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- Kiem, Anthony S., et al.
(författare)
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Natural hazards in Australia: droughts
- 2016
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Ingår i: Climatic Change. - : Springer Nature. - 0165-0009 .- 1573-1480. ; 139:1, s. 37-54
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Tidskriftsartikel (refereegranskat)abstract
- Droughts are a recurrent and natural part of the Australian hydroclimate, with evidence of drought dating back thousands of years. However, our ability to monitor, attribute, forecast and manage drought is exposed as insufficient whenever a drought occurs. This paper summarises what is known about drought hazard, as opposed to the impacts of drought, in Australia and finds that, unlike other hydroclimatic hazards, we currently have very limited ability to tell when a drought will begin or end. Understanding, defining, monitoring, forecasting and managing drought is also complex due to the variety of temporal and spatial scales at which drought occurs and the diverse direct and indirect causes and consequences of drought. We argue that to improve understanding and management of drought, three key research challenges should be targeted: (1) defining and monitoring drought characteristics (i.e. frequency, start, duration, magnitude, and spatial extent) to remove confusion between drought causes, impacts and risks and better distinguish between drought, aridity, and water scarcity due to over-extractions; (2) documenting historical (instrumental and pre-instrumental) variation in drought to better understand baseline drought characteristics, enable more rigorous identification and attribution of drought events or trends, inform/evaluate hydrological and climate modelling activities and give insights into possible future drought scenarios; (3) improving the prediction and projection of drought characteristics with seasonal to multidecadal lead times and including more realistic modelling of the multiple factors that cause (or contribute to) drought so that the impacts of natural variability and anthropogenic climate change are accounted for and the reliability of long-term drought projections increases.
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| 4. |
- McMillan, Hilary, et al.
(författare)
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Panta Rhei 2013-2015 : global perspectives on hydrology, society and change
- 2016
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Ingår i: Hydrological Sciences Journal. - : Taylor & Francis Group. - 0262-6667 .- 2150-3435. ; 61:7, s. 1174-1191
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Tidskriftsartikel (refereegranskat)abstract
- In 2013, the International Association of Hydrological Sciences (IAHS) launched the hydrological decade 2013-2022 with the theme "Panta Rhei: Change in Hydrology and Society". The decade recognizes the urgency of hydrological research to understand and predict the interactions of society and water, to support sustainable water resource use under changing climatic and environmental conditions. This paper reports on the first Panta Rhei biennium 2013-2015, providing a comprehensive resource that describes the scope and direction of Panta Rhei. We bring together the knowledge of all the Panta Rhei working groups, to summarize the most pressing research questions and how the hydrological community is progressing towards those goals. We draw out interconnections between different strands of research, and reflect on the need to take a global view on hydrology in the current era of human impacts and environmental change. Finally, we look back to the six driving science questions identified at the outset of Panta Rhei, to quantify progress towards those aims.
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| 5. |
- Niu, Jingyi, et al.
(författare)
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Quantification of Long-Range Dependence in Hydroclimatic Time Series: A Method-Comparison Study
- 2023
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Ingår i: Journal of Applied Meteorology and Climatology. - 1558-8424 .- 1558-8432. ; 62:12, s. 1921-1942
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Tidskriftsartikel (refereegranskat)abstract
- Accurate evaluation of the long-range dependence in hydroclimatic time series is important for understanding its inherent characteristics. However, the reliability of its evaluation may be questioned, since different methods may yield various outcomes. In this study, we evaluate the performances of seven widely used methods for estimating long-range dependence: absolute moment estimation, difference variance estimation, residuals variance estimation, rescaled range estimation, periodogram estimation, wavelet estimation (WLE), and discrete second derivative estimation (DSDE). We examine the influences of six major factors: data length, mean value, three nonstationary components (trend, jump, and periodicity), and one stationary component (short-range dependence). Results from the Monte Carlo experiments show that WLE and DSDE have greater credibility than the other five methods. They also reveal that data length, as well as stationary and nonstationary components, have notable influences on the evaluation of long-range dependence. Following it, we use the WLE and DSDE methods to evaluate the long-range dependence of precipitation during 1961–2015 on the Tibetan Plateau. The results indicate that the precipitation variability mirrors the long-range dependence of the Indian summer monsoon but with obvious spatial difference. This result is consistent with the observations made by previous studies, further confirming the superiority of the WLE and DSDE methods. The outcomes from this study have important implications for modeling and prediction of hydroclimatic time series.
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- Persson, Magnus, et al.
(författare)
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Utilisation de réseaux de neurones pour l'étalonnage de mesures par réflectométrie en domaine temporel
- 2001
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Ingår i: Hydrological Sciences Journal. - : Informa UK Limited. - 0262-6667 .- 2150-3435. ; 46:3, s. 389-398
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Tidskriftsartikel (refereegranskat)abstract
- Time-domain reflectometry (TDR) is an electromagnetic technique for measurements of water and solute transport in soils. The relationship between the TDR-measured dielectric constant (Ka) and bulk soil electrical conductivity ([sgrave]a) to water content (θW) and solute concentration is difficult to describe physically due to the complex dielectric response of wet soil. This has led to the development of mostly empirical calibration models. In the present study, artificial neural networks (ANNs) are utilized for calculations of θw and soil solution electrical conductivity ([sgrave]w) from TDR-measured Ka and [sgrave]a in sand. The ANN model performance is compared to other existing models. The results show that the ANN performs consistently better than all other models, suggesting the suitability of ANNs for accurate TDR calibrations.
