CMIP6-based Assessment of Anthropogenic influence on the 2015-19 Western Cape Drought

Abstract:

The 2015-19 cumulative precipitation over Western Cape was extremely low (a breaking record since 1901), which caused a multi-year drought and severe economic losses of six million residents. Is multi-year drought over Western Cape usual from the perspective of climate? Is there the anthropogenic influence on multi-year Western Cape droughts like the 2015-2019 drought? To answer these questions, we use the CMIP6 model simulations to assess the anthropogenic influence including the contribution of greenhouse gas-induced warming. The CMIP6 simulations include multiple ensemble runs (historical (44 ensemble members), natural-only (43), and greenhouse gas (37) runs) of seven climate models. We compute the duration of each drought using the SPI threshold values, -0.8 and 0.2, for drought onset and termination, respectively. Results of the CMIP6 model simulations suggest that greenhouse gas-induced warming would have increased the likelihood of multi-year Western Cape drought at least by a factor of two while the anthropogenic influence including anthropogenic aerosol effect is not statistically significant. Better understanding of the relative contribution of greenhouse gas-induced warming and anthropogenic aerosol effect is warrant for more reliable assessment of drought risk over Western Cape.