EFFECT OF EXPECTED CLIMATE CHANGES ON EVAPORATION LOSSES FROM ASWAN HIGH DAM RESERVOIR (AHDR)

Transcription

1 Thirteenth Interntionl Wter Technology Conference, IWTC 13 9, Hurghd, Egypt EFFECT OF EXPECTED CLIMATE CHANGES ON EVAPORATION LOSSES FROM ASWAN HIGH DAM RESERVOIR (AHDR) H. A. Bdwy Assistnt Professor, Ntionl Wter Reserch Center, Ciro, Egypt ABSTRACT At present, it ppers tht there is grdul increse in the tmospheric concentrtion of crbon dioxide (CO ) nd other greenhouse gsses. The continuous increse of such gses will cuse globl wrming during the 1 st century. Although most of the scientists re fully wre of such fcts but there re still uncertinties bout the incresing rte of tmospheric temperture in order to tke counter mesures. By pplying sophisticted models, some scientists hve estimted the globl temperture increse between C during the present century, if the countries ll over the world did not tke serious mesures to decrese the genertion rte of the crbon dioxide nd the other greenhouse gses. However no body hs predicted the exct vlues of the expected temperture increse. The increse in ir temperture will be ccompnied by globl chnges in other meteorologicl prmeters such s wind speed, sunshine hours, humidity, precipittion, rdition nd other prmeters. In Egypt, temperture increse will hve direct effect on the griculture nd domestic wter demnd. In the sme time losses of wter by evportion from Aswn High Dm Reservoir (AHDR) my be chnged. The im of the present pper is to estimte the evportion losses from (AHDR) t 5 due to the expected climte chnges. Dt concerning temperture, humidity, wind speed, evportion rte, nd rdition of the shore metrologicl sttion on the left bnk of AHDR re obtined from the Wter Nile Sector, Ministry of Wter Resources nd Irrigtion covering the period from Dt of 3 rft sttions which re Aswn, Allquy, nd Abu-Simble re lso obtined from Aswn High Dm for the period from These dt hve been sttisticlly nlyzed nd the trend of ll the meteorologicl prmeters hs been estimted for the shore sttion during the period The obtined trend ws used for estimting the meteorologicl prmeters for the three rft sttions t 5. Monthly evportion rte from (AHDR) hve been estimted by seven methods (Frere 1, Frere, Bulk 1, Bulk, Sdek, Doorenbos, nd McIlroy) for the yers nd 5. Although it ws expected tht due to the climte chnge, temperture will be incresed in 5 upon which wter losses by evportion will be lso incresed, however, results showed tht the evportion rte will not be ffected. This could be explined

2 Thirteenth Interntionl Wter Technology Conference, IWTC 13 9, Hurghd, Egypt due to the expected ir temperture rise nd the increse in humidity, followed by decrese in wind speed which hs not chnged much the evportion rte. INTRODUCTION Evportion from the lnd surfce includes evportion from open wter surfce, soil, shllow groundwter, nd wter stored in vegettion long with trnspirtion through plnts. The rte of evportion from the lnd surfce is driven essentilly by meteorologicl controls, medited by the chrcteristics of vegettion nd soils, nd constrined by the mount of wter vilble. Climte chnge hs the potentil to ffect ll of these fctors-in combined wy tht is not yet clerly understood-with different components of evportion ffected differently. The primry meteorologicl controls on evportion from well-wtered surfce (potentil evportion) re the mount of energy vilble (chrcterized by net rdition), the moisture content of the ir (humidity), nd the rte of movement of ir cross the surfce (wind speed). Incresing temperture generlly results in n increse in potentil evportion, lrgely becuse the wter-holding cpcity of ir is incresed. Chnges in other meteorologicl controls my exggerte or offset the rise in temperture, nd it is possible tht incresed wter vpor content nd decresed net rdition could led to lower evportive demnds. The reltive importnce of different meteorologicl controls, however, vries geogrphiclly. In dry regions, for exmple, potentil evportion is driven by energy nd is not constrined by tmospheric moisture content, so chnges in humidity re reltively unimportnt. In humid regions, however, tmospheric moisture content is mjor limittion to evportion, so chnges in humidity hve very lrge effect on the rte of evportion. Severl studies hve ssessed the effect of the chnges in the meteorologicl prmeters on evportion, using models of the evportion process. It ws found tht the projected increse in potentil evportion is lrgely relted to the increse in the vpor deficit resulting from higher temperture (Chttopdhyry et l 1997). It is importnt to emphsize, however, tht the different equtions for clculting the evportion give different estimtes for the bsolute evportion rtes. Therefore, it could rther be difficult to compre results from different studies. Equtions tht do not consider the explicitly of ll meteorologicl controls my give very misleding estimtes of chnge. The im of this study is to estimte the wter losses by evportion from the AHDR t 5 due to the expected climte chnges upon which the policy of wter mngement nd cultivted crops could be reconsidered.

