http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0102-77862014000400002
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3. RESULTS AND DISCUSSION[/FONT]
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The annual rainfall behavior during the delimited temporal scale showed a large variation, with a minimum of 1,296 mm in 1987 and a maximum of 2,492.8 mm in 1990. The average observed for the period was 1,868.4 mm, with a standard deviation of 302.29 mm. The annual rainfall distribution indicated that 52% of years had rainfall rates above average, among which 61.54% were concentrated on the first half of the observed period. In contrast, 48% of years showed rainfall below average rainfall, concentrated on the second half of the period, especially in the last eight years (Figure 1).[/FONT]
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The regression test revealed a significant decreasing polynomial tendency in rainfall due to deforestation (y = -0.3234x3 + 14.227x2 - 197.88x + 2600.2; R² = 0.46; p < 0.05).Similarly to this study, Debortoli (2009) pointed out a decreasing tendency in rainfall from the 1970s in Colíder (-6,064) and in some municipalities in northern Mato Grosso, including Alta Floresta (-7,262) and Itaúba (-10,057), both surrounding the study region. According to the author, this phenomenon is related to increased deforestation rates in the region, in the opposite direction to that observed in densely forested stations in latitudes of northwest Mato Grosso, which showed an increase in rainfall.[/FONT]
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The average of dry and rainy days was 251 and 114 days, respectively. The year 1991 had the highest number of dry days (296 days), while 1996 had the highest number of rainy days (159 days) (Figure 2). In the municipality of Alta Floresta (Mato Grosso), Debortoli (2009) found out that 2007 was the driest year, with 248 dry days, whereas 1992 was the year with the highest number of rainy days (160 days). By comparing data from Alta Floresta and Colíder, which are bordering municipalities, one notices that the driest and rainiest years werenot the same, demonstrating different behaviors in relatively close areas.[/FONT]
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Studies carried out by Rosa et al. (2007) revealed that, in a 10-year series, the rainfall behavior in central-western Mato Grosso was quite variable, where the highest rainfall levels (1,800 mm to 2,100 mm) occurred in the west, north, and south portions of the study area. It's worthy stressing that the heaviest rains were observed in the area's far west, comprising precisely the regions with denser vegetation cover.[/FONT]
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The behavior of the average monthly occurrence of dry and rainy days (Figure 3) showed that the rainy period within this temporal scale was concentrated between October and April, and the driest period was concentrated between June and August. The months presenting the highest number of rainy days were January and March, with 18 rainy days each. In turn, the month showing fewer rainy days was July, with an average of 0.5 days.[/FONT]
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According to Ferreira (2001), Colíder presents a dry period lasting three months, from June to August, something which was explicitly observed in this study. This behavior is also observed in other municipalities of Mato Grosso, such as Cáceres (Pizzato et al. 2012) and Tangará da Serra (Dallacort et al. 2011).[/FONT]
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The rainfall levels observed during the 28 years (1983-2011) presented the [/FONT]
β[FONT=Verdana, Arial, Helvetica, sans-serif]
parameter values of GPDF with variations of 17.96 in June and 74.89 in December, not exceeding 100, and the [/FONT]
α[FONT=Verdana, Arial, Helvetica, sans-serif]
parameter of this function presented minimum values of 0.17 in July and maximum of 6.61 in February (Figure 4), thus the [/FONT]
α[FONT=Verdana, Arial, Helvetica, sans-serif]
values are lower than the [/FONT]
β[FONT=Verdana, Arial, Helvetica, sans-serif]
values.[/FONT]
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The highest [/FONT]
β[FONT=Verdana, Arial, Helvetica, sans-serif]
parameter value was found in December and January; the latter was the month presenting the most intense rainfall averages (320.79 mm) and the larger standard deviation (145.24 mm), indicating a greater variability in rainfall. The lowest values coincided with the months of lower rainfall volume in June and July, 5.56 mm and 8.19 mm, respectively (Table 1).[/FONT]
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The scenarios observed through GPDF corroborate several studies carried out in the state of Mato Grosso, such as those by Martins et al.(2010), Moreira et al. (2010), Fietz et al. (2011b) and Pizzato et al.(2012), where this model presented an adequate adjustment, being widely used for determining the probable rainfall.[/FONT]
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According to Furlan (2009), probability function adjustment studies using theoretical functions with regard to a set of climatic data have brought benefits to the planning of human activities related to the most varied sectors of society such as economy, environment, and, especially, agriculture and livestock.[/FONT]
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Taking into account the cumulative totals of deforested area in the Amazon of Mato Grosso, a gradual increase in deforestation becomes quite evident within the period from 1989 to 2005 (13.17% p.y.), attenuating up to 2008 (2.75% p.y.), with a tendency to stabilize from this year on (0.86% p.y.) (Figure 5).[/FONT]
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One found out, by determining Spearman's [/FONT]
ρ[FONT=Verdana, Arial, Helvetica, sans-serif]
coefficient, that there's a negative correlation ([/FONT]
ρ[FONT=Verdana, Arial, Helvetica, sans-serif]
= -0.45) between the regional deforestation data and the local rainfall rates. The test showed that the larger the deforested regional area (Amazon of Mato Grosso), the lower the rainfall rate observed by restricting the data analysis only to the decade in which the deforestation rate in Colíder reached a value about 80% (1989-1999), the test revealed a strong negative correlation between the variables ([/FONT]
ρ[FONT=Verdana, Arial, Helvetica, sans-serif]
= -0.84) (Figure 6), demonstrating that the removal of vegetation cover implies a significant decrease in rainfall (Figure 7).[/FONT]
