Gabriel Constantino Blain

Monthly values of the standardized precipitation index in the State of São Paulo, Brazil: trends and spectral features under the normality assumption

The aim of this study was to describe monthly series of the Standardized Precipitation Index obtained from four weather stations of the State of Sao Paulo, Brazil. The analyses were carried out by evaluating the normality assumption of the SPI distributions, the spectral features of these series and, the presence of climatic trends in these datasets. It was observed that the Pearson type III distribution was better than the gamma 2-parameter distribution in providing monthly SPI series closer to the normality assumption inherent to the use of this standardized index. The spectral analyses carried out in the timefrequency domain did not allow us to establish a dominant mode in the analyzed series. In general, the Mann-Kendall and the Pettitt tests indicated the presence of no significant trend in the SPI series. However, both trend tests have indicated that the temporal variability of this index, observed at the months of October over the last 60 years, cannot be seen as the result of a purely random process. This last inference is due to the concentration of decreasing trends, with a common beginning (1983/84) in the four locations of the study.

Statistical considerations of eight monthly precipitations series of the state of São Paulo, Brazil

The correct understanding of the weather variability is a fundamental step in reducing the agricultural climate risk. The aim of the study was to evaluate the temporal variability of monthly precipitation data from eight regions of the State of Sao Paulo, Brazil. Investigations related to possible climate trends were also held. Using the wavelet analysis, the likelihood ratio test, and the Mann-Kendall test, it was observed a very high temporal variability of the monthly precipitation data in the eight analyzed regions. The treatment of such series as strictly stationary, or the use of statistical models (such as Fourier spectral analysis), that only reveals what frequency (spectral) components exist in the precipitation signal, will lead to the loss of important information about the modulating forcing of the precipitation temporal variability. Despite the high temporal variability, no trends on the rainfall series were detected. In the sense of agrometeorological applications, the high temporal variability of the monthly precipitation signal should be considerate on the agricultural zoning model of the State of Sao Paulo, Brazil.

Séries anuais de temperatura máxima média do ar no Estado de São Paulo: variações e tendências climáticas

The aim of the work was to detect climate trends or climate variations in eight annual average maximum air temperature series (Tmax) of the State of Sao Paulo. The study was based on parametric and non-parametric tests. In the Pindorama and Ubatuba series, positive trends in Tmax values were detected during the last 28/24 years. No significant trends were detected in the Cordeiropolis, Mococa, Monte Alegre do Sul, and Ribeirao Preto series. The probability density function associated with the series of Campinas and Piracicaba, shows significant shifts to the right. In the Campinas data series this shift on Tmax data distribution occurred 30 years (approximately) earlier than in the Tmax of Piracicaba data distribution. Thus, despite the majority of the data series have shown important variations on their statistical parameters, it was not possible to identify a temporal variability pattern on the eight Tmax analyzed series.

Revisiting the probabilistic definition of drought: strengths, limitations and an agrometeorological adaptation

Drought is a slow-moving hazard that occurs in virtually all countries of the world. In the light of this, several indices have been developed to improve the detection of drought’s onset, as well as quantifying other features of this phenomenon. The Standardized Precipitation Index (SPI) is often used in order to characterize meteorological droughts. In addition, this index is largely used by Brazilian’s agricultural institutions. In order to add important information to the drought literature, this review article described a general definition of drought, evaluated it from a statistical point of view, and also described the SPI strengths and limitations. An adaptation of the SPI that aims to develop a probability-based agricultural drought index was also presented. The results obtained herein, associated with several studies carried out throughout the world, demonstrated that the SPI is not an agricultural index. It is just a mathematical approach developed to transforming skewed distributions into the Gaussian form. If this standardization cannot be achieved, the use of this index becomes meaningless. Therefore, a normality test should be used in establishing a temporal lower limit for the SPI computations. It was also verified that for periods in which the probability associated with the zero precipitation value is close to 0.5, the SPI may erroneously indicate the end of an existing drought (or a decrease in its severity) in the presence of a decrease in the actual evapotranspiration values.

Variabilidade amostral das séries mensais de precipitação pluvial em duas regiões do Brasil: Pelotas-RS e Campinas-SP

The present work evaluated the sample variability of the Gamma distribution parameters fitted to monthly precipitation series in the regions of Campinas-SP and Pelotas-RS, which have data for the 1890-2006 and 1890-2005 periods, respectively. So, the sample spaces considered were of 58, 39 and 29 years for Campinas, and of 58 and 29 years for Pelotas. Analyses were done using the likelihood ratio test. The analyses showed significant sample alterations. No trend was detected in monthly precipitation series of the region of Campinas-SP. Increasing trends was detected in the monthly precipitation series of the region of Pelotas-RS considering the 1948 to 1976 and 1977 to 2005 samples.

Cento e vinte anos de totais extremos de precipitação pluvial máxima diária em Campinas, Estado de São Paulo: análises estatísticas

The aim of the work was to evaluate the probability of occurrence of daily extreme rainfall totals during each year (Preabs), considering the time series of 1890 to 2009 in the weather station of Campinas, State of Sao Paulo, Brazil. The probability calculations were based on the General Extreme Value distribution (GEV) from two methods of parameter estimations: the maximum likelihood and the L-moments. After evaluating the presence of no significant serial correlation, no trends, and no periodical components within the analyzed time series, it was verified that the GEV can be used to assess the probability of occurrence of the Preabs totals in the location of Campinas. The Lilliefors test and the Quantil-Quantil plots have indicated that the maximum likelihood method can be seen as a better model as compared to the L-moments in calculating the GEV parameters. It was also observed an increasing level of the wavelet energy after the 1990s. As the period between 1920 and 1935 has shown a similar feature on the wavelet sign, it can be inferred that the higher Preabs values are concentrated during these both periods (1920-1935 and after the 1990s).

