Average annual air temperatures in the MATOPIBA region vary from 19.8 to 29.1 ºC (Fig. 6). June (Jun) and July (Jul) are the months with the lowest air temperature, with values between 20 and 21 ºC in the southern portion of the region, located mainly in the extreme West of the Bahia state, and of 24 at 28 ºC in portion Center-West and Center-North of MATOPIBA (Figs. 6F and 6G). Elevated temperatures, above 30 ºC, are frequent between September (Sep), October (Oct), and November (Nov) in the Center-North and Northwest portion of MATOPIBA, where the states of Maranhão, Tocantins, and Piauí are located (Figs. 6I, 6J, and 6K). During this period, the occurrence of high temperatures coincides with the higher incidence of solar radiation and lower precipitation, which causes heating of the atmosphere through the emission of long-wave radiation on Earth (Reis et al. 2020). On the other hand, the low temperatures recorded in Jun and Jul can are associated with a lack of precipitation and the consequent reduction in air humidity, which causes less absorption of long wave radiation into the atmosphere at night (Reis et al. 2020).
The average air temperature is an abiotic factor that influences the agricultural activity of MATOPIBA because the plants are grown between October (Oct) and April (Apr), a period with high temperatures, where the plants can suffer stress that result in damage physiological, and less growth affecting, consequently, production. For soybeans, the main crop in the region, high temperatures during the rainy season (sowing season) shorten the crop cycle because the rate of degree-day accumulation is faster (Reis et al. 2020). In this sense, tolerant cultivars adapted to high-temperature conditions can be a strategy to keep crops productive on the MATOPIBA agricultural frontier.
In the MATOPIBA region, the average annual rainfall is 1,502.75 mm distributed mostly (88.75%) between Oct and Apr (Fig. 7). The highest rainfall levels occur in the Southwest, especially in the region predominated by Tocantins state, with high levels of rainfall distributed evenly during the rainy season (Oct-Apr), varying substantially only in Apr. High rainfall levels are also registered in the Southern of Maranhão and extreme West of Bahia. However, spatial reduction of rainfall indices occurs towards the Northeast region of MATOPIBA, especially in Piauí state, which has an average annual rainfall of 1,080.93 mm. Between May and September (Sep), the lowest levels of rain are observed, below 170 mm, a fact that shows the irregularity in the spatial distribution of rainfall.
Rainfall scenario in the MATOPIBA region is modulated by atmospheric systems at different scales, which associated with ecosystem and physiographic factors (as a transition between biomes) strongly influence the intra-seasonal variability of precipitation in the region (Valadão et al. 2017; Reis et al. 2020). However, even though the atmospheric systems formed by the equatorial positioning of the Intertropical Convergence Zone (ITCZ) and the South Atlantic Convergence Zone (SACZ) determine the occurrence of rainfall indices (Grimm 2011; Oliveira et al. 2017), the different levels of rainfall between Southwest and Northeast portion of MATOPIBA can be explained by the fact that the Northeast portion is located in transition biome between Cerrado and Caatinga (semiarid), having less influence of atmospheric systems. However, the Southwest portion is located in the transition of Cerrado and Amazon biomes, with about 100% of its surface in an Amazonian environment (Reis et al. 2020), therefore, influenced by atmospheric systems. Thus, the variable accumulation of rainfall in the MATOPIBA sub-regions is influenced by different vegetative configurations (Reis et al. 2020).
Real evapotranspiration is related to rainfall regime of the region because its occurrence is associated with the availability of water in the soil-plant system, being the main way to quantify the loss of water present in soil and plant for atmosphere (Milly; Dunne 2016). Thus, evapotranspiration in the MATOPIBA region occurs more intensely only during the rainy season (Oct-May), with average real evapotranspiration of 1,044.49 mm and a greater quantity of evapotranspirated water in the Southwest of MATOPIBA (Fig. 8). On the other hand, evapotranspiration values less than 40 mm were recorded between Jun and Sep, mainly in the Central and Northeast regions of MATOPIBA.
