Abstract
Abstract. 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.
Highlights
Human influence has been documented in several parts of the water cycle: atmospheric water vapour (e.g. Willett et al, 2007; Santer et al, 2007), land precipitation (e.g. Zhang et al, 2007), or land evapotranspiration (e.g. Douville et al, 2013)
Of global continental runoff, Labat et al (2004) documented an increasing global runoff at the end of the 20th century compared to the beginning
Our study investigates the large-scale runoff change over the late 20th and 21st century, as simulated by 14 Coupled Model Intercomparison Project 5 (CMIP5)
Summary
Human influence has been documented in several parts of the water cycle: atmospheric water vapour (e.g. Willett et al, 2007; Santer et al, 2007), land precipitation (e.g. Zhang et al, 2007), or land evapotranspiration (e.g. Douville et al, 2013). Based on data from 925 rivers, corresponding to 80 % of global runoff, Dai et al (2009) show a slight decrease in global runoff over the second half of 20th century. This discrepancy can be explained by the differences either in the number of gauging stations used, in the period of investigation, or in the method used to fill the gaps. Both studies were using some reconstructions (meaning gap filling) in order to provide a more comprehensive spatio-temporal coverage
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