The purpose of this paper is to provide a comprehensive presentation and interpretation of the Ensemble Kalman Filter (EnKF) and its numerical implementation. The EnKF has a large user group, and numerous publications have discussed applications and theoretical aspects of it. This paper reviews the important results from these studies and also presents new ideas and alternative interpretations which further explain the success of the EnKF. In addition to providing the theoretical framework needed for using the EnKF, there is also a focus on the algorithmic formulation and optimal numerical implementation. A program listing is given for some of the key subroutines. The paper also touches upon specific issues such as the use of nonlinear measurements, in situ profiles of temperature and salinity, and data which are available with high frequency in time. An ensemble based optimal interpolation (EnOI) scheme is presented as a cost-effective approach which may serve as an alternative to the EnKF in some applications. A fairly extensive discussion is devoted to the use of time correlated model errors and the estimation of model bias.

The Ensemble Kalman Filter: Theoretical formulation and practical implementation

On behalf of Mr. Koichiro Matsuura, Director-General of UNESCO, it is my great pleasure to welcome you all to this international scientific conference. Drylands are often considered fragile ecosystems, yet they have a remarkable resilience to stress. They are home to unique and well-adapted plant and animal species that we need to conserve. Some of the world’s greatest cultures and belief systems have originated in drylands. On the other hand, desertification and land degradation in drylands often result in poverty and cause environmental refugees to abandon their homes. These problems can only be addressed in a holistic manner, based on sound scientific research and findings. Solutions to the problems of dryland degradation need to be communicated as widely as possible through education at all levels. These are many reasons why UNESCO – within its mandate of science, education, culture and communication – took the intiative to organize this conference. And we are glad that so many partners have responded to our call. UNESCO considers this conference as its main contribution to the observance of the International Year of Deserts and Desertification in 2006. We have deliberately chosen the title ‘The Future of Drylands’ as we feel it is time to redefine our priorities for science, education and governance in the drylands based on 50 years of scientific research in arid and semi-arid zones. In fact UNESCO has one of the longest traditions, within the UN system, of addressing dryland problems from an interdisciplinary, scientific point of view. In 1955, the ‘International Arid Land Meetings’ were held in Socorro, New Mexico (USA). They were organized by the American Association for the Advancement of Science (AAAS), sponsored by UNESCO and supported by the Rockefeller Foundation. One important output of the International Arid Land Meetings was a book entitled The Future of Drylands, edited by Gilbert F. White and published in

United Nations Educational, Scientific and Cultural Organization (UNESCO)

The Prediction in Ungauged Basins (PUB) initiative of the International Association of Hydrological Sciences (IAHS), launched in 2003 and concluded by the PUB Symposium 2012 held in Delft (23–25 October 2012), set out to shift the scientific culture of hydrology towards improved scientific understanding of hydrological processes, as well as associated uncertainties and the development of models with increasing realism and predictive power. This paper reviews the work that has been done under the six science themes of the PUB Decade and outlines the challenges ahead for the hydrological sciences community.Editor D. KoutsoyiannisCitation Hrachowitz, M., Savenije, H.H.G., Bloschl, G., McDonnell, J.J., Sivapalan, M., Pomeroy, J.W., Arheimer, B., Blume, T., Clark, M.P., Ehret, U., Fenicia, F., Freer, J.E., Gelfan, A., Gupta, H.V., Hughes, D.A., Hut, R.W., Montanari, A., Pande, S., Tetzlaff, D., Troch, P.A., Uhlenbrook, S., Wagener, T., Winsemius, H.C., Woods, R.A., Zehe, E., and Cudennec, C., 2013. A d...

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A decade of Predictions in Ungauged Basins (PUB)—a review

Despite significant recent advancements, global hydrological models and their input databases still show limited capabilities in supporting many spatially detailed research questions and integrated assessments, such as required in freshwater ecology or applied water resources management. In order to address these challenges, the scientific community needs to create improved large-scale datasets and more flexible data structures that enable the integration of information across and within spatial scales; develop new and advanced models that support the assessment of longitudinal and lateral hydrological connectivity; and provide an accessible modeling environment for researchers, decision makers, and practitioners. As a contribution, we here present a new modeling framework that integrates hydrographic baseline data at a global scale (enhanced HydroSHEDS layers and coupled datasets) with new modeling tools, specifically a river network routing model (HydroROUT) that is currently under development. The resulting ‘hydro-spatial fabric’ is designed to provide an avenue for advanced hydro-ecological applications at large scales in a consistent and highly versatile way. Preliminary results from case studies to assess human impacts on water quality and the effects of dams on river fragmentation and downstream flow regulation illustrate the potential of this combined data-and-modeling framework to conduct novel research in the fields of aquatic ecology, biogeochemistry, geo-statistical modeling, or pollution and health risk assessments. The global scale outcomes are at a previously unachieved spatial resolution of 500 m and can thus support local planning and decision making in many of the world's large river basins. Copyright © 2013 John Wiley & Sons, Ltd.

