Patterns and drivers of evapotranspiration in South American wetlands

Evapotranspiration (ET) is a key process linking surface and atmospheric energy budgets, yet its drivers and patterns across wetlandscapes are poorly understood worldwide. Here we assess the ET dynamics in 12 wetland complexes across South America, revealing major differences under temperate, tropical, and equatorial climates. While net radiation is a dominant driver of ET seasonality in most environments, flooding also contributes strongly to ET in tropical and equatorial wetlands, especially in meeting the evaporative demand. Moreover, significant water losses through wetlands and ET differences between wetlands and uplands occur in temperate, more water-limited environments and in highly flooded areas such as the Pantanal, where slow river flood propagation drives the ET dynamics. Finally, floodplain forests produce the greatest ET in all environments except the Amazon River floodplains, where upland forests sustain high rates year round. Our findings highlight the unique hydrological functioning and ecosystem services provided by wetlands on a continental scale

Evapotranspiration mapping of commercial corn fields in Brazil using SAFER algorithm

SAFER (Simple Algorithm for Evapotranspiration Retrieving) is a relatively new algorithm applied successfully to estimate actual crop evapotranspiration (ET) at different spatial scales of different crops in Brazil. However, its use for monitoring irrigated crops is scarce and needs further investigation. This study assessed the performance of SAFER to estimate ET of irrigated corn in a Brazilian semiarid region. The study was conducted in São Desidério, Bahia State, Brazil, in corn-cropped areas in no-tillage systems and irrigated by central pivots. SAFER algorithm with original regression coefficients (a = 1.8 and b = –0.008) was initially tested during the growing seasons of 2014, 2015, and 2016. SAFER performed very poorly for estimating corn ET, with RMSD values greater than 1.18 mm d–1 for 12 fields analyzed and NSE values < 0 in most fields. To improve estimates, SAFER regression coefficients were calibrated (using 2014 and 2015 data) and validated with 2016 data, with the resulting coefficients a and b equal to 0.32 and –0.0013, respectively. SAFER performed well for ET estimation after calibration, with r2 and NSE values equal to 0.91 and RMSD = 0.469 mm d–1. SAFER also showed good performance (r2 = 0.86) after validation, with the lowest RMSD (0.58 mm d–1) values for the set of 14 center pivots in this growing season. The results support the use of calibrated SAFER algorithm as a tool for estimating water consumption in irrigated corn fields in semiarid conditions

Projecting Climate and Land Use Change Impacts on Actual Evapotranspiration for the Narmada River Basin in Central India in the Future

Assessment of actual evapotranspiration (ET) is essential as it controls the exchange of water and heat energy between the atmosphere and land surface. ET also influences the available water resources and assists in the crop water assessment in agricultural areas. This study involves the assessment of spatial distribution of seasonal and annual ET using Surface Energy Balance Algorithm for Land (SEBAL) and provides an estimation of future changes in ET due to land use and climate change for a portion of the Narmada river basin in Central India. Climate change effects on future ET are assessed using the ACCESS1-0 model of CMIP5. A Markov Chain model estimated future land use based on the probability of changes in the past. The ET analysis is carried out for the years 2009-2011. The results indicate variation in the seasonal ET with the changed land use. High ET is observed over forest areas and crop lands, but ET decreases over crop lands after harvest. The overall annual ET is high over water bodies and forest areas. ET is high in the premonsoon season over the water bodies and decreases in the winter. Future ET in the 2020s, 2030s, 2040s, and 2050s is shown with respect to land use and climate changes that project a gradual decrease due to the constant removal of the forest areas. The lowest ET is projected in 2050. Individual impact of land use change projects decreases in ET from 1990 to 2050, while climate change effect projects increases in ET in the future due to rises in temperature. However, the combined impacts of land use and climate changes indicate a decrease in ET in the future