Water surplus in the soil commonly occurs between November (Nov) and April (Apr) (Fig. 9), with a total accumulation of 479.57 mm; in this period, rainfall indices above 100 mm are frequent in MATOPIBA (Fig. 7). The largest water surplus (150 at 200 mm) is concentrated in the Northwest of MATOPIBA, specifically in the areas of Tocantins state that concentrate 47.48% of all water surplus. In Jun, July, Aug, Sep, and Oct there is no water surplus in the region due to low rainfall, an event that characterizes this period as dry season in MATOPIBA (Figs. 9F, 9G, 9H, 9I, and 9J). May presents a water surplus only in the extreme North of MATOPIBA, located in Maranhão, with 48.11% of all annual surplus and an average of 561.32 mm (Fig. 9E).
The water deficit is variable during all months of the year (Fig. 10). However, its concentration is greater from Jun to Sep and reaches all MATOPIBA territory, with a deficit average of 267.09 mm, corresponding to 74.44% of all annual water deficit (Figs. 10F, 10G, 10H, and 10I). Water deficit below 5 mm was found in Jan, Feb, Mar, Apr, Nov, and Dec (Figs. 10A, 10B, 10C, 10D, 10K, and 10L), the period in which there are marked volumes of rain. In Oct, the water deficit was zero only in the Southwest of MATOPIBA, represented by Tocantins state; however, in other regions of MATOPIBA, the water deficit can reach 150 mm (Fig. 10J).
MATOPIBA region presented climatic classification variable with four distinct classes distributed vertically throughout its delimitation (Fig. 11). Humid regions (class B1 and B2) were classified in 35.04% of MATOPIBA, with subclasses B1wA’a’ (20%) and B2wA’a’ (6%) more frequent (Fig. 13A). Class humid B1 predominated in the South, Central, and North of Tocantins, and occurred in small parts of the territories of Bahia and Maranhão; while the class humid B2 classification was represented only in small portions of West of Tocantins.
Moist subhumid (C2) was the second class with the greatest extension in MATOPIBA, distributed in 68.71%, 38.34%, 14.21% and 81.65% of th e Maranhão, Bahia, Tocantins, and Piauí area, respectively (Fig. 11). In addition, it comprised the subclasses C2sA’a’, C2w2A’a', and C2wA’a’, with this latter class more frequently in the region (Fig. 13A). It highlights that these subclasses delimit the areas where the largest producer of soybeans, corn, cotton, and beans are found (Fig. 14), indicating that these classifications have more appropriate climatic conditions for the development and production of crops. Class dry subhumid (C1) represented 12.67% of MATOPIBA, and comprised the subclassifications C1dA’a’, C1s2A’a’, C1sA’a’, and C2rA’a’, being located in the Southwest portion of Piauí and part of West of Bahia. Among the subclasses found, C2wA’a’, B1wA’a’, and C1sA’a’ showed the highest cumulative frequency (around 42%) (Fig. 13A), indicating that the classifications are more comprehensive in MATOPIBA.
Air temperature and rainfall volume, in climate change scenarios, altered the climatic characterization of the MATOPIBA region with extinction and/or inclusion of climatic classes (Fig. 12). Scenarios with increased air temperature showed a reduction in areas of climate humid (B1), mainly in Tocantins, and expansion of the Moist subhumid (C2) and Dry subhumid (C1) classes from the East for West of MATOPIBA (Figs. 12A and 12B). In addition, environments characterized as Semiarid (D) were observed in areas of Southwest Piauí and West of Bahia, especially when the scenario was + 3.0 ºC (Fig. 12B).
With increasing air temperature, the most frequent climatic subclasses in MATOPIBA were Das’a’, DdA’a’, C1sA’a’, B1wA’a’, and C2wA’a’ which presented an accumulative frequency around 76% (Figs. 13B and 13C). Although these subclasses occur in both + 1.5 ºC and + 3.0 ºC scenarios, greater coverage of the classes Moist subhumid (C2wA’a’), Dry subhumid (C1sA’a’), and Semiarid (das’a’) were found in scenarios of greater temperature increase (Figs. 12B and 13C). These results show that the increase in air temperature alters the climatic conditions of MATOPIBA, which would cause changes in the vegetative configurations of the region, resulting in changes in the transition of biomes, such as reduction of areas of the Cerrado biome and increase of environments with characteristics of biome Caatinga. In addition, the agricultural activity in the region would be drastically affected by climate change caused by the increase in temperature, resulting in risk climatic for the cultivation of plants, thus compromising the production of crops and the agroeconomic development of MATOPIBA.
