Development of Intensity-Duration-Frequency equation without rainfall data in semiarid regions/Desenvolvimento de equacoes Intensidade-Duracao-Frequencia sem dados pluviograficos em regioes semiaridas

The isozones rain disaggregation methodology was validated and used in this study for the development of IDF (Intensity-Duration-Frequency) equations for three municipalities in the Cariri Metropolitan Region--Ceara, devoid of recording rain gauges. For the validation, data from stations located in different climate regions of the Cariri Metropolitan Region, and from one station in the same climate region was used. To develop the IDF equations, annual daily maximum rainfall data were used, which were adjusted and tested according to Gumbel, Log-Normal II-P, Log-Normal III-P, Gama II-P e Gama III-P probability distributions. The rainfall intensity estimated by the isozones method presented high Willmott indexes, when compared to the amount estimated by the respective IDF equations. The maximum annual daily rainfall used in the application of the isozones method, adjusted respectively to the Gamma III, Normal-Log II and Gamma II. However, it was verified that other functions may be used without significant loss to the precision of the estimates. These results indicate the viability of using this method as an alternative to elaborate IDF equations for regions not monitored and without records of rainfall. Key words: intense rains isozones disaggregation probability distribution Neste estudo foram feitas a validacao da metodologia de desagregacao de chuvas das isozonas e sua utilizacao no desenvolvimento de equacoes IDF (Intensidade-Duracao-Frequencia) para tres municipios da Regiao Metropolitana do Cariri, Ceara, desprovidos de pluviografos. Na validacao utilizaram-se dados de estacoes localizadas em zonas climatologicas distintas da Regiao Metropolitana do Cariri e de uma estacao localizada na mesma zona. As precipitacoes maximas diarias anuais foram ajustadas e testadas pelas distribuicoes de probabilidade de Gumbel, Log-Normal II-P, Log-Normal III-P, Gama II-P e Gama III-P. As intensidades de chuvas estimadas pelo metodo das isozonas apresentaram altos indices de concordancia e desempenho de Willmott, quando comparadas com as estimadas pelas respectivas equacoes IDF. As precipitacoes maximas diarias anuais utilizadas na aplicacao do metodo das isozonas se ajustaram, respectivamente, as distribuicoes Gama III, Log-Normal II e Gama II; entretanto, verificou-se que outras funcoes podem ser utilizadas sem perda significativa na precisao das estimativas; esses resultados indicam a viabilidade da utilizacao do metodo das isozonas como alternativa na elaboracao d