Considerações estatísticas relativas a seis séries mensais de temperatura do ar da Secretaria de Agricultura e Abastecimento do Estado de São Paulo

O objetivo do trabalho foi detectar tendencias e variacoes climaticas nas series mensais de temperatura maxima (Tmax) e minima (Tmin) do Estado de Sao Paulo. A fim de obter melhor adequacao, entre a probabilidade de ocorrencia dos erros estatisticos tipo I e II, foram utilizados metodos parametricos (teste t, F e razao da verossimilhanca) e nao parametricos (teste sazonal de Mann-Kendall e de Pettitt). As series de Tmin das localidades de Campinas, Cordeiropolis, Ribeirao Preto e, especialmente Ubatuba, apresentam fortes indicios de tendencias e variacoes climaticas nos ultimos 60 anos. Nas series de Monte Alegre do Sul e Pindorama tais indicios sao observados de forma pouco significativa. As alteracoes de ordem climatica observadas nas series de Tmax sao bastante inferiores as observadas nas series de Tmin. Dentre todas as localidades analisadas, a de Ubatuba foi a que apresentou as tendencias de elevacao mais significativas nos dados de temperatura do ar. Os resultados tambem indicaram que no mes de Abril podem ser verificados, em todas as seis localidades, os indicios mais significativos de elevacao nos valores mensais da Tmax e, em especial, da Tmin. Em contra partida, o mes de Setembro mostrou-se o menos sujeito a elevacao nos valores dessas duas variaveis meteorologicas.

Distribuição temporal da precipitação pluvial mensal observada no Posto Meteorológico do Instituto Agronômico, em Campinas, SP

O conceito de alteracao climatica esta atrelado a definicao do termo clima. Assim, o primeiro passo no estudo de possiveis mudancas e de suas implicacoes nos diversos setores da sociedade e em especial na agricultura, e a correta caracterizacao do regime das variaveis meteorologicas de uma regiao, que nao deve ser desassociada da dinâmica das condicoes do tempo. O objetivo deste trabalho e caracterizar a distribuicao temporal de precipitacao pluvial mensal no posto meteorologico do Instituto Agronomico localizado no municipio de Campinas (1890 a 2005), buscando-se tendencias no regime desse elemento. A fim de avaliar possiveis mudancas na distribuicao de frequencia de precipitacao pluvial, os 116 anos de dados foram subdivididos em quatro periodos de igual duracao: de 1890 a 1918 (P1); de 1919 a 1947 (P2); de 1948 a 1976 (P3) e de 1977 a 2005 (P4). Os 48 agrupamentos (quatro periodos de cada um dos 12 meses) foram, entao, comparados por meio da funcao densidade de probabilidade gama. O grau de assimetria das distribuicoes pluviometricas mensais, evidenciado pelas grandes diferencas entre a media e a moda, mostrou ser discutivel a consistencia dos balancos hidricos climatologicos que utilizam valores medios mensais de chuva. O estudo nao detectou tendencia na variabilidade dos totais pluviometricos, na escala temporal utilizada, mostrando nao ter havido mudancas significativas no regime de precipitacao pluvial da serie do posto meteorologico do Instituto Agronomico em Campinas (SP).

Avaliação e adaptação do Índice de Severidade de Seca de Palmer (PDSI) e do Índice Padronizado de Precipitação (SPI) às condições climáticas do Estado de São Paulo

TEST AND ADAPTATION OF THE PALMER DROUGHT SEVERITY INDEX (PDSI) AND THE STANDARDIZED PRECIPITATION INDEX (SPI) TO THE CLIMATE CONDITI ONS OF THE STATE OF SAO PAULO, BRAZIL A drought event for the Palmer Drought Severity Index (PDSI) is defined as a period of time during which the actual moisture supply at a given place rather consistently falls short of the climate appropriate moisture supply. Based on historical precipitations series, which were fitted to the gamma distribution, the Standardized Precipitation Index (SPI) recognizes the importance of the time scale in the analysis of

Standardized precipitation index based on pearson type III distribution

The initial step in calculating the Standardized Precipitation Index (SPI) is to determine a probability density function (pdf) that describes the precipitation series under analysis. Once this pdf is determined, the cumulative probability of an observed precipitation amount is computed. The inverse normal function is then applied to the cumulative probability. The result is the SPI. This article assessed the changes in SPI final values, when computed based on Gamma 2-parameters (Gam) and Pearson Type III (PE3) distributions (SPIGam and SPIPE3, respectively). Monthly rainfall series, available from five weather stations of the State of Sao Paulo, were chosen for this study. Considering quantitative and qualitative assessments of goodness-of-fit (evaluated at 1-, 3-, and 6-months precipitation totals), the PE3 distribution seems to be a better choice than the Gam distribution, in describing the long-term rainfall series of the State of Sao Paulo. In addition, it was observed that the number of SPI time series that could be seen as normally distributed was higher when this drought index was computed from the PE3 distribution. Thus, the use of the Pearson type III distribution within the calculation algorithm of the SPI is recommended in the State of Sao Paulo.