Chuvas intensas no estado do Tocantins

Abstract

The State of Tocantins is located between the area of the Cerrado and the Amazon rainforest, which gives the same an important climatic diversity, especially with regard to rainfall. Knowledge of heavy rainfall allows proper planning considering the action of rainfall on soil erosion, floods in rural and urban areas, waterworks, among others. In this context, the objective of this study was the heavy rainfall mapping in the State of Tocantins, divided into three chapters with specific objectives: (1) based on 10 pluviograph stations, to determine disaggregation constants of heavy rainfall for the State of Tocantins; (2) promote heavy rainfall mapping at durations of 5, 10, 20, 30, 40, 50, 60, 120, 180, 240, 360, 720 to 1440 minutes associated with recurrences of 5, 10, 20, 30, 50, 100, 500 and 1000 years; and (3) to map the probable maximum precipitation for the state of Tocantins based on Hershfield methodology for durations of 10, 20, 30, 40, 50, 60, 120, 180, 240, 360, 720 and 1440 minutes. For modeling the frequency of intense rainfalls of different durations, was used the Gumbel distribution of probabilities for 10 pluviograph stations. For the mapping of heavy rainfall were applied historical series of 95 rain gauge stations belonging to the hydrometeorological network of the National Water Agency (NWA), provided by Hidroweb site, located on the Tocantins and nearby, considering the period 1983-2013, applying geostatistics and evaluating models of semivariogram spherical, exponential and gaussian. For the PMP mapping, was adopted the inverse-square-distance interpolator (ISD), being their quality assessed by cross-validation procedure from the calculation of the trend (bias) and the mean absolute percentage error. In the heavy rainfall disaggregation for the State of Tocantins, the constants were obtained: h10min/h30min = 0.46, h20min/h30min = 0.76, h30min/h1h = 0.68, h40min/h1h = 0.83, h50min/h1h = 0.92, h1h/h24h = 0.61, h2h/h24h = 0.72, h3h/h24h = 0.78, h4h/h24h = 0.82, h6h/h24h = 0.86, h12h/h24h = 0.93. For the heavy rainfall mapping, the model had the lowest average error obtained by cross-validation was applied to mapping by ordinary kriging process, having been observed good performance of the spherical model for maximum annual daily rainfall and gaussian to disaggregate and associated rains a return time. The regions of the Bico do Papagaio (north end), Bananal Island (extreme southwest) and northwest, under occurrence of Amazonian climate account for the critical values of heavy rainfall in the State of Tocantins. For longer duration evaluated PMP (24h), met blades ranging from 410.8 - 768.2 mm, while for the lowest measured duration (10') slides ranged from 62.5 - 104.6 mm with spatial distribution pattern similar to heavy rains mapped.