(DOI): 10.5777/PAeT.V4.N1.03 This article is presented in Portuguese and English with “resumen“ in Spanish. Brazilian Journal of Applied Technology for Agricultural Science, v. 4, n.1, p. 45-64, 2011. Scientific paper Variability in number of rainy days Abstract in state of Sergipe – SE Among the many factors that affect human activities, mainly Emerson Ricardo Rodrigues Pereira1 agriculture, the climate is distinguished by its decisive Joherlan Campos de Freitas2 influence on the variations presented by the irregularities in the dry and wet periods in the given region. Among the Antonio Ricardo Santo de Andrade3 variables that make up the climate, especially for annual Veneziano Guedes de Sousa4 crops, rain is the variable that most affects the result of crop production. In this sense, the objective was to evaluate the variability of rainfall data for the State of Sergipe, SE, through the preparation of maps of the average number of rainy days, and the coefficients of variation (CV) of rainfall and the number of rainy days for annual periods, dry and rainy. In this work it was used the series of monthly total rainfall of 40 rainfall stations with at least 30 years of data, continuous and seamless. We found that the highest values of the coefficient of variation are associated with lower levels of rainfall and number of rainy days. The variability of rainfall is lower in regions with rainy periods, when compared to dry periods. Key word: variation coefficient, rainy day, dry and wet periods. Introduction Kendall test, SILVA (2004) observed significantly decreasing tendencies in several places of this Rainfall is one of the most important variables region. He suggested that this variability may be in the hydrological cycle, since it influences various related with climate changes in the Northeast of human activities, as agriculture, fishing, livestock, Brazil, which reached not only the semi-arid of the and human and animal consumption of potable region, but also the coast area. Since the seasonal water. It has been extensively studied in different variation of the rainfall has great influence in the regions of the world as the main indicator of draught: agricultural planning, several researches have been Guiana (SHAW, 1987); Austria (EHRENDORFER, developing studies based on the number of rainy 1987); USA (GUTTMAN et al. 1993; ARNAUD et days (BRUNETTIA et al., 2001; SELESHI and ZANKE, al., 2002); Sahel (GRAEF and HAIGIS, 2001); Iran 2004; ZANETTI et al., 2006; MODARRES and SILVA, (DINPASHOH et al., 2004); Brazil (SILVA, 2004). 2007). Draughts are a serious problem to the human Still about this issue, HESS et al. (1995) society and the natural ecosystems (DINPASHOH et registered that the decrease in rainfall in the al., 2004). In this sense, different methodologies have Northeast of the arid zone of Niger resulted in a been used to analyze the variability of the rainfall. decrease in the number of rainy days. BRUNETTIA SILVA et al. (2003) studied the rainfall variability et al. (2001) observed that the decrease in the number in the State of Paraíba based on the entropy theory. of rainy days in Italy is more important in the study DINPASHOH et al. (2004) found coefficient of of the intensity of rainfall than the annual totals. variation (CVs) from the rainfall in Iran ranging The rainfall regime of the State of Sergipe from 18% at North, where it is located the mountains is associated with the atmospheric conditions and and 75% at South. MODARRES and SILVA (2007) synoptic systems which act in the sectors North and evaluated the trend of the rainfall also in Iran and East of the Northeast of Brazil (NEB) and it has one verified that the CV in the region is 44.4%. particular characteristic different from the other By analyzing the climate variability in regimes of the region of NEB. Due to its spatial the Northeast of Brazil, based on the Mann- geographic position, Sergipe has one characteristic Received in: 17/09/2010 Accepted for publication: 25/01/2011 1 Student of Doctor’s Degree in Meteorology, Academic unit of Athmospheric Sciences, UFCG, Campina Grande, PB, BRASIL. E-mail. [email protected]; 2 Master in Meteorology, Academic unit of Athmospheric Sciences, UFCG, Campina Grande, PB, BRASIL. E-mail. joherlancampos@ yahoo.com.br; 3 Prof. Doctor, Academic Unit of Garanhuns, UAG/UFRPE, Garanhuns, PE, BRASIL. E-mail: [email protected]; 4 D Student of Doctor’s Degree in natural Resources, Center of Technology and Natural Resources, UFCG, Campina Grande, PB, BRASIL. E-mail: [email protected] Applied Research & Agrotecnology v4 n1 Jan/Apr. (2011) Print-ISSN 1983-6325 (On line) e-ISSN 1984-7548 55 Pereira et al. (2011) of transition between the rainfall regime of North (S and W). It occupies an area of 21.910 km², and it (with maximum from February to May) and of South is the smallest Brazilian state. It is located between of the NEB sectors (December to February). This 9º 31’ S to 11º 33’ S and 36º 25’ W to 38º 14’ W, in