3 Thirteenth Interntionl Wter Technology Conference, IWTC 13 9, Hurghd, Egypt Fig. 1 Lke Nsser

4 Thirteenth Interntionl Wter Technology Conference, IWTC 13 9, Hurghd, Egypt Detection of Climte Chnge on Aswn High Dm Reservoir The cpcity of Lke Nsser (fig 1) is reching 16 billion m 3 t level 18. m. The lke lies between ltitudes 3 58 / N nd 7 / N, nd longitudes 3 7 / E nd / E, with bout 5 km long, 15 km in Sudn nd 35 km in Egypt. The mximum width of the lke is bout 6 km, with verge width of bout 1 km. The lke hs surfce re of 65 km t the 18 m level (bove men se level). The mximum depth of the lke is 9 m with verge depth of 5 m. The lke lies in hot nd extremely rid climte. A study of climte chnge implies the investigtion of the prmeters tht determine the climte of the region ws conducted. Consequently, ll the vilble meteorologicl dt which hve the effect in estimting the lke evportion were nlyzed in order to find the trends over the pst two decdes. Dt of mximum nd minimum temperture, dily men temperture, ir reltive humidity, globl rdition, nd wind speed hve been used in the present investigtion. The collected dt from the shore sttion t Aswn covered the period were nlyzed by using sttisticl technique. This type of nlysis could be the best for regionl climtic vribility's nd chnge. Sttisticl models re generlly ttempt to represent the observed dt by model consisting of deterministic trend plus "residuls" bout the trend, which represent nturl vribility. The model tkes the form: Y t = α + β t + ζ (1) Where is the expecttion of Y o where Y o is the vlue of y t time zero, the trend, Y t the meteorologicl prmeter under considertion, t represents time, nd is zero men time series of disturbnces which my be uto-correlted nd my disply stochstic behvior with long memory. This method ws pplied for every prmeter on monthly nd nnul bsis. Meteorologicl Sttions nd Dt For estimting the wter losses by evportion from AHDR, the meteorologicl dt for the lst yers (1986-6) of shore sttion of the lke t Aswn were obtined from the Wter Nile Sector, Ministry of Wter Resources nd Irrigtion. The dt hs included temperture, humidity, wind speed nd rdition. These dt were recorded dily from which the verge monthly ws clculted. Beside this sttion there re nother three utomtic rft metrologicl sttions hve been instlled long the lke in order to mesure the meteorologicl rft prmeters. These four sttions re described in the following:

