The Soil Moisture Regime Estimated by Means of Climatic Data

Home , Maaloula, Qatana, Saidnaya, Ustic

The Arab Center for the First Training Course in Agrometeorology for Arid Zones Studies of Arid Zones Damascus, h4ay and Dry Lands (A C S A D) IO - 23 I082

The Soil Moisture Regime estimated by means of Climatic Data.

Its relationships with Annual Rainfall and .._ with Bioclimatic Classifications under Mediterranean Climatic Conditions.

Paul BILLA.. Pedologi.st of the Oversea Scientific and technical research Institute (O R S T O hl. F'rance)

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Dans de nombreux pays les mesures du régime hydrique des sols sont rares et son estimation au moyen des données clinstiques ne peut se faire que pour un nombre limité de stations météorologiques. 11 est alors malaisé de délimiter avec une approximation suffisante les régions ayant un régime hydrique donné. C'est là une difficult6 pour l'utilisation de la Taxonomie américaine des sols. Le texte rappelle d'abord la définition des régimes hydriques selon la Taxonomie américaine et le principe de leur estimation au moyen des données climatiques. Les paragraphes suivants exposent les relations qui existent, dans quatre pays arabes B climat de type méditerranéen, entre les classes de régime hydrique estimé et a) la pluviométrie moyenne annuelle, b) les subdivisions bioclimatiques des systèmes d'Emberger et de Ragnouls et Gaussen. De telles relntións permettent, povr un pays donné, d'utiliser les cartes pluviométriques et bioclimntiques dans le but d'méliorer le tracé des limites entre les régions 8 régimes hydriqaes différents.

ABSTRACT

In many countries measured data concerning the Soil hloisture Regime (ShfR) are scarce; furthermore the ShfR estimation by means of climntic data is possible only for a somewhat limited number of meteo- rologiesl stations. As a consequence it is not easy to draw boundary lines between areas mith different SMR. This is a difficulty freqnent- ly met with when using the U.S. Soil Taxonomy. In a first part this pnper shortly recalls the definition of the Soil Moisture Regimes according to Soil Tmonomy and states the prin- ciples of their estimation by means of climatic data.

' The following paragraphs deal with the relationships found, for some arsb countries with mediterranean climate, between the classes of estimated ShlR and a) the average annual precipitstion, b) the bioclimste according to the bioclimatic classifications of Einberger and of Bagnoulls and Gaussen. Such relationships allow to use, in a given country, Annual precipitation maps and bioclimatic maps in order to mark with R better accuracy the boundaries between regions with diff ererrt ShR.

6 hilots-cl6s: Régime hydrique des sols. Estimation par donn6es climn,ti- ques. Relations avec Pluviométrie annuelle et, avec Bioclim3ts m6di terrmnéens ., CONTENT

, Page I. Introduction I' 2. The Soil Moisture Regimes according to "Soil Taxonomi)."; definitions I 2.1. Soil Moisture Control Section I 2.2. Moisture and Dryness 2 2.3. Soil Temperature Criteria 2 2.4. Classes of Soil Moisture Regime 2 2.5. Remarks 3. Estimation of the Soil Moisture Regime by means of Climatic data 3 3.1. Principle of estimation of the moist and dry periods in the moisture control section 3 3.2. Newhall's method 4. 3.3. Graphic method 5 3.4. Soil temperature estimation 5 3.5. Results of SMR estimation. Remarks 5 4. Relationships between estimated Soil Moisture Regime and average annual Precipitation 6 1

I 4.1. Estimated SMR and mean annual Precipitation . 1 and Air Temperature 7 4.2. Estimated Sm, "dry in all parts" period of the moisture control section and mean annual precipitation 7 4.3. Comparison of the relationships found for Syria, Lebanon, North Morocco and Tunisia 8 5. Tentative relationships between estimated SMRt-and Bioclimatic classifications 8 5. I. Estimated SMFt and Mediterranean Bioclimatic Stages of Emberger 8 5.2. Estimated SMR and Mediterranean Bioclimates of Bagnouls and Gaussen 9 6. Some conclusions 9-

References 10 Figures. Annexe. The Soil Moisture Regime estimated by means of Climatic data. Its relationships with Annual Rainfall and with Bioclimatic Classifications under Mediterranean Climatic conditions.

I 0 INTRODUCTION The Soil Moisture Regime is the succession of the moisture conditions in the various soil layers during the successive seasons of the year. Likewise the Soil TemperRture Regime is the succession of the temperature level in the soil layers throughout the year. The knowledge of these regimes is important: ci - to understand and explain the pedogenesis, i.e. the development (past and present) of the soil physical and chemicel properties; - to achieve R successful management of farming in rainfed areas. Water and heat are most impor$nnt factors for the chemical, physico- chemical and biological activities. Therefore it seems normal for B soil Classification to use, at any level, some criterin related to the Soil Moistlire and Temperatura Regimes. Most soil classifications include such criteria, one way or another. The French classificatim (1967) define the subclasses (second higher level) by reference to the "pedoclimatic" conditions, a synthesis of the soil regimes for moisture, temperature, red - ox conditions and soil solution concentration. The Canadian clrtssif ica - tion (1978) introduce the soil moisture regime at b lower class (soil family); et cetera ... . I However it is the recent U.S. Soil Taxonomy (1975) which uses the present Soil Moisture and Temperature Regimes in the most systematic way, at high classification levels and with precise quantitative criteria. In this paper it rill be dealt only with the Soil Moisture Regime (SMR) as defined in the U.S.%oil Taxonomy".

