Detection of global runoff changes: results from observations and CMIP5 experiments

This paper assesses the detectability of changes in global streamflow. First, a statistical detection method is applied to observed (no missing data which represent 42% of global discharge) and reconstructed (gaps are filled in order to cover a larger area and about 60% of global discharge) streamflow. Observations show no change over the 1958-1992 period. Further, an extension to 2004 over the same catchment areas using reconstructed data does not provide evidence of a significant change. Conversely, a significant change is found in reconstructed streamflow when a larger area is considered. These results suggest that changes in global streamflow are still unclear. Moreover, changes in streamflow as simulated by models from Coupled Model Intercomparison Project 5 (CMIP5) using the historic and future RCP 8.5 scenarios are investigated. Most CMIP5 models are found to simulate the climatological streamflow reasonably well, except for over South America and Africa. Change becomes significant between 2016 and 2040 for all but three models.