5 Thirteenth Interntionl Wter Technology Conference, IWTC 13 9, Hurghd, Egypt ) Shore Lnd Sttion This sttion ws instituted in 1986 ner the Hed Qurter of High Dm Authority, t 3 o 59 / N nd 3 o 8 / E t elevtion of 19 m bove the men se level. The monthly verge of mximum, men, nd minimum ir temperture, reltive humidity re mesured t 1.5- m bove ground. Wind speed is mesured by Lmbrecht Cupcounter t meter level. Globl Rdition is lso recorded t Aswn Airport Meteorologicl Sttion ( km to the north f the lke sttion). Mximum nd minimum ir tempertures were observed in Stevenson screen. Mesurements of evportion from "Clss A" pn were crried out in the sttion. The period of dt series covered the period , with months missing of ech prmeter. b) Automtic floting Sttion Three utomtic buoy sttions belong to the High Aswn Dm Authority were instlled in 1995, the sttions were locted upstrem of the dm, t Aswn ( km), El- Allquey (75 km) nd Abu-Simble (8 km). The utomtic system is recording hourly dt of mximum, minimum nd men ir temperture, reltive humidity, surfce wter temperture nd m depth wter temperture, wind speed nd wind direction. The sensor hs been fixed t m height bove wter surfce. The system is operted by chrgeble btteries through solr pnels. The dt hve been collected nd stored through dt-collecting unit during the period from 1998 to 5. METHODOLOGY AND RESULTS Estimtion of evportion rte is of utmost importnce in mny hydrologic problems ssocited with plnning nd mngement of reservoirs nd irrigtion systems. In rid nd semi rid zones such estimtion is prticulrly importnt to conserve scrce wter resources. However, the exct mesurements of evportion rte from wter bodies re indeed one of the most difficult tsks. In order to estimte the expected meteorologicl prmeters t AHDR in 5; the chnge of such prmeters trends should be first obtined. However, since the dt collected from the three rft sttions re covering period of less thn ten yers (1998-5), vritions trend for the meteorologicl prmeters were estimted ccording to the dt collected from Aswn Shore Sttion for period yers. Estimtions were crried out for four meteorologicl prmeters s follows: ) Monthly men ir temperture ( C), b) Monthly men ir reltive humidity (%), c) Monthly men ir wind speed (m/sec), nd, d) Monthly men globl rdition (MJ/m ).

6 Thirteenth Interntionl Wter Technology Conference, IWTC 13 9, Hurghd, Egypt Tble (1) presents the nnul correltion coefficient, trend, nd level of significnce for Aswn Shore. Tble (1) Trends nd Correltion Coefficient for Meteorologicl Prmeters for Aswn Shore Sttion Net. Prmeter Correltion Coefficient r Significnt level Trend T R H o WS RG T x T n Clss A Amount of wter evported from wter surfce is estimted by the following methods: ) Evportion guges, (tmometers, Clss "A" pn, GGI-3,.etc) b) Empiricl evportion equtions, (Bulk erodynmic eqution) c) Anlyticl methods, (wter-budget, energy-blnce, combintion of energyblnce nd Bulk erodynmic). The monthly evportion vlues were estimted using seven different methods (Empiricl nd Anlyticl) which re widely used s listed in the followings: EMPIRICAL METHODS 1. Bulk 1 Aerodynmic Eqution (El-Bkry, 1993) where E Bulk ( e e ) 1 =. 16 U s d () E Bulk1 = lke evportion in mm/dy e s = sturted vpor pressure t wter surfce temperture e d = ctul vpor pressure of overlying ir t specified height U is wind speed in m/sec t m height.. Bulk Aerodynmic Eqution (USSR) where E (.5 +. U ) ( e e ) Bulk =.13 7 (3) E Bulk = lke evportion in mm/dy e s = sturted vpor pressure t wter surfce temperture s d

