Analysis of variability and trends in rainfall over northern Ethiopia

Kiros, Gebremedhin; Shetty, Amba; Nandagiri, Lakshman

doi:10.1007/s12517-016-2471-1

Cited by 74 publications

(36 citation statements)

References 27 publications

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“…No major anomalies were seen over the central and southwestern regions of the country. In the third quarter (Figures (e) and (f); 1997–2005), the northern part of the country rebounded to wet conditions and some dry anomalies were evident in the far south, while in the most recent period (Figures (g) and (h); 2006–2014) dry conditions dominated over much of the country, with the exception of the far eastern region, which is consistent with previous studies (Conway et al, ; Bewket and Conway, ; Viste et al, ; Zeleke et al, ; Kiros et al, ). The two indices show only small differences in frequency and intensity over some regions due to differences in their formulation.…”

Section: Resultssupporting

confidence: 62%

“…The second dominant spring TPC of SPI3 explains the dipole trend patterns mainly over southeastern and northwestern Ethiopia (Figures (a) and (c)), while the summer season TPC2 is more relevant over the northern and eastern regions (Figures (b) and (d)). The temporal evolution of SPI3‐TPC2 during the summer season shows a dominant dry anomaly during the first decade of the study period and a wet anomaly in the middle decade, which is in agreement with earlier studies (Giannini et al, ; Bewket and Conway, ; Williams et al, ; Kiros et al, ). In general, low‐frequency high‐power signals dominate in both observational SPI3‐TPC2s and a discussion of this periodicity is found in the next section.…”

Section: Resultsmentioning

confidence: 94%

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Trend and periodicity of drought over Ethiopia

Zeleke

Giorgi

Diro

et al. 2017

Intl Journal of Climatology

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We analyse rainfall extreme events in Ethiopia from 1979 to 2014 using the standardized precipitation index (SPI) and the Palmer drought severity index (PDSI) derived from both station and satellite‐based observation data sets. Causal mechanisms of extreme events are also discussed. Trend principal component (TPC), regression, wavelet and composite analyses are used to investigate the trend, frequency and inter/intra‐annual variability of extreme events (dryness/wetness of rainfall) over Ethiopia. All methods of analysis, applied to monthly mean data, show that the north and northwest regions of Ethiopia experienced frequent and more severe drought conditions centred at the year 1983/1984, a recovery in the middle of the study period and a return to moderate dry events in recent years. For the southern and southwestern regions, drought conditions have become more frequent and intense during the study period, particularly since ∼1997. Analysis at the seasonal scale shows that the observed drying trend over the south and southwestern regions of the country is dominated by the spring season, which corresponds to the season of maximum precipitation. No observed long‐term trend is found in the north, northwestern and central mountainous regions of the country. This contrast reflects differing climate sensitivities of these different portions of the country: the observed periodicity of dryness/wetness over the northern regions corresponds largely to ENSO variability in both the spring and summer rainy seasons, while the drying trend in the south and southwest is associated with Atlantic Ocean warming and sea surface temperature gradients across the western Pacific Ocean.

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Section: Resultssupporting

confidence: 62%

Section: Resultsmentioning

confidence: 94%

Trend and periodicity of drought over Ethiopia

Zeleke

Giorgi

Diro

et al. 2017

Intl Journal of Climatology

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“…During this same period a reduction in lake levels and river flow in the Lake Naivasha Basin occurred, but commensurate trends in rainfall could not be found [ Odongo et al ., ]. Studies of rainfall in northern Ethiopia [ Conway et al ., ; Kiros et al ., ] found trends in northern Ethiopia to be generally insignificant and spatially diverse. Schmocker et al .…”

Section: Recent Trends and Extreme Eventsmentioning

confidence: 99%

Climate and climatic variability of rainfall over eastern Africa

Nicholson

2017

Reviews of Geophysics

547

425

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This review examines several aspects of the climate of eastern Africa. The climatic commonality throughout the region is the frequent occurrence of drought severe enough to incapacitate the population. Because of recent droughts and evidence of disastrous, long‐term climatic change, the region has become a major focus of meteorological research. This review covers six relevant topics: climatic regionalization, seasonal cycle, intraseasonal variability, interannual variability, recent trends, and seasonal forecasting. What emerges is a markedly different view of the factors modulating rainfall, the dynamics associated with the seasons, and the character of teleconnections within the region and the interrelationships between the various rainy seasons. Some of the most important points are the following. (1) The paradigm of two rainy seasons resulting from the biannual equatorial passage of the Intertropical Convergence Zone is inadequate. (2) The “long rains” should not be treated as a single season, as character, causal factors, and teleconnections are markedly different in each month. (3) The long rains have been declining continuously in recent decades. (4) The Madden‐Julian Oscillation has emerged as a factor in interannual and intraseasonal variability, but the relative strength of Pacific and Indian Ocean anomalies plays a major role in the downward trend. (5) Factors governing the short rains are nonstationary. (6) Droughts have become longer and more intense and tend to continue across rainy seasons, and their causes are not adequately understood. (7) Atmospheric variables provide more reliable seasonal forecasts than the factors traditionally considered in forecast models, such as sea surface temperatures and El Niño–Southern Oscillation.

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“…2a). This is 24 attributed to the complex local topography, which alters proximity to the sources of moist air and seasonal movementsof the ITCZ (Van der Entet al, 2010; Kiros et al, 2016).…”

mentioning

confidence: 99%

Comparison and validation of eight satellite rainfall products over the rugged topography of Tekeze-Atbara Basin at different spatial and temporal scales

Gebremicael

Mohamed

Zaag

et al. 2017

Preprint

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16Satellite rainfall products are considered important options for acquiring rainfall estimates in the absence of ground measurements. However, estimates from these products need to be 18 validated as their accuracy can be affected by geographical position, topography, and climate, as well as by the algorithms used to derive rainfall from satellite measurements. Eight Results show thatCHIRPS, TRMM,and RFEv2 performed well and wereable to capture the 26 rainfall measured by rain gauges. The BIASand correlation of these products were within ±25% and >0.5over different time steps.The remaining products poorly performed at daily 28 time step with higher BIAS (up to ±200%) and lower correlation (<0.5). CMORPH, PERSIANN, and ARCv2 were relatively better while CMAP and GPCP performed poorly 30 (r<0.4) in all conditions. The overall performance of all products was lower in the mountainous areas of the basin with station elevation>2500 m.a.s.l. Compared to the 32 lowlands, the BIAS at highlands increased by 35% whilst the correlation dropped by 28%. Underestimation and overestimation of rainfall dominated in the mountainous and lowland 34 areas, respectively.CMORPH and TRMM overestimated while the remaining products underestimated the rainfall at all spatiotemporal scales. CMAP, ARC2, and GPCP estimates 36 were the most affected by large underestimation. Unlike in temporal scale, the performance of the products did not show a uniform pattern with respect to spatial scale.Their performance 38 improved from point to aerial comparisons in the lowlandswhereas it slightly reduced athighland areas. Poor performance in the highlands contributed to a slightly lower

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Analysis of variability and trends in rainfall over northern Ethiopia

Cited by 74 publications

References 27 publications

Trend and periodicity of drought over Ethiopia

Trend and periodicity of drought over Ethiopia

Climate and climatic variability of rainfall over eastern Africa

Comparison and validation of eight satellite rainfall products over the rugged topography of Tekeze-Atbara Basin at different spatial and temporal scales

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