Uncertainties of the rainfall regime in a tropical semi-arid region: the case of the State of Ceará

Abstract

Abstract:The rural population of a tropical semi-arid region such as the northeast of Brazil is directly dependent on rainfall for agricultural production, pasture for livestock, and the storage of drinking water for human consumption. The region is characterised by the frequent occurrence of dry years and consecutive dry days (CDD) during the rainy season, demonstrating the vulnerability of rainfed agriculture. The aim of this study therefore, was to identify homogeneous regions of the State of Ceará where there is greater or lesser uncertainty of the rainfall regime. Accordingly, the occurrence of dry and very dry years were investigated as uncertainties between years, together with the occurrence of two classes of CDD (10-20 and 21-30 days) during the rainy season. To define similar regions as to the uncertainty of the rainfall regime, the technique of Hierarchical Cluster Analysis (HCA) was used. The study considered time series of least 30 years, from 77 rain gauge stations around the state of Ceará. The use of HCA resulted in the formation of seven homogenous groups in both of the phenomena being investigated. Municipalities in the Central Backlands, the Inhamuns Backlands and the Jaguaribana Region displayed a higher frequency of both inter-annual (dry years) and intra-annual (CDD) uncertainty, demonstrating the greater vulnerability of rainfed agriculture. The occurrence of a CDD event is not dependent on the total annual rainfall, as several stations with an average rainfall higher than that of the state showed potential for the occurrence of CDD. The number of CDD events recorded in the 11-20 day class was higher than in the 21-30 day class.

Hydrological Responses of a Watershed to Vegetation Changes in a Tropical Semiarid Region

“…The annual precipitation was above the average in the first two years evaluated (Table 2) and below the average in the last, which had less than 50% of the precipitation of the first and second years. This result confirms the high temporal variability of precipitation events that is typical of semiarid regions (GUERREIRO et al, 2013;ANDRADE et al, 2016). The total precipitation of 2008 and 2011 were similar, however, 2011 had 15 more precipitation events than 2008 ( Table 2), denoting that conclusions based on total annual precipitation for these regions must be complemented with analyzes of number of precipitation events or prior consecutive dry days (SANTOS et al, 2016).…”

“…Precipitation events >50 mm had the lowest frequency (17% in 2008, 11% in 2011 and 6% in 2013) (Table 3), however, this class had the highest percentage of precipitation events with runoff. These results are typical in semiarid regions, where rainfalls of great magnitude are concentrated in few precipitation events (ANDRADE et al, 2016).…”

“…Only two precipitation events with runoff occurred in 2013, which were >50 mm, i.e., the runoff occurred in 2013 were caused by extreme precipitation events. Thus, the precipitation in the Brazilian semiarid region is irregular, with great spatial and temporal variability (ANDRADE et al, 2016).…”

MODELING THE POTENTIAL DISTRIBUTION OF Anamaria heterophylla (GIUL. & V.C. SOUZA) V.C. SOUZA (PLANTAGINACEAE) IN THE CAATINGA

“…Throughout the Caatinga, annual rainfall varies greatly in time and space. Most of the region (68.8%) receives between 600 and 1000 mm of rain per year, with high evapotranspiration rates that characterize the semiarid Caatinga climate (Sampaio 2010, Andrade et al 2016). Although A. heterophylla is a rare-occurrence plant restricted to the margins of lakes or temporary ponds, the climatic conditions of its habitat are present in a large portion of the Caatinga area, when compared to the general bioclimatic characteristics of this biome.…”

Comportamento de chuvas intensas para bacia em região semiárida de Caatinga preservada

“…Nesse contexto, as chuvas intensas são fundamentais para análises hidroambientais, como mudanças climáticas e inundações (Lu et al, 2015); secas (Araújo & Bronstert, 2016); transporte de sedimentos e poluentes, capacidade de autodepuração dos corpos hídricos e dimensionamento de obras hídricas. Sobretudo na região semiárida do Nordeste brasileiro, que sofre com problemas de escassez hídrica em cerca de dois terços do ano, pouca profundidade e salinidade dos solos e sazonalidade do regime de chuvas (Araújo, 2012;Andrade et al, 2016;Costa & Silva, 2017).…”