7 Thirteenth Interntionl Wter Technology Conference, IWTC 13 9, Hurghd, Egypt e d = ctul vpor pressure of overlying ir t specified height U is wind speed in m/sec t m height. ANALYTICAL METHODS 1. Doorenbos et l. (1977) Dorembos et l eqution red s; *[.9RG σtk *.97 * (.3. E Doorenbos = e d ) (.1 + 9n / N )] +.67E where, E Doorenbos = Lke evportion in mm/dy = de/dt= Slope of sturtion vpor pressure curve t ir temperture T = psychrometer constnt =.67 for o C R= men extrterrestril rdition expressed in equivlent (mm/dy) = Stefn Boltztmn constnt T k = bsolute men ir temperture ( o K) (n/n) = rtio of ctul to possible hours of sunshine durtion e d = ctul vpor pressure t the sme temperture e s = Sturtion vpor pressure t wter surfce temperture U = wind speed t m (mile/dy) E = the so- clled erodynmic term E =.7 * ( * U ) * ( e e ) where ; U ( / sec) s d m (). Frere 1 et l. (1986) Frere 1 et l. eqution red s; E Frere1 = ( P o / P)* [.9R G 6T k ( ( P where, E Frere1= Lke evportion in mm/dy O e d ) / P)* +.67 (.1+.9 n / N ) ] +.67 E (5) E =.6( * u ) * ( e e ) ; u m/sec d 3. Frere et l. In cse of neglecting tmospheric pressure, the formul becomes;

8 Thirteenth Interntionl Wter Technology Conference, IWTC 13 9, Hurghd, Egypt [.9RG σ TK ( ed ) E frere = (.1+.9n / N)] +.67E (6). Sdek et l. (1997) Sdek et l. eqution red s; E sdek = [.9R.97σ T G k * (.1 +.9n / N) * (1 1. ( e +.67 / T k ) 1/ 7 ] +.67 E (7) where, E Sdek= Lke evportion in mm/dy E = * u ) * ( e e ) ; u m/sec ( s d 5. McIlroy formul (Sltyer&McIlroy 1961) McIlroy formul red s; E McIlroy 3 [.9R.97( σ T ) ( n / N ) T ] S = G K σ S u ( T T ) w where, S = slope of sturtion vpor pressure curve t wet bulb ir temperture. = (de/dtw) T = men ir temperture T w = wet ir temperture K (8) RESULTS AND DISCUSSION In the present study, dily observtions of temperture, humidity, wind speed, evportion rte, nd rdition of the shore meteorologicl sttion of AHDR re obtined for the period from 1998 to 6 s well s dt of 3 rft sttions which re Aswn, Allquy, nd Abu-Simble re lso obtined for the period from 1998 to 5. The verge monthly of the dt of 3 rft sttions were clculted. The verge nd monthly nd nnul vlues re considered s the meteorologicl dt for the yer. These dt hve been sttisticlly nlyzed nd the trend of ll the meteorologicl prmeters hs been estimted for the shore sttion. The obtined trend ws used for estimting the meteorologicl prmeters for the three rft sttions t yer 5.

