Kuniyoshi Takeuchi

IAHS decade on predictions in ungauged basins (PUB), 2003-2012: Shaping an exciting future for the hydrological sciences

Abstract Drainage basins in many parts of the world are ungauged or poorly gauged, and in some cases existing measurement networks are declining. The problem is compounded by the impacts of human-induced changes to the land surface and climate, occurring at the local, regional and global scales. Predictions of ungauged or poorly gauged basins under these conditions are highly uncertain. The IAHS Decade on Predictions in Ungauged Basins, or PUB, is a new initiative launched by the International Association of Hydrological Sciences (IAHS), aimed at formulating and implementing appropriate science programmes to engage and energize the scientific community, in a coordinated manner, towards achieving major advances in the capacity to make predictions in ungauged basins. The PUB scientific programme focuses on the estimation of predictive uncertainty, and its subsequent reduction, as its central theme. A general hydrological prediction system contains three components: (a) a model that describes the key processes of interest, (b) a set of parameters that represent those landscape properties that govern critical processes, and (c) appropriate meteorological inputs (where needed) that drive the basin response. Each of these three components of the prediction system, is either not known at all, or at best known imperfectly, due to the inherent multi-scale space—time heterogeneity of the hydrological system, especially in ungauged basins. PUB will therefore include a set of targeted scientific programmes that attempt to make inferences about climatic inputs, parameters and model structures from available but inadequate data and process knowledge, at the basin of interest and/or from other similar basins, with robust measures of the uncertainties involved, and their impacts on predictive uncertainty. Through generation of improved understanding, and methods for the efficient quantification of the underlying multi-scale heterogeneity of the basin and its response, PUB will inexorably lead to new, innovative methods for hydrological predictions in ungauged basins in different parts of the world, combined with significant reductions of predictive uncertainty. In this way, PUB will demonstrate the value of data, as well as provide the information needed to make predictions in ungauged basins, and assist in capacity building in the use of new technologies. This paper presents a summary of the science and implementation plan of PUB, with a call to the hydrological community to participate actively in the realization of these goals.

Monotonic trend and step changes in Japanese precipitation

For the purpose of detecting the possible long-term trends of Japanese precipitation, both parametric t-test and nonparametric Mann–Kendall and Mann–Whitney techniques are applied to the spatially averaged precipitation time series over Japan. The results indicate that although several step changes occurred in Japanese precipitation, the time series did not exhibit significant evidence of monotonic trend during the past century. When a step change is present, the number of observations required for detecting the trend of a given magnitude at a specified significance and power level is investigated with the power function of the t-test. Results indicate that if the magnitude of the step change reaches one or two times of its standard deviation, the previous 50-year of record together with 5 years or more of new data will be available for detecting the possible trend. This conclusion may be helpful for the detection of step changes in the regions where the precipitation has near-normal distributions.

Sustainability analysis for Yellow River water resources using the system dynamics approach

The water resource issue is one of the most significant problemsthat the Yellow River basin will face this century, and one which has received much attention by public and government for several years. Water authorities will face great challenges in meeting the in-stream flow requirements and providing more water for growing populations, industry and agriculture. In order toevaluate the sustainability of the water resource system inthe study area, an object-oriented system dynamics approachhas been used to develop a model for the water resourcessystem in the Yellow River basin, which is referred to asthe Water Resources System Dynamics (WRSD) model. It hasbeen developed for simulating a water resource system andcapturing the dynamic character of the main elements affectingwater demand and supply in the study area. For thebusiness-as-usual (BaU) scenario, the water demands in theYellow River basin are estimated 50.9, 56.5, and 59.5billion m3 for 2010, 2020, and 2030. The existing andpotential water supplies from surface water, aquifers andtreated waste-water are estimated, and potential waterdemands for domestic, industrial and agricultural uses areprojected. Various water supply and demand scenarios havethen been explored by changing variables and parameters,and the sustainability index of the water supply system isestimated for different sub-regions over various periods.

Flood protection and management: quo vadimus?

In the last decade, there have been many destructive floods in various parts of the world. Despite the extensive investment in flood control works, neither flood occurrences nor damages are decreasing. A possible consequence of climate change is an increased frequency of extreme meteorological events that may cause floods. Discussion is offered of some recent large floods in the world and of the experiences in combating floods in Japan. Floods change over time as societies change. There is no single universal remedy against floods and site-specific local efforts are necessary. It is essential to undertake damage mitigation measures together with physical control measures for flood management in an integrated approach, using a mixture of structural and non-structural means. A more disaster conscious society needs to be built with better preparedness and safe-fail (safe in failure) rather than, unrealistic, fail-safe (safe from failure) design of flood defences.

