Abstract
The Northeast region of Brazil (NRB) is the most populous semiarid area in the world and is extremely susceptible to droughts. The severity and duration of these droughts depend on several factors, and they do not necessarily follow the same behavior. The aim of this work is to evaluate the frequency of droughts in the NRB and calculate the return period of each drought event using the copula technique, which integrates the duration and severity of the drought in the NRB in a joint bivariate distribution. Monthly precipitation data from 96 meteorological stations spatially distributed in the NRB, ranging from 1961 to 2017, are used. The copula technique is applied to the Standardized Precipitation Index (SPI) on the three-month time scale, testing three families of Archimedean copula functions (Gumbel–Hougaard, Clayton and Frank) to reveal which model is best suited for the data. Averagely, the most frequent droughts observed in the NRB are concentrated in the northern sector of the region, with an observed duration varying from three and a half to five and a half months. However, the eastern NRB experiences the most severe droughts, lasting for 14 to 24 months. The probability distributions that perform better in modeling the series of severity and duration of droughts are exponential, normal and lognormal. The observed severity and duration values show that, for average values, the return period across the region is approximately 24 months. Still in this regard, the southernmost tip of the NRB stands out for having a return period of over 35 months. Regarding maximum observed values of severity and duration, the NRB eastern strip has the longest return period (>60 months), mainly in the southeastern portion where a return period above 90 months was observed. The northern NRB shows the shortest return period (~45 months), indicating that it is the NRB sector with the highest frequency of intense droughts. These results provide useful information for drought risk management in the NRB.
Highlights
Among adverse natural phenomena, drought is what most affects society by acting on large territorial extensions and lasting for long periods [1]
Given the need for more information to help with drought risk management and water use planning in the Northeast region of Brazil (NRB), the aim of this paper is to evaluate the frequency of drought in the NRB and to calculate the return period of drought events using the copula technique
The Brazilian Northeast is the most populous dry region in the world, with a marked climate variability that exposes the population to the risk of drought having strong environmental and social impacts
Summary
Drought is what most affects society by acting on large territorial extensions and lasting for long periods [1]. Drought is characterized as a sufficiently long period of water deficiency to significantly impact edaphic, meteorological, hydrological and social aspects [2,3,4,5,6,7,8]. There is a special interest in the study of drought in the NRB, as it is the most populous dry region in the world, with approximately 35 million inhabitants and a population density of about 34 inhabitants per square kilometer [12]. The phenomenon mainly affects the population that dwells in the semiarid region located in the most central portion of the NRB (Figure 1), creating scenarios that threaten water, food and energy security [13]. The drought of 2010–2016 has been the longest and most severe drought ever recorded in recent decades in the NRB, which has intensified the interest of the scientific community to study the subject [1,14]
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