
(RAK), UAE.

Methods for the Evaporation Estimates
Evaporation pans provide one of the simplest, inexpensive, and most widely
used methods of estimating rate of evaporation. The most useful methods for
estimating evaporation from a free water surface are those which require
meteorological input parameters. These methods estimate the evaporation
rate from a class A evaporation pan. The data can be used for the estimation
of evaporation from a large water body by applying a pan coefficient (The ratio
of evaporation of water in a large water body to that measured in an
evaporation pan). In this study, seven climatological methods (Table.1) were
used to analyze the rate of evaporation of water in Ras-Al-Khaimah and
AbuDhabi, UAE. The climatological data is collected from NASA Surface
meteorology and Solar energy Tables.

              Table1: Data required for evaporation estimates methods
            Method               Temperature       Humidity        Wind speed           Radiation
Kohler-Nodenson(K-N) (1955)
Penman (1948)
Penman-Monteith(P-M) (1965)
Bulk-Aerodynamics(BA) (2003)
Priestly-Taylor(P-T) (1972)
Hargreaves (1975)
Hamons (1961)


The other different parametrs like declination, hour angle, day length, vapor
pressure deficit, net radiation etc., were calculated based on the meteoroloical
data and the monthly mean evaporation rates in RAK were estimated (Table
2). Similar calculations were performed for Abu Dhabi and the comparison of

CSEM-UAE Innovation Center LLC                 Al Jazeera Al Hamra Area          T +971 (7) 244 6929
www.csem-uae.com                               PO Box 31208                      F +971 (7) 244 6951
                                               Ras Al Khaimah, UAE               info@csem-uae.com
                                                                  United Arab Emirates




annual average estimates in both regions Ras-Al-Khaimah and Abu Dhabi is
shown in Figure 1.
The interpretation of the current equations shows that there is highest
similarity is between P-M and P-T method estimates and Bulk Aerodymanics
method gives annual average estimates close to P-M equation. The estimates
based on K-N and Penman equation are high whereas the estimates based
on the Hargreves and Hamons methods are very low. In the later case, low
values are due to the dependency on a single parameter (temperature).
Therefore it shows that the evaporation estimates are significantly affected by
the meteorological parameters like Radiation, Humidity and wind speed.
          Table 1: Monthly mean estimates of evaporation rates in RAK
     Month           Penman      P-M     K-N     P-T      B-A       Hargreaves           Hamons
       Jan              11.3      9.2    10.7     9.7     4.8              2.3             0.8
       Feb              13.8     11.5    13.1    12.5     5.76             3.0             1.0
       Mar              12.1      9.7    12.2     10      7.1              2.5             1.1
       Apr              13.7     11.12   14.8    11.4     9.9              3.1             2.3
       May              17.9     15.0    20.6    15.3     15.1             4.2             3.7
       Jun              18.7     15.8    23.0    15.8     18.0             4.0             4.2
       Jul              17.3     14.9    23.4    13.9     19.8             3.2             3.5
       Aug              17.3     14.6    22.1    14.3     17.6             3.2             3.7
       Sep               17      14.0    20.2    14.1     15.0             3.4             3.2
       Oct              17.2     13.9    18.3    15.2     11.1             3.9             2.1
       Nov              14.4     11.5    14.4    12.8     7.5              3.2             1.8
       Dec              12.2     10.0    11.7    10.7     5.5              2.9             0.9
 Annual average         15.2     12.6    17.1     13      11.5             3.2             2.3




CSEM-UAE Innovation Center LLC                  Al Jazeera Al Hamra Area          T +971 (7) 244 6929
www.csem-uae.com                                PO Box 31208                      F +971 (7) 244 6951
                                                Ras Al Khaimah, UAE               info@csem-uae.com
                                                            United Arab Emirates




Penman's equations are based on the combination of energy budget and
aerodynamics methods. These are fairly complex functions of temperature,
humidity, wind velocity and radiation, so the results obtained could be reliable.
In order to compare the theoretical values obtained from climatological data
with the practical values of evaporation rate, Pan Evaporation experiments
are performed at CSEM-uae.
Pan evaporation is a measurement that combines the effects of several
climate elements: temperature, humidity, solar radiation, and wind. An
Evaporation pan is used to hold water for the determination of the quantity of
evaporation at a given location by observation. Experiments are conducted
continuously for a period of 3 months and based on the comparison of
experimental results with estimates, Penman-Monteith (P-M) Method is found
to be suitable to estimate the evaporation losses at RAK. Monthly average
estimates of Evaporation rates are calculated using the Penman-Monteith(P-
M) equation for both RAK and Adu Dhabi regions and the results are shown in
Figure.2.




Conclusion
It could be concluded the evaporation estimates by the variation of
temperature only are not suitable for the calculation of real evaporation
losses. Meteorological factors like wind velocity, air humidity and solar
radiation largely affect the evaporation estimates. The best estimates for
evaporation rates at RAK, UAE are given by the Penman- Monteith(P-M)
method which considers both heat and mass transfer processes by
evaporation. Based on the estimates, the annual evaporation in RAK (UAE in
general) is found to be around 4.5m. The maximum and minimum evaporation
values calculated by these equations were recorded in January and June
months respectively.


CSEM-UAE Innovation Center LLC            Al Jazeera Al Hamra Area          T +971 (7) 244 6929
www.csem-uae.com                          PO Box 31208                      F +971 (7) 244 6951
                                          Ras Al Khaimah, UAE               info@csem-uae.com

				
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posted:11/12/2011
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