Adaptation of the sebal model to estimate evapotranspiration in crop areas

A região do PAD-DF, localizada no Distrito Federal, é conhecida por sua alta produção agrícola, principalmente de grãos, onde se destacam principalmente a produção de soja, milho, sorgo, trigo e feijão. Entretanto, a disponibilidade de água para irrigação vem diminuindo paulatinamente ao longo do tempo. Sendo relevante estudos que auxiliem na gestão da água na região. O objetivo do estudo foi adaptar o Modelo SEBAL para gerar dados de evapotranspiração diária da área do PAD-DF, Distrito Federal, de forma prática, para utilizar dados dos satélites Sentinel-2 e Landsat-8. No modelo SEBAL foi substituído o Normalized vegetation index (NDVI) por Enhanced Vegetation Index (EVI), além usar equações de emissividade e albedo provenientes de outros estudos, bem como para o cálculo de calor sensível instantâneo (H), onde a rugosidade da atmosfera foi desprezada, pois o objeto de estudo foram culturas anuais de pequeno porte. Considerando as áreas agrícolas, estimou-se uma variação de valores de evapotranspiração de 0 a 14 mm/dia, sendo que os maiores valores foram relacionados com os meses em que ocorreram eventos de precipitação e os meses de seca apresentaram uma redução da taxa de evapotranspiração. O modelo SEBAL adaptado mostrou-se eficiente e prático, apresentando valores aos observados na literatura.The PAD-DF region, located in the Federal District, is known for its high agricultural production, mainly grains, where soy, maize, sorghum, wheat and beans are particularly prominent. However, the water availability for irrigation has been declining over time. Studies that help the water management in the region are relevant. The objective of the study was to adapt the SEBAL Model to generate daily evapotranspiration data for PAD-DF area, Federal District, in a practical way, using data from Sentinel-2 and Landsat-8 satellites. In the SEBAL model, the Normalized vegetation index (NDVI) was replaced by Enhanced Vegetation Index (EVI), using emissivity and albedo formulas from other studies and also the calculation of instantaneous sensible heat (H), where the roughness of the atmosphere was despised because the object of study are small annual crops. Considering the crop areas, it was estimated a variation of evapotranspiration values from 0 to 14 mm/day, and the highest values were related to the months in which precipitation events occurred and the drought months presented a reduction of evapotranspiration rate. The SEBAL model was efficient and practical, finding values within the range observed in the literature

geeSEBAL : uma ferramenta Google Earth Engine para estimativa de séries temporais de evapotranspiração

A estimativa acurada da evapotranspiração () é essencial para diversas aplicações na gestão de recursos hídricos. O uso de modelos de que utilizam produtos de sensoriamento remoto vem crescendo nos últimos anos com o desenvolvimento de novas tecnologias como computaçãoem nuvem, deep learning e processamento de alta performance. Esse estudo apresenta o gee SEBAL, uma nova ferramenta para estimativa automática de baseado no modelo Surface Energy Balance Algorithm for Land (SEBAL) e desenvolvido utilizando a plataforma Google Earth Engine(GEE). O uso de imagens Landsat e dados meteorológicos do Global Land Data Assimilation System (GLDAS) permite a estimação de longas séries temporais de . A estrutura da ferramenta é apresentada, bem como estudos de caso em diferentes condições climáticas do Brasil através da validação da estimativa de diária com dados de torres de fluxo com medições de covariância de vórtices turbulentos (EC) nos biomas da Amazônia, Cerrado, Pantanal e Pampa. As estimativas da diária apresentaram uma média de RMSD de 0,75mm dia-1, com um total de 224 imagens Landsat processadas. Por fim, é apresentado uma longa série temporal de (1984-2019) para uma pequena área localizada no bioma Cerrado, caracterizado por uma intensa expansão de agricultura com sistemas de irrigações. A ferramenta está disponível na plataforma GitHub (https://github.com/et-brasil/geesebal) e possui uma versão com interface gráfica do usuário (https://etbrasil.org/geesebal), permitindo importantes avanços na gestão de recursos hídricos em relação a mudanças na .An accurate estimation of evapotranspiration () is essential for many applications in water resources management. models using remote sensing products have flourished in recent years with new technologies as cloud computation, deep learning and high performance computing. This study presents geeSEBAL, a new tool for automatic estimation of based on the Surface Energy Balance Algorithm for Land (SEBAL) model and developed within the Google Earth Engine platform (GEE). The usage of Landsat images and meteorological data from the Global Land Data Assimilation System (GLDAS) allows estimating long term series. The tool framework is introduced, and case studies across multiple climate conditions in Brazil are presented by validating daily with eddy covariance (EC) data in the Amazon, Cerrado, Pantanal and Pampabiomes. Daily estimations yielded an average RMSDof 0.75mm day-1, with a total of 224 Landsat images being processed. Finally, we present a long term assessment (from 1984 to 2019) in a small area located in the Cerrado biome, characterized by an intense irrigated cropland expansion over the last decades, demonstrating the potential of the tool to understand the effects of land cover changes and water use in agriculture. The tool is freely available on GitHub (https://github.com/et-brasil/geesebal) and has a graphical user interface (https://etbrasil.org/geesebal), allowing important advances in water resources management regarding changes

