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Anthropogenic warming of Western V sea surface temperatures contributed to East African drought. Extremely warm (FAR = I) Western V SST doubled the probability of drought, contributing to widespread food [...]

We studied the effects of upwelling on nutrient and phytoplankton dynamics in the pelagic and littoral zones of Lake Tanganyika near Kigoma, Tanzania. During the dry season of 2004, a rise in the thermocline and sudden drop in surface water temperatures indicated a substantial upwelling event. Increases in concentrations of nitrate, soluble reactive phosphorus, and silica in the surface waters occurred simultaneously after the temperature drop. Within days, chlorophyll a concentrations increased and remained elevated, while inorganic nutrient concentrations returned to preupwelling levels and organic nutrient concentrations peaked. We observed parallel temporal patterns of water temperature, nutrient concentrations, and phytoplankton chlorophyll in both the pelagic and the littoral zones, demonstrating that upwelling strongly affects the nearshore ecosystem as well as the pelagic zone. Concurrent records from 12 littoral sites indicated spatial variation in the timing, magnitude, and biological response to upwelling. There was no discernable latitudinal pattern in the timing of upwelling, suggesting that mixing did not result from a progressive wave. Our monitoring, as well as other multiyear studies, suggests that dry-season upwelling occurs during most years in northern Lake Tanganyika. The observed sensitivity of littoral nutrients and phytoplankton to upwelling suggests that reductions in upwelling due to global climate change could strongly affect the dynamics of the spectacular nearshore ecosystem of Lake Tanganyika, as has been proposed for the pelagic zone.

Mechanistic analyses of past climate change in the tropics have been hampered by the fragmentary or poorly dated nature of palaeoclimate data from key regions; but also by ambiguity about [...], External climate forcings-such as long-term changes in solar insolation--generate different climate responses in tropical and high latitude regions (1). Documenting the spatial and temporal variability of past climates is therefore critical for understanding how such forcings are translated into regional climate variability. In contrast to the data-rich middle and high latitudes, high-quality climate-proxy records from equatorial regions are relatively few (2-4), especially from regions experiencing the bimodal seasonal rainfall distribution associated with twice-annual passage of the Intertropical Convergence Zone. Here we present a continuous and well-resolved climate-proxy record of hydrological variability during the past 25,000 years from equatorial East Africa. Our results, based on complementary evidence from seismic-reflection stratigraphy and organic biomarker molecules in the sediment record of Lake Challa near Mount Kilimanjaro, reveal that monsoon rainfall in this region varied at half-precessional (~11,500-year) intervals in phase with orbitally controlled insolation forcing. The southeasterly and northeasterly monsoons that advect moisture from the western Indian Ocean were strengthened in alternation when the inter-hemispheric insolation gradient was at a maximum; dry conditions prevailed when neither monsoon was intensified and modest local March or September insolation weakened the rain season that followed. On sub-millennial timescales, the temporal pattern of hydrological change on the East African Equator bears clear high-northern-latitude signatures, but on the orbital timescale it mainly responded to low-latitude insolation forcing. Predominance of low-latitude climate processes in this monsoon region can be attributed to the low-latitude position of its continental regions of surface air flow convergence, and its relative isolation from the Atlantic Ocean, where prominent meridional overturning circulation more tightly couples low-latitude climate regimes to high-latitude boundary conditions.

Identifying the nature of the association between climate, environmental, socio-economic and political context and disease remains a major challenge, yet a better comprehension of the linkages is imperative if predictive models to guide public health responses are to be devised. Our understanding of the relationships could be improved through investigations of historical epidemics. In this paper we draw on a range of published and unpublished documents to explore the complex relationship between climate, environmental change and epidemic disease (re)emergence in East Africa, and Uganda in particular. This is a region which has experienced climate variability at a range of temporal and spatial scales, but which also has a long history of episodic epidemic disease. We focus on the late nineteenth and early twentieth centuries--a time of social, economic and political reordering in East Africa associated with European colonial intervention, but also a period which witnessed a variety of climatic, ecological and disease events. It will be argued that these developments coalesced, creating a set of spatially distinctive social and environmental conditions which fostered the emergence and prolongation of one of the most deadly episodes of disease in East African history, the sleeping sickness epidemic of c. 1900-20. KEY WORDS: Uganda, climate, sleeping sickness, missionary archives

In classical theory, species are assumed to achieve dominance through competitive exclusion, but if food resources are limiting, cross-habitat trophic subsidies could also underpin dominance. The impact of dominant species on community dynamics may depend on the energy base of population size. We report on an unusual, spatially subsidized population of a tropical, stream-dwelling crab that dominates the benthic fauna of a Kenyan stream. Diet and stable isotope analyses indicated that this crab is a true omnivore, with terrestrial subsidies dominating both plant and animal resources. Unusually, the animal prey included almost no aquatic invertebrates. Instead, a single species of ant constituted ~35% of the annual diet (stomach contents analysis) and up to 90% of assimilated nitrogen (estimates from stable isotope analysis). Ants may be pivotal to enabling crab dominance, and this crab may be largely disconnected from the local trophic network for its dietary needs. The paucity of other invertebrates in the stream community suggests that this super-dominant crab is a strong interactor that suppresses aquatic invertebrate populations. Common stabilizing attributes of spatially subsidized food webs (e.g., asynchronous prey availability, wide feeding niche, consumer migration) were absent from this system, and although apparently stable, it may be vulnerable to disturbance in the donor habitat. Key words: diet; East Africa; freshwater crabs; mixing model; Potamonautes; spatial subsidy; stable isotopes; stomach contents.