Global river hydrography and network routing: baseline data and new approaches to study the world's large river systems

. Current global precipitation (P) datasets do not take full advantage of the complementary nature of satellite and reanalysis data. Here, we present Multi-Source Weighted-Ensemble Precipitation (MSWEP) version 1.1, a global P dataset for the period 1979–2015 with a 3-hourly temporal and 0.25° spatial resolution, specifically designed for hydrological modeling. The design philosophy of MSWEP was to optimally merge the highest quality P data sources available as a function of timescale and location. The long-term mean of MSWEP was based on the CHPclim dataset but replaced with more accurate regional datasets where available. A correction for gauge under-catch and orographic effects was introduced by inferring catchment-average P from streamflow (Q) observations at 13 762 stations across the globe. The temporal variability of MSWEP was determined by weighted averaging of P anomalies from seven datasets; two based solely on interpolation of gauge observations (CPC Unified and GPCC), three on satellite remote sensing (CMORPH, GSMaP-MVK, and TMPA 3B42RT), and two on atmospheric model reanalysis (ERA-Interim and JRA-55). For each grid cell, the weight assigned to the gauge-based estimates was calculated from the gauge network density, while the weights assigned to the satellite- and reanalysis-based estimates were calculated from their comparative performance at the surrounding gauges. The quality of MSWEP was compared against four state-of-the-art gauge-adjusted P datasets (WFDEI-CRU, GPCP-1DD, TMPA 3B42, and CPC Unified) using independent P data from 125 FLUXNET tower stations around the globe. MSWEP obtained the highest daily correlation coefficient (R) among the five P datasets for 60.0 % of the stations and a median R of 0.67 vs. 0.44–0.59 for the other datasets. We further evaluated the performance of MSWEP using hydrological modeling for 9011 catchments ( http://www.gloh2o.org .

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MSWEP: 3-hourly 0.25° global gridded precipitation (1979–2015) by merging gauge, satellite, and reanalysis data

Ensemble Streamflow Predictions in the Três Marias Basin, Brazil

Mesoscale Climate Evaluation Using Grid Computing

A atividade antropica em bacias hidrograficas frequentemente gera efluentes que poluem cursos de agua e tendem a gerar problemas ambientais diversos. Uma ferramenta muito util para auxiliar a avaliacao destes problemas e a modelagem matematica. Uma classe especifica de modelos matematicos com aplicacoes promissoras na area de recursos hidricos e controle da poluicao sao os modelos baseados em agentes. Neste trabalho e apresentado como um modelo baseado em agentes pode ser desenvolvido e utilizado para a simulacao de plumas de constituintes conservativos e nao conservativos em cursos de agua. Sao apresentadas as suposicoes feitas para a representacao dos fenomenos de adveccao, dispersao e decaimento de primeira ordem no modelo. Posteriormente foi feita uma comparacao entre os resultados do modelo e a solucao analitica unidimensional da equacao de adveccao-dispersao. Os resultados das comparacoes mostram uma boa representacao dos processos pelo modelo baseado em agentes, e evidenciam a importância da definicao da discretizacao da massa dos constituintes lancados para essa classe de modelo.  As solucoes desenvolvidas e apresentadas mostram-se promissoras para a aplicacao de agentes na simulacao de impactos de despejos em cursos de agua, bem como o modelo desenvolvido apresenta-se atualmente como uma ferramenta educacional simples para o entendimento destes fenomenos.

http://www.scielo.br/pdf/esa/v21n4/1809-4457-esa-21-04-00739.pdf

Modelagem baseada em agentes para a simulação da dispersão de poluentes em cursos d'água

Hydrological Retrospective of floods and droughts: Case study in the Amazon

The Muskingum-Cunge method is widely used to calculate streamflow routing in rivers, especially as a module for more complex hydrological models. In its non-linear form, this method allows representing flood routing in rivers with flood plains and allows estimating the extreme flows more effectively. However, volume conservation problems may occur because of the use of non-linear schemes. Recent modifications were proposed for the non-linear Muskingum-Cunge method, to compensate or avoid these volume errors. This modification was called MuskingumCunge-Todini (method (MCT). The present paper evaluates the MCT method comparing it to other streamflow routing methods in a hypothetical canal, besides looking at its application in a stretch of River Sâo Francisco, Brazil. To evaluate the results , two performance indicators were used: the Nash-Sutcliffe coefficient and volume error. The comparative application in the hypothetical canal confirmed that the conventional non-linear MuskingumCunge model does not conserve the volume adequately, and that this problem is more marked in low slope rivers (error greater than 4% for a 0.0001 m/m slope). Besides, it was observed that the MCT model practically eliminates the conservation errors of volume (error of 0.01% for a slope of 0.0001m/m ). The MCT method used for a stretch of the River Sao Francisco also presented satisfactory results. The Nash-Sutcliffe coefficient achieved a maximum value of 0.98, while the mean volume error was only 0.8%

Walter Collischonn

Papers

Ensemble Streamflow Predictions in the Três Marias Basin, Brazil

Mesoscale Climate Evaluation Using Grid Computing

Modelagem baseada em agentes para a simulação da dispersão de poluentes em cursos d'água

Hydrological Retrospective of floods and droughts: Case study in the Amazon

Conservação de Volume em Modelos Simplificados de Propagação de Vazão