Search

The drivers of precipitation variability in the Ethiopian Highlands are complex, and they have considerable impact on the local rural economy of the region. While interannual variability has been studied extensively, relatively less study has focused on intra-seasonal variability in precipitation, even though this variability can be critical for agricultural activities. In this study, we examine the impacts of the Boreal Summer Intra-Seasonal Oscillation (BSISO) on precipitation variability in the Upper Blue Nile Basin (UBNB) during the rainy season (June–September). In order to optimally capture Intra-seasonal variability, we developed a customized ISO index based on leading modes of the variability in the UBNB, and found that this index shares the general character of a standard BSISO index. Analyses performed with both the customized and standard BSISO indices show that a core convective region centered on the Indian Ocean propagates to the northwest, eventually exerting significant influence on Ethiopian rainfall. The primary mechanism of influence appears to be BSISO influence on both lower and upper level tropospheric wind fields over the western Indian Ocean that influence moisture flux, convergence, and convection in the study region. This includes BSISO modulation of the East Africa Low-Level Jet and the Tropical Easterly Jet. We also find that the BSISO influence on Ethiopia is consistent with a BSISO-associated Rossby wave signal, but the magnitude of the Rossby wave signal is small relative to other mechanisms of influence. [ABSTRACT FROM AUTHOR]

There is increasing concern that avoiding climate change impacts will require proactive adaptation, particularly for infrastructure systems with long lifespans. However, one challenge in adaptation is the uncertainty surrounding climate change projections generated by general circulation models (GCMs). This uncertainty has been addressed in different ways. For example, some researchers use ensembles of GCMs to generate probabilistic climate change projections, but these projections can be highly sensitive to assumptions about model independence and weighting schemes. Because of these issues, others argue that robustness-based approaches to climate adaptation are more appropriate, since they do not rely on a precise probabilistic representation of uncertainty. In this research, we present a new approach for characterizing climate change risks that leverages robust decision frameworks and probabilistic GCM ensembles. The scenario discovery process is used to search across a multi-dimensional space and identify climate scenarios most associated with system failure, and a Bayesian statistical model informed by GCM projections is then developed to estimate the probability of those scenarios. This provides an important advancement in that it can incorporate decision-relevant climate variables beyond mean temperature and precipitation and account for uncertainty in probabilistic estimates in a straightforward way. We also suggest several advancements building on prior approaches to Bayesian modeling of climate change projections to make them more broadly applicable. We demonstrate the methodology using proposed water resources infrastructure in Lake Tana, Ethiopia, where GCM disagreement on changes in future rainfall presents a major challenge for infrastructure planning. [ABSTRACT FROM AUTHOR]

Headwater streams in the highland regions of Ethiopia are exposed to severe human disturbances because of rapid population growth. Protection and management of headwater streams require the development of informative indices that can capture disturbance and assess streams water quality in highland regions. Therefore, we developed a multi-metric index based on macroinvertebrate communities, to assess the ecological condition of the headwater streams in the Ethiopian highlands. We reviewed 38 potential metrics, representing various aspects of the macroinvertebrate assemblages, and selected four of them [total family richness, Simpson index, percentage of shredder, and family richness of EOT (Ephemeroptera, Odonata, and Trichoptera)] as final core metrics. A trisection inter-quartile range system was applied to derive scores for each core metric at impaired and reference sites. The macroinvertebrate multi-metric index (MMI) distinguished well between impaired and reference stream sites and was negatively correlated with the degree of disturbance. The results suggest that the MMI is robust measure of disturbance and can be used as a sensitive tool for evaluating the ecological condition of headwater streams in Ethiopian highlands. [ABSTRACT FROM AUTHOR]

For at least four decades, archaeologists have identified irrigation as playing a potentially major role in the rise of Aksumite civilization. Based on a systematic survey covering the area between Aksum and Yeha (Ethiopia), Joseph Michels proposed that large-scale irrigation systems introduced from Southwest Arabia contributed to the rise of Yeha as a major center of Pre-Aksumite civilization. To evaluate spatial patterning of archaeological sites with respect to water availability, this paper reports on results from archaeological survey of a 100 km2 region surrounding Yeha conducted by the Southern Red Sea Archaeological Histories (SRSAH) Project from 2009 to 2016. The SRSAH Project recorded 84 sites dating from the Pre-Aksumite to the Post-Aksumite periods (c.800 BCE to 900 CE). No ancient irrigation systems were identified and results do not show a correlation between archaeological sites and water resources. This suggests that irrigation was less important than Michels contended and that rainfed agriculture, terraces, and small-scale irrigation comparable with practices evident in the region today were sufficient to sustain ancient populations. [ABSTRACT FROM AUTHOR]