2. THE SOIL MOISTURE REGIMES ACCORDING TO "SOIL TAXONOMY" DEFINITIONS. The SMR are defined by the length of moist and dry periods in a soil control section and, in addition, by some soil temperature criteria. 2.1. Soil Moisture Control Section (MCS). "The upper boundary of the MCS is the depth to which B dry (water tension > I5 bars but not air dry) soil rill be moistened by 25 mnr of water within 24 hours. The lower boundary is the depth to which a dry soil will be moistened by 75 mm of water within 48 hours. These depths are exclusive of the depth of moistening along any cracks or animal burrows that are open to the surf ace". The depth and thickness of MCS depend on the soil physical charac- , teristics which determine the soil Available Water Capacity (AWC). As a rough approximation the depth of the upper and lower boundaries are: -in fine loamy, silty, clayey soils: IO - 30 cm; - in coarse loamy soils: 20 - 60 cm; - in sandy soils: 30 - 90 cm.

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If the soil is shallow over R hard rock or indurated layer, the ' lower boundary of the MC9'is the upper limit of the hard material. In this case it needs less than 75 mm of water to moisten the soil down to the lower boundary. 2.2. Moisture and Dryness. The soil is "moist" if it holds water at a tension 4 I5 bars (available waxer). This implies that the water content of the"moist" soil may vary widely, between saturation and the wilting point. The soil is rldrylf if it holds only water a't a tension 3 I5 bars.' (Suah high tension may occur in moist but very salty soile, the soil is then considered physiologically dry.) The MCS may be %oist in all parts" (i.e. throughout its whole depth) or "dry in all parts", or"moist in some part" (which is equiva- lent to "dry in some part"). The lenght of the moist and dry periods of the MCS is measured by a number of either consecutive or cumulative drtys. Under mediterranean climatic conditions the moist period as well as the dry period are normally composed of consecutive drtys. 1 2.3? Soil Temperature Criteria. These are: - ,The Idean Annual Soil Temperature (WT); It may be obtained by mea- ' suremenkat a minimum depth of 50 cm made at regular time intervals throughout the year. - The Difference (DIF) between the mean summer and winter soil tempe- raturesat 50 cm depth (or at a lithic or paralithic contact).* - The periods during which the soil temperature at 50 cm depth (ST 50) is either > SOC or between 8 and 5OC or <5OC. They may be deduced . from the curve of the mean monthly soil temperature at 50 cm depth. 2.4. Classes of Soil hfoisture Regime. The criteria of definition for the SMR classes (except Aquic) are put in a comparative way in Table I. - Aridic (= Torric) : the moisture regime of arid regions and part of the semi-arid regions; in-st years rainfed cultivation is not pos- aible; there is no leaching; soluble salts accumulate. - Xeric: the typic moisture regime of regions with mediterranean climate, i.e. cool or cold rainy winter, warm and dry summer. The rainfall, coming ip winte&hen evapotranspiration is minipun, is particularly effective for leaching. - Udic: occurs in regions of humid climste (temperate or tropical) with well distributed precipitation throughout the year. Water moves down through the soil at least at some time.

*MAST and DIF are also used in the U.S. Soil Taxonoqy to define the Soi 1 Temperature Regime (STR) ; for instance : MAST = 0-8OC 8-15OC 15-22OC > 22oc with DIF>5OC, STR: frigid mesic thermic hyperthermic with DIF< 5OC, STR: isofrigid isomesic isothermic isohyperthermic

.I Table-t - Definition of the soil moisture reqime . classes ! (except Aquic) according ta Soil Taxonomy i -4 Gonsecutiye days 4 C umulat iv e time 1 / A Seasonal conditions ~ Others conditions Part of the time Others conditions when ST-.> 5@c (days) -5 I t $ [ !4months I -4monUls i I I I I f I I when 5TS,)8*C 1 I* I AR1 O I I IC I l I I moi&/MOIST < 90 piK-[ (=Tsrr¡c) 1 I I I I (most (most years 1 I I years) I I 1 I 1 I I f I f I I MAST 222.C I I .jdry/DRY)SOI or l II I (most years) I I I DIF / 61ycars/ IO) I (most years) i I I I I when ST,, > 8.C i MAST C 22% F XERIC i í I l I f if I I I -i

UDlC I (most years) I i 4 ’ Maisture control section MOIST, : moist in alt parts dry : dry. in soma part i‘ mai& /MOIST : mois% in soma or tlt pads dry/ DRY : dry in soma or al! ports i 1 , moist : moist: in some part: DRY : , dry in dl ports t d I *. I {, 1. “;i . 3

