## 4 Discussion  
The composition of the analyzed variables (Elevation, LST, Rainfall, and WUE) directly influenced the PC1, and they can be explained by the fact that WUE has a high sensitivity to climate change and by geographical aspects of the environment, for which its modifications affect the behavior of the vegetation, altering the WUE. Recently, [PERSON] et al. [59] and [PERSON] et al. [60] identified an opposite relationship between elevation and air temperature. This is due to the thermal contrast between soil and atmosphere and also due to the effect of variations in air mass and humidity, which is in line with [PERSON] et al. [61], who observed the highest values of air temperatures at higher altitudes and the lower values at lower altitudes. In the regions with high elevations, climate change affects several environmental  
Figure 4: Land use and land cover variation in 2001 (**a**), 2019 (**b**) e WUE 2001 (**c**), 2019 (**d**). factors (temperature, humidity, and light, among others) [62] and, consequently, the WUE. In this study, WUE significantly increased with elevation in the function of the agricultural areas present in these portions of the MATOPIBA (west of the state of Bahia). LST and Rainfall are used as indicators of the relationship between vegetation and climate change because they directly impact vegetation growth [63; 64]. Land-surface temperature exerts a strong influence on vegetation development. [PERSON] et al. (2019) found that the ideal temperature for global productivity for all vegetation types is \(23\pm 6\)\({}^{\circ}\)C. In tropical forests, the ideal temperature must be close to the mean temperature during the growth season [65]. In some instances, the increase in WUE is conditioned to high temperatures [66; 67] as long as it is within a certain threshold. It is noteworthy that the ideal temperature for photosynthesis is between 20 \({}^{\circ}\)C and 30 \({}^{\circ}\)C [68], and temperatures beyond this range contribute to decreasing the WUE of the crop, resulting in increased transpiration and soil evaporation [69]. In this manner, high temperatures (>30 \({}^{\circ}\)C) force plants to adapt to greater carbon dioxide (CO\({}_{2}\)) absorption along with a smaller loss of H\({}_{2}\)O by evaporation, thus impacting the carbon-water cycle of the vegetation [70]. The effects of the rainfall are variable and depend on the species present in the ecosystem [71]. The rainfall aids in the biophysical processes of the vegetation [72; 73]. It is noteworthy that the association of lower rainfall with high evapotranspiration rates contributes to increased stress in plants [74]. Thus, plant growth depends on the rainfall regime; if rainfall is insufficient, then growth will depend exclusively on the groundwater availability [75], forcing the plants to adapt to minimizing the loss of H\({}_{2}\)O by transpiration. In turn, excess rainfall associated with cloud cover reduces the incidence of solar radiation on the ground and, thus, impairs the photosynthetic processes [76]. Water use efficiency, the most prominent variable in PC1, can be explained by its input variables in Equation (1) (GPP and ET), which are measures related to the exchange of C and H\({}_{2}\)O between plants and the atmosphere (photosynthesis) [77; 78] and, therefore, dependent on the environment. The highest GPP values were observed along with areas where ET values were high (N of Maranhao), associated with greater rainfall availability in this region [2; 3]. [PERSON] et al. [79] and [PERSON] et al. [80] found the highest total annual GPP values in areas of dense vegetation and evergreen broadleaf forests. [PERSON] et al. [81] highlighted the areas with high vegetation density that presented higher ET values than croplands. [PERSON] and [PERSON] [82] evaluated the behavior of ET over the state of Rio Grande do Sul and identified that the regions with the highest ET values were those with less anthropic influence (dense forests and lakes).