Avaliação de produto global de evapotranspiração real estimado com dados do MODIS em áreas irrigadas no bioma cerrado

Trabalho de Conclusão de Curso (especialização)—Universidade de Brasília, Instituto de Geociências, Curso de Especialização em Geoprocessamento Ambiental, 2019.Dado o aumento da população mundial ao longo do tempo, a demanda no uso dos recursos hídricos seguirá o aumento demográfico, fazendo-se necessário o uso de técnicas e ferramentas que visem sua utilização menos predatória. A busca por novas metodologias também demonstram ser ponto fundamental na gestão racional da água. O sensoriamento remoto tem demonstrado potencial para estimativas do balanço de energia, da evapotranspiração e em estudos com modelos hidrológicos e climáticos. A variável evapotranspiração é um dos principais parâmetros no cálculo do balanço hídrico. O presente estudo buscou avaliar o produto global de evapotranspiração real – ETr MODIS calculado através do modelo SSEBop para as culturas do feijão, trigo e soja, todas irrigadas por pivôs centrais na região do PAD/DF e Cristalina, GO. Os valores estimados de ETr pelo SSEBop foram feitas por imagens do sensor MODIS e comparadas aos valores de evapotranspiração real das culturas avaliadas (ETrc), cujas estimativas foram obtidas pelo método da razão de Bowen, advinda de estações meteorológicas instaladas no interior dos pivôs centrais. Foram analisadas imagens nas escalas temporais decendiais e mensais. Todos os valores obtidos por meio do sensoriamento remoto resultaram em valores de % Bias < 0, o que indica a subestimação dos valores de ETr quando comparados aos valores calculados por meio da razão de Bowen. As estimativas de ETr pelo SSEBop na escala mensal para a soja e o feijão apresentaram boa correlação positiva ( CC = 0,76) quando avaliadas pelo valor máximo do pixel associado ao pivô central estudado. No período chuvoso, as estimativas de ETr indicaram correlação positiva (CC = 0,77) também quando analisada sob o valor máximo dos pixel associados ao pivô central. Apesar subestimados, os valores oriundos do produto global de ETr avaliado no presente estudo demonstrou ser uma importante ferramenta auxiliar na gestão de áreas agrícolas sob manejo de irrigação, comprovando ser um instrumento adequado de apoio ao gerenciamento dos recursos hídricos na região.Since the global population is still rising and the demand on water use will follow the demographic growth, the usage of techniques and tools that brings rational exploitation is necessary. The pursue for new methodologies is a critical point. Remote sensing has demonstrated the potential for energy balance estimation, evapotranspiration and in studies with hydrological and climatic models. The evapotranspiration variable is one of the main parameters in the calculation of the water balance. The study aimed to evaluate the global Actual Evapotranspiration (Eta) product, which offers estimated ETa values calculated using the SSEBop model for beans, wheat and soybean crops, all irrigated by central pivots in the PAD/DF region and in Cristalina, GO. The estimated values of Eta were generated using MODIS sensor images, corresponding to the culture periods of the crops, and compared to the ETa values calculated by the Bowen ratio method, which were generated from meteorological stations installed within the central pivots. All images were analyzed at the decadal and monthly time scales. All values obtained by remote sensing resulted in % Bias values < 0, which indicates the underestimation of ETa when compared to the values calculated using the Bowen ratio methodology. Estimates of ETa by the SSEBop model, in the monthly scale, for soybean and beans indicated a good positive correlation (CC = 0.76) when evaluated by the maximum value of the pixels associated to the central pivot which was assessed. In the rainy season, estimated ETa values indicated a positive correlation (CC = 0.77) also when analyzed under the maximum pixel value reference. Although systematically underestimating the ETa values from the global SSEBop product evaluated in the present study, proved to be an important alternative tool for the management of water resources in the region

