3.1 Changes and Variability in Rainfall Onset Dates
The spatial patterns of mean state of RODs over eight IGAD member states in Eastern Africa are presented in Fig. 2. The four seasons namely MAM, JJA, SON and DJF are discussed. The mean RODs for MAM season show that the progression dates occurred from the southwestern to northeastern in March and May respectively. The earliest onset date occurred in the first week to fourth week of March over most parts of southern and central districts of Uganda, highlands of western and Nyanza regions in Kenya and southern Nation’s zone in south-western Ethiopia. Most parts of coastal, north-eastern and central Kenya, southern and central parts of South Sudan, southern and central Somalia, southern, central and north-eastern Ethiopia, north-eastern Uganda observed earliest rainfall onset date in the first week to third week of April (Fig. 2a). By the first week of June to second week of July, most parts of South Sudan, Ethiopia, southern parts of Sudan and northern Uganda have fully met rainfall onset thresholds and criteria, while southeastern Ethiopia, most parts of Somalia and Kenya except highlands of western and coast experiencing the dry conditions (dry season) during JJA season (Fig. 2b). Similarly, Djibouti, north-eastern Ethiopia, most parts of Eritrea and central Sudan observed the earliest rainfall onset date in August. By the first week of October, there were no indicators of rainfall activities in Djibouti, Eritrea, central and northern Sudan, north-eastern Ethiopia and north Somalia. However, the short rains onset dates predominate over most parts of Kenya, southeastern Ethiopia, southern Somalia by the second week of October (Fig. 2c). The DJF are dry months over Sudan, South Sudan, northwestern and central Ethiopia, Djibouti and Somali (Fig. 2d). Furthermore, the Lake Victoria basin shows continuation of rainfall onset throughout the MAM, JJA, SON and DJF seasons. In other words, the rainfall total of 20mm over 5 days with at least 3 rain days and dry spell not exceeding 7 days in the next 21 days criteria are met from March to November. The RODs patterns suggested, the progression during MAM and OND coincided with movement of The Intertropical Convergence Zone (ITCZ) near the equator as reported by Camberlin & Okoola, (2003). The advance and retreat patterns of onset over southern, central and northern parts of Kenya, southeastern Ethiopia, central Somalia during MAM, JJA and SON seasons confirmed the bimodal rainfall patterns. These could promote planting and harvest of food crops twice a year, which will enhance food supply, increase food availability and reduction in rainfall related postharvest losses.
Figure 3 shows the spatial patterns of the mean state of variability in RODs patterns for MAM, JJAS and OND seasons. The results show that variability in RODs over the IGAD region varies within seasons and geographical locations, however, the variability is generally less than 40% across the four seasons (MAM, JJA and SON and DJF). The highest variability (20–30%) during MAM season was recorded over Shewa and Wollo zones in central, Afar zone2 and zone 4 of northern Ethiopia, Kapoeta east county in Eastern Equatoria of South Sudan, Turkana, scattered areas in central and coastal counties in Kenya (Fig. 3a). Similarly, the highest variability ranges between 20–35% during JJA season recorded over southern and western districts in Uganda, highlands of western and Nyanza region in Kenya, Eastern Equatoria in southeastern South Sudan, while western and southwestern parts of South Sudan, highlands of central and western Ethiopia zones recorded lowest variability ranges between 1–5% (Fig. 3b). Furthermore, OND season recorded lowest variability ranges between 1–10% over most parts of counties in South Sudan and southern parts of Sudan, Amhara zones in western Ethiopia, while rift Valley in Kenya, Karamoja region in northeastern Uganda, scattered areas in southern parts of Ethiopia recorded highest variability ranges between 20–30% (Fig. 3c). The DJF season recorded highest variability ranges between 24–35% over most parts of Uganda, Nyanza counties and southern parts of Kenya, southwestern Ethiopia (Fig. 3d). The DJF is dry season over most parts of the IGAD region, therefore, RODs variability criteria are not met over Sudan, Djibouti, Eritrea, Somalia, ASALs in Kenya. The RODs variability patterns seem to suggest that low/high variability in the mean state of RODs is linked to rainfall intensity, timing of main rainy season, aridity of climate conditions and closer areas to water bodies.
