Water resources management in the context of drought

During the last decades water resources managers are facing severe challenges all over the world and the trends of increasing temperature and decreasing precipitation intensify this situation. Climate change is a major global challenge facing water resources managers. Rising global temperatures will lead to an intensification of the hydrological cycle, resulting in dryer dry seasons and wetter rainy seasons, and subsequently heightened risks of more extreme, longer and frequent floods and droughts. Drought is considered by many to be the most complex but least understood of all natural hazards, affecting more people than any other hazard. Drought is a natural hazard temporarily affecting almost every region in the world. The main target of this thesis is to provide some analyses and to evolve appropriate and interdisciplinary tools and techniques for drought characterization and for enhanced management of water resources systems during drought periods. The proposed methodologies are applied to the Ruhr river basin as a case study. In this thesis, the climate change in the Ruhr river basin has been investigated using a set of data containing precipitation, temperature and inflow. All data series have been subjected to homogenization procedure. The data homogenization is described in detail. Yearly and seasonal trend analyses have been performed on all data series using the Mann- Kendall test. The frequency distributions of warm/cold days and very/extremely wet days have been examined using percentile indices. Results of the hydrological analysis showed that a significant increase in the mean temperature is considered over all time scales in the study area. The occurrence of warm days in both winter and summer has a significant increase while the occurrence of cold days in both seasons showed a similar proportion of significant decrease. These results give evidence that the winter becomes warmer and the summer becomes hotter. Results of the precipitation analysis give evidence on a significant increase in winter precipitation while the increases in summer and the annual precipitation were statistically insignificant. The number of consecutive dry days displayed decreasing tendencies in winter while there is no indication of statistically significant change in the summer. Analysis of very & extremely wet days showed that the main identified trends are an increase of the very wet days in the winter. For the inflow analysis, the results showed that there is a significant increase in winter inflow while the increases in summer and annual inflow were found to be statistically insignificant. Correlation calculations, which have been applied to the data series, showed that variations of streamflow from year to year were much more strongly related to precipitation changes than to temperature changes; this is corresponding to actual common results in hydrological research.