Changes and Variability in rainfall onset, cessation and length of rainy season in the IGAD region of Eastern Africa

Omay, Paulino Omoj; Muthama, Nzioka John; Oludhe, Christopher; Kinama, J.M.; Artan, Guleid; Atheru, Zachary

doi:10.21203/rs.3.rs-2313664/v1

Cited by 2 publications

(8 citation statements)

References 47 publications

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“…Onset and cessation dates of two main seasons (MAM and SOND) were determined using appropriate definitions modified from scientists (Sivakumar 1988;Omay et al 2022). Mann-Kendall (MK) statistical test was employed show trends in both seasonal, annual rainfall, as well as in maximum and minimum temperature.…”

Section: Discussionmentioning

confidence: 99%

“…Deficit rainfall and drier conditions are observed during the years 2000-2007 across all the stations as revealed by the downward standardized anomaly. The second main rainfall season over Southwestern Uganda occurs during the southward movement of the ITCZ which happens around September to December (Ngarukiyimana et al 2018;Nicholson 2018;Omay et al 2022). It is also not directly possible to suggest from the anomalies that rainfall is increasing or decreasing over the region as mixed results of increase and decrease in rainfall were revealed.…”

Section: Relationships Between Rainfall Pet and Temperature Variablesmentioning

confidence: 97%

“…The rainfall cessation dates (RCDs) is determined when Water Balance (WB) falls below 5 mm in 7 consecutive days in the last month of the expected season (May and December) for the first and second season respectively. The Potential Evapotranspiration (PET) and Water Balance (WB) criteria is commonly used in determining RCDs (Omay et al, 2022)…”

Section: Onset (Start) and The Cessation (End) Of The Rainy Seasonmentioning

confidence: 99%

“…The Onset (start) and the cessation (end) of the rainy season were calculated based on the modified definition used by scientists (Sivakumar 1988;Omay et al 2022), which considers the influence of the occurrence of the Inter-Tropical Convergence Zone (ITCZ) as the governing force in rainfall formation within the Tropics and the principal amounts of rainfall that must be received during a stated period and the dry spell that must not follow. First, the threshold for rainy days (RD) were defined as having rainfall amount equal to 0.85 mm and dry day (DD) is when rainfall is less than 0.85 mm based on the recommendation that the accumulation can improve on soil moisture and temperature modification (Abera et al, 2018).…”

Section: Onset (Start) and The Cessation (End) Of The Rainy Seasonmentioning

confidence: 99%

“…The annual rainfall ranged from 737.8 mm to 1664.6 mm recorded at Mbarara and Bushenyi station respectively. The March-May (MAM) rainfall season coincides with the northward movement of the intertropical convergence zone (ITCZ) over East Africa(Ngarukiyimana et al, 2018;Nicholson, 2018;Omay et al 2022). Rainfall variability over Uganda has been widely discussed(Nicholson 2017;Jury 2018;Ngoma et al 2021;Obubu et al 2021).…”

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confidence: 99%

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Patterns of Rainfall and Temperature and their Relationships with Potential Evapotranspiration rates over recent years (1981-2022) in Southwestern Uganda, East Africa.

Ojara,

Babaousmail,

Aribo

et al. 2023

Preprint

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Uganda in East Africa is experiencing highly variable rainfall that is exacerbated by temperatures warming at faster rates. This study analyzed rainfall and temperature patterns in comparison with the potential evaporation transpiration rates (PET) for southwestern Uganda for varying period from 1981-2022. For rainfall onset date (OD), threshold of 0.85 mm for a rainy day, rainfall of 20 mm accumulated over 5 days with at least 3 rain days and dry spell not exceeding 9 days in the next 30 days were used. The rainfall cessation dates (RCDs) is determined when Water Balance (WB) falls below 5 mm in 7 days in the last month of the expected season (May and December) for the first and second season respectively. Standardized rainfall anomaly was utilized to show seasonal and annual rainfall variability. Pearson’s correlation (r) coefficient was used to show the relationship between weather variables (rainfall, temperature) and PET at five rainfall stations. Results showed highly varied onset and cessation dates for March-May (MAM) seasonal rainfall compared to those of September-December (SOND). Results further revealed statistically significantly increasing trends in both maximum and minimum temperatures across the region, with the highest rate of increase of maximum temperature of 0.70oC and 0.65oC for minimum temperature per decade respectively. Moreover, the maximum temperature and PET showed strong positive correlation coefficient (r) that ranged from 0.82 to 0.90 across the regions, which likely contributes to excess evaporation from the surfaces, soil moisture deficits that negatively affect plants biomass production, low crop yields and food insecurity. We recommend water management and conservation practices such as mulching, zero tillage, planting drought-resistant crops, and using affordable irrigation systems during period of water deficit.

