No abstract

The mountainous region of Rio de Janeiro has a history of natural disasters. The aim of this study was to understand the hydrology of this region. A dataset (up to 70 years) from four rainfall gauges and three stream gauges in Piabanha watershed (2065 km 2 ) was used for this purpose. Mean annual rainfall ranged from 2900 mm (at the headwaters) to 1250 mm in the central area of the watershed. The results showed good correlation between rainfall and stream gauges data. There is a seasonal pattern of dry winters (average month rainfall ranging from 15 to 90 mm) and 20 m 3 /s mean monthly discharge at the watershed outlet and a rainy summer (average month rainfall ranging from 150 to 450 mm) and 80 m 3 /s mean monthly discharge at the watershed outlet. The historical rainfall and discharge dataset showed a cyclicity of about 15 years bounded by the driest years. The most catastrophic events that occurred in the mountainous region of Rio de Janeiro were during the years around the top of the rainfall and discharge cycles. According to the historical trend the last cycle began at 1999 and the present moment (2015)(2016) matches the end of a drier period. However during this last cycle rainfall and discharge trends are not very clear. Together with an increase of great magnitude natural disasters frequency in recent years this may be a sign of an anthropogenic effect. Keywords: rainfall; streamflow; cycle; historical dataset; natural disasters ResumoA região serrana do Rio de Janeiro apresenta um histórico de desastres naturais. Com o objetivo de entender o comportamento hidrológico da região foram analisados dados de chuva (4 estações) e de vazão (3 estações) na bacia do rio Piabanha (2065 km 2 ) com séries históricas de até 70 anos. O total anual médio de pluviosidade variou de 2900 mm (na cabeceira) a 1250 mm na região central da bacia. Os resultados demonstraram boa correlação entre as estações e a existência de sazonalidade com inverno seco (valores médios mensais entre 15 e 90 mm de chuva) e vazão média na foz de 16 m 3 /s e verão chuvoso (valores médios mensais entre 150 e 450 mm de chuva) e vazão média na foz de 80 m 3 /s. As séries históricas de chuva e vazão apresentaram uma ciclicidade, de aproximadamente 15 anos, marcada por anos mais secos. Os dados apontam que os registros existentes de eventos catastróficos regionais foram em anos próximos aos ápices dos ciclos de pluviosidade e vazão propostos. O último ciclo identificado iniciou-se em 1999 e o período atual (2015)(2016) representa o fim deste ciclo, representado pela fase mais seca. Entretanto, neste último ciclo o comportamento da chuva e, principalmente, da vazão é muito variável. Isto, em conjunto com o aumento recente da frequência de desastres naturais de grande magnitude, pode ser um indicativo de efeito antrópico.

<p>Stable isotopes are an important tool to describe the movement of water through the hydrosphere. They are used as tracers to characterize hydrograph properties. In field studies, stable isotope analyses using hourly and bulk end-member calculations can be used to estimate baseflow/precipitation contributions and to relate hydrograph response to land cover across a watershed. To enable proper planning of paved surface expansions and the nature of storm drainage systems, advanced understanding of the influences of spatial land-use patterns on Mediterranean streamflow regimes are needed to support water management in peri-urban catchments. This study focuses on Ribeira dos Covões, a small peri-urban catchment (around 6 km<sup>2</sup>), located in central continental Portugal. The catchment is composed of sandstone in the west portion (56%) and limestone in the east portion (41%), with some alluvial deposits (3%) in the main valleys. Flow and precipitation data were collected every five minutes during storms for several years. In 2018, sampling campaigns also included the collection of pre-event, event, and post-event water stable isotopes in different seasons of the year for streamflow at four sites, representing distinct land coverage and lithological landscape combinations. Preliminary results using precipitation and baseflow fraction calculations based on oxygen-18 measurements show that the catchment outlet provides a 49% baseflow contribution (old water fraction) at the beginning of the dry season and 36% in the wet season. An 85% baseflow contribution was estimated for Quinta (mainly forest area in sandstone) during the dry season, and 64-74% for Espírito Santo (largely urban in sandstone) during the wet season. The baseflow contribution at Porto Bordalo (urban area in limestone) is not significant because the flow is controlled by precipitation. Further investigation will involve connecting the results of most recent stable isotope data analyses to the approaches that were used in the past (e.g. separation of baseflow based on low-pass digital filters). Such connection will clarify streamflow response from distinct peri-urban pattern and lithological landscape combinations and their contributions to catchment runoff, aiming to explore the similarities and differences among these methods and quantify the effects of hydrological regime and land use changing patterns over time.</p>

<p>The assessment of surface-groundwater fluxes is crucial for understanding pollutant pathways through the natural environment. Several techniques to characterize these surface-subsurface interactions have been applied as an attempt to quantify these fluxes in the humid temperate Northeastern USA. Most recently, stable isotopes are considered to be an important tool to describe the movement of waters through the hydrosphere. This study was conducted in the Quabbin-Wachusett Reservoir System, which supplies water for the Boston Metropolitan Area in Massachusetts and depends on water quality management based on environmental trends. Recent trends indicate that despite efforts to reduce road salt application during the winter, salt indicator trends are still increasing in the watershed. Salt transport characterized by monitoring trends of specific conductivity and chloride across the watershed demonstrate that subsurface water concentrations are significantly higher than the streams and reservoir (for chloride, median value is 204 mg/L for wells and 102 mg/L for streams). The present investigation hypothesizes that salt infiltrates through the subsurface during the cold months (October-March) and then releases back to surface water throughout the year. Since groundwater can act as salt storage, an important question for water management relates to the timeframe needed to observe a reduction of salt presence in the watershed after road salt reduction policies and other mitigation strategies take place. To investigate this, oxygen isotopes are being used to identify the dominant hydrological pathways influencing groundwater recharge patterns.  Stable water isotope compositions for warm precipitation (δ<sup>18</sup>O -2.14 to -8.98 per mille), cold precipitation (δ<sup>18</sup>O -4.57 to -13.57 per mille), and groundwater (δ<sup>18</sup>O -8.27 to -9.66 per mille) were used to assess proportional recharge dominance via local winter and summer precipitation isotope end-members. Preliminary analyses indicate that the groundwater recharge is winter dominant (92% obtained from the winter bias seasonal recharge ratio Rwinter/Rannual; values >= 80% represent winter dominance), thus the applied road salt during cold months can be contributing to sustained increases in conductivity in the groundwater. The results show potential dynamics that explain higher levels of specific conductivity and chloride in the subsurface water and the continued increases in stream and reservoir concentrations. Further investigation is being conducted with larger datasets in order to have a better understanding of sample frequency needed to be representative of the system’s predominant seasonal recharge and runoff generation patterns, as well as, how the water isotopic composition is variable spatially and temporally in the region.</p>

No abstract