- Ustic: intermediate between Aridic and Udic. The moisture is limited but is present at a time when conditions are suitable for plant growbh. Normally in regions wkth rainfall during a warm season. - Aquic: this regime implies reducing conditions; the soil is free of dissolved oxygen because it is satumted (at least temporaryly) by ground water or by water of the aapillary fringe. 2 .5 . Remarks. - Restrictives conditions: "The definition of the SMR applies only to aoils under netural conditions, i.e. non irrigated or non frrllowed to increase the amount of stored water. These cultural practices affect the soil moisture conditions as long as they are continued." - It must be noted that the moisture condition of the surface layer (above the control section) is not taken into account. This may introduce some discrepancy between the plant growing period and the moist period of the control section. - The definition of the SMR classes is based on the knowledge of moisture regimes in well studied soil series in the U.S.A.. It is possible that in some cases they do not exactly fit the soil moisture conditions of other countries. Some futur changes in the definitions are not ex- cluded.

3. ESTIMATION OF THE SOIL MOISTURE REGIME By MEANS OF CLIMATIC DATA. To know accurately the soil moisture regimes of a given country it would be necessary to make field measurements of soi1 moisture and temperature during several years and in a number of stations representative of various soil and climate conditions. This is a serious difficulty; in many countries there is no or only few measurements of that kind. What then if the soil scientists of these countries want to em- ploy the U.S. Soil Taxonomy which is now widely used as one of the reference classifications ? Here the agrometeorologist comes to assist the pedologist. The difficulty is turned by estimating the SMR by means of climatic data. As a matter of fact,"the intent in defining the moisture control section= to facilitate such method of estimakion". 1 3.1. Principle of estimation of the moist and dry periods in the MCS. The data to be used are: the average monthly values of Precipita- tion, P, and of Potential Evapotranspiration, PE. As there are only . few available measurements of evapotranspiration, PE is mostly estimated by means of climatic data. There are several methods for PE estimation, each of which has some shortage. The simpler is that of Thornthwaite based on average monthly air temperature and day lenght.

~ Other methods, like Penman's or Turc'sc or Papadakists, give in arid and semi-arid regions better resul-ts as compared with measured PE, but they need data whiah are not available in all the stations. The principle of estimation of the moist and dry periods in the , MCS is as follow. a) For each month (or part of month) the difference (P - PE) is calculated. Beginning from the month'when P becomes > PE the differences (P - PE), firstly positive then negative, are added up. The cumulative results are used to draw a curve (Fig.1, curve S) which represents the

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evolution of the available water stored in the soil. b) When the amount of stored water increases, there is a wetting front progressing downwards in the soil. According to the definition of the MCS (5 2.1) when the soil has stored 25 mm of water the wetting front has just reached the upper boundary of the MCS. Between 25 and 75 mm , during the descent of the wetting front, the MCS is "moist in some part". At 75 mm of stored water the lower boundary of the hKS is rewhed and from this time onwards the MCS is "moist in all parts". The intersection of curve S with horizontal lines corresponding to 25 and 75 mm indicate the beginning of the periods when the MCS is first partly then completely moist. c) When P becomes < PE, the drying of the soil progresses roughly as follows. At first the soil dries progressively in all its layers (above, inside and below the MCS) but the water remains held Rt tension < I5 bars and consequently the MCS remains moist in all parts. Then, beginning from the surface, the soil dries up to a tension & I5 bars and a drying front progresses downwards. The MCS becomes Ildry in some part" when its upper boundary has .'.I .been reached by the drying front. This occurs approximativelyl'after 75 mm of PE if there is no additional precipitationtl. At last when the amount of stored water becomes equal to zero the MCS becomes "dry in all parts". 3.2. Newhall's method. It is one of the most used computntion method. It is barJed on the following assumptions (R.Tavernier and A. Van Vambeke, 1976) : - Rainfall distribution. The monthly precipitation is divided in two equal parts: I) a single storm falls on the 15th of the month and penetrates integrally into the soil; 2) the other half falls in small sho- vers, uniformly distributed throughout the first and the second halfs of the month, and only the part exceeding PE penetrates into the soil. - The soil AWC is 200 nnn (soil depth of approximately I50 cm for a fine-loamy particle size). The water in excess is considered as lost by percolation or ran-off. In addition, ,the soil is supposed well drai- ned, without groundwater and without surface crust or inside layer hindering water penetration. - Potential evapotranspiration is estimated by Thornthwaite's method. - During the drying period, the -amount of energy required to remove one unit of water increases when the amount of water remaining in the soil decreases, and also with the depth of this remaining water. Newhall's method uses a mathematic model which ensbles to achieve the calculations by means of an electronic computer. The inputs are only the average monthly precipitation and air temperature. An exemple ', of printed output is given in Appendix I.