The changes in spatial patterns of mean RODs in last four decades (1981–1990,1991–2000,2001–2010 and 2011–2020), average of 40 years (1981–2020) and differences between current 20 year (2001–2020) and previous 20 years (1981–2000) compared to climatology (1981–2010) are presented in Fig. 4 columns one to six respectively. The patterns are assessments of whether on average, a certain place is experiencing a delayed onset (positive values) represented with brown colors or early onset dates (negative values) in green colors. The results show delayed RODs over South Sudan and Uganda in 1980s; most parts of Ethiopia, Uganda, Somalia and Kenya in 1990s and 2000s; while last decade (2011–2020) observed early ROD over most parts of the region during MAM and JJA seasons. The delayed onset in the 1980s over Sudan, South Sudan and Ethiopia suggested the contribution of intra-seasonal characteristics in devastating droughts which happened 1983–1985. In addition, the delayed MAM RODs results are consistent with decline in total rainfall trend from the 1980s to late 2000s as reported by researchers as Long Rains of Eastern Africa Paradox. The early RODs in recent years (2011–2020) may explain the increase or recovery in rainfall trend especially. The impacts of opposite signals (delayed and early) onset dates in 1980s,1990s and 2000s compared to 2010s indicated early RODs dominated the average patterns of all 40 years (1981–2020) over most parts of Kenya, southeastern Ethiopia, central Somalia during MAM and most parts of Uganda, and highlands of western and Nyanza regions in Kenya and eastern and southern parts of South Sudan. The fluctuation in mean onset anomalies during past four decades detected 14–21 days (approximately of 2–3 weeks) delayed RODs over zones around Addis Ababa and southern Amhara region in central Ethiopia, coastal counties of Kwale, Mombasa, Kilifi and Lamu, counties in central and Turkana and Marsbit in north-eastern Kenya, Jubbada, Gedo and Bay districts in Somalia and early onset dates detected over sporadic parts in southern and central South Sudan, sub-zones in Somali region of southeastern Ethiopia, districts in central Somalia and southern Uganda during long rain period of MAM season (Fig. 4a-f). The JJA season RODs observed a delayed 7–14 days (1–2 weeks) over northern and southern Kordofan region in Sudan, and early RODs of 7–21 days (1–3 week) observed over much parts of central Equatoria, Jonglei and upper Nile states in South Sudan, sporadic parts of Uganda, western Darfour, Kordofan and White Nile states in western and southern parts of Sudan (Fig. 4m-r). The SON season, observed 7–14 days early RODs over central Equatoria and Jonglei states in southern and central parts of South Sudan, most districts southern and central Uganda, Tana River and Isiolo counties, Nyanza region and highlands of western Kenya, Jubbada Hoose, Buaala and Jubbada Dhexe districts in southern Somalia, while delayed onset over southern Oromia region in Ethiopia (Fig. 4m-r). The criteria of RODs are not met over Sudan, Eritrea, Djibouti, Somalia, northern and eastern Ethiopia, South Sudan, Semi-arid counties in northeastern and northern Kenya during DJF season (Fig. 4s-x).