the transition is observed in the beginning of the rainy tropical zone and it has as main climate problem the season changing the rainfall and causing veranicos1. spatial irregularity of the rainfall decreasing from the The maximum rainfall occurs in May, however Lest Coast to the Sertão, Semi Arid. when there is one anomalous displacement of the It was used daily time series of 40 rainfall Inter-Tropical Convergence Zone (ITCZ) towards stations in all the state of Sergipe, SE, with more than the South, the beginning of the rainy season of the 30 years of data, continuous and without failures, of East of the NEB sector is affected considerably, even rainfall and the number of rainy days. In this study with the existence of veranicos in May. In the end of it was considered as rainy days those with rainfall the rainy season, end of July to September, it is seen above 1 mm. In Table 1 it is indicated each rainfall the elevations of the rainfall in some years due to the station and its respective geographic coordinates, passage of frontal systems trough the south of the which are used in the work. NEB sectors and which reached Sergipe (KOUSKY, These rainfall stations are spatially well 1980). distributed in all the state of Sergipe and located The success of the cultures implanted in in different climate regions, according to what is rainfed agriculture depends on the rainfall to showed in Figure 1. maintain the soil humidity needed for the culture In order to identify the behavior of the rainfall development. The irregularities in the rainfall regime data range which was obtained from the 40 rain gauge are caused by changes in frequency and/or intensity stations, spatially well distributed, it was calculated of the rainfall events. The best understanding of the the values of the coefficient of variation (CVs) of the behavior of the rainfall, aiming at its maximum use rainfall and the number of rainy days in the state of in the agricultural activities, may be obtained with Sergipe, for the annual, dry and rainy periods. The the study of the number of rainy days. Besides that, coefficient of variation of the data set CV (%) was for several water appliances, as for modeling, the calculated trough the equation, indicated by JENSEN knowledge of the variability of the rainfall becomes and PEDERSEN (2005): essential (BUYTAERT et al., 2006). 1 It is important the knowledge of the 2 2 1 n 1 n 2 distribution of the rainfall in the State of Sergipe, for ∑ x i - ∑ x i s n -1 i=1 n i=n (1) the formulation of strategies and in indentifying the CV = ×100 = ×100 appropriated regions for the implantation of rainfed m 1 n ∑ x i cultures, considering the great variation of the rainfall n i=n average in the place. Moreover, the spatial and time variability of the rainfall in the state of Sergipe is -9.6 40 little studied even though it is very important for 9 -9.8 the purpose of formulation of strategies of combat 21 12 24 29 to the effects of draught in the semi arid. Thus, the -10 1 6 7 30 objective of the present study is to analyze the spatial -10.2 31 25 ) 18 S variability of the rainfall in the state of Sergipe, º 23 ( -10.4 26 E 5 aiming to identify the areas more susceptible to D 32 U 16 T 17 I -10.6 4 14 longer droughts. T 36 8 A L 37 22 -10.8 19 35 20 2 39 15 -11 3 33 Material and methods 34 38 27 -11.2 The studied region was the State of Sergipe 13 10 11 located in the Northeast region of Brazil, having as -11.4 28 limits Alagoas (NW), Atlantic Ocean (E) and Bahia -11.6 -38.2 -38 -37.8 -37.6 -37.4 -37.2 -37 -36.8 -36.6 -36.4 LONGITUDE (ºW) Figure 1. Location of the 40 rain gauge stations 1 ‘Veranico’ is a Brazilian word to define dry periods during the wet season. located in the State of Sergipe, SE. Applied Research & Agrotecnology v4 n1 Jan/Apr. (2011) Print-ISSN 1983-6325 (On line) e-ISSN 1984-7548 56 Variabilidade do número de dias chuvosos... Variability in number of rainy days... p.45 - 65 Variabilidad en el número de días lluviosos… Table 1. Geographic localization of the rainfall stations of the State of Sergipe. Number Station Code Lat. Long. Alt. 1 AQUIDABA 4805595 -10.07 -37.2 217 2 ARACAJU 4815891 -10.9 -37.05 3 3 BONFIM 4824131 -11.05 -37.85 230 4 CAMPO DO BRITO 4815501 -10.65 -37.6 180 5 CAPELA 4815087 -10.5 -37.07 148 6 CARIRA 4804761 -10.2 -37.7 351 7 CRUZ DAS GRACAS 4805904 -10.2 -37.48 259 8 CURRAL DO MEIO 4816418 -10.72 -36.92 30 9 CURRALINHO 3894467 -9.7 -37.67 80 10 ESTANCIA 4825514 -11.3 -37.43 53 11 ESTANCIA-1 4825513 -11.4 -37.45 53 12 ILHA DO OURO 3895851 -9.9 -37.6 40 13 ITABAIANINHA 4824545 -11.27 -37.78 225 14 ITABAIANA 4815319 -10.68 -37.42 186 15 ITAPORANGA D AJUDA 4815942 -10.97 -37.3 10 16 JAPARATUBA 4816211 -10.6 -36.85 79 17 JAPARATUBA-1 4816213 -10.63 -36.95 79 18 JAPOATA 4806741 -10.35 -36.8 89 19 JENIPAPO 4815705 -10.87 -37.48 100 20 LAGARTO 4814868 -10.92 -37.67 183 21 LAGOA DA SERRADINHA 4804268 -9.9 -37.8 80 22 LARANJEIRAS 4815667 -10.8 -37.17 9 23 MOCAMBO 4814174 -10.4 -37.63 204 24 N.