Crops distribution is currently marginalized by climate limits worldwide, either by default or by an excess of the vital needs for the individuals within different biotypes. Right from the moment the planting is performed, the plants are submitted to the climate components asynchronous variations, having those turned into the most determinant factors for the success of any given crop [18] [19] [20] [21] [22] .

The particular needs and requirements of such crops are most commonly described in ranges, being usually reported by species or even genotype. The result of the diagnosis shall rely on the intervals taken into account; as a result, if optimal values are considered, the resultant potential areas may indeed provide a better yield and cultivation profitability.

The following criteria were considered to determine the rainfed potential areas for Cyamopsis tetragonoloba: 1) those where all of the appropriate variables interacting with each other were considered as the most suitable for an optimal development; 2) those where the correct climatic and soil characteristics interaction prevailed, despite some restrictions, were considered as suboptimal; 3) finally, those considered as inadequate for the mechanical settlement of Guar cultivations were reported, too. Potential areas were determined taking into account only those opened for cultivation. Altitude, soil, temperature and annual rainfall levels were also taken into account in addition to climate, in order to define the optimal, suboptimal and inadequate Cyamopsis tetragonoloba cultivation areas (Table 1).

The Arc/View version 3.3., software—developed by the American company ESRI—was the program used for data process and analysis. Geo-referenced data can be represented with it, as well as the analysis of characteristics and distribution patterns for such data, looking forward to have it reported, afterwards [23] . All of the Arc/View activity took place within the project parameters, which were a collection of related documents controlled during the Arc/View session.

*Types of climates: Aw = Tropical savanna climate; Cw = Humid subtropical climate; Cf = Warm oceanic climate; Bs = Warm semi-arid climate; Cs = Warm Mediterranean climate. Source: Own elaboration based on consultation of experts and different sources of information.

Projects may contain as many as five different views, tables, charts, layouts (or printouts) and scripts. The names of all of the documents contained in an Arc/View project were displayed through the Project window; then, a project had the status of all of these documents properly organized and stored; next, the project decided how and where such documents were meant displayed, keeping the document selection active and with the appearance of the application window defined, which is the same as making a quick picture of the Arc/View status at the moment of saving it. The project information was further stored in an ASCII format file, always with an *. Apr. Extension, Arc/View, which was mainly a maps vector generator.

The procedure was performed in Arc/View 3.3 (Figure 1) to take the variables intersection process into consideration in order to generate optimal, suboptimal and unsuitable potential areas. The maps were generated through cartographic intersections between polygons and potential classes were described and maintained in each process of intersection in vector processing; as a result, the final map provided information on all of the variables that were intercepted. These

maps were more representative vector models as they were more accurate to generate estimates of a given area, due to the fact that the maps involved in the processes were polygonal. Crop requirements were identified, and those suitable for the cultivation with regards to each variable that were analyzed in the study hereby; then, the performance of the mapping features were selected intersections.

Based on the agroecological requirements of C. tetragonoloba, the following criteria were considered to determine the potential areas under rainfed conditions: 1) high potential areas where all variables of climate, digital elevation and soil behave as optimal conditions for the crop; 2) medium potential areas where the above mentioned variables are suboptimal; and 3) no suitable areas where all variables are limiting factors for crop development.

According to results, Mexico has a total of 1,125,803 hectares to be cultivated under rainfed conditions; 901,138 hectares have a high potential and 224,665 hectares have a medium or suboptimal potential (Table 2). The areas of high potential are mainly distributed in the Pacific states such as: Sinaloa, Nayarit, Jalisco, Michoacan, Guerrero, Oaxaca and Chiapas; however, there are some important areas in the central region (the State of Mexico and Morelos) and in the Gulf of Mexico region (Veracruz and Tamaulipas) as well as the Yucatan Peninsula (Figure 2). The middle or suboptimal zones were found in the states of

Sonora, Jalisco, Baja California Sur, Durango, Nuevo Leon, Queretaro, Puebla, Hidalgo and Colima (Figure 2).

The optimal soils for the cultivation of guar gum are those with pH from 7.5 to 8.0. It grows very good in well-drained soils with light to medium texture with sandy loam texture [24] . This annual crop is not demanding for very fertile soils; tolerates saline soils and drought [1] [25] . It could be considered as an intercropped alternative with cereals and vegetables [26] . In addition, it can enrich soil fertility through the atmospheric fixation of N [7] . Luvisols, Fluvisols, Nitisols and Regosols are being considered optimal whilst Cambisols with good drainage are suboptimal (Table 1). The optimal soils are distributed mainly in the soils located along the Gulf’s river basins, The Yucatan Peninsula and all the states that make up the Pacific region (Figure 3).

The Rainfall. Cyamopsis tetragonoloba in its natural state grows in arid and semi-arid regions with an annual precipitation of 200 - 600 mm [27] . In United States it grows well in areas with 900 mm [28] . However, this crop can be adapted to tropical and subtropical regions [1] . For the Mexican study, 600 to 1200 mm was considered as an optimal condition whereas for suboptimal conditions both ranges: from 400 to 600 mm and from 1200 to 1500 were considered. The extreme conditions of under 400 mm and those over 1500 mm were not eligible (Figure 4). However, Liu et al., (2007) [29] indicates that sowing

dates should be taken into account due to rain effect on seeds blackening which can strongly affect potential yields, seed gum quality and commercial value.

The Climate. Temperature is one of the main environmental factors that affect seed germination [30] . It has to be considered at planting time keeping in mind the crop cycle which can be longer than 160 days in large cycle genotypes [30] . The climates considered as optimal for Mexico were both: the sub-humid zones cataloged as Aw, Bs, Cf and the temperate regions Cs and Cw (Table 1) while the optimum temperature was in the range of 25˚C to 30˚C. Suboptimal conditions ranged from both: 11˚C to 25˚C and from 30˚C to 40˚C. Those temperatures under 11˚C and greater than 40˚C were not suitable (Figure 5).