a)Annual precipitation: We selected data on monthly and annual precipitation from meteorological series of 27 meteorologicalstations in the basin. The results obtained were interpolated in a geographic information system forthe generation of maps with the regionalization of data through the IDW.Was admitted risk of annual precipitation less than 1500 mm and presenting an adequate precipitation during the year, with, approximately, 120 mm monthly(SANTOS FILHO et al., 2005).

c)Average Annual Temperature (Ta): We used Meteorological data from historical series of average temperatures to estimate the average annual temperature. The risk classes defined for Ta were as follows: high risk –High risk: less than18°C and low risk:from18to31°C (SANTOS FILHO et al., 2005; CALDANA et al., 2019).

d)Maximum Daily Temperature: We used meteorological data from historical series of maximum daily temperatures observed inside meteorological shelters to estimate the average annual temperature. The following risk classes forATwere defined: High Risk: annual frequency superiorthan 20% probability of occurrence of absolute maximum temperatures above 36°C (SANTOS FILHO et al., 2005).

e)Thermal unit: We calculated the accumulation of degrees daily considering the base temperature for the citrus (minimum 13° C and maximum 39°C). So that it is possible to estimate the regional cycle of the species. The restrictive factor was at least 2,000°C accumulated during the year (WREGE et al., 2004; SANTOS FILHO et al., 2005).

f)Frost Risk:We used meteorological data from the thirteen-season historical series, taking into account occurrences of temperatures of 0°C or below as observed within the meteorological shelters, to calculate the risk of frost. The probabilities of annual frost occurrence were calculated and correlated with altitude and latitude, obtaining a regression equation for the risk of frost. When we observe values greater than 20%, we consider to be high risk (WREGE et al., 2004; SANTOS FILHO et al., 2005; CALDANA et al., 2019).

For the creation of thematic maps and the final zoning map, ArcGIS software was used. Firstly, the numerical values from the meteorological stations were transformed into points, according to their geographical coordinates. We then used the edaphoclimatic requirements of the avocado species to produce data spatialization, which was used for the delimitation of the representative bands of the avocado climate requirements. Thus, the station values were replaced by “1. Apt” or “2. Restricted”, according to the physiological requirements for each meteorological variable analyzed.

The next step was to combine the matrix images. Each pixel was assigned with the values “1” or “2”, as already described. If the combination for a point was filled only with values“1”, the region was classified as fit. If it had a value of “2” it was restricted by a given variable. If two or more “2” values were assigned, the location was classified as unfit.

Then, standardization of the pixels using classifications was performed by dissolving the vector classes. In this way, the agroclimatic zoning classes were grouped, thus defining regions of suitability for the studied species. The final map showing the agroclimatic zoning of each crop will provide an estimate of the representative area of each risk class, ensuring its suitability for the site.

The precipitationof the basin of Paraná River III was not restricted for cultivation of lemon tree(map 2). The annual requirements for citrus are between 900 mm and 1,500 mm (SANTOS FILHO et al., 2005). As noted in the graphs, precipitation less than 1,000mm does not occur in the region, but less than 1,500mm can occur frequently, but does not present a risk to productionof lemon. The lowest record was 1680mm at the northern end of the basin in the Guaíra region

Acid lime is a drought-resistant species. In the North, Northeast and Midwest regions of Brazil, apt regions are classified with water surpluses above zero and annual water deficiency below up to 300 mm. For the production success limit in the South, the acceptable limit in the water balance was 100 mm (SANTOS FILHO et al., 2005).

Map 2
Annual rainfall average in the hydrographic basin of Paraná River III.
Caldana et al. (2019), adapted and organized by the authors (2020)

However, as noted, even in extremely dry years, such as in 1978 (map 2), the water balance exceeds the acceptable average of water deficit for production in Brazil. The producer should be aware that, in the event of extreme drought or prolonged summer, water deficiency causes the citrus leaves to curl, the most evident symptom in regions with a warmer and drier climate. This symptom subsequently leads to partial closure of the stomata and reduced sweating and photosynthesis, due to dehydration of the canopy of the plants, under conditions of water limitation, which can cause serious losses to production (MACHADO et al., 1999; SILVA et al., 2005; VOLPE et al., 2009).

For the water balance verified in the region (graphics panel 1) as the risk observed was 100 mm accumulatedannually, no season presented a risk for the cultivation of the lemon tree. In municipality of Guaíra, that presented significant deficiency, the accumulated figure was 56 mm. The extracts show less favorable water balance in the months from January to April, thanks to high temperatures and an increase in evapotranspiration, and the farmer have to pay attention to the species during this period, and in extreme cases, utilizing appropriated irrigation systems.

Graphics panel 1
Water balance for papaya tree crop in the hydrographic basin of Paraná River III
Caldana et al. (2019), adapted and organized by the authors (2020)

The air temperature is the conditioning factor of the internal and external color of the citrus orchards. The color of the peel is associated with low temperatures (< 13°C) during maturation. The averages temperatures between 25° C and 30° C, during the day, and 10° C to 15° C, during the night, are the most suitable for the color, flavor and size of the fruits. According tothe literature, we established the average temperature average standard of at least 18°C in the average annual (SANTOS FILHO et al., 2005).

No area in the basin was inapt for these variables(map 3).The highest average temperatures were observed in the region of Guairá, in the far north of the basin, reaching over 23°C, while the lowest do not exceed 20.5°C, in the region of Cascavel.

Map 3
Annual average temperature in the hydrographic basin of Paraná River III.
Caldana et al. (2019), adapted and organized by the authors (2020).

