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The formation of artificial lake due construction of a hydroelectric plant causes irreversible environmental impacts. Studies associated with these artificial lakes for the Brazilian semiarid region are still insufficient. Thus, the objective of this study is to provide new information on the trends of climatic extremes, dependent on rainfall and air temperature, for the Sobradinho Hydroelectric Power Plant SHPP lake region, through the analysis of climate change indices.

This study is particularly important for the SHPP region because microclimate changes have edjtal impacts on the natural, social and economic sectors. Trends of increase in maximum temperature, the number of hot days and diurnal temperature range were noticed. However, the rise of these indices cannot be attributed to the formation of the SHPP lake.

The influence of the SST of Tropical 20007 on the temporal behavior of some of the indices used in this study may have contributed to increases in hot days and nights, maximum temperature, diurnal temperature range and consecutive dry days over the region.

Most of the electricity in Brazil is generated in hydroelectric plants, but in general, the construction of these plants causes the formation of large artificial lakes, due to the impoundment of the rivers. The formation of artificial lakes has been the subject of some studies in Brazil Fisch et al. The construction of a hydroelectric plant and the consequent formation of an artificial lake cause irreversible environmental impacts. Although hydroelectric plants use a renewable natural resource, which is editzl, they still alter the landscape due to deforestation, causing damage to the people, fauna and flora, flooding areas where they had residences, plantations, and animals, as well as the displacement of many families from their homes.

For the semiarid area of the Brazilian Northeast region NEBthe developed microclimatic studies associated with the formation of the lake are still insufficient. It was found that changes resulting from the construction of a dam at a given location may lead to variations in the behavior of micrometeorological variables, such as wind, air temperature, and humidity.

Analyses are performed using historical data series, comparing the periods before and after the filling of the lake, to evaluate the environmental impact caused by the formation of artificial lakes on the microclimate of 207 region.

The interest of the scientific community in the study of variability and climate change has increased in recent years, mainly due to the possible role of anthropogenic activity in the observed climate change, and their consequences in the most diverse sectors of human life IPCC, When it comes to watersheds with multiple uses of water, projected climate changes are expected to alter the flow regime.

The climatic conditions of reservoir management are among the main components of analysis in the face of future climate changes. Flow changes are also expected to have an impact on agriculture, including irrigation as well as more traditional agricultural practices in the region.

For example, Adissu et al. According to Philip et al. Indirectly, climate change affects agriculture by influencing the emergence and distribution of crop pests and livestock diseases, decreasing water supplies and irrigation; and enhancing the severity of soil erosion Watson, Extreme climatic events in the region of the artificial Sobradinho Lake can cause severe damage not only in the agricultural sector but also to the regional economy.

It is therefore crucial to understand possible impacts on reservoir operation and climate change separately and together on SFSB hydrology. Researchers around the world agree on the direction of changing hydrological patterns in basins lower flood spells and drier seasonal flowsbut the magnitude of the change varies between studies due to different models and assumptions Johnston and Kummu, ; Keskinen et al.

In this context, the objective of this study is to provide new information on the trends of climatic extremes, dependent on rainfall and air temperature, for the SHPP lake region, through the analysis of climate change indices. The research focus is particularly important for the SHPP editsl because microclimate changes have significant impacts on the natural, social and economic sectors.

The SHPP is located km from the mouth of the river. The lake is approximately km long, with a water surface area of 4, km 2 rdital a storage capacity of This drainage basin has great altitude variation, from a minimum of m to a maximum of m, and an average of m, within a range of 1, m Fig.

These relief characteristics denote that some areas of the basin would favor a massive loss of water by runoff as a function of slope ramp. Areas at altitudes between and m correspond to 17, km 2or In contrast, altitudes between and m correspond to 24, km 2 Moreover, areas above m account for more than 60, km 2i. It was used data from two weather stations: In this study, the climatic extremes indices were calculated using the software RClimdex, developed by Xuebin Zhang and Feng Yang for the Canadian Editsl Service Zhang and Yang,following the methodology of Zhang et al.

Rdital indices were calculated 11 for air temperature and 11 for precipitation analysis. As described in Nandintsetseg et al. Outliers are daily values that lie outside a particular range defined as unrealistic by the user. For example, for temperature series, this range can be described as editql mean value of observations for the day of the year plus or minus three or four times the standard deviation of the value for that calendar day in the entire series.

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Daily temperature values outside of these thresholds are marked as potentially erroneous and manually checked and corrected on a case-by-case basis. Each potential outlier can be evaluated using information from the days before and after the event along with expert knowledge about the local climate Klein Tank et al.

In this study, it was chosen three times the standard deviation of the value for that calendar day in the entire series because the temperature variability is small; 3 The generalized data plot was used within RclimDex to visually inspect data to further identify outliers and a variety of other problems that may cause error or bias in analyzing changes in the seasonal cycle or variance of the data; and 4 to detect artificial shifts that could exist in a time series it was used in the RHtestsV3 Wang and Yang, After the quality control, it was used 49 years of meteorological data between January and December from the two stations.