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| 7. |
- Sivakumar, Bellie, et al.
(författare)
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Catchment classification framework in hydrology: challenges and directions
- 2015
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Ingår i: Journal of Hydrologic Engineering. - 1084-0699. ; 20:1
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Tidskriftsartikel (refereegranskat)abstract
- The past few decades have witnessed the development of numerous catchment models, often with increasing structural complexity and mathematical sophistication. While such models have certainly provided a better understanding of catchments and associated processes, they are also often catchment-specific, region-specific, or process-specific. Serious concerns on this modeling trend have been increasingly raised in recent times and, consequently, the need for a generic catchment classification framework in hydrology has been emphasized. There have indeed been some attempts to advance the idea of such a classification framework. Such studies have investigated different ways of developing a framework, including river morphology, river regimes, hydroclimatic factors, landscape and land use parameters, hydrologic similarity indexes, hydrologic signatures, ecohydrologic factors, geostatistical properties, entropy, nonlinear and chaotic properties, data mining, and other relevant characteristics and methods. Although useful in their own ways, these studies are largely inadequate for a generic classification framework. In addition to the limitations that exist in each of the different forms, a coherent effort to bring these disparate forms together for a workable classification is also missing. This study highlights the challenges that the existing approaches pose in the development of a generic classification framework. It argues for an appropriate basis, a suitable methodology, and key components for such a framework. In particular, it discusses the vital role of system complexity as an appropriate basis for the classification framework and the potential of nonlinear dynamics, networks, and other modern concepts of complex systems science for assessing system complexity. The study also offers a three-step procedure for formulation and verification of a catchment classification framework.
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| 8. |
- Sivakumar, Bellie, et al.
(författare)
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Modeling and prediction of complex environmental systems
- 2009
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Ingår i: Stochastic Environmental Research and Risk Assessment. - : Springer Science and Business Media LLC. - 1436-3240 .- 1436-3259. ; 23:7, s. 861-862
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 9. |
- Sivakumar, Bellie, et al.
(författare)
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Monthly runoff prediction using phase-space reconstruction
- 2001
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Ingår i: Hydrological Sciences Journal. - : Informa UK Limited. - 0262-6667 .- 2150-3435. ; 46:3, s. 377-387
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Tidskriftsartikel (refereegranskat)abstract
- A nonlinear prediction method, developed based on the ideas gained from deterministic chaos theory, is employed: (a) to predict monthly runoff; and (b) to detect the possible presence of chaos in runoff dynamics. The method first reconstructs the single-dimensional (or variable) runoff series in a multi-dimensional phase space to represent its dynamics, and then uses a local polynomial approach to make predictions. Monthly runoff series observed at the Coaracy Nunes/Araguari River basin in northern Brazil is studied. The predictions are found to be in close agreement with the observed runoff, with high correlation coefficient and coefficient of efficiency values, indicating the suitability of the nonlinear prediction method for predicting the runoff dynamics. The results also reveal the presence of low-dimensional chaos in the runoff dynamics, when an inverse approach is adopted for identification, as: (a) an optimal embedding dimension exists, and (b) the prediction accuracy decreases with an increase in prediction lead lime.
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| 10. |
- Sivakumar, Bellie, et al.
(författare)
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Nonlinear dynamics and chaos in hydrology
- 2010
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Ingår i: Advances in Data-Based Approaches for Hydrologic Modeling and Forecasting. - : WORLD SCIENTIFIC. - 9814307971 - 9789814307970 - 9789814307987 ; , s. 411-461
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Bokkapitel (refereegranskat)abstract
- During the last two decades, applications of nonlinear dynamic and chaos theories to hydrologic systems and processes have been on the rise. Early applications of these theories focused mainly on the investigation and prediction of chaos in rainfall and river flow dynamics. Subsequent years witnessed their applications for other purposes (e.g. data disaggregation, missing data estimation, reconstruction of system equations) and to other processes (e.g. rainfall-runoff, sediment transport). More recently, additional inroads have been made through their applications to the problems of scaling, groundwater contamination, parameter estimation, and catchment classification. The outcomes of these studies are certainly encouraging, especially considering the exploratory stage of the concepts in hydrologic sciences. The objectives of this chapter are: (1) to provide a comprehensive review of the applications of nonlinear dynamic and chaos theories in hydrology; and (2) to discuss the hope and scope for the future and also the challenges that lie ahead. In regards to the challenges, particular emphasis is given to discussing the need to improve our understanding of these largely less-understood concepts and to find appropriate ways for integrating them with other concepts that are already in existence or emerging. With the clear recognition that none of the existing one-sided ‘extreme-view’ modeling approaches is capable of solving the hydrologic problems, an urgent call for a balanced ‘middle-ground’ approach that can integrate different methods is also made.
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