Inundações em múltiplas escalas na América do Sul : de áreas úmidas a áreas de risco

South America hosts some of the major river systems on Earth, often associated with large floodplains that are inundated every year, such as the Pantanal and many Amazon wetlands. Interfluvial wetland complexes are also found across the continent, with particular geomorphic settings and unique savanna or grassland vegetation. South American wetlands can provide distinctive ecosystem services such as biodiversity supporting, food provision and flood attenuation. On the other hand, humans have settled around wetlands for millennia, benefiting from all resources they provide, and have adapted to its flood regime as well adapted its landscape, defining what has been called human-water systems. Yet, an increasing number of South American people have been negatively affected by extreme floods. Moving from continental to local scales, this thesis invites the readers to a journey across major South American wetland systems and their unique hydrological dynamics, under the light of the satellite era and the breakthrough advances on hydrologic-hydrodynamic modeling in the last decades. This work is founded on the proposition of a continental wetland research agenda, and based on a comparative hydrology approach. Floods are studied through both natural wetland processes and hazard dimensions. The first part presents a set of studies on the Amazon basin wetlands, from the development of 1D and 2D models to simulate hydrological processes in contrasting wetland types in the Negro river basin to the basin-wide intercomparison of 29 inundation products and assessment of long-term inundation trends. While most wetland studies have been conducted over the central Amazon floodplains, major knowledge gaps remain for understanding the hydrological dynamics of interfluvial areas such as the Llanos de Moxos and Negro savannas, where the inundation is less predictable and shallower. The second part of the thesis leverages satellite-based datasets of multiple hydrological variables (water levels, total water storage, inundation extent, precipitation and evapotranspiration) to address the hydrology of 12 large wetland systems in the continent. It shows the major differences among river floodplains and interfluvial wetlands on the water level annual amplitude, time lag between precipitation and inundation, and evapotranspiration dynamics. Finally, the third part addresses the flood hazard component of human-wetland interactions through large-scale assessments of flood hazard dynamics and effects of built infrastructure (dams) on flood attenuation. The dynamics of the great 1983 floods, one of the most extreme years ever recorded in the continent, is assessed with a continental hydrological model. Then, the capabilities of continental models to simulate the river-floodplain-reservoir continuum that exists across large river basins are assessed with case studies for major river basins affected by human intervention (Itajaí-Açu and upper Paraná river basins in Brazil). While this thesis enlightens some relevant hydrological processes regarding South American floods and their positive and negative effects to human societies and ecosystems in general, major knowledge gaps persist and provide great research opportunities for the near future. The launching of many hydrology-oriented satellite missions, and an ever-growing computational capacity, make the continental hydrology agenda related to wetlands and floods a great research topic for the upcoming years.A América do Sul abriga alguns dos maiores sistemas hídricos do planeta, frequentemente associados a grandes planícies de inundação, como o Pantanal e várias