Mudanças na cobertura da terra e alterações na resposta hidrológica de bacias hidrográficas na Amazônia
To evaluate the hydrological impacts of deforestation, three studies at different spatial scales, from regional to local were realized. At the first, scale, the larger basins of Amazônia have been delineated to quantify the area of deforestation and protected areas in each one of these. At the secon...
| Autor principal: | Trancoso, Ralph |
|---|---|
| Grau: | Dissertação |
| Idioma: | por |
| Publicado em: |
Instituto Nacional de Pesquisas da Amazônia - INPA
2020
|
| Assuntos: | |
| Acesso em linha: |
https://repositorio.inpa.gov.br/handle/1/4950 http://lattes.cnpq.br/5623625148804473 |
| Resumo: |
|---|
|
To evaluate the hydrological impacts of deforestation, three studies at different spatial scales, from regional to local were realized. At the first, scale, the larger basins of Amazônia have been delineated to quantify the area of deforestation and protected areas in each one of these. At the second scale, river discharges and precipitation time series over the larger watersheds with highest deforestation leveis were analyzed. At the third and smallest scale, which covers two catchments with different land cover types, forest and grass, a field experiment has been implemented. The objective of the experiment was a comparativa analysis of hydrological behavior between the catchments. The large watersheds with major deforested areas are Madeira, Tapajós and Xingu river basins with 113350, 94670 and 68117 Km^ deforested respectively. The same watersheds showed highest annual deforestation rates from 2001 to 2004, where
their headwaters are predominantiy impacted. Trend analysis of streamflow histórica! records of these three large watersheds did not show any increase signal to deforestation, instead 40% of river gauge stations demonstrated a decrease. Although deforestation comprises up to 60% of the watershed drained area, no alterations in hydrological regime were found according to statistical tests used. Precipitation historical records showed similar patterns to streamflow with a decrease of 40% over the watershed area. Regression analysis between annual trend slopes of streamflow and precipitation revealed that streamflow decrease is due to precipitation decrease (R =0,45; p=0,006). These resuits show that in large basins, even with high deforestation leveis, changes in streamflow regime are due to climatic variability, not to land cover changes. Despite the difficulty to detect hydrological changes related to land cover changes in large basins, in small catchments, hydrological changes are evident. In spite of precipitation similarity between catchments with differences of only 20 mm, within the analyzed period, significant differences were found in water balance componente. Evapotranspiration was 1,1 mm.day'"* below within the pasture catchment. Streamflow and water storage were respectively 0,98 mm.day'^ e 0,25 mm.day"^ higher within the pasture catchment. Stormflow yield was 15,28% within forest and 26,41% within pasture. Runoff coefficients (relation Q/P) were 0,17 and 0,32 for forest and pasture respectively. The isolated events of precipitation and discharge revealed significant differences in speed response to precipitation between fores and pasture. The flow duration curves showed irregularities in streamflow componente in the pasture catchment. Forest absorbs a great part of available water by evapotranpiration, it exercises an important ecological role in the balance of hydrological cycles. For this reason, forest replacement has significant impacts on the ability to regularize floods during the wet season and droughts in dry seasons. This study among others of experimental catchment approaches, suggest that large scale deforestation within the headwaters of Madeira, Tapajós and Xingu river basins, should show hydrological responses at the local scale. Though, these seem to be attenuated with increase of the catchment size. |