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3.3. Graphic method. The method developped in 0 3.1 and Fig.1 is useful for estimation of a limited number of SMR. For the calculation onemay use either the same assumptions (rainfall distribution, ATVC, PE) than in Newhall's method or other ones. This method does not take into account an increase of energy of PE when the available water is low. However the results are not far from those of Newhall*and the clames

of estimated results are the same. I 3.4. Soil teniperatures estimation. Soil temperature data are available for a limited number of stations. In most cases the soil temperfitures required as criteria in the SMR definitions (0 2.3) must be estimated from air temperature. In Syria, Lebanon and Jordan the average relationships between measured soil and air temperatures were computed (Y.O.A.El Kawasma, 1979; P.Billaux, 1980) : - annual: MAST = MAAT + 2OC - summer: MSST(50 cm) = MSAT + I9Q0C - winter: MWST (50 cm)æ MWAT + 2.5OC (Syria plus Jordwn) = MWAT + 1.7OC (Syria plus Lebanon) - Average monthly relRtionships between soil temperature at 50 cm depth and air temperature were also computed. It is noteworthy that during . winter the STEiOis always higher than ;the air temperature by a few degrees C. In other countries the measured relationships may be different. For instance Soil Taxonomy proposes for the U.S.A.: MAST = MAAT + IOC, and MSST = MSAT - 0,6OC. Likqwise, some temperature relationships used in the computation program for Newhall's method did not fit well with the data oljtained in Syria and Lebanon: DIF estimation was too small and the estimated soil temperature a%50 cm depth in winter was too low (Appendix I). It is advisable to use regional rather than general temperature relationships. 3.5. Results of Soil Moisture Regime estimation. Whichever method is used, the results appear as lenghts of moist and dry periods of the MCS. By comparing these periods (together with the soil temperatures) with the criteria of SMR classes (9 2.4) the SMR estimation is obtained. Fig.2 shows examples of results fo,r some stations of Arab countries under mediterranean climatic conditionsw. In such countries the esfi-' mated SMR. are mostly Xeric and Aridic, occasionally Ustic.

* For the stations of Syria and Lebanon the "moist in some part" period of the MCS, at the end of the drying process, is shorter by an average of eleven days as compared with Newhall's method. ** Computation with PE according to Thornthwaite and with monthly rainfall distribution according to Newhall assumption.

. II'/.I rataop i ne (Tuni sie ) ,l'i I pa :121+mtp-Ta:20°1 ' 33O55 N - 8"lO E - 4Sm EXTREME ARIDIC-HYPERTHERMIC !I" Remarks. a) The apparent precision of dates and number of days must not lead to forget that these results are only estimations depending on the original hypotheses (6 3.2). Besides, the monthly values of precipitation used for the computation are average data which hide large interannual variations. Moreover, the Soil Moisture Regime is only a partial function of climate3 other factors interfere,such as the position in the landscape, the runoff, seepage,... . b) In most cases the computation results allow to place the estimated SMR of a station, without hesitation, inside one of the SMR classee defined in Soil Taxonomy. However there are some cases which do not meet well the definitions of Soil Taxonomy. An instance is given by the station of Kharabo (Syria; Fig.2) the estimated SMR of which is neither Aridic nor Xeric nor Ustic; such SMR will be called in this IC paper: "intermediate between Aridic and Xerictt. * c) In each of the SMR classes defined by Soil Taxonoqy there is, as a matter of fact, a range of different moisture regimes. This is evident for Xeric (Fig.2: Damascus and Kassab) as well as for Aridic (Fig.2: Tataouine and Tapoudannt) and Ustic (see Fig.9). Some subdivisions are necessary; they are under study at the present time, particularly in the International Committee on Moisture Regimes in the Tropics (ICOMMORT). For instance an ttF2&reme Aridic" SMR has been proposed, in which the MCS is completely dry during the whole yettr.

4. RELATIONSHIPS BET\yEEN ESTIMATED SOIL MOISTURE REGIhff!, AND AWAGE ANNU& PRECIPITATION. An important utilization of soil classifications lies in soil mapping. It raises a difficult problem: how to extend to sometimes large areas the SMR estimated from the local data of meteorological stations ? It is clear that the greater the number of lo-cal estimations the easier the drawing of boundaries between areas with different SMR. Now, in many countries, out of the total number of meteorological stations, only a part sypply data which enable to estimate the SMR (Table 2). Table 2 Meteorological Syria Lebanon Tunisia North Morocco s tati ons (1977) (1972) (1976) (1976) Total. number I73 I37 83 301 Only P data available 75 73 30 190 Data allowing SMR estimation: . with PE Thornthwaite 98 64 53 III . with PE Penman I2 2 8 9

* It must be noted that in the definition of some soil sub-groups in the U.S. Soil Taxonomy, the ShB is described as "Aridic bordering Xeric" (Xerollic sub-groups of Aridisols; Aridic sub-groups of Mollisols).

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It would be an useful improvement if the SMFt estimations could be extrapolated to the numerous stations with' only precipitation data available. With this in view the eventual relationships between esfi- mated SMR and mean annual P were studied for the stations where SMR estimation was possible. The study concerns Syria, Lebanon, North Morocco and Tunisia, four countries.with mediterranean climate. The number of selected stations cover nearly all local climate conditions inside each country. The results are stated hereafter..* 4.1. Estimated SM€¿ and mean annual precipitation and air temperature. Fig.3, 4 and 5 display the estimated SMR of the stations compared with mean annual P and air T. From these figures the following statements may be drawn. r- a) Definite annual precipitation values may be considered as threshold values between the Aridic (plus the intermediate aridic - xeric) SMR. and the Xeric SMR. These values are not the same in the different countries. b) In the climatic conditions of these countries the threshold value of P between Aridic and Xeric is practically independant of the mean annual air temperature. c) Ustic moisture regimes appears, in the ranges of precipitation corresponding to Xeric and to intermediate aridic - xeric, when the mean

