Spatial and temporal variability of rainfall in the Tocantins-Araguaia hydrographic region

Abstract

Current paper examines the space-time dynamics of yearly rainfall of the Tocantins- Araguaia Hydrographic Region (TAHR), foregrounded on rainfall volume from isohyet maps and interpolated by Kriging geo-statistical method. Rainfall space dynamics was undertaken by the analysis of descriptive statistics, Index of Meteorological Irregularity (IMI) and Variation Coefficient. Temporal dynamics was analyzed through the distribution of total annual volume precipitation for each TAHR subbasin by the Standardized Anomaly Index, trend and magnitude test provided by Mann-Kendall and Sen Tests. Results correlated with meteorological anomalies of the Atlantic (Dipole) and Pacific (ENOS) Oceans show a highly heterogeneous rainfall behavior with temporal variability. Or rather, a decrease of rainfall extensiveness during years of intense meteorological anomaly with a rainfall increase south of the High Tocantins and Araguaia sub-basins and a decrease of rainfall in the Lower Tocantins sub-basin, with El Niño features. Although the Mann-Kendall test does not show statistically a significant trend for rainfall in the TAHR region, Sen’s estimator reveals a decrease in rainfall in the High Tocantins (-1.24 km³ year-1) and Araguaia (-1.13 km³ year-1) sub-basins and a rainfall increase in the Lower Tocantins sub-basin (0.53 km³ year-1) and in the TAHR region (-1.5 km³ year-1).