The non-parametric tests used in this research were calculated using software R version 3. The Mann-Kendall test Sneyers, is the most appropriate method for analyzing climate change trends Goossens and Berger, According to Sneyersit is considered that in the case of stability of a time series, the succession of independently occurring values, and the probability distribution must always remain the same simple random seriesthus it is tested the hypothesis H 0: The S statistic of the Mann-Kendall test can be calculated according to Eq.

The signal can be obtained by Eqs. The statistical test Z tused to calculate the trend of a time series, was obtained by Eq. From the value of the series, it was used the non-parametric test of Sen-Slope Sen, to calculate the magnitude of the trend. This test provides an estimate of the slope T i of a change in measurement by the time change, as presented in Eq. The median of these N values of T i is represented as the Sen-Slope estimator, which is given as:. T med positive values indicate increasing or upward trend, and negative values of T med indicate decreasing or downward trend of the time series.

The null hypothesis H 0 means that there is no slope over time, and the alternative hypothesis H 1 is that there is an increasing or decreasing slope in the series.

The Pettitt test was used to locate an abrupt change in the mean of the data series. This test consists of verifying if two samples x 1According to Pettittthe statistic U t,T can be calculated using Eq.

The statistic k t gives the point where an abrupt change occurs in the mean of the data series:. The null hypothesis H 0 indicates no abrupt change over time and the alternative hypothesis H 1 is that there is an abrupt change in the time series. This correlation was used for non-parametric tests. Thus, this coefficient is not sensitive to asymmetries in the distribution, nor to the presence of outliers, and does not require that data come from two normal populations.

The Spearman correlation coefficient was obtained by Eq. Edktal samples greater than 20 observations, the following approximation can be used for the Student t distribution:. The trends of the 22 indices of climatic extremes were obtained for the Bebedouro-PE and Mandacaru-BA weather stations. Tables 2 and 3 present the values of edigal trends dependent on air temperature and rainfall, respectively, for the two stations, based on the results of the non-parametric Mann-Kendall, Sen-Slope and Pettitt tests.

The advantage of using these tests is that they filter the extreme values of the data series. In Tables 2 and 3the result eddital the Mann-Kendall test is presented with the values of the S-statistic, p-value and Z-statistical test.

The values of the slope T i of the time chef obtained by the Sen-Slope test are also presented in these two tables, as well as the value of the statistical test K tits p-value and the year of possible abrupt change in the time series, calculated by the Pettitt 22007. Observing Table 2it can be noticed that all indices depending on air temperature for the Bebedouro-PE station presented results with statistical significance.

The precipitation indices did not cheesf statistical significance. The results obtained from the air temperature trends for the Bebedouro-PE station Table 2 show increasing trends in 9 of the 11 indices.

The hot days index SU Fig. There was also an increase in the frequency of warm nights TR Eital. The maximum maximum temperature TXx Fig. These results indicate a trend of increase for both the maximum and minimum temperature in the Bebedouro-PE chezf. It is possible to observe a gradual increase in the maximum and minimum temperatures during the last decades, which can be identified through the temporal distributions of these indices.

These results agree with those found by Lima et al. The increase in maximum and minimum temperatures in the region of study corroborates with the projections of the IPCC which has identified that minimum temperatures have increased faster than maximum temperatures.

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With the increase in maximum and minimum temperatures and in the occurrence of hot days and nights, it is expected that the occurrence of cold days and night will decrease. This assumption can be identified in the trend values of the cold days TX10p Fig.

Additionally, the hot days TX90p Fig. The diurnal temperature range DTR Fig. A statistically significant decrease in the number of days with precipitation wdital or greater than 10 mm R10mm Chessf. Therefore, it is observed that the decrease in rainfall greater than or equal to 10 mm and 20 mm agrees with the reduction of total precipitation, as well as with the reduction of the SDII.

The index very humid R95p Fig. By applying the Pettitt test, it was possible to obtain the point at which the abrupt change occurred in the time series last column of Tables 2 and 3. The precipitation dependent indices for these stations did not present significant results.

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The Sen-Slope test is intended to obtain the magnitude of the trend in the historical series. Tables 2 and 3 show the slope values T i of the data series. Positive values indicate an upward trend and negative values provide the downward trend of the dataset. The SU index Fig. However, for TR index Fig. The indices referring to the maximum temperature indicate an increasing trend during the studied period. The TN90p index agrees with the result obtained for the TR index, both indicating a decrease in the hot nights in the Mandacaru station region.

There is also a downward trend of cold days, as shown by the trend value of the TX10p index. The DTR index Fig. The results obtained from the rainfall trends for the Mandacaru-BA station Table 3 did not present statistical significance for any index, however, in general, it is possible to observe decrease trends, as well as in Bebedouro – PE station.

Of the 11 indices dependent on precipitation, 7 presented a precipitation decreasing trend. Precipitation is a determinant variable of the climatic conditions in the Brazilian semi-arid, and the analysis of its behavior is of great importance, due to the great irregularity presented in temporal and spatial scales, not only under the climatic approach but also due to the consequences in the socioeconomic sector, as well as in the population comfort.