The changes in spatial patterns of mean variability in RODs during the past four decades are presented in Fig. 5a-x. The areas with an increase in variability (positive values) in brown colors or decreasing in onset dates (negative values) in green colors. The increase in variability observed in the 1980s over most parts of South Sudan, Ethiopia, southern and central Uganda during MAM, most parts of South Sudan, southern parts of Sudan during JJA season. In 1990 to late 2000s, the decrease in variability was observed over most parts of the region during MAM and JJA seasons. Comparing departure of patterns of 1981–1990,1990s,2000s from climatology, the increase (5–10%) variability in RODs is observed over most parts of Ethiopia, southern parts of Uganda, and decreases over most parts of Kenya, northern Uganda and southern Somalia during MAM rainy season (Fig. 5a-f). The JJA season recorded widespread decrease in RODs variability over most parts of South Sudan, central Sudan, highlands of central and northern Ethiopia, while southwestern Ethiopia observed increase (< 5%) in variability (Fig. 10g-l). The SON short rain recorded an increase in variability over northeastern Kenya, southern Somalia, southwestern Ethiopia especially the Southern Nations, Nationalities, and Peoples' Region (Fig. 5m-r). The last decade (2011–2020) observed lowest variability in RODs, therefore the trend of rainfall shows recovery and more wet conditions. The 5–20% decrease in variability observed in 2011–2020 and increase in variability ranges between 5–15% in early 1980s across all MAM, JJA, SON and DJF seasons neutralized the changes and reduced variability in RODs to less than 5% on average of 1981–2020 (Fig. 5e-w). No changes in variability during DJF season because most parts of IGAD region are dry climatology (Fig. 5s-x).
3.2. Changes and Variability in Rainfall Cessation Dates
Figure 6a-d illustrates the spatial pattern of MAM, JJA, SON and DJF mean RCDs, the results revealed that the earliest mean cessation dates for MAM season occurred from 26 April, 3rd May and 17 May over lower eastern and northern Kenya, Southeastern Ethiopia and most parts of Somalia respectively (Fig. 6a). The JJA season showed mean cessation occurred from 1st June over southern, northeastern and northern Kenya, central and northern Somalia as confirmation of perceived dry season over most parts of Kenya and Somalia. Similarly, the rainy season which starts from June and July over most parts of northern sector of IGAD region shows signs of cessation from 3rd August over most parts of central Sudan, northeastern Ethiopia, western Eritrea and most parts of Djibouti. in addition, no cessation criteria met as rainfall of the boreal summer continued over South Sudan and central and northern Ethiopia, long rain continued over highlands of western Kenya, most parts of Uganda up to the end of November (Fig. 6b). The Arid and Semi-Arid (ASALs)areas in Kenya, central Somalia, south-eastern Ethiopia already experienced rainfall cessation by 10 June as the beginning of dry season which continues to end of September. However, SON season shows the ceased rainfall patterns over most parts of Kenya and Somalia, Somali region of Ethiopia started again in October and continued to end of November (Fig. 6c). The cessation occurred fully from 1st of December over most parts of region during DJF with exception of Lake Victoria basin sides in Kenya and Uganda and southwestern Ethiopia while rainy season continued up to 5th of January over highlands of western and Nyanza region in Kenya and southern parts of Uganda (Fig. 6d). Moreover, the dry conditions which occurred in DJF season over most parts of IGAD member states continued in MAM, JJA and SON seasons over extreme northern parts of Sudan, which are not considered as cessation dates because these areas are dry Climatology. Similarly, no significant signals of rainfall cessation occurred over highlands of western Kenya, most parts of Uganda and Ethiopia during MAM, JJAS and SON seasons. These areas favored a conducive environment for rain-fed agriculture from March to November, unlike ASALs areas in Somalia, Kenya, southeastern and northeastern Ethiopia, where food insecurity and drought emergencies are stories of days exacerbated by initial conditions of long cessation of JJA and DJF rainfall over these areas (Fig. 6b,6d).