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Section: Discussionmentioning

confidence: 99%

Section: Relationships Between Rainfall Pet and Temperature Variablesmentioning

confidence: 97%

Section: Onset (Start) and The Cessation (End) Of The Rainy Seasonmentioning

confidence: 99%

Section: Onset (Start) and The Cessation (End) Of The Rainy Seasonmentioning

confidence: 99%

mentioning

confidence: 99%

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Patterns of Rainfall and Temperature and their Relationships with Potential Evapotranspiration rates over recent years (1981-2022) in Southwestern Uganda, East Africa.

Ojara,

Babaousmail,

Aribo

et al. 2023

Preprint

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Observed changes in wet days and dry spells over the IGAD region of eastern Africa

Omay,

Muthama,

Oludhe

et al. 2023

Sci Rep

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Changes in wet and dry patterns have an impact on rain-fed agriculture, crop productivity, and food security in Eastern Africa. The purpose of this research is to look into the changes in wet days and dry periods within the Intergovernmental Authority on Development (IGAD) region. Climate Hazards Group Infrared Precipitation with Station Data (CHIRPS) and Multi Models Ensembles (MME) of 10 historical simulations and projections from Coupled Model Intercomparison Project (CMIP6) models were employed as the data source. Several statistical approaches, as well as wet and dry spell thresholds, were used to calculate patterns of change in wet and dry spells on a decadal (10-year), 20, 30, and 41-year time scale. The results show the region exhibits decrease a decrease in the number of wet days and protracted dry spells in the 1980s, followed by an extraordinary (exceptional) increase in wet days in the subsequent decades (2011–2020) during March–May (MAM), June–September (JJAS), and October-December (OND). In Kenya, Somalia, southeastern Ethiopia, Eritrea, and Djibouti, the probability of surpassing 7, 14, 21, 28 days (1, 2, 3, 4 spells) was less than 5%. Furthermore, floods in 1997, 2018, 2019, and 2020, as well as droughts in 1983, 1984, 1985, and 2021, were triggered by an increase or decrease in the number of wet days and dry spells over most of the region. The number of wet days is projected to decrease by 10–20% during the MAM season across Sudan, South Sudan, and central and northern Ethiopia, JJAS is projected to increase by 30–50% across central and northern Sudan. However, during the OND season, increases are projected over Uganda, Ethiopia, and Kenya under three Shared Socioeconomic Pathways (SSP1-2.6, SSP2-4.5, and SSP5-8.5) scenarios. These findings contributed to the advancement of scientific knowledge in the IGAD region, as well as decision-making, food security, and the development of adaptation and mitigation strategies. We encourage rain-fed agriculture, crop variety planning, and irrigation supplement.

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Changes and Variability in rainfall onset, cessation and length of rainy season in the IGAD region of Eastern Africa

Cited by 2 publications

References 47 publications

Patterns of Rainfall and Temperature and their Relationships with Potential Evapotranspiration rates over recent years (1981-2022) in Southwestern Uganda, East Africa.

Patterns of Rainfall and Temperature and their Relationships with Potential Evapotranspiration rates over recent years (1981-2022) in Southwestern Uganda, East Africa.

Observed changes in wet days and dry spells over the IGAD region of eastern Africa

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