Uncertainties Involved in the Use of Thresholds for the Detection of Water Bodies in Multitemporal Analysis from Landsat-8 and Sentinel-2 Images.

Although the single threshold is still considered a suitable and easy-to-do technique to extract water features in spatiotemporal analysis, it leads to unavoidable errors. This paper uses an enumerative search to optimize thresholds over satellite-derived modified normalized difference water index (MNDWI). We employed a cross-validation approach and treated accuracy as a random variable in order to: (a) investigate uncertainty related to its application; (b) estimate non-optimistic errors involving single thresholding; (c) investigate the main factors that affect the accuracy's model, and (d) compare satellite sensors performance. We also used a high-resolution digital elevation model to extract water elevations values, making it possible to remove topographic effects and estimate non-optimistic errors exclusively from orbital imagery. Our findings evidenced that there is a region where thresholds values can vary without causing accuracy loss. Moreover, by constraining thresholds variation between these limits, accuracy is dramatically improved and outperformed the Otsu method. Finally, the number of scenes employed to optimize a single threshold drastically affects the accuracy, being not appropriate using a single scene once it leads to overfitted threshold values. More than three scenes are recommended.

Uso de técnicas de geoprocessamento na otimização do traçado de sistemas adutores de abastecimento de água com a utilização de uma base de dados de alta definição / Use of geoprocessing techniques in the optimization of the pipeline alignment of water supply systems with the use of a high definition database

RESUMO Neste trabalho discute-se um modelo de otimização multicritério baseado em Sistemas de Informações Geográficas (SIGs), que tem por finalidade a determinação dos locais com maior potencial para locação do traçado de adutoras por meio da utilização de variáveis de custo, bem como do melhor caminho para esse traçado. Em decorrência disso, foi possível simular rotas de custo mínimo para o traçado da adutora, considerando critérios relacionados com: as declividades e as altitudes da área, as distâncias de rios e áreas alagadas e a proximidade de rodovias. A análise leva em consideração a importância (peso) de cada critério no modelo. Para minimizar a subjetividade na escolha dos valores desses pesos, buscou-se a opinião de especialistas com relação aos critérios analisados. O método Análise Hierárquica de Pesos (AHP) foi utilizado para a ponderação dos critérios. Para aplicação da metodologia, utilizou-se como área de estudo um trecho da Adutora do Pajeú no Estado de Pernambuco e uma base de dados de alta definição do Programa Pernambuco Tridimensional (Programa PE3D), além da base de dados Shuttle Radar Topography Mission (SRTM)/TOPODATA. Os resultados obtidos por meio de SIG permitiram identificar as áreas consideradas de maior aptidão para a locação do traçado da adutora e determinar uma rota otimizada para esse traçado. Na prática, significou na determinação de uma rota para implantação da tubulação da adutora, o que sugere que a utilização de SIG e técnicas de otimização pode auxiliar a tomada de decisão no que se refere aos projetos de sistemas adutores de abastecimento de água.

ABSTRACT This paper discusses a multi-criteria GIS-based optimization model, which aims to determine the locations with the highest potential for the location of the water mains through the use of cost variables, as well as the best path for this tracing. As a result, it was possible to simulate minimum cost routes for the pipeline layout, considering criteria related to: the slope and altitude of the area, the distances of rivers and flooded areas and the proximity of highways. The analysis takes into account the importance (weight) of each criterion in the model. To minimize subjectivity in choosing the values of these weights, expert opinion was sought regarding the criteria analyzed. The HWA (Hierarchical Weight Analysis) method was used to weigh the criteria. To apply the methodology, the study area used an excerpt from the Pajeú pipeline in the state of Pernambuco and a high definition database from the Pernambuco Three-dimensional Program, as well as the SRTM/TOPODATA database. The results obtained through GIS allowed us to identify the areas considered to be the most suitable for the location of the pipeline and to determine an optimized route for this route. In practice, it meant determining a route for the pipeline installation, which suggests that the use of GIS and optimization techniques can help decision making regarding the design of water supply systems.

Dialogic science-policy networks for water security governance in the arid Americas.

Addressing wicked problems challenging water security requires participation from multiple stakeholders, often with conflicting visions, complicating the attainment of water-security goals and heightening the need for integrative and effective science-policy interfaces. Sustained multi-stakeholder dialogues within science-policy networks can improve adaptive governance and water system resilience. This paper describes what we define as "dialogic science-policy networks," or interactions -- both in structural and procedural terms -- between scientists and policy-makers that are: 1) interdisciplinary, 2) international (here, inter-American), 3) cross-sectoral, 4) open, 5) continual and iterative in the long-term, and 6) flexible. By fostering these types of interactions, dialogic networks achieve what we call the 4-I criteria for effective science-policy dialogues: inclusivity, involvement, interaction, and influence. Here we present several water-security research and action projects where some of these attributes may be present. Among these, a more comprehensive form of a dialogic network was intentionally created via AQUASEC, a virtual center and network initially fostered by a series of grants from the Inter-American Institute for Global Change Research. Subsequently, AQUASEC has significantly expanded to other regions through direct linkages and additional program support for the International Water Security Network, supported by Lloyd's Register Foundation and other sources. This paper highlights major scientific and policy achievements of a notable suite of science-policy networks, shared practices, methods, and knowledge integrating science and policy, as well as the main barriers overcome in network development. An important gap that remains for future research is the assessment and evaluation of dialogic science-policy networks' long-term outcomes.