Figure 7a-d shows the spatial patterns of the mean state of variability in RCDs for MAM, JJAS and OND seasons. During MAM, JJAS and OND seasons, it is observed that RCDs variability ranges between 5–40%. The highest variability ranges (between 30–40%) is observed over southern parts of South Darfour, South Kordofan in Sudan, Nyanza counties of lake Victoria in Kenya during MAM season (Fig. 7a), sub-counties of El renk, Melut and Maban in Upper Nile states in northeastern parts of South Sudan, white and Blue Nile, Khartoum and Nile states in Sudan, Afar, Tigray and Wdllo zones in northern and central Ethiopia during JJAS season (Fig. 7b), Mudug in central Somalia Red seas costal parts of Sudan and Eritrea during SON season (Fig. 7c) and central zones of Shewa and Addis Ababa in central Ethiopia during DJF season (Fig. 7d). The lowest variability in RCDs ranging between (1–10%) observed over Wajir and Mandera counties in Eastern and northeastern Kenya, Gedo and Bakol districts in southwestern Somalia during MAM season, Somali region of Ethiopia, Mudug, Nugaal and Bari districts in central and northern Somalia, Kajado, Ukumbani region, Isiolo, Wajir, Marsabit and Mandera counties in Kenya during JJA season, most parts of South Sudan and Sudan states and counties during OND, while Kabale,Rukengiri, Masaka and Lake Victoria side in Uganda, lower and Upper eastern counties of Tana river and Wajir, coast counties of Mombasa, Kilifi and Lamu in Kenya during DJF season. It is also clear that the OND season observed lower variability (5–15%) in RCDs compared to MAM and JJAS seasons over South Sudan and Sudan.
Figure 8 shows the spatial patterns of changes in mean RCDs. The changes or shifts in RCDs are assessed by comparing the four decades (1980s,1990s,2000s and 2011s), average of 40 years and current 20 years (2001–2020) compared with the past 20 years (1981–2000). The results show the late onset patterns contributed to drought conditions over southern parts of Sudan, central Equatoria and northern Bar el gazal state in South Sudan in 2000s during MAM, South Sudan, Sudan and Ethiopia in 1980s during JJA season. Comparing the 2001–2010,2011–2020 with 1981–1990, 1991–2000, the results show the current years recorded a shift or delay of 7–14 days in mean cessation dates over northern upper Nile state in northern parts of South Sudan, Turkana region of northwestern Kenya, Jebel Marra(Marra Mountains) in western Sudan, sporadic parts in northern Somalia, central and northwestern Ethiopia, while earliest or faster RCDs over central Equatoria and Bahr el Ghazal region of South Sudan(Fig. 8a-f). The JJA season experienced 7–21 days delayed cessation dates over most parts of Khartoum and river Nile states in Sudan, Lake and Unity states in South Sudan, Arua and Moyo districts in northern Uganda, Afar sub-zone in northeastern Ethiopia, while early cessation observed over Kordofan and white Nile states in Sudan, Bushenyi, Kabarole and Luwero districts of south westerns and central Uganda (Fig. 8g-l). Similarly, OND season experienced 14–21 days delayed cessation over Maridi and Yei sub-counties in southeastern South Sudan, Afder zones in Ethiopia, Galguduuo and Mudug districts in central Somalia (Fig. 8m-r), while central and south Tigray, south and north Wdlo and dire Dawa zones in central and northern Ethiopia observed 14–21 days early cessation dates (Fig. 8s-x).
The changes in variability of Rainfall Cessation Dates (RCDs) during the MAM, JJA, SON and DJF seasons show an increases in variability(beween5-15%) over Marrah Mountain in western Sudan, Aweil and Warrap states in northern parts of South Sudan, Turkana and Tana river sub-county in Kenya, sporadic parts in southern and central Uganda, while decrease in variability(between 5–15%) observed over Nebbi districts and other sporadic parts in central and southwestern districts of Uganda, while decreasing in variability range between 5–15% over Turkan and Marsabit counties in Kenya northern and northern Kenya, Galguduud and Mudug districts of Somalia, Gonder districts in Amhara region in Ethiopia(Fig. 9a-f). Moreover, the JJA season shows the decrease in RCDs variability (10–20%) observed western Equatoria, eastern and western Lakes states, Wau, Raja, Aweil, Bentiu sub-counties in South Sudan, squall line of west Darfour, northern Kordofan, Khartoum in central parts, Kasalla and Qadaref in eastern parts of Sudan, Gonder and Gojam zones in Ethiopia (Fig. 9g-l). However, the SON season observed and a decreased variability of RCDs over most parts of Moyo and Gulu districts of northern region, central districts of Apac, Lira, Soroti and Kyoga in Central Uganda, Yei and Yambio sub-counties in western Equatoria and southern Kapeata County in South Sudan, Marsabit and central parts of Taita Taveta county in Kenya, southern parts of Afder zone in southeastern Ethiopia, Galguduud and Mudug districts in Somalia (Fig. 9m-r). The DJF season shows an increase in Variability of cessation over Turkana central and Tana River sub-county in Kenya, while an increased variability over northern parts of Marsabit in Kenya, northern Afar, southern Afder and Shabelle and Shrile sub-zone of northeastern Ethiopia (Fig. 9s-x).