'1 annual air temperature is 2OOC. Ustic SMR occurs also in Tunisia in the highest range of precipitation but with T< 20OC. ** 4.2. Estimated SMR, "dry in all parts" period of the moisture control section and mean annual precipitation. In Fig.6,7 and 8 the estimation of SMR is represented in a more detailed way by means of the total number of days when the MCS is "dry in all parts" (as a rule under mediterranean climate these days are consecutive ones) . The distribution of the stations in the graphs clearly indicates that there is a dominant relationship between the estimated SMR and the annual precipitation. A consequence of this relationship is the possibility of extrapolating the estimated Aridic and Xeric SMR to the stations where only precipitation data are available (however if the climate is warmer than the average the possibility of a Ustic SMR must be kept in mind). A valuable approximation of SMR may thus be provided i- for a number of stations which otherwise would be unused. Fig 6, 7 and 8 display side by side the result of SMR computations made by using either Thornthwaite's or Penman's potential evapotranspi- r- ration. The results with Penman's PE are few but nevertheless enough to draw average curves which allow to estimste the threshold values of P between the Aridic and Xeric regimes. These values are, of course,

~ * Syria and Lebanon: SMF¿ computation by Newhall method ( A. van Vambeke, Cornel1 University, ItheÆa. U.S.A.). Graphic method if PE Penman is used. Morocco and Tunisia: SMR estimation by graphic method with monthly rainfall distribution according to Newhall assumption (P.Billaux, ACSAD) . ** This estimated Ustic SMR cover a very wide range of moisture conditions and it is questionable if the definition of Ustic is well fitted to mediterranean climates. . higher than those found by means of Thorntwwnitels PE. It is not possible to decide, without field meRsurement of SMR, which method is the better in a given country. Anyw~y the comput4tion with ThornthwRite'a PE allows to obtain a far greater number of estimations and the method is widely used to compare the SMR on a world scale. 4.3. Comparison of the relationships found for Syria, Lebanon, North Morocco and Tunisia. The relationships between estimated SMR and average annual precipitation are compared in Fig.9. This figure emphasizes the differenes of the threshold values of P between the Aridic and Xeric SMR. Such differences reflect various regional climatic conditions inside the general type of mediterranean climate. Without going into details, let u8 say thet the main factor concerned is the distribution of precipi- r- tation t,hroughout the year. A same level of annual precipitation is distributed in Morocco and Tunisia through a longer period of time than in Syria and Lebanon. ...- PEGiMES 5, TENTATIVE R.ELATIONS€IIPS BETWEEN ESTIMATED SOIL MOISTURE /AND BIOCLIMATIC CLASSIFICATIONS. In most countries bioclimatic maps at various scales are available. In such maps the bioclimatic classes and subdivisions are defined . by the value of bioclimatic indexes computed from the data of meteorological stations. But the boundaries of the mapping units, specially in medium scale maps, are drawn vith the help of phytoecological studies and surveys. As a matter of fact bioclimrtte classes and natural vegetation are closely related. On the other hand, the type of natural vegetation is evidently dependant on the moisture status of the soil throughout the year: the vegetation represent a natural link between bioclimate classes and SMR. If there is a relationship between bioclimatic indexes and estimated SMR (which is very likely, both being calculated from climatic data) it will be possible to use the bioclimatic - phytoecological maps as a help to draw boundary lines between diPferent estimated SlllR, For that purpose a comparison has been made between estimated Sh.fq. and two of the systems of bioclimatic classification used in mediterranean countries: the Bioclimatic Stages of Emberger and the Bioclima-

r- tes of Bagnouls and-Gaussen (for both systems the relations with vegetation have been well studied). 5.1. Estimated SMR and Mediterranean Bioclimatic Stages of Emberger. P- In this system the "stages" and "sub-stages" are represented on a t:Plwiothermic Climagram" (Fig. IO) as functions of the "Pluviothermic Quotient", Q2,*and of the average minimum tempersture of the coldest month, m. The limits of the bioclimstic stages are drawn according to the data of reference stations for which the natural vegetation as well Q2 and m are thoroughly known. * as .1000 P P: average annual rainfall (m) average m%. temperature of the warmest month (OK) '2' M+m M: -x(M-m) m: average min. temperature of the coldest month (OK) 2 I

