Locally defined seasonal rainfall characteristics within the Horn of Africa drylands from rain gauge observations

Katherine Cocking aSchool of Earth and Environmental Sciences, Cardiff University, Cardiff, CF10 3AT, United Kingdom

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Michael Bliss Singer aSchool of Earth and Environmental Sciences, Cardiff University, Cardiff, CF10 3AT, United Kingdom
bEarth Research Institute, University of California Santa Barbara, USA
cWater Research Institute, Cardiff University, Cardiff, CF10 3AX, United Kingdom

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David MacLeod aSchool of Earth and Environmental Sciences, Cardiff University, Cardiff, CF10 3AT, United Kingdom

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Mark O. Cuthbert aSchool of Earth and Environmental Sciences, Cardiff University, Cardiff, CF10 3AT, United Kingdom
cWater Research Institute, Cardiff University, Cardiff, CF10 3AX, United Kingdom

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Rafael Rosolem dSchool of Geographical Sciences, University of Bristol, Bristol, BS8 1SS, United Kingdom

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Flavian Muthusi eFood and Agriculture Organization of the United Nations, Somalia Water and Land Information Management (SWALIM) Project Office, P.O. Box 30470-00100, Nairobi, Kenya

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Paolo Paron eFood and Agriculture Organization of the United Nations, Somalia Water and Land Information Management (SWALIM) Project Office, P.O. Box 30470-00100, Nairobi, Kenya

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Joyce Kimutai fKenya Meteorological Department (KMD), Nairobi 00100 GPO, Kenya

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Phillip Omondi gIGAD Climate Prediction and Application Centre (ICPAC), P.O. Box 10304-00100, Nairobi, Kenya

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Ahmed Mohamed Hassan hSomali Ministry of Energy and Water Resources, Bondhere District, Mogadishu, Somalia

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Asaminew Teshome iEthiopian Meteorological Institute, P.O.BOX 1090, Addis Ababa, Ethiopia

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Katerina Michaelides bEarth Research Institute, University of California Santa Barbara, USA
dSchool of Geographical Sciences, University of Bristol, Bristol, BS8 1SS, United Kingdom

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Abstract

Seasonal rainfall is critical to lives and livelihoods within the Horn of Africa drylands (HAD), but it is highly variable in space and time. The HAD rainfall seasons are typically defined as March-April-May (MAM) and October-November-December (OND). However, these three-month periods are only generalised definitions of seasonality across the HAD, and local experience of rainfall may depart from these substantially. Here, we use daily rain gauge data with a duration of at least 10 years from 69 stations across Kenya, Somalia, and Ethiopia to locally delineate key rainfall seasons. By calculating local seasonal rainfall timings, totals, and extremes we obtain more accurate estimates of the spatial variability in rainfall delivery across the HAD, as well as climatological patterns. Results show high spatial variability in season onset, cessation, and length across the region, indicating that a homogenous classification of rainfall seasons across the HAD (e.g. MAM and OND) is inadequate for representing local rainfall characteristics. Our results show that the ‘long rains’ season is not significantly longer than ‘short rains’ season over the period of study. This could be related to the previously documented decline of the ‘long rains’ rainfall totals over recent decades. Several rainfall metrics also vary spatially between seasons, and the rainfall on the most extreme days can accumulate to double the mean seasonal total. The locally defined rainfall seasons better capture the bulk of the rainfall during the season, giving improved characterisation of rainfall metrics, consistent with the aim of a better understanding of rainfall impacts on local communities.

© 2024 American Meteorological Society. This is an Author Accepted Manuscript distributed under the terms of the default AMS reuse license. For information regarding reuse and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).

Corresponding authors: Katherine Cocking, CockingK@Cardiff.ac.uk and Michael Singer, bliss@eri.ucsb.edu

Abstract

Seasonal rainfall is critical to lives and livelihoods within the Horn of Africa drylands (HAD), but it is highly variable in space and time. The HAD rainfall seasons are typically defined as March-April-May (MAM) and October-November-December (OND). However, these three-month periods are only generalised definitions of seasonality across the HAD, and local experience of rainfall may depart from these substantially. Here, we use daily rain gauge data with a duration of at least 10 years from 69 stations across Kenya, Somalia, and Ethiopia to locally delineate key rainfall seasons. By calculating local seasonal rainfall timings, totals, and extremes we obtain more accurate estimates of the spatial variability in rainfall delivery across the HAD, as well as climatological patterns. Results show high spatial variability in season onset, cessation, and length across the region, indicating that a homogenous classification of rainfall seasons across the HAD (e.g. MAM and OND) is inadequate for representing local rainfall characteristics. Our results show that the ‘long rains’ season is not significantly longer than ‘short rains’ season over the period of study. This could be related to the previously documented decline of the ‘long rains’ rainfall totals over recent decades. Several rainfall metrics also vary spatially between seasons, and the rainfall on the most extreme days can accumulate to double the mean seasonal total. The locally defined rainfall seasons better capture the bulk of the rainfall during the season, giving improved characterisation of rainfall metrics, consistent with the aim of a better understanding of rainfall impacts on local communities.

© 2024 American Meteorological Society. This is an Author Accepted Manuscript distributed under the terms of the default AMS reuse license. For information regarding reuse and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).

Corresponding authors: Katherine Cocking, CockingK@Cardiff.ac.uk and Michael Singer, bliss@eri.ucsb.edu
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