Impact of Atmospheric Circulation on Flooding Occurrence and Type in Luxembourg (Central Western Europe)

<p>In the second half of the 20<sup>th</sup> century, hydrological regimes in central Western Europe were largely characterised by large-scale winter floods. This type of event was predominantly triggered by westerly atmospheric fluxes, bringing moist and mild air masses from the Atlantic Ocean to the European continent. Since the late 1990’s, major flooding events seem to have shifted in time and magnitude. Flash flood events, while being a well-known phenomenon in Mediterranean catchments, are increasingly also reported at higher latitudes. Unlike the large-scale winter flood events, flash floods are of very narrow spatial extension and triggered by rather short, but highly intense rainfall events.</p><p>Here, we focus on the specific case of rivers in Luxembourg that have experienced several flash flood events in recent years, while only small to moderate winter flood events have been reported since the late 1990’s. National hydro-meteorological monitoring and flood forecasting systems have been designed for large-scale floods and are not suited for simulating local flash flood events. Therefore, there is a need to increase our understanding of the hydro-meteorological processes underlying flash flood occurrences in our area of interest.</p><p>While increasing air temperature is known to allow a higher air moisture content that can lead to more intense rainfall events and possible flooding, we moreover hypothesize that the recent increase in flash flood occurrences in Luxembourg is reinforced by a change in atmospheric circulation patterns. To test this hypothesis, we analyse the prevailing atmospheric patterns on rainy days during summer and winter months over the period 1954 - 2019, with a particular focus on rainfall events that lead to moderate and extreme floods. In a next step, we intend to extend our findings for Luxembourg in a larger European context. This analysis should allow to better assess the current situation of hydrological extreme events in central Western Europe in order to take precaution measures and prepare for a diversifying hazard.</p>

The Involvement/Exclusion Paradox of Spontaneous Volunteering

This article focuses on the involvement and management of spontaneous volunteers (SVs). It develops a new theory—which we call the “involvement/exclusion” paradox—about a situation which is frequently manifested when SVs converge in times of disaster. After reviewing research and policy guidance relating to spontaneous volunteering, we present findings from a study of responses to winter flood episodes in England. Taking together the empirical findings and the literature, the article analyzes elements inherent in the involvement/exclusion paradox and develops a conceptual model to illustrate and explain the paradox. Implications for managers and future research are discussed.

The effect of winter flood irrigation with saline water on groundwater in a typical irrigation area

Flood irrigation in the winter has been widely applied in northwest China for several years, but little attention has been paid to the flood irrigation program to date. In order to seek a reasonable irrigation quota, a flood irrigation experiment using two common quotas (1,800 and 1,200 m3 ha−1) was conducted in an area irrigated by saline water in the Nanjiang basin with shallow groundwater. Soil electrical conductivity in six treatments irrigated by saline water, with various salinity backgrounds, was investigated using Hydra and DDS-307 before and after flood irrigation. The results indicate that the quota of 12,00 m3 ha−1 was small enough to prevent soil salt from leaching out of the root zone. Although the quota of 1,800 m3 ha−1 may guarantee regular plant growth in the following year, it resulted in at least 267.2 g m−2 of salt entering the shallow groundwater. Therefore, flood irrigation had an important and profound effect on plants, soil environment, and shallow groundwater. The quota of flood irrigation in winter should be determined cautiously according to the hydraulic characteristics and salt background of the soil.

Modelling Snow Accumulation and Snowmelt in the Bystřice River Basin

Effectively dealing with spring flooding issues should focus primarily on their causes. It is therefore important to study the processes of snow accumulation and snowmelt, especially in mountain areas. In this article, we use the lumped modelling approach of the rainfall-runoff model HEC-HMS, along with the temperature-index method for snow accumulation and snowmelt computation. Three winter periods were used for model calibration and testing: 2005/06, 2007/08 and 2008/09. Developments in the snow-water equivalent were simulated and the accuracy of simulated hydrographs was assessed, against actual observations, in the Ostrov outlet in the Bystřice River basin in the Krušné Hory Mountains. The published results present fundamental uncertainties in winter flood modelling and demonstrate the influence of the course and character of a given winter on the model’s capability to simulate the snow water equivalent and runoff.