Análise das variabilidades interanuais e interdecenais de índices climáticos para o Rio Grande do Norte.

Abstract

The climate in the Northeast Region of Brazil is characterized especially by the spatial and temporal irregularities of the precipitation, with periods of great drought interspersed by floods periods that vary from a few years to decades. The interannual variability of precipitation in the Northeast Region, in particular, in the State of Rio Grande do Norte is influenced mainly by the interannual variations in SST of the Equatorial Pacific and Tropical Atlantic. In this sense, the need arises to study if these variabilities influence the classification of the climate. The present study has the objective of analyzing the influence of interannual and interdecadal oceanic/atmospheric variability on the climate indices: aridity index of the United Nations Environment Program (IaUNEP), and moisture index of Thornthwaite (Im) for the state of Rio Grande do Norte in the period from (1950 to 2016). The homogeneous precipitation regions of the State were determined by the K-means method. The climatic water balance of Thornthwaite and Mather (1955) was performed yearly for 24 locations. The 24 locations are spatially distributed across on the State. The Im and IaUNEP indices were used for the climate classification of the homogeneous regions in different periods. The interannual periods were El Niño/La Niña and Gradient of SST anomaly of Tropical Atlantic, and interdecadal periods were Pacific Decadal Oscillation (PDO) and Atlantic Multidecadal Oscillation (AMO). Student's t test was used to verify if the Im and IaUNEP indices of the various times periods associated with SST anomalies in interannual and interdecadal scales are statistically different. As a result, it is observed that, in general, for the same region the classification with Im presents drier climates than IaUNEP. Using the Im the greatest climate variability was observed in region 1, with four distinct types of climate, from semiarid to humid, while the lowest, with two types of climate in region 6, with a climate ranging from semiarid to subhumid dry. In regions 2, 3, 4 and 5, three types were observed, and the climate ranged from arid to dry subhumid. Using IaUNEP, the highest interannual variability was observed in region 5, with climatic classification varying from arid to humid subhumid, that is, four distinct types of climate, in the other regions three types of climate were observed. In regions 2 and 6 variability from semiarid to subhumid wet, at 3 and 4 from dry to dry subhumid and 1 from dry to wet subhumid. Regardless of the index used, it was verified that in all the regions the wetter periods are associated to the years of La Niña combined with negative phase of the AMO, while the more arid occurred during the periods of El Niño and positive phase of the AMO. The differences in the means of the Im or IaUNEP indices of these two periods are statistically significant at p ≤ 0.01 for all six regions.