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The estimated Shm of various stations of North Morocco and Tunisia were placed on the climagrams of these countries (Fig.10 and II). &om thesa figures one can deduce the following statements: - There is, in a general ray, a fairly good correspondance . of the Aridic (and intermediate aridic - xeric) SMR with the Saha- rian and Arid mediterranean stages, .and of the Xeric ShiR with the min part of the Semi-arid stage and with the Sub-humid and Humid stages (except In the upper part of the last where a Ustic SMR occurs in Tunisia). -In the details, however, the transition between Aridic and Xeric SMR is different from one country to the other: in Tunisia it occurs in the lower part of the Semi-arid stage while inMorocco the transition variea from the upper part of the Aridstage to the upper part of the Semi-arid stage according to the temperature "m". 5.2. Estimated SMR and Mediterranean Bioclimetes of Bagnouls and Gaussen. In this system the bioclimates are defined by the "Xerothermic Ind&, X, which represents the number of "biologically dry" days during the total of the lldryt' months of the year.* The advantage of this index comes from its taking into account monthly climatic data. Unfortunately its computation requires data &v&ilobleonly in a limited number of s teti ons . An example of comparison with estimated SMR is given for Syria and Lebanon (Fig.I2), with additional reference to the mean annual temperature. The correspondance between estimated SIIR and the bioclimates is evident. The figure shows the transition between Aridic and Xeric SMR for X = 220 (except in cold semi-arid mountains where it'$s slightly lower) In other countries, however, the transition between Aridic and Xeric SMR occurs at other values of X. For instance in Tunisia (where precipitation is distributed during a longer period than in Syria)it corresponds to X values between I25 and 175.

6. SOME CONCLUSIONS. - Concerning the estimated ShtR one must not forget that it is only an approximation (though an useful one). The actual moisture regime depends not only on climate but on topographic and edaphic aonditions and also, .in some cases, on the vegetation. In each country the relia-. bility of the estimated ShiIR should be checked by means of adequate moisture measurements in the field, in some well chosen representative stations. * 19ry1'month if P5 2T (P, T: meen monthly rainfall and air temp.) N: total days X = {(x of the cldry" months) r: rainy dRys of a "dry" f: days with fog or x of a trdry" month = h=LD if [N (r +%)) h - re1 ative d.7 if 80 < H < 90 humidity of

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- In the present state of knowledge in several countries, estimation of SMF¿ is a necessity for the soil scientists who want to use any soil classification system including moisture regime criteria. The relationship between estimated SMR and the average annual precipitation, in a given country, will allow to extend the estimations of SMR to a good deal of stations where only P data are available. But such a relationship is not totally applicable to another country: the trsnsi- tion values of P between two moisture regimes are different. I ¿if+ er! nt - To draw the boundary lines between areRs.with/moisture regimes, the knowledge of natural vegetation is probably one of the best ways towards a good accuracy. Such bioclimatic maps as are available in Morocco and Tunisia, based both on climatic indexes and vegetation studies, should be useful in extrapolating the estimated SMR of a station to an $rea of similar vegetation. In a general ray, any available phyto-ecological study and map should be taken in consideration by soil cartographers concerned with SMR.

References Soil Taxonomy. U.S. Department of Agriculture. (1975). R.TAVERNIER,, A.VAN VAhUH3KE (1976) - Qétermination du régime hydrique * des sols du MRghreb d''après Newhall. Pédologie, XXVI, 2, p.168-173. Gand. Y.O.A. EL KAWASMA (1979) Soil temperature regimes in arid and semi- arid regions. IIp + 5 fig. ACSAD, Damascus. P.BILLAUX (1980) - Correlation of soil and air temperature in Syria and Lebanon. I2p + 6 fig. ACSAD, Damascus. Ch.SAWAGE (1963) - Etages bioclimstiquea; notice explicative. Atlas du NiBroc; 6.b. 44p + I fig. Rßbet. M.GOUNOT, H.N. LE IIOUEXLOU ( 1967). Carte bioclimatique au 1/600.000 de la Tunisie septentrionale; étages et variantes. Annales INRA; , 42, I,(annexes). TUNS. Climatological Atlas of Syria (1977) . Ministry of Defense; Meteorolo- gical Department. Damascus. J.PLASSARD (1972). - Notice explicative de la carte plwiométrique du Liban au 1/200.000. Service météorologique du Liban. Beyrouth - Ksqra. Agroclimatological studies in the Arab countries (1976) : Tunisia, Syria, Lebanon, Morocco. League of Arab states. Arab organization for Agri- culture Development. Khartoum.

I P mm 1700 - o 71

1600 -

A70 PE accordingto 1500 - 69 A Thornth wake between Xeric i- and Aridic 1400 - 0 24 A67 A 68 s Aridic o23 ~66 1300 - o 22 8 : Noof station I200 -

A 65 21 1100 - 64 A 0 o 20 ‘ -- 63A o19 1000 - / 018 / / I- - 900 - 462 61 /O17 60459 pi5 QI6 014 .958 800 - A 56 700 - Coastal o9 re g ions

60 07 o5 600 - A 54 A 53 .* A 52 A51 500 -. A 50 Yarmuk D 49 I( lower valley ‘9 k8 o4 03 46a A4.7 A45 400 - A4b A 43 A 42

300-

200-

100-

I I l l I I 10 II 12 13 14 15 ik ,117 IB ib io 2’1 2’2 T~C

I Fig. 3 - Syria and Lebanon - Estimated soil moisture regime .as related to average annual precipitation and air temierature - A52 , ! I ! ,' I i "I i

!Iit

I 1 il I Syria

I ustic ,i 9 I' I/I

r-.

I ,Xeric III

I yria .and Lebanqn .cp-

.... "._...... " ...... ^.._ ,* -...... "...... " "."._....._...... -._ ",...... -. "...... --.- I-"...