3.3. Changes and Variability in Length of Rainy Season
The spatial patterns of mean LRS, mean number of rainy days between onset and cessation of rain dates are presented in Fig. 10 for four seasons. The results revealed that most parts of Uganda recorded the highest rainy days (60–80 days) during MAM season, however, Arid and Semi- areas in Djibouti, Eritrea, northern Somalia, everywhere in Sudan, central and northern parts of South Sudan, western and northern Ethiopia received LRS between lowest rainy days ranged between 1 and 20-days (Fig. 10a). The JJA, which is main rain-fed agriculture activities over South Sudan, Sudan and Ethiopia, the season is significantly longer over western Equatoria and western Bahr el Ghazal states in South Sudan, highlands of Amhara region in western and central Ethiopia with length of rainy days exceeding 80 days (Fig. 10b). The northern Uganda districts, highlands of western and Nyanza counties in Kenya, south-eastern and north-eastern parts of South Sudan, eastern and north-eastern Ethiopia and southern parts of Sudan recorded rainy days ranging between 30 to 70 days during SON season (Fig. 10c). During the DJF season (Fig. 10d), which is dry over most parts of the region, revealed that all districts in southern parts of Uganda recorded highest rainy days of 50 to 70 days while most of counties in coast and Nyanza in Kenya, central and northern Uganda observed 20–50 days mean LRS (Fig. 10d). The overall patterns of LRS shows Arid and semi-arid counties in Kenya, everywhere Sudan, South Sudan, Eritrea and Djibouti, central and Somalia are dry climatologically as central and northern Sudan during MAM and OND seasons. The determination of LRS failed over extremes northern parts of Sudan all the way from January to December, ASALs in southern and northern Kenya, southeastern Ethiopia, southwestern Uganda and most parts of Somalia during JJA and SON seasons due to variation in RODs and RCDs which leads in some cases to differences of 1–40 days as a result shortage of rainy days between identified RODs and failed RCDs criteria.
The spatial patterns of mean state of variability in Length of Rainy Season (LRS) presented in Fig. 11. The low variability (< 15%) in LRS observed over Arid and semi-arid lands (ASALs) and counties of Marsabit, Wajir, Tana river, Garissa and Kitui in Kenya, all districts of southern and central Somalia, Raja, Aweil, Warrap, Unity and Upper Nile states in South Sudan, while southern nations and most parts of northern Oromia of Ethiopia, districts of central and northern Uganda, western Equatoria sub-counties of Yei, Maridi, Mundri and Kapoeta in eastern Equatoria of South Sudan(Fig. 11a). The higher variability (> 35%) in LRS observed in south Darfour, South Kordofan, White Nile and Blue Nile states in Sudan, central Equatoria, Jonglei and Upper Nile states in South Sudan and Most parts of districts in central and northern Uganda, while western Equatoria in South Sudan and highlands of western Ethiopia experienced lower variability during JJA (figure (11 b). The SON season experienced highest variability over sporadic parts of central districts in Uganda, western Ethiopia and southern Somalia (Fig. 11c). The results show clearly, the region with high rainfall intensity has lower LRS variability compared to Arid and semi-arid. The patterns of variability in LRS not captured well over dry areas due to failed and inconsistent timing of rainfall onset and cessation dates.
