Assessing Crop Yield Sustainability under the Climatic and Bioclimatic Change in the Area of Palestine ()
1. Introduction
The climate in Palestine is Mediterranean character with a dry summer season from May to October. The rainy season and agricultural year begin in September-October and the rainfall ends in April-May [1] . The winter rain regime has been extensively studied [2] -[7] and also the long-term changes in annual rainfall patterns [8] [9] . Therefore, Palestine is situated in the subtropical dry lands of south-western Asia at a very sensitive climatic position. Palestine bioclimatic belt belongs to the infra-Mediterranean to meso-Mediterranean thermo-type [10] . The atmosphere of Palestine is clear and its air is pure. Summer temperatures reach 35˚ centigrade and in the winter, temperature may drop to zero. The inconsistency of rainfall throughout the months and years requires that most vegetable cultivation is supplemented with irrigation to ensure normal growth.
Olive (Olea europaea L.) is one of the most important fruit trees in Palestine, with cultivars as Souri, Nabali Mohassan, Nabali Baladi, Roumi and others. Olive is a Mediterranean species with a very specific biology, as its root system is extremely disperse and does not penetrate deeply into the soil, making it thus considerably susceptible to climate change [11] [12] . Grape (Vitis vinifera L.) is one of the plants fruit trees affected by climatic and biological factors [13] , and grapevines are grown in distinct climatic regimes worldwide that provide ideal situations to produce high quality grapes [14] . Whereas, fig (Ficus carica L.) is one of the plants that can tolerate seasonal drought, and the Middle Eastern and Mediterranean climate is especially suitable for the plant. Also the biology of the plant allows its root system to penetrate deeply into the soil in search of the lower levels of the water table.
The aim is to study the relationship between the climatic and bioclimatic factors on plant production, and the effects of climate change on crops.
2. Materials and Methods
2.1. Study Area
Palestine is located between longitudes 34˚15' and 35˚40' east and between latitudes 29˚30' and 33˚15' north. The geographic location of Palestine plays a major role in affecting the features of its climate and the climate diversity between the southern and northern parts.
2.2. Data Analysis
Data were used from the meteorological stations in Palestine in Table 1, Figure 1 for the years 1993 to 2008 (15 years), and for the same years for production of plants (Table 2). The bioclimatology of the aforementioned stations was studied, and the value of the bioclimatic indices as ombrothermic index (Io), continentally index (Ic), and compensated thermicity index (It/Itc) and the climatic factors were obtained according to Rivas-Martinez [15] -[17] and [18] .
We analyzed the relationship between the dependent variables as olive, grape and fig production; the indepen- dent variables (climate factors) such as average temperature (T), precipitation (P), soil water reserves (R),
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Table 1. Coordinates of meteorological stations in Palestine.
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Table 2. Represents of independents variables (bioclimate factors as annual ombrothermic index, simple continentally index and compensated thermicity index, and climate factors as a temperature, precipitation, deficit water, and soil water reserve); independents variables are consist of olive, fig, and grape production.
Yield: kg/dunum.
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Figure 1. Location of the meteorological Palestinian stations.
and water deficit (Df), and the bioclimatic variables or factors as Io, Ic, and It/Itc, in order to establish the variables that had the greatest influence on agricultural production in the regions of Palestine.
In this study, the Shapiro-Wilk and Jarque-Bera normality tests were applied [19] -[22] , and the p-value was obtained for the seven variables. We applied an ANOVA linear regression analysis to each of the ten independent and dependent variables, the three bioclimatic variables and the four remaining physical variables (climate factors), and each of the dependent variables olive, grape and fig production, in order to obtain the coefficient of regression R2 and the multiple regression line, and canonical correspondence analysis (CCA) were subsequently applied in order to determine the influence of independent variables on production. These statistical analyses were done using the XLSTAT software.
3. Results and Discussion
Effect of the Bioclimate and Climate Change on Plant
We used the bioclimatic classification of earth to Salvador Rivas-Martinez to analyses of the climate factors and bioclimatic parameters (independent variables). After application of the Shapiro-Wilk normality test, the p-value obtained from the variables studied tended to be below 0.05, a conventionally accepted value.
The analysis of variance (ANOVA), with a 95% confidence interval, applied to each of the three production variables olive, grape and fig, with the seven independent variable factors T, P, R, Df, Io, Ic and It/Itc, reveals significant differences in the case of olive, grape, and fig production, implying the influence of the seven factors on the production of olive, grape and fig, may be that changes in climatic and bioclimatic factors have an impact on the sustainability of plant production, in the multiple regression analyses, the case of olive and grape production shows a better linear regression correlation with the values of R2 = 0.984, 0.960 respectively, being close to 1, although the correlation of fig production is small than olive and grape, as R2 is low (0.892). The linear regression correlation analyses between each of the three dependent variables, olive, grape and fig production and the three independent bioclimatic variables have a different level of significance. There are no significant differences in the case of olive and fig production, but there is a statistically significant difference for grape production, as the histogram is positive (Figure 3), because grape production is high in south of Palestine (Table 2). Moreover, the high linear regression correlation between the bioclimatic factors and olive production with values of R2 = 0.984, and the value of R2 = 0.960 for grape production, shows the high influence of the independents variables of bioclimate Io, Ic, P, Df, R on the grape production, but low in the case of olive and fig production (Figures 2-4), and that these results are very close, as conducted by Ighbareyeh, J.M.H., et al. [23] .
