Headwater catchments are essential water sources for sustaining low flow in downstream rivers. The montane region of Serra da Mantiqueira in Southeast Brazil is the largest water supplier for the densely populated area of São Paulo, where we investigated the hydrological response of a subtropical catchment and four of its sub‐catchments. We discussed the relationships between rainfall, streamflow, baseflow, stormflow, soil moisture, and water table depth using high‐frequency field observations over 4 years. Baseflow accounted for most of the streamflow during the dry season and for half of streamflow in the wet season. In contrast, the variations in soil moisture were dampened, with increases in the early wet season preceding the increase in streamflow and decreases in the late wet season following the decrease in streamflow. The mean runoff coefficient and baseflow index varied from 23% to 37% and from 62% to 75% across the catchments, respectively. At the event scale, all catchments had a pronounced threshold behaviour, where stormflow increased sharply when event precipitation reached ≃10 mm, soil moisture reached ≃51% and water table depth decreased to ≃135 cm. The event stormflow coefficient was highly variable, with a maximum of 25%. The temporally integrated stormflow coefficient was low for conditions below a soil moisture threshold (≃3%–10%) and high above a soil moisture threshold (≃8%–15%). Our estimates of flows and threshold behaviours were consistent across the various study catchments, improving our understanding of runoff generation at a catchment scale. This information should help improve the management of water resources focused on water and food security in a context of climate change.
Headwater basins are central for meeting water management and, in humid tropical areas, essential to understand the baseflow, the discharge component that maintains water availability during the dry season, and the stormflow generated from recurrent convective clouds that can lead to flash floods. We measured field data in a typical headwater basin and four sub-basins, in subtropical climate region of Serra da Mantiqueira/South-East Brazil, with a multi-instrument hydrometeorological set (precipitation, streamflow, baseflow, stormflow, soil moisture SM, water table depth WTD), towards providing regional data, to our knowledge, hitherto non-existent, on hydrological response patterns, and variation of stormflow generation with boundary conditions and scale. Precipitation recovered in September and peaked in January concurrently with streamflow. Baseflow responded for most of the streamflow during the dry season and about half in the wettest months, and peaked ahead in March, highly covariated with WTD. In contrast, SM described a longer yearly memory, that recovered 3 months earlier than streamflow, and depleted 2 months latter in March. The monthly scale stormflow responded significantly to rainfall although with low predictability. At the event scale, revealling patterns for all basins showed thresholds of precipitation (≃ 10 mm), SM (≃45% to 57%) and WTD ≃135 cm, below which stormflow was modest. The event stormflow coeficient (eSC) reached up a maximum of 25%, albeit with large variance and little seasonality of the median. Estimates of eSC with double mass and SM thresholds showed pronounced spatial and temporal differences (3.2 to 9.6% in drier conditions and 7.7 to 15.4% wetter conditions). Mean streamflow and runoff coefficient were quite lower at the main basin (21% compared to about ≃32% between sub-basins), where there possibly exists groundwater flux exportation, that discharge on a larger spatial scale, by water exiting the basin without passing through the surface outlet.
Primeiramente, não assumo sozinha nenhum crédito pelo ganho de conhecimento e pelos resultados gerados por esta tese, pois todas as etapas tiveram contribuição de mais pessoas, além de mim, empenhadas em fazer essa pesquisa dar certo. Ao Prof. Humberto, obrigada pela confiança de me aceitar como aluna e pela inesgotável dedicação em me conduzir de maneira exímia e sensata como pesquisadora. Sem o seu sim e sem sua paciência esse trabalho não existiria.Ao Thiago, meu amado esposo, obrigada por ser minha fonte de generosidade e perseverança. Seu apoio incondicional durante meus anos de pós-graduação foi o que me fez chegar até aqui.Aos meus pais e irmãos, à tamanha dedicação e apoio que sempre recebi.Ao Duda e ao Helber, por todo apoio e companheirismo em campo, principalmente no objetivo de fazer os instrumentos funcionarem, e à Emília, pela dedicação e ajuda no processamento dos dados.À Carla, pela dedicação em fazer as coisas darem certo e por compartilhar as mesmas dificuldades que um trabalho de campo proporciona, e à Raianny e ao Léo, pela pronta disponibilidade em me ajudar sempre que precisei.Aos meus atuais e ex-colegas do LCB, pela convivência, companheirismo, amizade e trabalho em equipe: Eduardo, Evandro, Izabella, Patrícia, Pierre, Rodolfo e Thomas.Ao pessoal do DAEE e da SABESP, pela prontidão e colaboração em diversas etapas deste trabalho, em especial ao Prof. Gré, ao Samir e ao Vinicius.À The Nature Conservancy pelas informações da região de estudo e suporte. Em especial à Eileen pelas discussões e esclarecimentos no início da jornada. Ao Prof. Dr. Jonathan Mota, por ter me guiado no início do doutorado.Ao Prof. Dr. Rafael Rosolem, pela dedicação em me receber e me guiar na realização da BEPE.Aos professores, pesquisadores e alunos das várias universidades e institutos que desenvolveram seus trabalhos em Extrema e contribuíram de alguma forma com minha pesquisa.Ao pessoal da Secretária de Meio Ambiente do Município de Extrema por todo apoio na logística e na manutenção em campo.Aos funcionários e professores do IEE e do IAG.À Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) pelos auxílios concedidos, sob processos 2015/
We estimated the seasonal patterns of evapotranspiration (ET) using measured field data in a typical headwater basin and four sub-basins, in subtropical climate region of Serra da Mantiqueira/South-East Brazil, with a multi-instrument hydrometeorological set (standard weather station variables, discharge, soil moisture, and surface-atmosphere turbulent fluxes), towards providing regional data, to our knowledge, hitherto non-existent, of independent ET from micrometeorological methods (eddy covariance EC and Bowen ratio BR), energy balance closure corrections, and water budget based modelling, to discuss the magnitude and seasonality of the most accurate ET possible to be obtained. We had an unsatisfactory closure of the energy balance for the EC method, and the BR method likely also did not meet satisfactory estimates, as both suffered from the non-ideal conditions of the experimental site imposed by secondary atmospheric circulations. The comparison of the mean annual ET among 3 correction methods with the water budget showed an agreement in the range from 2.6 to 2.9 mm d , that was particularly met by the approaches of Mauder et al. (2013) and Twine et al. (2001), of 2.8 mm d . These corrections respected upper limits of potential evapotranspiration. Nighttime corrections were not applied, that possibly explains how daily totals of the H + LE sum overestimated about 9% of the available energy, that led to an overestimated ET of roughly less than 5% by those corrections. The seasonal variability of ET ranged from the minimum of 1.3 mm d-1 in July, and high fluxes in the wet season of about 3.5 mm d-1. The maximum H flux in September indicated how the onset of rainfall and the quick response of soil moisture recovery prevented H to increase onwards on the rhythm of radiation. Soil moisture appeared to play a key role in not only ET but in controlling the energy partition.
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