9 Thirteenth Interntionl Wter Technology Conference, IWTC 13 9, Hurghd, Egypt Seven equtions (Bulk 1, Bulk, Doorenbos, Frere 1, Frere, Sdek, nd McIlory) were pplied for estimting the monthly evportion rte t the meteorologicl three rft sttions for the yers nd 5. Of these seven equtions, two methods re depending on Bulk erodynmic (Bulk 1 nd Bulk ) using dt of temperture, humidity nd wind speed. The other five methods (Doorenbos, Frere 1, Frere, Sdek, nd McIlory) re bsed on combintion equtions, from which four equtions re depending on Penmn eqution nd the fifth eqution which is the lst depends on combintion using McIlory eqution. These five methods were pplied using the bove prmeters s will s rdition nd erodynmic terms. Intensive clcultions were conducted where the obtined results re presented in figures to 7. Figure shows tht the mximum vlue of the monthly evportion rte of Aswn rft sttion t the yer ws 9.88mm t June nd July by using McIlory method, while the minimum vlue ws 3.3mm t Jnury by using McIlory method. In the sme time Figure 3 shows tht the mximum vlue of the monthly evportion rte of Aswn rft sttion t the yer 5 ws 1mm t June nd July by using McIlory method, nd the minimum vlue ws 3.mm t Jnury by using McIlory method. Figure shows tht the mximum vlue of the monthly evportion rte of Allquy rft sttion t the yer ws 8.3mm t June nd July by using Frere 1, Frere, nd Doorenbos methods, in the sme time the minimum vlue ws 3.mm t Februry by using Bulk method. For Allquy rft sttion, Figure 5 shows tht the mximum vlue of the monthly evportion rte t the yer 5 ws 8.8mm t June by using Frere 1 nd Frere methods, while the minimum vlue ws.9mm t Februry by using Bulk method. For Abu-Simble rft sttion, figure 6 shows tht the mximum vlue of the monthly evportion rte of t the yer ws 1.mm t August by using Bulk 1 method, while the minimum vlue ws 3.mm t Jnury by using McIlory method. While figure 7 shows tht the mximum vlue of the monthly evportion rte of Abu- Simble rft sttion t the yer 5 ws 9.6mm t August by using Bulk 1 method, nd t June using McIlory method, nd the minimum vlue ws 3.5mm t December by using McIlory method. Evportion Losses t Aswn Evportion Losses t Aswn 5 E v p o rtio n L o ss es Frere1 Frere Bulk1 Bulk Sdek Dorenbs Mcilioy Evp ortio n Losses Frere1 Frere Bulk1 Bulk Sdek Dorenbs Mcilioy Months Months Fig Averge Monthly Evportion Fig 3 Averge Monthly Evportion Rtes for Aswn Rft t Rtes for Aswn Rft t 5

10 Thirteenth Interntionl Wter Technology Conference, IWTC 13 9, Hurghd, Egypt Evportion Losses t Allquy Evportion Losses t Allquy 5 E v p o r tio n L o s s e s Frere1 Frere Bulk1 Bulk Sdek Dorenbs Mcilioy E v p o r tio n L o s s e s Frere1 Frere Bulk1 Bulk Sdek Dorenbs Mcilioy Months Months Fig Averge Monthly Evportion Fig 5 Averge Monthly Evportion Rtes for Allquy Rft t Rtes Allquy Rft t 5 Evportion Losses t Abu-Simble t Evportion Losses t Abu-Simble t Evportion Losses 8 6 Frere1 Frere Bulk1 Bulk Sdek Dorenbs Evportion Losses 8 6 Frere1 Frere Bulk1 Bulk Sdek Dorenbs Mcilioy Mcilioy Months Months Fig 6 Averge Monthly Evportion Fig 7 Averge Monthly Evportion Rtes for Abu-Simble Rft t Rtes for Abu-Simble Rft t 5 Tble The Averge Annul Evportion Rte for the three Rft Sttions for the yers nd 5 Aswn Aswn 5 Allquy Allquy 5 Abu- Simble Abu- Simble 5 Bulk Bulk Dor Fre Fre Sd Mcl Men

