Analysis of the occurrence, robustness and characteristics of abrupt changes in streamflow time series under future climate change

Understanding and quantifying the effects of future climate change is currently one of the most pressing challenges in science and of high relevance for society. Most future climate change studies consider changes between arbitrary time periods. We specify these time periods by splitting climate-change impacted streamflow time series at instances of highest change, by using statistical tests. We used the daily streamflow from 2000 to 2099 simulated from a comprehensive ensemble of the EURO-CORDEX climate change data in three basins across Germany (Treene, lowland; Kinzig, mid-range mountain; and Ammer, pre-alpine). Change points in each basin were detected by using six change point tests. The robustness of changes was analyzed with a bootstrapping procedure. A set of 32 Indicators of Hydrologic Alteration (IHA) was used to examine characteristics of hydrologic changes in the simulated discharge time series between pre- and post-change-point period in absolute change and in deviation of the Range of Variability Approach (RVA). The results show that the occurrence of change points due to climate change is spread throughout the decades, but strongly clustered in the current and upcoming decade. The selection of global and regional climate models impacts the occurrence of change points to a greater extent than the choice of greenhouse gas emission scenarios and bias correction method. The highest significant alteration of IHA occurs in the lowland-, less in the alpine- and least in the mid-range mountain catchment. The transition of hydrologic regimes to an alternative state after the identified change points is likely to occur because the majority of indicators move out of the current state of RVA. We further notice ecoregion-dependent changes in summer discharges and extreme low flows, which increase in the lowland and decrease in the pre-alpine catchment. This may have a detrimental effect on local aquatic communities. We conclude that the combined analysis of simulated climate scenarios, change points and IHA enables a better interpretability of potential future hydrological changes both in timing and severity and provides an early warning signal of changes for climate change mitigation.