S. Demuth

Linking streamflow drought to the occurrence of atmospheric circulation patterns

The growing use of surface water resources calls for more intense research on low flow causes and characteristics. This paper presents an investigation linking regional streamflow drought to the occurrence of atmospheric circulation patterns (CPs). Streamflow drought events of 74 basins in southern Germany were determined using the threshold level approach. The regional classification of the basins through a cluster analysis of the drought series provided the basis for the definition of a regional drought index and the following investigation of the influence of CP occurrence on drought. Frequency cross-tabulation showed several high-pressure and anticyclonic CP types to be strongly associated with streamflow drought in southern Germany. The influence of these CPs on streamflow drought was quantified using a logistic regression model. The model results revealed important regional differences concerning the time lag of the drought response and the relevant CPs.

The application of a GIS-based decision support system to predict nitrate leaching to groundwater in southern Germany

Abstract A decision support system has been developed in New Zealand which links national databases with a physically-based, basin-scale surface water quality model within a geographical information system (GIS) interface. In this study, the system is applied to a drainage basin in southern Germany, part of which is underlain by an aquifer which provides water for potable supply. The contamination of the groundwater resource by nitrate is of much concern in this area, and to aid in the prediction of groundwater contamination, the system is modified so that it can predict the concentrations of nitrate leached to groundwater. Model predictions over a six year period are compared with measured flow and concentration data from the river and concentration data from numerous boreholes. Model output in terms of nitrate leaching is displayed as a map over the extent of the aquifer so that areas particularly susceptible to nitrate leaching can be identified.

Assessment of the Vulnerability of a River System to Drought

Based on the regionalisation of recession parameters a method has been developed to estimate streamflow drought vulnerability along a river system. Drought predisposition of a river is defined by the time period TD until the threshold for drought flow QD is reached under dry weather conditions. A multiple regression analysis with basin properties was carried out using the parameters of 55 gauged catchments. Recession parameters, initial discharges QMS and drought threshold discharges were regionalised. Supported by GIS functions and network topology, aggregated recession curves were derived for every 2.5 km along the river network and thus the time period TD could be estimated. This first test of the method was carried out in the study area of southwest Germany and the results and comparisons with earlier studies are satisfying. The visualised results show the degree of vulnerability of river stretches to droughts.