The extreme maximum temperatures also interfere with the development of the lemon tree, since, from 32°C, there is a decrease in the growth rate, until it stops completely above 39°C. At temperatures equal to or greater than 36°C, it is observed that the respiration rate is higher than that of photosynthesis. With excessive heating of the leaves, there is destruction of chlorophyll and blockage of water translocation resulting in the disorganization of the nutritional balance of the lemon tree (SANTOS FILHO et al., 2005). The risk for maximum temperatures per decade was estimated with a probability of occurrence higher than 20 %.

On average, the areas with the highest altitudes(map 3), close tomunicipality ofCascavel, had the lowest average maximum temperatures, around 25°C and the lowest region, the highest average temperatures. The southern, western and northern region of the basin, closer to the Paraná River channel, presented average values above 26°C, along its entire length. The highest average temperatures were observed in the Guairá region, in the farnorth of the basin, reaching over 27.5°C

Map 4
Annual average and maximum temperature and probabilities of extreme temperature occurrences for the lemon, in the basin of Paraná River III.Importar imagen
Caldana et al. (2019), adapted and organized by the authors (2020).

Through the graphs, a risk of 38°C was identified in just one decade of Cascavel, with a probability of occurrence of 4%, even if temperatures above 35°C remain low in this season, not exceeding 30%. In municipality of Toledo, the risk remains low as well, not exceeding the probability of occurrence of 10% per 10-year period

In municipality of Guairá, temperatures above 35°C showed a high frequency in the spring and summer months. The risk of temperatures above 38°C increases in that season, but does not present a risk greater than 20%. The strip near the Paraná River channel is not inapt for cultivation due to this variable, however, it is restricted, and the farmer in that area can use practices that protect the cultivars when the thermometers reach these temperatures.

Map 5
Annual average of thermal sum distribution in degree days for the lemon in the basin of Paraná River III
Caldana et al. (2019), adapted and organized by the authors (2020).

To recommend the planting season, attention should be paid to the fact that citrus orchards are more sensitive to water deficit during budding, flower buds emission, fruiting and the beginning of fruit development until it reaches 2.5 cm in diameter, when the demand for water is considerable(SANTOS FILHO et al., 2005). It is recommended the cultivation mainly of small change, should be carried out, in the spring, in October, with low risk of water deficit throughout the region.

Considering the accumulationof 2.000 degrees dayfor the annual cycle of the species, it was identified that from October, the day degrees continue increasing until the month of March, being able to complete the cycle of the species, in good part before the winter (Graphics panel 2).

Graphics panel 2
Monthly average of thermal sum in degree days for the lemon tree.
INMET (2019), adapted and organized by the authors (2020).

In municipality of Assis Chateaubriand, for example, considering the time from October to March, the accumulation of degrees day reaches, on average, the accumulation of 2,200. While in the colder region of Cascavel, the cycle would only be completed in April.

Citrus, in general, has good resistance to cold winds and frost, and thoseof low intensity do not cause severe damage (SANTOS FILHO et al., 2005). The risk of severe frost (below 0ºC) in the region (map 5)presented a distribution similar to the average temperature, with a greater risk in the eastern portion, close tothe municipalities ofCascavel and Santa Tereza do Oeste, in the highest portion of the basin, and in some valley bottoms of the central portion. While the central portion of the basin presents a risk of 5 to 10% while in the lower portions, close to the valley ofthe Paraná River III, mainly on the North-South axis from Guaíra / Terra Roxa to Foz do Iguaçu / Santa Terezinha de Itaipu the risk falls to 0%

Map 6
Frost risk in the hydrographic basin of Paraná River III
Caldana et al. (2019), adapted and organized by the authors (2020).

The final climatic zoning map (map 7) was defined admitting restrictions of maximum temperature and severefrost, the former interfering in the complete development of the species and fruit quality, and the latter being able to lead to senescence of the species (COELHO et al., 1998).

Thus, the highest region in the basin(map 1) and, consequently, the coldest (Figure 03) exhibitedrestriction for cultivationof lemon tree. The entire central and eastern regionof the basin was classified as inapt for cultivation. A small area located in the intermediate bands was classified as restricted, where the risk of frost is 10%. In this case, the farmer must be careful of occurrences of frost.

Map 7
Agroclimatic Risk Zoning of lemon (Citrus latifolia) in the basin of Paraná River III.
Caldana et al. (2019), adapted and organized by the authors (2020).

Even in aptregions, the risk of frost remains. The farmer should avoid valley bottoms, at the end of the slopes, and give preference to cultivation in areas that are not considerable sloping, to facilitate the displacement of cold air. Preferably, the top of the spike and half slope should be used, mainly on the faces facing north, since, as highlighted, the cold front has preferential displacement in the south / southwest direction, northeast direction (CALDANA et al., 2018; CALDANA et al., 2019; CALDANA; MARTELÓCIO, 2019).

WREGE et al., (2005) zoned citrus cultivars for Rio Grande do Sul State, Brazil. They indicated that frost tolerance was studied at 2°C, as it has a wider range of species, in addition to ascertaining the thermal sum of the degrees day and precipitation. Only a small strip in the northwest ofthe state proved to be apt, other areas should use rootstocks for protection from extreme cold, or even, they had insufficient thermal sum. The latitudinal factor interferes with citrus production, since these adversities were not present in the basin of Paraná River III.

It should be noted that zoning does not eliminate the risks, but only presents more favorableconditions for the development of lemon treeorchards. As agriculture is a risky activity, all activities are susceptible toclimateextreme events, which may or may not cause harmfor the farmer.In the context of sustainable agriculture and climate change, agroclimatic zoning provides greater security in decision-making, agricultural planning, in the hydrographic basin of Paraná State III.