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

Resumo: A drenagem urbana tem sido desenvolvida dentro de premissas estruturais onde os impactos sao transferidos de montante para jusante sem nenhum controle de suas fontes No escoamento esse processo tem provocado aumento da frequencia das enchentes e entupimento dos condutos e canais por sedimentos e a degradacao da qualidade da agua Dentro desse contexto o controle da erosao urbana e fundamental tanto na manutencao da capacidade de escoamento do sistema de drenagem como na qualidade ambiental As caracteristicas da producao dos sedimentos em bacias urbanas e de seu controle dentro da experiencia internacional sao descritas Buscando destacar indicadores que possam ser aplicados as condicoes de urbanizacao de cidades brasileiras, sao apresentadas estimativas de producao de sedimentos para bacias urbanas

Drenagem urbana e controle de erosão

Analysis of flow measured at 20 sites, rainfall measured at 36 sites, and a 95-year record of water-levels at a site in the basin of the river Paraguay (area 1095 10 3 km 2) showed that the flow regime during the approximate period 1960-70 differed substantially from the flow regime both before and after. The long record of Ladario water-levels suggested that the changes between one period and the next were abrupt, and that the periods differed not only in terms of mean water-levels but also in terms of the year-to-year correlational structure within the record. Despite the fragmentary nature of rainfall records from 36 sites, an explanation for the increased flows since 1970 was found in the increased rainfall, as assessed in terms of the frequency of annual rainfalls rather than the long-term mean rainfall. There was some degree of consistency in the change of rainfall pattern across the Paraguay basin as a whole. A detailed examination of daily rainfall characteristics at two gauges where records were fairly complete showed that during the 1960-70 period, when river flows were low, dry spells were more persistent and, on days when rain did fall, the amounts of rain were generally smaller. The results obtained were compared with results obtained by other researchers using flow records from the Rivers Paraguay, Paraná, Negro and Uruguay in the la Plata basin, and rainfall records from other parts of South America. There is now strong evidence of changes in the runoff regime of the la Plata basin during the last 40 years, not all of which can be attributed to land-use change, as there is complementary evidence of change in rainfall regime. The results were also compared with findings from the Congo basin, which appears to exhibit changes in flow regime that are a mirror image of those found for the Paraguay at Ladario. Key-words: hydrological change; rio Paraguay.

Variabilidade Temporal no Regime Hidrológico da Bacia do Rio Paraguai

As part of a research project aimed to improve medium-range streamflow forecasts used in the operational planning of Brazilian hydro- electric power systems, a large-scale distributed hydrological model has been used to obtain streamflow forecasts for up to 12 days in advance using observed and predicted precipitation data Observed streamflow data up to the time of forecast start were used to update state variables calculated by the model This data assimilation was performed by applying an empirical procedure Several configurations of this empirical procedure have been tested and this paper presents results obtained in applying it to the Rio Grande basin, one of the test beds of the Hydrologic Ensemble Prediction Experiment (HEPEX), focusing on forecasts at Furnas sub-basin (51 900 km 2 ) Results show that flow forecasts were not improved by updating state variables related to river flow, while significant improvements were obtained by updating state variables related to groundwater storage

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Data assimilation in a large-scale distributed hydrological model for medium-range flow forecasts

https://rmets.onlinelibrary.wiley.com/doi/pdf/10.1002/asl.165

Short- and long-term flow forecasting in the Rio Grande watershed (Brazil)

Real-time updating of channel flow routing models is essential for error reduction in hydrological forecasting. Recent updating techniques found in scientific literature, although very promising, are complex and often applied in models that demand much time and expert knowledge for their development, posing challenges for using in an operational context. Since powerful and well-known computational tools are currently available, which provide easy-to-use and less time-consuming platforms for preparation of hydrodynamic models, it becomes interesting to develop updating techniques adaptable to such tools, taking full advantage of previously calibrated models as well as the experience of the users. In this work, we present a real-time updating procedure for streamflow forecasting in HEC-RAS model, using the Shuffled Complex Evolution - University of Arizona (SCE-UA) optimization algorithm. The procedure consists in a simultaneous correction of boundary conditions and model parameters through: (i) generation of a lateral inflow, based on Soil Conservation Service (SCS) dimensionless unit hydrograph and; (ii) estimation of Manning roughness in the river channel. The algorithm works in an optimization window in order to minimize an objective function, given by the weighted sum of squared errors between simulated and observed flows where differences in later intervals (start of forecast) are more penalized. As a case study, the procedure was applied in a river reach between Salto Caxias dam and Hotel Cataratas stream gauge, located in the Lower Iguazu Basin. Results showed that, with a small population of candidate solutions in the optimization algorithm, it is possible to efficiently improve the model performance for streamflow forecasting and reduce negative effects caused by lag errors in simulation. An advantage of the developed procedure is the reduction of both excessive handling of external files and manual adjustments of HEC-RAS model, which is important when operational decisions must be taken in relatively short times.

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Walter Collischonn

Papers

Drenagem urbana e controle de erosão

Variabilidade Temporal no Regime Hidrológico da Bacia do Rio Paraguai

Data assimilation in a large-scale distributed hydrological model for medium-range flow forecasts

Short- and long-term flow forecasting in the Rio Grande watershed (Brazil)

Real-time updating of HEC-RAS model for streamflow forecasting using an optimization algorithm