áreas da Amazônia. Áreas úmidas (AU’s) interfluviais são também encontrados no continente, com características geomorfológicas particulares, e vegetações de savana e gramíneas únicas. As AU’s da América do Sul provêm diversos serviços ecossistêmicos, como suporte à biodiversidade, provisão de alimento e atenuação de cheias. Humanos têm se estabelecido ao redor de AU’s por milênios, se beneficiando dos recursos providos por elas. Eles se adaptaram ao seu regime de inundação, e adaptaram sua paisagem, definindo o que tem sido chamado de sistemas sociedade-água. Por outro lado, um número crescente de pessoas têm sido negativamente afetado por cheias extremas. Da escala continental à local, esta tese convida o leitor a uma jornada através de importantes AU’s da América do Sul e suas particulares dinâmicas de inundação, sob a luz da era dos satélites e dos grandes avanços em modelagem hidrológica-hidrodinâmica das últimas décadas. Este trabalho é baseado na proposta de uma escala continental de pesquisa sobre AU’s, e é baseado em uma abordagem de hidrologia comparativa. Inundações são estudadas em múltiplas dimensões, de processos de AU’s naturais à questão do perigo para humanos. A primeira parte apresenta uma série de estudos sobre as AU’s da bacia amazônica, desde o desenvolvimento de modelos 1D e 2D para simular processos hidrológicos em tipos contrastantes de AU’s na bacia do Rio Negro, até a intercomparação de 29 produtos de inundação e avaliação de tendências de inundações de longo prazo para a escala da bacia amazônica. Enquanto a maioria dos estudos de AU’s foi conduzida nas várzeas do rio Amazonas, importantes lacunas do conhecimento permanecem para a compreensão da dinâmica hidrológica de áreas interfluviais como Llanos de Moxos e as savanas do rio Negro, onde a inundação é menos previsível e mais rasa. A segunda parte da tese utiliza dados oriundos de satélites relacionados a múltiplas variáveis hidrológicas (níveis d’água, armazenamento total de água, extensão de áreas inundadas, precipitação e evapotranspiração) para estudar a hidrologia de 12 grandes sistemas de AU’s do continente. São destacadas as grandes diferenças entre planícies de inundação e AU’s interfluviais em termos de amplitude anual de níveis d’água, defasagem entre precipitação e inundação, e dinâmica de evapotranspiração. Por fim, a última parte da tese aborda o componente de perigo de inundação das interações sociedade-água através de avaliações em grande escala da dinâmica de inundação e dos efeitos de infraestruturas construídas (como barragens) na atenuação de cheias. A dinâmica das grandes cheias de 1983, um dos anos mais extremos já registrados no continente, é avaliada com um modelo hidrológico continental. Depois, a capacidade de modelos continentais para simular o continuum entre rios, planícies de inundação e reservatórios que existe em grandes bacias hidrográficas é avaliada com estudos de casos para importantes bacias afetadas pela intervenção humana (bacia dos rios Paraná e Itajaí-Açu). Enquanto esta tese avança a compreensão de relevantes processos hidrológicos relacionados a inundações na América do Sul em múltiplas escalas, bem como seus efeitos positivos e negativos nas sociedades humanas e ecossistemas em geral, importantes lacunas do conhecimento persistem e fomentam importantes oportunidades de pesquisa futuras. O lançamento de várias missões satelitais orientadas a hidrologia, e uma cada vez mais crescente capacidade computacional, faz da agenda continental de hidrologia relacionada a AU’s e inundações um grande tópico de pesquisa para os próximos anos

Estimating energy fluxes and evapotranspiration of corn and soybean with an unmanned aircraft system in Ames, Iowa

