Relações entre instabilidades das chuvas e indicadores de produção de lavouras de sequeiro no semiárido cearense, Brasil

Abstract

Most of the Brazilian Semiarid region is located in the Northeast region of the country, with Ceará the state that holds the largest relative area inserted in this ecosystem, representing approximately 95% of its territory, besides having the largest number of municipalities inserted in areas susceptible to desertification in Brazil. The instability of rainfall is one of the main characteristics of the Semiarid region, with irregular rains and long periods of drought, constituting one of the main adversities faced by those who live in this region, especially by those who carry out agricultural activities on dry land crops, because they depend practically on rainfall for their development. From these considerations, it is assumed that there should be interactions between rainfall irregularities and the variables that define the technical and economic results of the land-salt productions in the Semiarid state of Ceará. For these reasons, the research tries to answer the following question: How do rainfall instability interact with the defining variables of the production of the food crops studied in the eight (8) climatic regions classified by FUNCEME? From this perspective, the present work has as general objective to evaluate the instabilities of rainfall in the municipalities of Ceará, with consequences for the eight (8) climatic regions, demonstrating how these instability affects the defining variables of bean, cassava and corn production, main crops cultivated under the drie plantation regime, between the years 1974 and 2019. Specifically, the study seeks: a) identify probable rainfall distribution patterns in the municipalities of Ceará and in the eight (8) climatic regions defined by FUNCEME for Ceará in the period from 1974 to 2019, comparing them with what happened in the state between 1947 and 2019; b) to measure the levels of rainfall instability estimated in the period from 1974 to 2019 for the municipalities of Ceará and for the eight (8) climatic regions defined by FUNCEME for Ceará; c) to measure the interactions between rainfall instability and the production of beans, cassava and corn in the climatic periods and in the regions of Ceará between 1974 and 2019; and d) to evaluate how the climatic regions of the State of Ceará behave in relation to the interactions between rainfall instabilities and the production of beans, cassava and corn between 1974 and 2019. Secondary rainfall data released by the Cearense Foundation for Meteorology and Water Resources (FUNCEME) are used, as well as information from the Municipal Agricultural Survey (PAM), published by the Brazilian Institute of Geography and Statistics (IBGE). The annual averages and coefficients of variation (CV) of rainfall, yields and production values per hectare of bean, cassava and corn crops between 1974 and 2019 are computed. The variables associated with agricultural production are aggregated through weighted means and the estimated weights by means of the factor analysis method with decomposition into main components. It is tested whether there is statistical difference between rainfall, yields and production values per hectare aggregated beans, cassava and corn of each region using regression analysis, as well as dummies variables to distinguish the regions. The Crop Instability Index (INSL) and the Rainfall Index (INC) are created and the interaction between them is evaluated through regression analysis. The results confirm the hypothesis that there are interactions between rainfall instability and the variables that define the technical and economic results of the production of sealand crops in the Semiarid state of Ceará. The high instability in the distribution of rainfall in Ceará over the years studied is confirmed. It was shown that it is possible to transfer to the period from 1974 to 2019 the classification of rainfall in periods of drought, normality and rainy season, confirming that rainfall instability is higher in the years that presented rainfall levels characterized as dry years. In addition, the results show that there is greater instability in the production of dryland crops during the rainy season in the state. It appears that the production of land-based crops in Ceará experiences great instability due to their practically total dependence on the rainfall regime. The general conclusion of the research is that there are synergies between rainfall, productivity and production values per hectare of land-based crops. It is also concluded, as were the expectations, that rainfall and variables that define technical aspects (productivity) and economic aspects (production value per hectare) of beans, cassava and corn present joint movement in the same direction and directions. In periods of lower rainfall, the variables associated with production present lower values, in the years of better rainfall, the opposite happens. It was observed that this synergy is not restricted only to productions, but to their instabilities. Thus, rainfall instabilities radiate to the variables associated with bean, cassava and corn production in the State of Ceará between 1974 and 2019.