A seca e seus impactos quali-quantitativos na disponibilidade hídrica de reservatórios na Região Semiárida
Drought is a natural and recurring phenomenon, especially in the Brazilian semiarid region, which is vulnerable to interannual climate variability. In this sense, aquatic ecosystems, especially continental ones, as reservoirs, are increasingly susceptible to the actions of extreme events (severe...
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Formato: | Dissertação |
Idioma: | pt_BR |
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Universidade Federal do Rio Grande do Norte
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Endereço do item: | https://repositorio.ufrn.br/handle/123456789/30258 |
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Resumo: | Drought is a natural and recurring phenomenon, especially in the Brazilian semiarid
region, which is vulnerable to interannual climate variability. In this sense, aquatic
ecosystems, especially continental ones, as reservoirs, are increasingly susceptible
to the actions of extreme events (severe drought, intense rains). Thus, the
characteristics of semi-arid regions, such as the intermittency of rivers and high rates
of evaporation, combined with prolonged drought, tend to increase the levels of
nutrients and the residence time of reservoir water, favoring the eutrophic condition
and the unfeasibility the use of these for human activities. The aim of this study was
to identify the occurrence and characteristics of drought, and how it is associated
with the temporal variability of the water volume stored in the springs of the semiarid
region. In addition, the study sought to assess the impacts of prolonged drought on
the water quality of these sources, verifying whether there was a change in their
trophic state during the occurrence of drought events. To this end, the study was
carried out in two small reservoirs (~ 12.7 and 10.4 km²) in the Piancó-Piranhas-Açu
River basin, in the semi-arid region of the state of Rio Grande do Norte. To identify
the periods and characteristics of the meteorological and hydrological droughts, the
SPI (Standardized Precipitation Index) was used, calculated from a 57-year-old
rainfall database (1963-2019) (EMPARN), and the anomaly of the stored water
volume in reservoirs for 19 years (2001-2019) (IGARN). The results showed that the
36-month SPI (SPI-36) was the best suited for classifying droughts associated with
water volume. Spearman's correlation between SPI-36 and monthly stored volume of
reservoirs was 0.79 and 0.89 for Boqueirão (12.7 km²) and Passagem das Traíras
(10.4 km²), respectively (p <0.0001). During the years 2001 to 2019, four drought
events of different intensities and durations occurred in the two reservoirs studied
(2001-2002, 2003, 2007-2008, 2012-2019), with the Boqueirão reservoir showing the
highest intensity and frequency, corresponding ~ from 22 to 11% of the total events,
while the reservoir of Passagem das Traíras (10.4 km²), moderate, severe and
extreme droughts corresponded to ~ 15, 11 and 9%, respectively. On the other hand,
the hydrological drought is more intense in the reservoir of Passagem das Traíras.
The most intense drought in both reservoirs lasted ~ 8 years (2012-2019). In the
qualitative approach, during the years 2012 to 2019, the results indicated that there
was an increase in chlorophyll-a, electrical conductivity, pH and turbidity due to the
reduction in the water volume of the reservoirs. As well, when comparing the periods,
it was verified a variation in the concentrations of total phosphorus and dissolved
reactive phosphorus. In this sense, the study also demonstrated that the prolongation
of drought had an impact on the intensification of eutrophication, changing the trophy
status of Boqueirão de Parelhas, changing from mesotrophic to eutrophic. For the
reservoir Passagem das Traíras the permanence of the eutrophic state was
evaluated, but with more intensified impacts, such as an increase in algal biomass,
confirming the hypothesis of the work. Understanding the impacts of drought on
reservoirs, as well as the result of it on water availability, qualitative and quantitative,
can be a facilitating means to better manage water resources in the region, as well
as an important means in decision-making to mitigate the impact of drought in the
population that depends on reservoirs for human supply, fishing, animal drinking and
others. |
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