Was the 2020 Lake Victoria flooding linked to anthropogenic climate change? An event attribution study

Heavy rainfall in East Africa between late 2019 and mid 2020 caused devastating floods and landslides throughout the region. These rains drove the level of Lake Victoria to a record-breaking maximum in the second half of May 2020, when the lake reached its highest level since measurements began in 1948. The high lake levels and consequent shoreline flooding triggered international attention, with media sources proposing a causal link with climate change. However, a formal attribution study identifying the possible role of anthropogenic climate change in increasing the likelihood of such record-breaking water levels has not been carried out so far.

We present an attribution study that estimates how anthropogenic climate change influenced the likelihood of observing the rate of change in Lake Victoria’s level that was recorded in 2020. To this end, we reconstruct the record-high lake level using an observational water balance model for Lake Victoria. We first investigate the influence of the different water balance terms on the resulting lake level. Then, we apply the water balance model in a probabilistic event attribution framework by forcing it with historical and natural forcing only (hist-nat) bias-adjusted precipitation from six Earth system models from the Coupled Model Intercomparison Project phase 6 (CMIP6) ensemble, as made available through the Inter-Sectoral Impact Model Intercomparison Project phase 3b (ISIMIP3b). The study contributes to a better understanding of impacts caused by climate and weather extremes in the Greater Horn of Africa by disentangling the role of anthropogenic climate change and natural internal variability in a high-impact flood event.