RESUMO
The increase in global air temperatures as well as variability in rainfall shifts due to climate change has been affecting the dynamics of water level fluctuations and thermal regimes in lakes and reservoirs. It is expected that at the end of this decade, such impacts will be even more noticeable and may harm the inland waters use. However, little is known about the possible consequences of climate change in multipurpose subtropical reservoirs. Using data generated by a regionalized climate model (RCM) as input to a simple hydrological model and a one-dimensional vertical hydrodynamic model, we forecast potential changes in the Itupararanga reservoir, São Paulo, Brazil, in an exemplary time period (2028-2030) in the next decade. Two Representative Concentration Pathway (RCP) scenarios were considered: an optimistic one corresponding to a CO2 increase of about 650 ppm (RCP 4.5) and a pessimistic scenario where CO2 exceeds 1000 ppm in 2100 (RCP 8.5). We found a significant reduction in the reservoir water level for both scenarios of 35% compared to current conditions. The surface water temperature is expected to increase (+0.6 °C); on the other hand, there would be a cooling of the hypolimnion (RCP 4.5 =-0.3 °C; RCP 8.5 = -1.2 °C). Another consequence is an increase of the duration of stratification periods that would start earlier in the dry period (between July and August), as well as the intensification of the stability of the water column (+43% compared to current conditions) and a deepening of the thermocline. The hydrodynamic modeling results suggest that the water level drop may threaten the reservoir multiple uses, in particular drinking water supply and power generation. Furthermore, the heating of surface water layers and increase of the number of stratified days and thermal stability can have negative impacts on water quality.
RESUMO
RESUMO A exploração indiscriminada de água subterrânea pode causar o colapso dos aquíferos costeiros. Nesse escopo, este trabalho avaliou o comportamento da cunha salina em parte do sistema Barreiras/Marituba, que fica na costa da região metropolitana de Maceió (AL), fazendo uso de modelagem e índices hidrogeoquímicos. O modelo foi calibrado tanto para o fluxo subterrâneo como para a concentração de sólidos totais dissolvidos, nos quais atingiu coeficiente de correlação de 0,764 e 0,682, respectivamente. Foram analisados dois cenários distintos, que permitiram verificar o efeito da explotação de água subterrânea na cunha salina para uma projeção de dez anos. O primeiro considerou a explotação existente até 2015, sem acréscimos de bombeamentos. Como resultado, verificou-se o avanço da cunha salina em duas áreas do domínio e outra área sofreu recuo, além da formação de cones com ascensão vertical da água do mar. No segundo cenário, foram adicionadas, além das licenças de obras hídricas já existentes, como poços, a hipótese de instalação de 36 novos poços de bombeamento, considerando o crescimento da cidade. Porém, nesse caso, não foi possível visualizar variações significativas na zona de mescla em relação ao primeiro cenário. A análise dos índices hidrogeoquímicos apontou para maiores concentrações de cloretos na região próxima à linha do Oceano Atlântico, com pouca influência do nitrato e, no geral, indicou a existência de intrusão de água do mar.
ABSTRACT The groundwater overexploitation can cause the collapse of coastal aquifers. In this scope, this study evaluated the behavior of the salt wedge in part of the Barreiras/Marituba system aquifer present on the coast of the Metropolitan Region of Maceió, Alagoas, using hydrogeochemical modeling and indexes. The model was calibrated for both the underground flow and the total dissolved solids concentration, obtaining a correlation coefficient of 0.764 and 0.682, respectively. Two different scenarios were analyzed, which allowed verifying the effect of the exploitation of groundwater in the salt wedge for a projection of 10 years. The first considered the existing operation until 2015, without any additional pumping. Results shows that saline wedge advanced in two areas of the domain and another site was retreated, in addition to the formation of cones with vertical rise of the sea water. The second scenario, besides the already existing waterworks licenses, was also added by the installation of 36 hypothetical pumping wells, based in the city growth. However, in this case, it was not possible to visualize significant variations in the melting zone in relation to the first scenario. The analysis of hydrogeochemical indices shows to higher concentrations of chlorides in the region near the Atlantic Ocean line, with little influence of nitrate and, in general, indicated the existence of sea water intrusion.