Figure 12 present the spatial patterns of changes in LRS on decadal and seasonl time scale. The increase of 7–14 days in LRS observed over Korahe and Dollo sub-zones of Somali region in southeastern Ethiopia, Galguduud and Mudug districts of central Somalia, Yambio county in western Equatoria State of south-western South Sudan, Ntungamo, Bushenyi and Mbarara districts of south-western Uganda and decrease of 7–14 days experienced over isolated parts in Kenya, Tororo and Mbale districts of western Uganda, Jimma and Shewa zone and southern Nations region of Ethiopia in the recent years(2000s and 2011s) compared to previous decades (Fig. 12a-f), however, the LRS for JJA season became longer with 14–21 days over many parts in central Equatoria, Jonglei and Unity states in South Sudan, central Ethiopia, Arua,Moyo, northern parts of Gulu, Kigum districts of northern Uganda (Fig. 12g-l). In addition, the SON became longer with 12–21 days over central Equatoria and Jonglei states in South Sudan and most parts of districts in southern, central and northern Uganda (Fig. 12m-r). Furthermore, the DJF season became very short with 14–28 days over all districts of south-western and western Uganda, zones in south-western Ethiopia, while the season extended with 7–14 days over Kajado county in Kenya (Fig. 12s-x).
The change in the Length of Rainfall Season (LRS) variability for MAM, JJA, SON and DJF seasons presented in Fig. 13. The highest increased variability observed over South Sudan and Ethiopia in 1998s Fig. 13a-s, while highest decreased observed in 2011–2020(Fig. 13d-v). The average of variability of in 40 year (1981–2020) stands at 1–5% due to lower variability in 2000s and 2011s compared to 1980s and 1990s (Fig. 13e-w). the difference between current 20 years(2011–2020) and previous 20 years(1981–2000) shows the is decrease of -5 to -20% in mean state of variability over most parts of Wollo and Shewa sub-zone of eastern Amhara region, Borena, Liben, Afder, Gode, Shabelle, Korahe and Dollo sub-zones of Somali region of southeastern Ethiopia, Mudug and Nugaal districts of Somalia during MAM (Fig. 13a-f), similarly, the a decreased variability of -5 to -20% experienced over Raja, Aweil, Warrap and Unity, Yei, Maridi, and Mundri sub-counties in northern and southwestern parts of South Sudan during JJA season (Fig. 13g-l),while an increase in Variability of 10 to 20% experienced over sporadic parts in southern nation zone in southwestern Ethiopia, highland of western and Mount Kenya in SON (Fig. 13m-r) and most parts of districts in Uganda during DJF season(Fig. 13s-x). The lowest variability in LRS associated with increased trend (more wet years), while highest variability coincided with decreased in trend (more dry years).
3.4 Temporal variation in onset, cessation dates and Length of Rainy Season
The patterns of RODs, RCDs and RCDs averaged at each state in Sudan, districts in Uganda, counties in Kenya and South Sudan local administrative levels presented in Fig. 14. The results show yearly cyclic variation in patterns of RODs, RCDs and LRS, with early onset dates in March over Uganda and Kenya, April -May over Ethiopia, and June -July over South Sudan and Sudan. The progression onset northward coincided with months and movement of ITCS fluctuation. By end of August and with retreat of movement of ITCS southward, the northern sector of IGAD countries such as Sudan observed beginning of rainfall cessation dates in September, October, November and December over Sudan, South Sudan, Ethiopia, Kenya and Uganda respectively. The bio-modal rainfall regime patterns are not represented in RODs and RCD over Highlands of western Kenya and most parts of Uganda. These imply that the rainfall activity starts from March-to November over Kitale and Arua sub-region. These situations promoted the longer mean length of rainy season over western Kenya and most parts of Uganda to a range of 200–260 days (7–9 months), which favor better conditions for agricultural activities three times a year, which is better chances for agriculture production and improved food security. The northern parts of the region, especially Sudan and northern parts of South Sudan, the LRS not exceeding 150 days (3 months) in most cases in Sudan, 150–269 days (5–6 months) in Ethiopia. This is clear proof and impacts of unimodal patterns of rainfall over Sudan, Ethiopia and northern parts of South Sudan, which promote the one season crop production and harvest.