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Figure 2. Regression correlation analysis for the olive and independent variables.
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Figure 3. Regression correlation analysis for the grape and independent variables.
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Figure 4. Regression correlation analysis for the fig and independent variables.
On the other side, bioclimatic variables that were not taken into account in the model published by Galán et al. [24] for the Andalusian olive grove. We observed that the olive and fig production were influenced by the climate change as temperature and bioclimate factors as compensated thermicity index because the histogram is positive, while the P, Df, R, Io, and Ic, were negative histogram (Figure 2 and Figure 4).
Nevertheless, when the multiple regression correlation analysis is applied to each of the dependent variables and the seven physical parameters (independent variables), significant differences (p < 0.05) can once again be observed in all cases. These differences are lower in the case of olive production; again in this case the value of R2 obtained in the multiple regression line is 0.984, thus highlighting the high correlation between olive production and physical parameters.
In view of the linear regression correlation obtained, we applied a canonical correspondence analysis (CCA). This was done by comparing the dependent variables olive, grape and fig production with the total independent variables, the three bioclimatic parameters Io, Ic and It/Itc, and with the four physical parameters, from nine sampling plots. In the first place it was observed that the Nablus, Jenin, Jericho and Gaza type plots are located at the left of axis 1, and plots are more affected by the T and It/Itc, while all the Hebron, Bethlehem, Jerusalem, Tulkarem and Ramallah type plots are at the right of axis 2, and reveal the influence of annual ombrothermic index, continentally index, precipitation, water deficit and soil water reserve, with a large proportion of the variance explained by axis 1 (86.41%), as opposed to axis 2 (13.58%) (Figure 5), hence, we note that there is the impact of these factors on the production and sustainability of these plants; also, we indicated the climatic andbioclimatic factors affecting biology and plant communities [25] .
We observed that there is confirmation of the Nablus, Jenin, Jericho and Gaza type plots were conditioned by the T, It/Itc, underlining the fact that olive and fig production in these plots depends on It/Itc and T, whereas gra- pe production is less influenced by these factors. Therefore, olive and fig production in the Nablus, Jenin, Jeri- cho and Gaza type plots are conditioned by temperature and compensated thermicity index. However, the nature of the relationship between biological system, atmospheric dynamics and temperature is changing [26] -[29] .
Hebron, Bethlehem, Jerusalem, Tulkarem and Ramallah were conditioned by continentally index, water defi- cit and others factors, as in the upper thermo-Mediterranean and lower meso-Mediterranean environments, the optimum for the production of olives is achieved with values of Ic more than 18 and Io = 3.6 - 4.0 [30] [31] , and Io = 3 - 4, and It/Itc is about 300 for the production of grape [23] , grape is a very responsive to their surrounding environment with a seasonal variation in yield of 32.5% [13] . Climate is one of the key controlling factors in grape production, [32] affecting the suitability of certain grape varieties to a particular region as well as the type
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Figure 5. Canonical correspondence analysis (CCA), with independent variables (climate and bioclimate factors) and variables dependents.
and quality of the wine produced. However, the interaction between climate-soil-variety will in some cases come under threat from the effects of climate change. Identification of genes underlying phonological variation in grape may help to maintain consistent yield of particular varieties in future climatic conditions [33] . Mild to cool and wet winters followed by warm springs, then warm to hot summers with little precipitation provide adequate growth potential and increase the likelihood of higher wine quality [34] -[36] and [14] .
In the (CCA), with a variance of 86.41% (Figure 5) between production and environmental factors (T, It/Itc) explained by axis 1, whereas in plots type Hebron, Tulkarem, Bethlehem, Jerusalem and Ramallah, production depends on precipitation, also, the annual precipitation rates are deemed likely to fall in Palestine decreasing with an increased risk of summer drought [25] [37] [38] , and the effect of reduced precipitation could result in reducing annual groundwater recharge in the West Bank by 30% of existing value [39] ; and soil water reserves and water deficit, maybe, this is probably also due to the lack of rainfall in general for these areas and the type of soil, therefore, storm water runoff are affected by soil types and local variations [40] [41] . And so we need to study strategic climate change adaptation planning and monitoring of groundwater quality and quantity, and the soil type and quality.
4. Conclusions
Bothclimatic and bioclimatic factors play a very important role in plant biology, in the production, sustainability of crop yield and lead to an increase in economy in Palestine. The annual precipitation rates are deemed likely to fall in Palestine decreasing with an increased risk of summer drought.
The multiple regression analysis reveals that bioclimatic variables have a greater influence on grape and olive production than that on fig. The canonical correspondence analysis leads to the identification of two types of plots: Nablus, Jenin, Jericho and Gaza, whose production depends on the temperature and compensated thermicity index, which is the result of temperature nearly 20˚C, and a high compensated thermicity index. These conditions favor the production of olive and fig but not of grape, as these crops need values of annual ombrothermic index ˂ 3. Whereas, Hebron, Bethlehem, Jerusalem, Tulkarem and Ramallah are the plots whose production depends on the bioclimatic factors as ombrothermic index and continentally index, and climatic factors as precipitation, water deficit and soil water reserve.
Moreover, this study demonstrates for each crop the bioclimatic optimum, in which maximum production occurs, and in these situations, the use of water from the soil is not required for irrigation, also the highest production of grape is found in the south of Hebron, with olive production in the north and fig production in the central and other areas of Palestine.