Drivers and subseasonal predictability of heavy rainfall in Equatorial East Africa and relationship with flood risk

MacLeod, David A. ORCID: https://orcid.org/0000-0001-5504-6450, Dankers, Rutger, Graham, Richard, Guigma, Kiswendsida, Jenkins, Luke, Todd, Martin C., Kiptum, Augustine, Kilavi, Mary, Njogu, Andrew and Mwangi, Emmah 2021. Drivers and subseasonal predictability of heavy rainfall in Equatorial East Africa and relationship with flood risk. Journal of Hydrometeorology 22 (4) , 887–903. 10.1175/JHM-D-20-0211.1

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Abstract

Equatorial East Africa (EEA) suffers from significant flood risks. These can be mitigated with preemptive action; however, currently available early warnings are limited to a few days’ lead time. Extending warnings using subseasonal climate forecasts could open a window for more extensive preparedness activity. However, before these forecasts can be used, the basis of their skill and relevance for flood risk must be established. Here we demonstrate that subseasonal forecasts are particularly skillful over EEA. Forecasts can skillfully anticipate weekly upper-quintile rainfall within a season, at lead times of 2 weeks and beyond. We demonstrate the link between the Madden–Julian oscillation (MJO) and extreme rainfall events in the region, and confirm that leading forecast models accurately represent the EEA teleconnection to the MJO. The relevance of weekly rainfall totals for fluvial flood risk in the region is investigated using a long record of streamflow from the Nzoia River in western Kenya. Both heavy rainfall and high antecedent rainfall conditions are identified as key drivers of flood risk, with upper-quintile weekly rainfall shown to skillfully discriminate flood events. We additionally evaluate GloFAS global flood forecasts for the Nzoia basin. Though these are able to anticipate some flooding events with several weeks lead time, analysis suggests action based on these would result in a false alarm more than 50% of the time. Overall, these results build on the scientific evidence base that supports the use of subseasonal forecasts in EEA, and activities to advance their use are discussed.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Earth and Environmental Sciences
Publisher:	American Meteorological Society
ISSN:	1525-755X
Date of Acceptance:	18 January 2021
Last Modified:	08 Nov 2024 16:16
URI:	https://orca.cardiff.ac.uk/id/eprint/173294

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