...... STATION : HASSAKEH ...... LAT I TU0E,.. .: .... 36 .... ,30 "_..N ...... _.."...... _...... "...... ;...... _...... "_._...

INPUT. DATA: ...... JAN . ,,?Sß MAR ..... Apt? ,".,. MAY...... JUN ...... JUlt . AUG ...... SEP .OLT ..... NOV ..... -DEC ......

PRECIPITATION: --58.5 34-8 40.2 30.3 - 23,1--028 ---O,O- 0.0 1.0 - 11.9 -.18.9-.40.2 __ I c TEMPERATUNE : 5.9- 7.7---11.6--16.5 23.9 26.7 31.0 30.5 25.7 19.5 13.3 7.5 . OYrPJT+******+****+*************~**********+~****~** ...... ~4**************ci+**********~ : CALCULATED EVAPOTRANS?lRATION ACCORDING TO TtiORNTHWAITE ...... 5.4 9.1 25.6 56.2 132.0 164.7 208.3 191.6 130.4 69.8 28.3 8.6,-,,,,...... ANNUAL RAINFALL : 259.7 MM ANNUAL EVAPOTRANSPIRATION :1030 e2 MH i. I_--__._. .__I--.---_- --.-.- '501 L-. TE P(P ERA TU-RE R €GI M€.. 'A'? -5 0-C M--ÖEP'T-H- ES T Ï~A-fËõ?Rö-14 ÄÏ k- T EMP .'O ATA BY ADDING 2.5C TU ANNUAL MEAN AND REDUCING AMPLITUDE UY A FACTOR 0.66 ...... ?' *+*****************0*4***** **k*.ff******4**99* t*****~*****ci+*********$+*+**** * MEAN SOIL TEdPERATURES * SEASONS ljHEN SOIL TEMPERAT,URE ,* ...... *,...... * (DEGREES CENTIGRAdESl * IS HIGHER THAN * * ****~*****~*****5*~****A***~* FIVE ... -_...... OEGilEES--P..... -EIGH~-DEGR_~ES* REGIME.-. -*, ___.,,_ ___,_,,_, _._ OLF- * * * * *ANNUAL SUMMER WINTER FEREN ********+********************************a*****, ...... _._.. CE *8EGIN LENGTH *BEGIN LENGTH 9 * * * ...... 49.8 ~ ...... (DAYS)...... * (DAYS) ...... -...... *$ *

13.3 i4.a * 360 * 2 MAR ~ 296 * THERMIC * ._.__-I-- -2- ********:**4ci+***~~**~*~~**4~*~94*****4~~***ci+~*~~*****+****ira* sozL TEMPfRATURE ...... MOISTURE CONDIT ION .CA'ENOAR ......

.....[-: T<5 _.,..; ?:., 5s... ?...... 2 =PARTLY .DAY.,. ST )' ......

MONTH, ,, . ."...... ^ ._...... 5555555555 5555555555 5555555555 JAN 2222222222 2222233333 33'33333333 5555555555 5555555555 5555555555 FE8 3333333333 3333333333 3333333333 , ,_. ,._,,.. 5a88888.388 d888d88888 d8888d8888 MAR 3333353333 3333333333 3333333333 daßaaaaa8d 8888amasa aa888adasa APR 3333333333 3333333333-3333333333. __, - 3 MEí a 88 M d tJ ¿3 8 8 b8 tl d a 8 8 8 8 8 8 8 a Y 8 8 8 MA Y .- -33 3 3 3 3 33 3 3 33 3 3 3333 3 3 3 33 333 33 22 . . 88d88888dB 8888888888 3888888888 JUN ,2222222221 11 1lllllll 1111111111 ...... 88386d8888 d68d88d888 8888888868 ' JUL 1111111111 1111111111 1111111111 68dddad8da 888d8888da 8888888888 AUG 11111 1111 1 11 111 11 11 1 IlIl 11 11 11 .,_,_.,..,_.,,_.__._ - 8888808688 6d8d888dGB 8888888888. SEP - ' 1111111111 1111111111 LllllLllll - -. - 8808808888 88.58888688 8888638868 OC I Llllllllll ~111lLlL111~1111111111 _,._.____,I 8 88 adda 8 ti 8 d CI86.8 d d d 8 8 8 8 8 88 a 8 8 8 a--"- NGV-- ~ I 11 1 1 1 1 1 1 L 1 1 1 11 1 1 1 1 1 1 1 1 11.1 1 1 1 1

. 88888dd888 8888888880 ...... ,."...... - ^ 398888a555.. , 955 ",.,111111!.111..1!,11!2222?,, ?2?22222?2 "_._