Evapotranspiration (ET) is a key hydrological variable and has been studies to plan irrigation schedule, understand surface-atmospheric interactions, assess crop sensitivity to droughts, etc. On top of that, ET is a proxy for evaluating water availability in trees canopies and assess soil moisture content. The recent advent of the Unmanned Aircraft Systems (UAS) has presented new opportunities and challenges in mapping ET at a much finer scale and under various atmospheric conditions. In this research, we integrate traditional remote sensing techniques with the novel UAS technology to estimate ET and surface energy fluxes for a corn and soybean field near Ames, Iowa, in five different stages of crop development: establishment, vegetative, flowering, yield formation and ripening. Multispectral and thermal cameras onboard the UAS were used to collect imagery that served as primary data for running the Surface Energy Algorithm for Land (SEBAL) model that estimates ET as a residual of the surface energy budget. Other data and materials used for the development of this research include eddy covariance flux towers, meteorological data, leaf area index measured in-situ, ground control points and surface reflectance and surface albedo measured with a field spectroradiometer. The eddy covariance flux towers are managed by the United States Department of Agriculture (USDA) and their data were utilized for calibrating and validating the model. Each tower has an approximated fetch of approximately 200 meters, and 24 tower footprints calculated for each tower using the Flux Footprint Predictions (FFP) model, that accounts for surface roughness, wind speed and friction velocity. The footprints were used to extract the mean value for each raster-energy flux that was compared with the observed values from the flux towers. Statistical methods for validating the energy fluxes produced by SEBAL include linear regression, residual plots, the root mean squared error, mean absolute error and confidence coefficient. The crosscomparison between observed and estimated values for the Net Radiation (Rn) showed an R squared of R2 = 0.71, for the Soil Heat Flux (G) an agreement of R2 = 0.17 for plate 1 and R2 = 0.22 for plate 2, for the Sensible Heat Flux (H) R2 = 0.50 and for the Latent Heat Flux (LE) an agreement of R2 = 0.82. The findings also indicate that ET rates are reliant upon the stage of crop development, where the corn plot had higher ET rates up until the appearing of the tassel, rapidly declining afterwards. The soybean field had a more consistent rate of ET from May through September, possibly due to its extended length of growth. This research concludes that the SEBAL model can be integrated with a a UAS platform for estimating ET and surface energy fluxes at very fine scale, however, atmospheric conditions still affect the accuracy and quality of remotely sensed data

Análisis comparativo de la evapotranspiración mediante el modelo SEBAL y el método tanque evaporímetro en la cuenca Huancané - Puno

El presente trabajo de investigación propone realizar el análisis comparativo de la evapotranspiración mediante las metodologías del modelo SEBAL y Tanque Evaporímetro en la cuenca Huancané - Puno. Los objetivos específicos fueron, estimar la evapotranspiración mediante el modelo SEBAL a partir de imágenes Landast 8, estimar la evapotranspiración real mediante el método Tanque Evaporímetro a partir de datos meteorológicos de las estaciones Huancané y Muñani, y realizar la comparación y validación de resultados de evapotranspiración obtenidos a partir del método tanque evaporímetro con el modelo SEBAL. Las etapas metodológicas que se considera para el logro de los objetivos, son; la recopilación de datos meteorológicos del SENAMHI e imágenes satelitales Landsat 8 y procesamiento de la información existente. Para el modelo SEBAL, los valores de evapotranspiración más bajos corresponden a zonas con suelos sin cultivos o baja cobertura vegetal (NDVI0.41) representan valores entre 1.50 a 4.20 mm/día. El método tanque evaporímetro permitió determinar la evapotranspiración real (ETR), en promedio son 2.10, 2.44, 1.76 y 2.04 mm/día de zonas en análisis. La comparación y validación de los valores de evapotranspiración observados (ETR tanque evaporímetro) y estimados (ETR SEBAL), para las zonas de análisis cercanas a la estación de Huancané presentan un error medio cuadrático de 0.26 y 0.25, coeficiente de determinación de 0.97 y una eficiencia de Nash-Sutcliffe de 0.81 y 0.83. Igualmente, para las áreas cercanas a la estación de Muñani en donde muestran un error medio cuadrático de 0.13 y 0.14, coeficiente de determinación de 0.97 y 0.93; y una eficiencia de Nash-Sutcliffe de 0.81 y 0.82. Los resultados obtenidos con el modelo SEBAL son muy satisfactorios, lo cual demuestra que es viable su utilización.Tesi