11 Thirteenth Interntionl Wter Technology Conference, IWTC 13 9, Hurghd, Egypt Tble shows the verge nnul evportion rte for the three rft sttions using the seven equtions for the yers nd 5. It is cler from tble tht the nnul men evportion rtes for Aswn meteorologicl sttion t yer nd 5 for the seven equtions were 6.37mm nd 6.3mm respectively. For Allquy sttion, the men evportion rte for yer nd 5 were 5.7mm nd 5.81mm respectively. For the third meteorologicl sttion Abu Simble, the men evportion rte for yer nd 5 were 7.mm nd 6.96mm, respectively. Tble 3 The Averge Annul Evportion Rte for the Three Rft Sttions 5 Chnge % Aswn Allquy Abu-Smile Men Lke Tble 3 shows the verge nnul evportion rte for the three rft sttions nd the evportion rte of the whole AHDR for the yers nd 5. It's cler from the tble tht the verge evportion rte from AHDR which estimted by using the seven equtions were 6.37mm nd 6.3mm for the yers nd 5 respectively with chnge percent of -.7. At Allquy the vlues were 5.7mm nd 5.81mm for the yers nd 5 respectively with chnge percent of 1.9, while t Abu-Simble the verge evportion rte for the yers nd 5 were 7.mm nd 6.96mm respectively with chnge percent of By ssuming tht the men vlues of evportion rte of the three rft meteorologicl sttions is representing the evportion rte of the whole lke, it ws found tht the verge vlues for these three sttions were 6.36mm nd 6.37mm for the yers nd 5 respectively with chnge percent of.9. It is cler tht, lthough the temperture is expected to increse in yer 5 thn tht of yer, however, the verge chnge percent in the evportion rte for the lke will be.9 which prove tht the men evportion losses of the lke will be incresed by.9% compred with tht for yer. This negligible chnge cn be explined due to the effect of temperture increse, followed by increse humidity nd decrese wind speed which hve negtive effect on evportion. However it ws found tht there is considerble chnge in evportion between nd 5 in some months (winter nd summer). In generl it ws proved tht the men nnul vlues of evportion will not hve much chnge during the study period (-5). It is known tht the lke-to-pn coefficients vry ccording to size nd type of pn, type of instlltion, nd climte condition. For clss "A" pn, this coefficient vries between.6 in wrm nd rid res, nd.8 in humid res. Men nnul evportion from clss "A" pn t Aswn Shore Sttion for the period ending by the ws found 13.9 mm/cm, rte of climte chnge for clss "A" pn.16 mm/cm /yer, nd hve nnul evportion for clss "A" pn for the period ending by 5 ws 11.8 mm/cm. Totl chnge in nnul clss "A" evportion ws

12 Thirteenth Interntionl Wter Technology Conference, IWTC 13 9, Hurghd, Egypt -.8 mm/cm /5 yers with -1.9% from the reference yer evportion. It is cler tht the mesure of evportion vlues obtined by Clss "A" pn is quite higher thn the verge vlues obtined by the seven equtions. This chnge is due to the selection of the lke-to-pn coefficient. CONCLUSIONS It ws ssumed tht the three rft sttions (Aswn, Allquy, nd Abu-Simble) re representing the whole AHDR. Since the first is t distnce. km, the second t distnce of 1 km while the third t distnce of 8km upstrem AHD respectively. The distributions of the three sttions re lmost covering 9% from whole lke re. The Meteorologicl dt of the three Rft Sttions, Aswn, Allquy, nd Abu-Simble re collected nd considered in this study where results were nlyzed in order to evlute the evportion losses from AHDR t yer 5. The evportion losses from the lke were clculted twice for ech sttion. The first one ws for yer representing the present condition, while the second one ws for 5, representing the expected future vlues of evportion. Tble showed tht the men vlue of evportion for Aswn Sttion in were 6.37mm nd 6.3mm respectively in 5 which equl to 6.mm. However, the men chnge percent for the results of the seven equtions ws -.7%. For Allquy Sttion it ws found tht the men vlue of evportion for the seven equtions in nd 5 were 5.7mm nd 5.81mm respectively, while the men chnge percent between nd 5 ws 1.9%. For Abu-Simble Sttion the men evportion vlue for the seven equtions ws 7.mm for yer nd 6.96mm for 5, nd the men chnge percent ws -.57%. These dt showed tht by pplying the seven equtions for the three meteorologicl sttions, the differences in evportion vlues nd the chnge percent were quite negligible. Finlly this study hve proved with no doubt tht the chnge percent in evportion for the three sttions Aswn, Allquy, nd Abu-Simble were -.7, 1.9, nd -.57% respectively nd the finl chnge percent for whole lke is.9% (Tble 3). This men tht the expected climte chnge nd the temperture rise in 5 will hve quite negligible effect on evportion losses from Lke Nsser, it will be incresed by.9% due to the expected temperture rise which will increse the humidity nd decrese the wind speed. Wind speed is considered one of the min prmeters tht hve direct effect on evportion rte. At the beginning of this work it ws born in mined tht the evportion losses from AHDR will be definitely incresed, but fter the thoroughly clcultions by pplying the vilble relible published methods nd by using the ctul dt collected from the three rft meteorologicl sttions in the lke. However, the obtined results showed tht the evportion losses from AHDR will be incresed by very negligible chnge percent of.9%. This unexpected result

