Blake, George, Michaelides, Katerina, Kendon, Elizabeth, Cuthbert, Mark  ORCID: https://orcid.org/0000-0001-6721-022X and Singer, Michael Bliss ORCID: https://orcid.org/0000-0002-6899-2224
2025.
The impact of convection-permitting model rainfall on the dryland water balance.
Hydrology and Earth System Sciences
29
, pp. 7098-7125.
10.5194/hess-29-7093-2025
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Abstract
In drylands, rainfall is typically delivered during short-lived, localised convective storms, whose characteristics strongly influence how water is partitioned into different terrestrial stores. However, the rainfall data often used in modelling future projections of water resources is typically derived from climate models that are too coarse to represent convective processes occurring at scales smaller than the model grid. In this paper we quantify the impact of climate model representation of convection on the simulated water balance at four locations in the Horn of Africa: a humid site in the Ethiopian Highlands, a semi-arid site in southern Kenya, an arid site in eastern Ethiopia, and a hyper-arid site in northern Somalia. We benchmark a novel pan-Africa convection permitting climate model (CP4A) and its parameterised counterpart (P25) against high-resolution satellite-derived gridded datasets of rainfall (IMERG) and potential evapotranspiration (PET) (hPET). The comparison shows that explicitly resolving convection improves the representation of dryland rainfall characteristics, such as rainfall frequency, intensity, and the relative contribution of low vs. high-intensity rainfall to annual totals. We also demonstrate that convective representation can impact model PET, but differences are more muted relative to rainfall, and both CP4A/P25 can capture seasonal and diurnal PET dynamics. To establish how the impact of convective representation on rainfall characteristics can control hydrology, we used Hydrus 1-D to run one-dimensional vadose zone hydrological simulations at our four study sites, where Hydrus is driven by rainfall and PET from CP4A and P25 (and hPET). We find that the “drizzle” bias in P25 means that when rainfall is propagated through Hydrus, wetting fronts are confined to upper soil layers, resulting in higher evaporative losses, lower soil moisture, and lower bottom drainage in drylands. The improved representation of dryland rainfall characteristics in CP4A means that cumulative (in mm) surface runoff is up to ten times higher (over the ten-year simulation), bottom drainage (indicative of potential recharge) is up to 25 times higher, and soil moisture remains above the wilting point for longer compared to P25 Hydrus runs (despite simulating lower total rainfall and infiltration). Whereas at our humid site, water partitioning is less sensitive to rainfall characteristics and hydrological fluxes more closely follow annual rainfall totals. Our results demonstrate that dryland vadose zone hydrology is highly sensitive to the impact of convective representation on rainfall characteristics, and that studies focused on modelling future water resources using climate models that parameterise the average effects of convection risk misrepresenting societally relevant fluxes such as soil moisture, groundwater availability, and surface runoff.
| Item Type: | Article |
|---|---|
| Date Type: | Publication |
| Status: | Published |
| Schools: | Schools > Earth and Environmental Sciences |
| Publisher: | Copernicus Publications |
| ISSN: | 1607-7938 |
| Date of First Compliant Deposit: | 20 November 2025 |
| Date of Acceptance: | 7 November 2025 |
| Last Modified: | 17 Dec 2025 10:12 |
| URI: | https://orca.cardiff.ac.uk/id/eprint/182528 |
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