Future Changes in Global Runoff and Runoff Coefficient From CMIP6 Multi‐Model Simulation Under SSP1‐2.6 and SSP5‐8.5 Scenarios

• Published in: Earth's future Vol. 10; no. 12
• Main Authors: Wang, Aihui, Miao, Yue, Kong, Xianghui, Wu, Huan
• Format: Journal Article
• Language: English
• Published: Bognor Regis John Wiley & Sons, Inc 01.12.2022; Wiley
• Subjects: Climate change; CMIP6; Drought; Floods; Freshwater resources; Global warming; Hydrologic cycle; Hydrology; Modelling; multi‐model uncertainty; Precipitation; projection; River basins; Rivers; Runoff; Runoff coefficient; Simulation; Spatial distribution; total runoff; Vegetation; China
• ISSN: 2328-4277; 2328-4277
• DOI: 10.1029/2022EF002910

This paper assesses the performances of runoff (Ro) and runoff coefficient (α, the ratio of runoff to precipitation) simulations from 23 models during the historical period and then projects their future changes under the two emission scenarios (SSP1‐2.6 and SSP5‐8.5) in the Coupled Model Intercomparison Project. Compared with the UNH/GRDC Ro dataset (0.82 mm day−1), the multi‐model median (MME) Ro of 1995–2014 produces a comparable global mean magnitude (0.80 mm day−1), displays a similar spatial distribution of mean Ro, and also well captures the seasonal cycles at both global and basin scales. The global mean Ro of MME is projected to be increased by 0.01–0.02 mm day−1 (SSP1‐2.6) and 0.02–0.10 mm day−1 (SSP5‐8.5) during the twenty‐first century. Regional hotspots for strong increasing Ro appear across most areas of northern high latitudes, Africa, and southeastern Asia, with high inter‐model consistency. The global mean α is projected to be slightly decreased (−0.17 to −0.63%) except for the long‐term under the SSP5‐8.5 (0.26%). Although signs of changes in Ro vary with the river basins, periods, and scenarios, α in more than half (7 out of 12) river basins are projected to decrease. The uneven distributions of projected Ro changes over global land areas are related to the response of multiple hydroclimatic variables to the global warming. Given regions with inconstancy change signs of the projected precipitation, we speculate that changes in Ro are affected by more complicated hydroclimatic processes that warrant further investigations with physical‐based approaches. Plain Language Summary Evidence has indicated that the terrestrial hydrology would be changed unevenly over global land areas under a warmer climate. Runoff (Ro) is one of the key components of the land water budget and it represents the natural freshwater resource on the earth. This study assesses the historical simulation performances and then projects future changes in Ro and α (the ratio of runoff to precipitation) under two emission scenarios (i.e., SSP1‐2.6 and SSP5‐8.5) based on the simulations from 23 CMIP6 models. The results show that the multi‐model median Ro during the historical period is highly consistent with the reference dataset and captures the seasonal variation in most river basins. During the twenty‐first century, the multi‐model median of global mean Ro is overall projected to increase in the future and the α would slightly decrease except for the long‐term under the SSP5‐8.5. While signs and magnitudes of projection changes depend on regions and basins, those changes are more evident under higher warming levels. The uneven distributions of projected changes of Ro over global land areas are related to the response of other land surface hydrological variables to the global warming induced by anthropogenic emissions in climate models. Key Points The runoff (Ro) and runoff coefficient (α) in CMIP6 are assessed and their future changes are projected under two SSPs in global and basin scales The global mean magnitude, spatial pattern, and seasonal cycles over most river basins are well reproduced by multi‐model median Ro The global mean Ro (α) is projected to increase (decrease), but their projections vary with basins and scenarios