Search

Estimation of both the frequency and variation of spring floods is a key issue for the assessment and management of flood risks. Changes in river floods in Estonia, Latvia and Lithuania have been investigated in few national studies. However, there are no studies of the changes of flood patterns by using a common methodology for the rivers of this region. In this study flood pattern changes in the rivers of the Baltic countries were estimated applying trend and frequency analysis for the periods of 1922–2010, 1922–1960, 1961–2010 and 1991–2010, i.e. for the whole spring flood data sets, periods before and after 1960 (this year was considered as the beginning of the remarkable climate change), as well as for the two past decades. A comparative study of five probability distributions was performed in order to estimate which distribution at best represents statistical characteristics of the flood data. The results showed that maximum discharges of spring floods decreased over the whole studied period. Only some insignificant positive trends of maximum discharges were found in the last time period in continental and transitional rivers. Generalized extreme value distribution provided the best approximation to the maximum discharge data series of the rivers of Baltic countries for the whole observation period. [ABSTRACT FROM AUTHOR]

Extreme floods can be caused by various combinations of hydrological and meteorological factors and river basin conditions that have not been observed for a long time. Long-term observational series permit estimation of both the frequency and variation of spring floods - the key issues of protection systems. Fortunately, Baltic States have a long-term record of hydrological data for the last 80 years. In this research, spring flood parameters (maximum discharge, height of maximum discharge and its timing) for the Baltic countries were assessed for four periods (1922-2008, 1941- 2008, 1961-2008 and 1991-2008). In total, 70 hydrological data series of spring flood parameters were used. To detect trends in time series for these periods, the Mann-Kendall test and the nonparametric Sen's method for the magnitude of the trend were used. The index flood method was used to estimate the maximum discharge in ungauged catchments. The results showed that maximum discharges and heights of spring floods decreased over a longer period. Spring flood peaks took place on earlier dates. Only some significant trends of maximum discharges and their timing were found in the last time period (1991-2008). All these changes could be caused by the increasing ambient temperature and precipitation in the later decades. [ABSTRACT FROM AUTHOR]

Within the SMIRES COST Action (Science and Management of Intermittent Rivers & Ephemeral Streams, www.smires.eu), examples of intermittent rivers across Europe were collected, including gauged catchments with both natural and highly influenced river flow regimes. The examples will be published in a catalogue to give a good overview of the variety of intermittent streams in Europe. Information on the gauged intermittent rivers is summarised in a two-page template: The first page of the template describes the main characteristics of the catchments (land-use, geology, climate, etc.) and the river flow regime. Two panels display hydrographs and flow durations curves and a table gives metrics specific to river flow intermittence relevant for ecology. These hydrological indices have been computed by the SMIRES R package (https://homepage.boku.ac.at/h0540352/smires/framework.html) applied to daily discharge data. The second page of the template is dedicated to the description and reasons for intermittence. A short description about the spatio-temporal pattern of zero-flow events (encompassing seasonal behaviour, observed long-term trends, locations with frequently observed zero-flow events along the river network, etc.). The monitoring network, including gauging stations and other types of observations (e.g. visual inspection of the flow states at different locations along the river) in the catchment, is also described. This presentation gives examples of the pages in the catalogue and a preliminary classification of intermittent rivers at the European scale. [ABSTRACT FROM AUTHOR]