Twenty-three unsolved problems in hydrology (UPH) – a community perspective

This paper is the outcome of a community initiative to identify major unsolved scientific problems in hydrology motivated by a need for stronger harmonisation of research efforts. The procedure involved a public consultation through on-line media, followed by two workshops through which a large number of potential science questions were collated, prioritised, and synthesised. In spite of the diversity of the participants (230 scientists in total), the process revealed much about community priorities and the state of our science: a preference for continuity in research questions rather than radical departures or redirections from past and current work. Questions remain focussed on process-based understanding of hydrological variability and causality at all space and time scales. Increased attention to environmental change drives a new emphasis on understanding how change propagates across interfaces within the hydrological system and across disciplinary boundaries. In particular, the expansion of the human footprint raises a new set of questions related to human interactions with nature and water cycle feedbacks in the context of complex water management problems. We hope that this reflection and synthesis of the 23 unsolved problems in hydrology will help guide research efforts for some years to come

Padrões espaciais e temporais da propagação de secas meteorológicas para hidrológicas no Brasil

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Ambiental, Florianópolis, 2021.Eventos de secas meteorológicas se propagam pelo ciclo hidrológico dando origem a secas hidrológicas. Compreender como esse processo funciona é essencial para melhorar o monitoramento, a previsão e a gestão dos eventos de secas. No entanto, os efeitos do clima e as características das bacias na propagação de secas hidrológicas variam regionalmente e ainda permanecem desconhecidos. Neste trabalho, foram identificados e caracterizados os eventos de secas meteorológicas e hidrológicas em 457 bacias hidrográficas no Brasil para o período de 1980 a 2015. Para isso, foi utilizado o Índice de Precipitação e Evapotranspiração Padronizado (SPEI) como indicador de seca meteorológica e o Índice de Vazão Padronizado (SSI) como indicador de seca hidrológica. Cinco indicadores foram utilizados para estimar o tempo de propagação entre secas meteorológicas e hidrológicas. O primeiro utilizou a correlação de Pearson para comparar as séries de SPEI e SSI. Os outros quatro indicadores representam a diferença entre início, pico, final e centro de massa dos eventos de seca. Além disso, foi calculado o tempo de recuperação das secas meteorológicas e hidrológicas e analisada a relação dos principais controles nos eventos de secas. Os resultados indicam que as secas hidrológicas são geralmente mais duradouras, severas e possuem um tempo de recuperação mais lento comparado com as secas meteorológicas. Enquanto a maioria dos eventos severos de secas meteorológicas acontecem em regiões úmidas (i.e., Amazônia e o Sul do Brasil), a maioria dos eventos severos e duradouros de seca hidrológica ocorrem nas regiões secas (i.e., Nordeste) ou em regiões com maior influência antrópica (i.e., Sudeste). Secas hidrológicas nessas regiões mais secas podem levar quatro vezes mais tempo para se recuperar do que os eventos de seca meteorológicas. Bacias com alto índice de escoamento de base possuem menos eventos de seca hidrológica, porém esses eventos são mais duradouros e mais severos. A região Sul apresentou uma propagação em torno de 2 meses para todos os indicadores analisados. Já para as outras regiões o tempo de propagação variou dependendo do indicador utilizado. O tempo de propagação depende completamente do indicador e metodologia utilizada. Sendo assim, os resultados destacam a importância da utilização de multi-indicadores para caracterizar os mecanismos que controlam o desenvolvimento e propagação de secas ao longo do ciclo hidrológico.Abstract: The propagation of meteorological droughts through the hydrological cycle gives rise to hydro-logical droughts. Understanding how this process develops is essential to improving the monitoring, forecasting, and management. However, the effects of climate and basin characteristics on drought propagation vary regionally and are still poorly understood. In this work, we identify and characterize meteorological and hydrological droughts events for 457 basins in Brazil for the period 1980 to 2015. The Standardized Precipitation and Evapotranspiration Index (SPEI) is used as an indicator of meteorological drought and the Standardized Streamflow Index (SSI) as an indicator of hydrological droughts. We use five indicators to estimate the propagation time from a meteorological to a hydrological drought. The first indicator is based on Pearson?s correlation of the SPEI and SSI series. The other four indicators estimate the drought propagation based on the time difference of the onset, peak, end, and center of mass between the meteorological and hydrological droughts. We also analyze the recovery time of meteorological and hydrological droughts and droughts main controls. The results show that hydrological droughts are more long-lasting, severer, and have a slower recovery time in comparison to meteorological droughts. While most severe meteorological drought events occurred in humid regions (i.e., Amazon and Southern Brazil), most severe and long-lasting hydrological drought events occurred in dry regions (i.e., Northeast) or in a region with greater anthropic influence (i.e., South-east). Hydrological droughts, in those drier regions, can take over four times longer to recover than meteorological drought events. Basins with high baseflow index had fewer hydrological droughts, but these events were longer-lasting and more severe. Drought propagation in the southern region is around 2 months for all indicators analyzed. For the other regions, the propagation time varied depending on the indicator. Therefore, we conclude that the analysis of the propagation time may depend completely on the methodology being used. This thesis highlights the importance of using multi-indicators to characterize the mechanisms that control the development and propagation of droughts throughout the hydrological cycle

Twenty-three unsolved problems in hydrology (UPH)–a community perspective

This paper is the outcome of a community initiative to identify major unsolved scientific problems in hydrology motivated by a need for stronger harmonisation of research efforts. The procedure involved a public consultation through online media, followed by two workshops through which a large number of potential science questions were collated, prioritised, and synthesised. In spite of the diversity of the participants (230 scientists in total), the process revealed much about community priorities and the state of our science: a preference for continuity in research questions rather than radical departures or redirections from past and current work. Questions remain focused on the process-based understanding of hydrological variability and causality at all space and time scales. Increased attention to environmental change drives a new emphasis on understanding how change propagates across interfaces within the hydrological system and across disciplinary boundaries. In particular, the expansion of the human footprint raises a new set of questions related to human interactions with nature and water cycle feedbacks in the context of complex water management problems. We hope that this reflection and synthesis of the 23 unsolved problems in hydrology will help guide research efforts for some years to come