Rainfall in the Horn of Africa Drylands and its impact on the Water Balance

Cocking, Katherine 2026. Rainfall in the Horn of Africa Drylands and its impact on the Water Balance. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

Drylands are water-limited environments highly vulnerable to climatic variability and change. In the Horn of Africa Drylands (HAD), increasing exposure to drought and flash flooding poses significant risks to agropastoral livelihoods that depend on seasonal rainfall. Despite this vulnerability, key uncertainties remain in how rainfall seasonality is locally expressed, how rainfall is organised into discrete events across seasons and aridity gradients, and how these rainfall characteristics translate into hydrological responses at regional scales. Rainfall gauge data is used to delineate local rainfall seasons, better reflecting the ground-based experience of rainfall. Further, a high-resolution gridded rainfall dataset is used to identify and characterise rainfall events across seasons and aridity classes. These rainfall events are compared with modelled soil moisture, discharge, and groundwater recharge generated using a dryland-tailored hydrological model. Results show that the long rains and short rains are now of comparable duration and magnitude, reflecting the decline in the – now recovering - long rains, alongside an increased intensification of the short rains. However, equivalence in seasonal totals does not imply equivalent hydrological reliability. The short rains are increasingly dominated by temporally and spatially concentrated rainfall events, while the long rains remain more vulnerable to drought. In the most arid regions, particularly north-eastern Somalia, extreme rainfall events associated with cyclones dominate seasonal rainfall when they make landfall. These systems are primarily a source of flood hazard rather than a reliable supply of groundwater recharge. Hydrological response across the HAD is controlled by antecedent conditions, rainfall organisation and basin connectivity rather than rainfall totals alone. This thesis demonstrates that hydrological controls previously identified in small dryland catchments also govern basin-scale responses across this large, data-poor region.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Schools > Earth and Environmental Sciences
Date of First Compliant Deposit:	18 August 2026
Last Modified:	18 Aug 2026 14:07
URI:	https://orca.cardiff.ac.uk/id/eprint/189056

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