13 Thirteenth Interntionl Wter Technology Conference, IWTC 13 9, Hurghd, Egypt will encourge for more investigtions when more metrologicl dt for the rft sttions re obtined. ACKNOWLEDGEMENT The uthor would like to thnk Prof. Dr. Abd-El-Ftth Motwe Chirmn of Wter Nile Sector, (MWRI) nd Dr. Abd. El-Ltif Mehnn for their support for providing the study with the needed dt. REFERENCES - Chttopdhyry, N. nd M. Hulme, 1997: Evportion nd Potentil Evpotrnspirtion in Indi under Conditions of Recent nd Future Climte Chnge. Agriculturl nd Forest Meteorology El-Bkry, M.M., 1993: Hydrometeorologicl Mesurements over the Lke of Aswn High Dm nd Evportion Estimte. Nile Conference, Aswn, Egypt, Februry El-Bkry, M.M., 199: Net Rdition Over Aswn High Dm Lke. Theor. Apph. Climtol. 9, Dorembos, J., nd Pruit, W.O., 1977: Crop Wter Requirements. FAO Irrigtion nd Dringe Pper no., 1P. - Frere, M. And Popov, G.F., 1986: Erly Agrometeorogicl Crop Yield Assessment. FAO Plnt Production nd Protection Ppers, Tech. Pper No Hoy, R.D. nd Stephens, S.K. (1977): Field Study of Evportion Anlysis of Dt from Lkes Eucumbene, Ctrct, Mnton, nd Mundering. Rs. Project 68/s, Tech. Pper No.1, A.W.R.C., Cmben, A.C.T., 195 PP. - Omr, M.H., nd M.M. El-Bkry, 1981: Estimtion of Evportion from the Lke of Aswn High Dm (Lke Nsser) bsed on mesurements over the Lke. Agric. Meteorol., 3, Omr, M.H., nd M.M. El-Bkry, 1997: Estimtion of Evportion from Lke Nsser by the Het Budget Method, nd Morton ' s CRLE Model. Meteorology nd Environmentl Cses Conference, -6 Mrch 1997, Egyptin Meteorologicl Authority, Ciro, Egypt. - Penmn, H.L., 198: Nturl Evportion from Open Wter, Bre Soil nd grss: Proceedings Royl Society, London A 193,1. - Penmn, H.L., 1956: Vegettion nd Hydrology. Technicl Comm. No. 53, Commonwelth Bureu of Soils. - Sdek, M.F., M.M, Shhin, nd C.J. Stigter (1997): Evportion from the Reservoir of High Aswn Dm, Egypt: Anew Comprison of Relevnt Methods with Limited Dt. Theor. Appl. Climtol. 56, pp Sltyer, R.O., nd I.C. McIlroy, 1961: Prcticl Microclimtology. Melbourne, CSIRO, Austrli, pp Webb, E.K., 1965: Aeril Microclimte. Meteorol. Monogr., 6(8): 7-58, July 1965.

14 Thirteenth Interntionl Wter Technology Conference, IWTC 13 9, Hurghd, Egypt - WMO, 1966: Mesurements nd Estimtion of Evportion nd Evpotrnspirtion. Tech. note 83, Genev, World Meteorologicl Orgniztion, 11 pp. - WMO, 1983: Guide to Hydrologicl Prctices. WMO No. 168, Vol. Chpters 5-7: , Genev: World Meteorologicl Orgniztion.