Evidence for new hydrological drought types: do regime changes lead to fewer or more droughts in monsoon and snow climates?

We normally see hydrological drought as a period of low streamflow and/or groundwater levels caused by a long lack of rainfall in the summer period, combined with high temperatures and high evaporation. But there are more mechanisms underlying hydrological drought development, which encouraged Van Loon and Van Lanen (2012) to define six hydrological drought types. In some of these types low temperatures play an important role in the development of hydrological drought through the lack of recharge to the groundwater system due to the accumulation of snow. From studying time series of hydrometeorological variables of catchments in cold climates and monsoon climates, we now found evidence for hydrological drought types that were not studied before. Analysis of drought events in selected catchments in Ethiopia showed that variability in the start of the monsoon leads to hydrological droughts that can last throughout the wet season. Analysis of drought events in rivers in high Northern latitudes showed that a lack of snowfall in the winter season leads to a drought during the snow melt period. This is crucial for water resources management, because the snow melt period is needed to fill up reservoirs. From recent climate research there is some confidence that global warming will lead to a regime change in both hydroclimatic regions. Snowmelt peaks are expected to be earlier and lower and the variability of the start of the monsoon will increase in the future. The consequence is that the hydrological drought types mentioned above will occur more often. This might cause serious problems as societies have adjusted to the occurrence of peak flow of a certain magnitude in a certain perio