Introduction of block-wise use of TOPMODEL and Muskingum-Cunge method for the hydro-environmental simulation of a large ungauged basin

Abstract For the sustainable management of water quantity and quality, a hydrological model that can simulate the hydro-environmental dynamics of river basins at arbitrary locations is valuable. There are several streamflow simulation models suitable for such a purpose. Yet the lack of data commonly poses a serious problem for their application. This is a serious problem encountered for the sustainable management of water resources at a basin scale. This paper describes a combination of TOPMODEL with the Muskingum-Cunge flow routing method to overcome the problem at least partially. The resultant block-wise version of TOPMODEL is used to simulate daily flows in the data-rich 3570 km2 Fuji-kawa basin, central Honshu, Japan and in the data-poor 20 750 km2 northern part of Minjiang basin above Dujiangyan, Sichuan Province, China. The results demonstrate the potential use of the model for hydro-environmental simulation in a large data-poor basin.

Increasing vulnerability to extreme floods and societal needs of hydrological forecasting

Abstract Recent climatic variability seems to be intensifying the hydrological extremes resulting in devastating hydrological hazards, especially floods all over the world, including the arid regions. Disasters are always more tragic in poor countries than in rich ones, as more poor people seem to suffer and die, and the economic losses have a greater impact. On the other hand, in advanced countries, although flood control can reduce the number of deaths, it cannot always reduce economic losses despite the large public investments that have long been applied. This is due to the ever increasing damage potential in a basin where reliance on safety has been created by flood control measures. It is proven that proper prediction and preparedness are the only practical means that can be relied upon to reduce the death toll and economic losses. In a time of climatic variation, physically-based distributed models are to be pursued to obtain reasonable predictions, since the climate is non-stationary and both basin land use and water use are constantly changing. The proper integration of a distributed watershed model with atmospheric circulation models, four-dimensional data assimilation and mesoscale hydrometeorological nested models is the direction for hydrologists to be heading.

Development and application of a new algorithm for automated pit removal for grid DEMs

Abstract Pits and flat surfaces in raster digital elevation models (DEMs) have been unavoidable obstacles in the extraction of drainage networks. A new automatic method of “pits filling” is presented that eliminates all pits and flat areas simultaneously. Spatially distributed elevation increments of pits are computed. Based on this new approach, drainage networks of more than 10 medium- to large-sized basins have been extracted, including the Mekong River and the Yangtze River. Overlaying the computed drainage networks onto the digitized actual stream networks, good visual consistency was obtained. Besides, the calculated flow pattern over a flat area has been shown to be convergent. The results indicate that the proposed algorithm is easy to use and applicable to DEMs with a wide range of terrain relief and resolution.

2020s scenario analysis of nutrient load in the Mekong River Basin using a distributed hydrological model

A distributed hydrological model, YHyM, was integrated with the export coefficient concept and applied to simulate the nutrient load in the Mekong River Basin. In the validation period (1992-1999), Nash-Sutcliffe efficiency was 76.4% for discharge, 65.9% for total nitrogen, and 45.3% for total phosphorus at Khong Chiam. Using the model, scenario analysis was then performed for the 2020s taking into account major anthropogenic factors: climate change, population, land cover, fertilizer use, and industrial waste water. The results show that the load at Kompong Cham in 2020s is 6.3 x 10(4)tN a(-1) (+13.0% compared to 1990s) and 4.3 x 10(3)tP a(-1) (+24.7%). Overall, the noticeable nutrient sources are cropland in the middle region and urban load in the lower region. The installation of waste water treatment plants in urban areas possibly cut 60.6%N and 19.9%P of the estimated increase in the case without any treatment.

Annual maximum series and partial-duration series — Evaluation of Langbein's formula and Chow's discussion

Abstract Langbeins formula derived in 1949, which relates the hydrological recurrence intervals calculated from an annual maximum series and from a partial-duration series, has long been in practical use. In the present paper, his derivation of the formula has been reviewed and some questions that were unanswered are pointed out. An alternative derivation procedure is then presented. The resultant formula is identical to Langbeins, but the condition to be satisfied for the formula to hold is replaced by a new, more relaxed one. With this revision, the validity of the formula was reconfirmed and its practical use encouraged. Furthermore, discussions made by Chow in 1950 regarding his paper were also reconfirmed to be valid. The analyses showed that if the number of exceedances of hydrological extremals in a year follows a Poisson distribution, Langbeins formula is exact, on average, and that the relation is not very sensitive to its distribution. The sample distribution of the number of exceedances in a year is presented as well as the sample correspondences of the two recurrence intervals, using daily and hourly precipitation data at various stations in Japan.

Forging a paradigm shift in disaster science

Despite major advancements in knowledge on disaster risks and disasters caused by natural hazards, the number and severity of disasters are increasing. Convolving natural, engineering, social and behavioral sciences and practices with policymaking should significantly reduce disaster risks caused by natural hazards. To this end, a fundamental change in scientific approaches to disaster risk reduction is needed by shifting the current emphasis on individual hazard and risk assessment dominant in the geoscientific community to a transdisciplinary system analysis with action-oriented research on disaster risk reduction co-produced with multiple stakeholders, including policymakers. This paradigm shift will allow for acquisition of policy-relevant knowledge and its immediate application to evidence-based policy and decision making for disaster risk reduction. The need for the paradigm shift is more critical now than ever before because of the increasing vulnerability and exposure of society to disaster risk and the need for cross-cutting actions in policy and practice related to climate change and sustainability.