ABSTRACT Above and underground hydrological processes depend on soil moisture (SM) variability, driven by different environmental factors that seldom are well-monitored, leading to a misunderstanding of soil water temporal patterns. This study investigated the stability of the SM temporal dynamics to different monitoring temporal resolutions around the border between two soil types in a tropical watershed. Four locations were instrumented in a small-scale watershed (5.84 km2) within the tropical coast of Northeast Brazil, encompassing different soil types ( Espodossolo Humilúvico or Carbic Podzol, and Argissolo Vermelho-Amarelo or Haplic Acrisol), land covers (Atlantic Forest, bush vegetation, and grassland) and topographies (flat and moderate slope). The SM was monitored at a temporal resolution of one hour along the 2013-2014 hydrological year and then resampled a resolutions of 6 h, 12 h, 1 day, 2 days, 4 days, 7 days, and 15 days. Descriptive statistics, temporal variability, time-stability ranking, and hierarchical clustering revealed uneven associations among SM time components. The results show that the time-invariant component ruled SM temporal variability over the time-varying parcel, either at high or low temporal resolutions. Time-steps longer than 2 days affected the mean statistical metrics of the SM time-variant parcel. Additionally, SM at downstream and upstream sites behaved differently, suggesting that the temporal mean was regulated by steady soil properties (slope, restrictive layer, and soil texture), whereas their temporal anomalies were driven by climate (rainfall) and hydrogeological (groundwater level) factors. Therefore, it is concluded that around the border between tropical soil types, the distinct behaviour of time-variant and time-invariant components of SM time series reflects different combinations of their soil properties.

RESUMO A falta de procedimentos de classificação baseados em processos pode levar a uma projeção irreal de hietogramas devido à complexa oscilação das lâminas precipitadas quando assimiladas em altas resoluções temporais. Quatro anos consecutivos de dados pluviográficos sub-horários foram assimilados em três áreas de estudo (Guaraíra, GEB, São João do Cariri, CEB, e Aiuaba, AEB) sob climas distintos (semiárido muito quente e tropical úmido). O objetivo deste estudo foi definir os eventos chuvosos (para Tempo Mínimo entre Eventos, MIT, e Altura Mínima de Precipitação, MRD, iguais a 30 min e 1.016 mm, respectivamente), classificar seus tipos de hietograma (retangular, R, unimodal com pico oblíquo à esquerda, UL, oblíquo à direita, UR, e centrado, UC, bimodal, B, e disforme, SL), e comparar suas principais propriedades de precipitação (frequência, duração, altura, taxa e pico). Um processo de agregação de pulsos de precipitação permitiu remodelar os eventos SL para seis períodos de tempo variando de 2 a 30 min. Os resultados revelaram que a área costeira possuía predominantemente eventos R (64% de eventos e 49% de lâmina precipitada), no semiárido ocidental prevaleceram os eventos UL (57% de eventos e 63% de lâmina precipitada), enquanto no semiárido oriental a maioria foram os eventos R (61% de eventos e 30% de lâmina precipitada) semelhante à área costeira. Conclui-se que cada tipo de formação de nuvens teve efeitos importantes sobre as propriedades dos hietogramas, diferenciando-os até dentro do mesmo clima.

ABSTRACT The lack of process-based classification procedures may lead to unrealistic hyetograph design due to complex oscillation of rainfall depths when assimilated at high temporal resolutions. Four consecutive years of sub-hourly rainfall data were assimilated in three study areas (Guaraíra, GEB, São João do Cariri, CEB, and Aiuaba, AEB) under distinct climates (very hot semi-arid and tropical wet). This study aimed to define rainfall events (for Minimum Inter-event Time, MIT, and Minimum Rainfall Depth, MRD, equal to 30 min and 1.016 mm, respectively), classify their hyetograph types (rectangular, R, unimodal with left-skewed, UL, right-skewed, UR, and centred peaks, UC, bimodal, B, and shapeless, SL), and compare their key rainfall properties (frequency, duration, depth, rate and peak). A rain pulse aggregation process allowed for reshaping SL-events for six different time spans varying from 2 to 30 min. The results revealed that the coastal area held predominantly R-events (64% events and 49% rainfall depth), in western semi-arid prevailed UL-events (57% events and 63% rainfall depth), whereas in eastern semi-arid mostly were R-events (61% events and 30% rainfall depth) similar to coastal area. It is concluded that each cloud formation type had important effects on hyetograph properties, differentiating them even within the same climate.

Os mapas de vulnerabilidade de contaminação das águas subterrâneas, elaborados a partir de Sistemas de Informações Geográficas (SIG’s), vêm sendo cada vez mais utilizados para dar suporte aos planos de gestão ambiental dos órgãos governamentais e não-governamentais. Este artigo mostra o mapeamento das áreas vulneráveis à contaminação do aquífero livre da bacia hidrográfica do rio Gramame (BRG). Os métodos DRASTIC e DRASTIC modificado foram as ferramentas utilizadas nesta pesquisa. Esses métodos calculam o índice de vulnerabilidade a partir do somatório de parâmetros ambientais. No DRASTIC modificado, além dos sete parâmetros já utilizados no DRASTIC (profundidade da zona não saturada do solo, recarga, material do aquífero, tipo de solo, topografia, material da zona não saturada e condutividade hidráulica), foram incluídos os fatores cobertura e uso do solo. Os resultados do DRASTIC mostram que, para o período chuvoso, foram identificadas três classes de vulnerabilidade (baixa, moderada e alta) para a área de estudo, com predominância da classe moderada. Para o período de estiagem, a vulnerabilidade apresentou, basicamente, apenas duas classes de vulnerabilidade: a baixa e a moderada. Com a inserção dos fatores uso e cobertura do solo, as áreas de vulnerabilidade alta passaram para o nível muito alto, e as áreas de vulnerabilidade moderada passaram para a classe de risco de contaminação alta. A aplicação do DRASTIC mostra a importância do uso dos SIG’s na proteção das águas subterrâneas quanto ao risco de contaminação.

The contamination vulnerability maps of groundwater, created with help of Geographic Information Systems (GIS), are being increasingly used to support environmental management plans of governmental and non-governmental organizations. This paper shows the mapping of vulnerable areas to contamination of the free aquifer of Gramame river basin (BRG in Portuguese). The methods DRASTIC and modified DRASTIC were the tools used in this research. These methods calculate the vulnerability index based on the sum of environmental parameters. The DRASTIC considers seven factors: Depth to water, net Recharge, Aquifer media, Soil media, Topography, Impact of vadose zone and hydraulic Conductivity, whereas the modified DRASTIC considers also the land use and land cover factors. The results show that the DRASTIC, for the rainy season, identified three vulnerability classes (low, moderate and high) for the study area, with a predominance of moderate class. For the dry period, the vulnerability had basically two vulnerability classes: low and moderate. When the land use and land cover factors where considered, areas of high vulnerability became very high level, and areas of moderate vulnerability became high risk class of contamination. The DRASTIC application shows the importance of the use of GIS’s in groundwater protection to risk of contamination.