1,720,978 research outputs found
Strategies to community building in hydrology - Focus session of the hydrological sciences division of EGU
No full textOrganisation of the main scientific symposium of the hydrological sciences division of EGU
Climate change impacts—throwing the dice?
No full textWhen two experts estimate the 100-year flood in a small ungauged catchment, chances are that their estimates are very different. When two groups predict the effects of future hydrological changes on stream flow and recharge for the same catchment, the results will hardly be consistent. Yet, climate change impact analyses have become a standard method in our tool box for addressing issues that seem to be of overwhelming concern to the society today. In this paper, we argue that impact studies often tend to be overly optimistic about the reliability of their predictions, and overly pessimistic about the effects on society. Just as a medical doctor who, when in doubt, would say that his patient is going to die—to be on the safe side. We will contrast this assessment with our views on the current state of change prediction, and outline the opportunities in this exciting field of hydrologic research
Challenges of reservoir planning and management in a changing world
No full textPossible shifts of the rainfall regime in the next decades may have important implications for reservoir planning and management. Also, land use change may alter the inflow regime to reservoirs, including the water and sediment dynamics. This paper reviews challenges to reservoir planning and management, and emerging approaches to address these issues in a changing world. Changing persistence of stream flow may increases the uncertainties of sizing reservoir storage, and changing floods may increase the uncertainties associated with spillway design. Short term reservoir operation can be supported by ensemble forecasts and robust operation models to assess the uncertainties of management alternatives. Reservoir sedimentation is a major issue in many parts of the world which may be exacerbated by changes in catchment land use. It is argued that robust bottom-up approaches are needed that are vulnerability or resilience centred to complement the traditional top-down (scenario) approaches to reservoir planning and management
Detecting flood-type-specific flood-rich and flood-poor periods in peaks-over-threshold series with application to Bavaria (Germany)
Full text linkPrevious studies suggest that flood-rich and flood-poor periods are present in many flood peak discharge series around the globe. Understanding the occurrence of these periods and their driving mechanisms is important for reliably estimating future flood probabilities. We propose a method for detecting flood-rich and flood-poor periods in peak-over-threshold series based on scan-statistics and combine it with a flood typology in order to attribute the periods to their flood-generating mechanisms. The method is applied to 164 observed flood series in southern Germany from 1930 to 2018. The results reveal significant flood-rich periods of heavy-rainfall floods, especially in the Danube river basin in the most recent decades. These are consistent with trend analyses from the literature. Additionally, significant flood-poor periods of snowmelt-floods in the immediate past were detected, especially for low-elevation catchments in the alpine foreland and the uplands. The occurrence of flood-rich and flood-poor periods is interpreted in terms of increases in the frequency of heavy rainfall in the alpine foreland and decreases of both soil moisture and snow cover in the midlands
Controls on event runoff coefficients in the eastern Italian Alps
No full textAnalyses of event runoff coefficients provide essential insight on catchment response, particularly if a range of catchments and a range of events are compared by a single indicator. In this study we examine the effect of climate, geology, land use, flood types and initial soil moisture conditions on the distribution functions of the event runoff coefficients for a set of 14 mountainous catchments located in the eastern Italian Alps, ranging in size from 7.3 to 608.4 km2. Runoff coefficients were computed from hourly precipitation, runoff data and estimates of snowmelt. A total of 535 events were analysed over the period 1989–2004. We classified each basin using a ‘‘permeability index” which was inferred from a geologic map and ranged from ‘‘low” to ‘‘high permeability”. A continuous soil moisture accounting model was
applied to each catchment to classify ‘wet’ and ‘dry’ initial soil moisture conditions. The results indicate that the spatial distribution of runoff coefficients is highly correlated with mean annual precipitation, with the mean runoff coefficient increasing with mean annual precipitation. Geology, through the ‘permeability index’, is another important control on runoff coefficients for catchments with mean annual precipitation less than 1200 mm. Land use, as indexed by the SCS curve number, influences runoff coefficient distribution to a lesser degree. An analysis of the runoff coefficients by flood type indicates that
runoff coefficients increase with event snowmelt. Results show that there exists an intermediate region of subsurface water storage capacity, as indexed by a flow–duration curve-based index, which maximises the impact of initial wetness conditions on the runoff coefficient. This means that the difference between runoff coefficients characterised by wet and dry initial conditions is negligible both for basins with very large storage capacity and for basins with small storage capacity. For basins with intermediate storage capacities, the impact of the initial wetness conditions may be relatively large
Long-term changes of flood probabilities in Europe|Langfristige Änderungen der Hochwasser-wahrscheinlichkeiten in Europe
No full textThe extreme floods of recent years underline the urgency of studying long-term changes of floods and their driving processes. This paper reports results on this issue obtained within the framework of subproject 6 of the DFG research group SPATE (Space-Time Dynamics of Extreme Floods). The analyses use an extensive dataset of flood observations at rivers and complementary information to determine and explain significant changes in flood probabilities. The data show that the flood-rich periods of the last 500 years in Europe have been significantly colder than usual. Over the last 60 years, the number of flood-rich periods in north-western Europe has increased. This increase is due to more intense precipitation. In medium-sized and large catchments of southern and eastern Europe, on the other hand, lower soil moisture and less snow cover have led to decreasing flood probabilities. These results are intended as a basis for more reliable design flood estimates in a changing world
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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