Changes in extreme precipitation events in the Zambezi River basins based on CORDEX-CORE models, Part II: Future projections under 1.5, 2.0, and 3.0 degrees C global warming levels

This study examines the potential implications of 1.5, 2.0, and 3.0 degrees C global warming levels (GWLs) on the austral summer (November-March) extreme precipitation indices over the Zambezi River basin (ZRB) relative to the control period (1971-2000). We computed extreme precipitation based on daily data from observations and the Coordinated Regional Downscaling Experiment (CORDEX)-Coordinated Output for Regional Evaluations (CORE) multi-model ensemble mean (ENSMean). First, we evaluated the performance of the CORDEX-CORE ENSMean in simulating extreme precipitation based on six indices; the number of rainy days (RR1), simple daily intensity index (SDII), maximum consecutive wet days (CWD), maximum consecutive dry days (CDD), heavy precipitation days (R10), and very heavy precipitation days (R20). The results indicate that the CORDEX-CORE ENSMean can simulate the spatial distributions of extreme precipitation over the ZRB. However, CORDEX-CORE largely overestimates the magnitudes of RR1 and CWD. The projected changes show a decrease in RR1, CWD, and R10 under all GWLs, with a robust and pronounced decrease under 3.0 degrees C GWL. In contrast, CDD and SDII are projected to increase under all GWLs, with a robust and pronounced increase in CDD under 3.0 degrees C GWL. The regionally averaged changes show that the median values of CWD, RR1, and R10 (SDII and CDD) are projected to decrease (increase) under all GWLs over the ZRB and sub-basins. The probability density function (PDF) shows negative (positive) shifts in the mean of CWD, RR1, and R10 (SDII and CDD) over the ZRB and sub-basins under all GWLs. In contrast, R20 is projected to increase (decrease) over most of the western (eastern) ZRB under all GWLs. Assessing the implications of an additional 0.5 and 1.5 degrees C (1.0 degrees C) warming to 1.5 degrees C (2.0 degrees C) GWL shows that limiting GWL to 1.5 degrees C would restrict the future exposure of the ZRB to extreme precipitation.