Inter-annual variability of onset and cessation dates, and Length of Rainy Season (1981–2021) over five potential agricultural production areas in the IGAD region presented in Fig. 15. The results shows the rains began in second week of March in Arua, April in Kitale and Robe, June in Elrenk and El gadaref(Fig. 15a), the cessation of rainfall occurred in third week of September in El Gadaref, first week of October in El renk, third week of November to first week of December over Robe, Kitale and Arua (Fig. 15c). The LRS longer over Arua(240–260 days), Kitale(220–240 days), Robe(180–210), 90–120 days over El renk and El Gadaref ((Fig. 15e). The anomaly results (Fig. 15b-f) have shown that during The longer/shorten in LRS directly linked to early/late onset and cessation, these clearly could be seen clearly in Arua in Uganda, where the RODs anomalies show the highest five years delayed onset are 2009 and 2019 (24 days delayed up to 9-Apr), 2007(27 days delayed up to 13-April), 1983 and 2008 (35 days, delayed up to 21-Apr ), while highest five years observed earliest dates are 1987(-25 days occurred earlier by 20-February), 1993 and 2010(-29 days occurred earlier by 17-February),1988 and 2017(-30 days occurred earlier by 16-February).The delayed rainfall cessation observed in 2020(17 days), 1993 and 2013(18 days), 1989(21 days) and 2007(23days), while earliest cessation observed in 1992(-5 days), 2017(-6 days),2008(-7 days), 1990(-22 days), 2002(-66 day). The LRS shorten by 55 days in 2002 due to 66 days early cessation, shorten by 42 in 2008 due to 35 delayed onset and 7 days early cessation, shorten by 35 in 1983 due to 35-day delayed onset, shorten by 26 days in 2009 due to 24 delayed onset and 2 days early cessation, shorten by22 days in 2021 due to 19 days delayed onset and 3 days early cessation. However, 1997,2012 and 2019 exceeded criteria due to cessation factor. No RCDs dates observed in 1997, 2012 and 2019 because of extra-ordinary rainfall continued from January to December. The RODs over Kitale, Kenya show that the season shorten by 129, 69,66,55,52,40 days in 2021,2018,2007,1994,2014 and 1983 respectively due to early cessation, while 40,43,47,59 and 69 days increase in LRS observed in 1995,2019,2016,2017 and 1989 due to early cessation and delayed cessation. For example, in 2021 as one driest year, although the RODs started early by 9 days from the mean the RODs which is 13 April, however, the season shortened by 121 dues to 139 days early cessation. Robe in Ethiopia, the failed RODs during MAM and JJA seasons in 1999,2002,2008 and 2016, leads to unclear LRS, Similarly, 118, 95, 62,53,32 days shorten LRS in 2021,2011,1995,1989 and 2015 attributed to early cessation and late onset. furthermore, the 48, 38,35,31 days early RODs in 2016,2017,1991,1997 and 1993 over El renk, South Sudan, resulted in increased LRS, while late onset in 2020,1981,2000,2015,1982 and 1984 resulted in shorten of LRS by at least 18–34 days. The 71 days early cessation and 4 days late onset in 2021 resulted in 75 days reduction in LRS. The 30 days delayed RCDs in 2018 with 7 days early RODs, 22 days delayed RCDs and 16 days early RODs in 2019 over El Gadaref in Sudan, resulted in increased LRS with 37 days in 2018 and 38 days in 2019. In general, the RODs, RCDs and LRS patterns of five sub-regions examined here show historical successful farming and crops harvest cash and food crops one time in Sudan and northern parts of South Sudan, 1–2 times in central Ethiopia, 2–3 times farming and crops harvest happens in highlands of western Kenya and northern Uganda. In other words, the onset, cessation and length of season patterns are greater asserts and potential agricultural capacity and if utilized fully, then the food insecurity and food exports could be issue and story of past in the IGAD region.