In Thornthwaite climatic index, the rainfall regime becomes the most influential parameter to determine the climatic classes. In scenarios with changes of + 30% in the rainfall regime, the humid class (B4, B3, B2, and B1) occupied 58.14% of the MATOPIBA region (Fig. 12C). However, a greater number of climatic subclasses was found in this scenario, with subclasses C1sA’a’ (Dry subhumid), B2wA’a’ (Humid), B3wA’a’ (Humid), B1wA’a’ (Humid), and C2wA’a’ (Moist subhumid) occurring more frequently (Fig. 13D). The greater coverage of humid class in MATOPIBA environments, in addition to characterizing the extent of the Amazon biome, indicates that the climatic conditions presented would allow to expansion of agricultural areas, increase the number of harvests per year and increase crop productivity. Thus, the increase of + 30% in the rainfall regime becomes the most promising scenario for agroeconomic development in this region.
When the scenario is of reduction (-30%) in the rainfall regime, the MATOPIBA region presented the climatic classes Moist subhumid (C2), Dry subhumid (C1), and Semiarid (D), with 40.12% of the area occupied by class C1 (Fig. 12D). The number of subclasses determined was lower with an expressive frequency of C1sA’a’, DdA’a’, DsA’a’, and C2wA’a’ (Fig. 13E). In this scenario, Semiarid environments expanded to areas which were previously classified as Dry subhumid (Fig. 11), in the Center-South portion of Maranhão, Southwest Piauí, and part of West of Bahia. The West region of Tocantins was classified as Moist subhumid, while the Dry subhumid class occupied the Central, North, and South portion of MATOPIBA.
In the scenario of lower rainfall, both the Cerrado biome environments and the transition areas, between Cerrado and Caatinga biomes, can be reduced in the MATOPIBA region; however, areas of the Caatinga biome may increase as the Semiard class expands. In addition, the scenario of reduction in the rainfall regime negatively impacts agricultural activity because with low water availability in the soil the plants reduce their photosynthetic efficiency and, consequently, do not reach their productive potential (Taiz et al. 2017).
Productive areas located in environments of transition between biomes require technological efforts that encourage an increase in crop production (Araújo et al. 2019), because, in a transition environment between different biomes, ecosystems and climatic conditions are highly diversified, making these areas particularly vulnerable to climate change (Silva et al. 2016). In this sense, areas of MATOPIBA with high production of soy, corn, cotton, and beans would have a strong impact of climate change, since they are located largely in environments of transition from the Cerrado and Caatinga biomes (Fig. 14).
Regions of the extreme West of Bahia, South of Maranhão, and Southwest of Piauí present the largest productions of soy, corn, cotton, and beans (Fig. 14), being environments classified as Moist subhumid climate. However, in climate change scenarios with increased temperatures and reduced rainfall, these regions suffer changes in climatic conditions, with transition of climate classes between Moist subhumid, Dry subhumid, and Semiarid (Figs. 12B and 12D).
In the perspective of climate change, studies by Zilli et al. (2020) suggest a reduction in crop production, such as soybeans and corn, in areas of the Cerrado biome, mainly in the MATOPIBA region, with the displacement of productive areas to subtropical regions of the Atlantic Forest. However, part of the impact of climate change on MATOPIBA could be offset by increased productivity, which would maintain the agricultural scenario of region. Thus, efforts are required to invest in technology and changes in management processes, such as adapting the sowing schedule for crops, using drought-resistant cultivars, using irrigation, efficiency in crop fertilization, improving structural and soil conditions, soil fertility, and precision agriculture (Zilli et al. 2020). Therefore, following these strategies makes it possible to adapt the crops to the climatic conditions of the region and may increase or maintain the productive potential of the crops, alleviating the impacts caused by climate change.