***********a* ****~***ci++*****t*****~******~~***~***~9*****~***~*******~...... -. .. *NiN48ER OF CUMULATIVE OAYS THAT * HIGkEST NU:IBER OF CONSE-* * *THE I-IOISTUHE CONTRCL SECTIGbI *iECdTIVE CAYS THAT MCS IS*---'-.'.- -'-* -. ------a * ***** *** ***** ** ****+***+*4 *t***o ** **** **** f *** **** ***O.$*** 4 ...... -..... *DURING ONE YEAK**HE~J SOIL TE!lP.* HOIST IN * DRY *MOIST * MOISTURE * * IS * ABOVE 5 OEG. *SOHE PARTS *AFTER *AFTER * * ...... * ***O A * * * 4 8 * * * 9 * * 48* 4 * * + * 1: 3 + i* * * * * 9 *O 1: 4 * t4* 8 ****A ** -+ o H E G I :.I E * DRY MUIST MO1 DRY MOIST MOI IN hHEN*SUMMER*wINTER* ,.___-_____ * * -. . * * ______* . OR . ST *' OK ST'* &NE'- TEMP* SUL- * SOL- * * *. DK Y t DR Y *YEAR > 8 *STICE *STICE *. * ...... ' k+f**4**+*4*****+$*****~**************~***~*~****~*******+*********?** 186' 41 133 186 41 133 98 120 105 XERIC * * * 174 * * * * * . ' ..' ' ...... * * * * * * f.** * * *+o* 4: * 4 5 'o * 9 9 * * 4 * 9 *I * * * * * * 8 4 * * * * * * 0 f 4 * ** 4 $4 * * * **o* * * o 19 * * * *+ * COAP\ITED BY FORTRAN PROGRAM VHOB ,MARCH 1976 DATE :04/12/80 Cornell UnivQr5 i+.j -

...... -

I_ , 3 '. .. Meteorological station8 rejE-TwnLed in Fig. 2 to 12. Syria --Morro c O 51 Zabadani 'I Rissani i:l Im-ache 'I Sabaa Ear i2 Azrou 2 Jaba1 el Tenf 52 Madaya 2 Erfoud 3 'l'izni .t í3 Oue mane 3 Abu Kama1 53 Ain el Arab@) 4 Ouarzazate i4 Chechaouene 4 Qaryatein 54 Rouj 13alaa 6 Figuig 55 Ifrane' 5 Damascus airpor 35 Jisr el Shogh 3G Quneitra 6 Ksar e6 SOuq 56 Zoumi 6 Deir ez Zor agr Bab bou Idir 57 Lattaquia 7 Guercif j7 7 rr.4 CI 8 Midelt 8 l'almyra 58 Arwad 9 Semrìr l'unis 1 rt 9 Nrtbek 59 Es Sin IO Taroudaimt IO Deir el Ilajjar 60 Tartous 1 Tozeur Il Agadir II El Kom 61 Mina el Baida 2 TaZlnouine I2 Outerbate 12 Kharabo 62 Arida 3 Gafsa 13 BergueiiC I3 Deir ez Zor st- 63 Joureen 4 Medenine I4 IIassia 64 Qastal Maef 14 Chemaia 5 Cabes I5 Abu ITureireh 5 Safita la Marrn,kech 6 Djerba 16 Marqndeh 5 Misyaf J6 l$ì Xelna dos SI 7 Sfax '17 Wadi el Rzib 7 Slenfeh T7 %.lralla Tnlierk, 8 Jlar%"rs Youssoufis 'I8 Douma 3 Qadmous 18 O El Djenl 'I9 Km.47 3 Ain el Kroum 19 Uenguerir TO Kairouan 20 Forglos O Kassab 20 Dar Ilri ow 11 Sousse 2'1 Es Snouirca, I 21 Itaqqa I Jowbet Bourg 2 XIanmiame t 22 Bailaneh 2% Midnr 3 Medjez el Bab 23 K3nnasser Le banon [4 Soliman 24 1)ankscus hfe zZel I Fnkehe Carthage 25 Qousseir 2 Baalbek 16 'Phala I7 Mepzel b.Zelfa 2G Maaloula 3: lioch Dahab Sou$ el Arban, 27 El Hall 4 IIoch Sneid I8 Bir Mcherga 28 Sanamein 5 Rayak I9 20 Tebourba 29 Ranqous 6 Tel Amara 21 Grombalia 30 Ukeirubat 7 Ksara 22 Maldar 31 Saidnaya 8 El Qasmiyeh Zaghouan 32 Qatana 9 Taanayel 23 24 Le Kef 33 Hnssakeh [O Amyoun 25 Tebour 34 Tel Abiad Alma Chaab s ouk [I 26 Dar Chichou 35 Izraa L2 Lebaa 27 I,e Thibar 36 Salamiyeh 13 El Abde 28 Beja 37 Jerablus 14 Jamhour 29 Bizerte 38 Rleppo I5 Beyrouth A.U. 30 Sedjenclne , 39 Hama 16 Zouk Mikayel 40 Ain el Arab (N I7 Tripoli Mina 33 TRbarka 32 El Feid,ja 41 Salkhad I8 Les Cèdres 33 Ain &aham 42 Sweida 19 Ghazir 43 Rastan 2 O &bani ye j i sr 44 Maarret en NOW 21 KnPtoun 45 Qattineh 22 Bikfafa 40 Qamishli 23 Jezzine 47 El Ilnjel) 47 Fiq 24 Qartaba 48 'l'etouan 48 El Himeh 40 Tangel. 49 Homs 50 Oulines 50 Hawrat Amourec