[1] The western branch of the East African Rift is composed of an arcuate succession of elongate asymmetric basins, which differ in terms of interaction geometry, fault architecture and kinematics, and patterns of uplift/subsidence and erosion/sedimentation. The basins are located within Proterozoic mobile belts at the edge of the strong Tanzanian craton; surface geology suggests that the geometry of these weak zones is an important parameter in controlling rift development and architecture, although other processes have been proposed. In this study, we use lithosphere-scale numerical models and crustal-scale analogue experiments to shed light on the relations between preexisting structures and rift architecture. Results illustrate that on a regional scale, rift localization within the mobile belts at the curved craton's western border results in an arcuate rift system, which implies that under a constant extensional stress field, part of the western branch experienced orthogonal extension and part oblique extension. Largest depocenters are predicted to form mostly orthogonal to the extension direction, and smaller depocenters will form along the oblique parts of the rift. The varying extension direction along the rift zone furthermore results in lengthwise varying rift asymmetry, segmentation characteristics, and border fault architecture (trend, length, and kinematics). Analogue models predict that discrete upper crustal fabrics may influence the location of accommodation zones and control the architecture of extension-related faults at a local scale. Models support that fabric reactivation is responsible for the oblique-slip kinematics on faults and for the development of Z-shaped or arcuate normal faults typically documented in nature. doi:10.1029/2006TC002086.

Operationalizing research and development (R&D) within a fluid continuum encompassing both understanding and application can be a daunting task. This paper presents a typology of distinct learning approaches designed to operationalize research-for-development. It summarizes lessons for achieving quality within each approach, and for their integration into a fluid continuum of theory and practice. A set of cases is presented to illustrate the critical importance of each learning approach and their integration in practice. The paper concludes with a discussion of implications for institutional arrangements and partnerships that may best enable the application of the approach within everyday R&D practice. Key words--action research, eastern Africa, research methods, natural resource management, research for development, agricultural research

We use the oxygen isotopic composition of tooth enamel from multiple mammalian taxa across eastern Africa to present a proxy for aridity. Here we report tooth enamel [[delta].sup.18]O values of 14 species from 18 locations and classify them according to their isotopic sensitivity to environmental aridity. The species are placed into two groups, evaporation sensitive (ES) and evaporation insensitive (EI). Tooth enamel [[delta].sup.18]O values of ES animals increase with aridity, whereas the tooth enamel [[delta].sup.18]O values of EI animals track local meteoric water [[delta].sup.18]O values, demonstrating that bioapatite [[delta].sup.18]O values of animals with different behaviors and physiologies record different aspects of the same environment. The enrichment between tooth enamel [[delta].sup.18]O values of ES and EI animals records the degree of [[delta].sup.18]O enrichment between evaporated water (ingested water or body water) and source water, which increases with environmental aridity. Recognition of the ES-EI distinction creates the opportunity to use the [[delta].sup.18]O composition of bioapatite as an index of terrestrial aridity. bioapatite | East Africa | oxygen-18 | mammals | water use

The incidence of malaria in the East African highlands has increased since the end of the 1970s. The role of climate change in the exacerbation of the disease has been controversial, and the specific influence of rising temperature (warming) has been highly debated following a previous study reporting no evidence to support a trend in temperature. We revisit this result using the same temperature data, now updated to the present from 1950 to 2002 for four high-altitude sites in East Africa where malaria has become a serious public health problem. With both nonparametric and parametric statistical analyses, we find evidence for a significant warming trend at all sites. To assess the biological significance of this trend, we drive a dynamical model for the population dynamics of the mosquito vector with the temperature time series and the corresponding detrended versions. This approach suggests that the observed temperature changes would be significantly amplified by the mosquito population dynamics with a difference in the biological response at least 1 order of magnitude larger than that in the environmental variable. Our results emphasize the importance of considering not just the statistical significance of climate trends but also their biological implications with dynamical models. amplification of temperature increase | climate change | vector-transmitted disease | mosquito population dynamics

Climates of equatorial East Africa and subtropical Southern Africa have varied inversely over long periods of time. The high-resolution [[delta].sup.18]O stalagmite record from Cold Air Cave in the Makapansgat valley in South Africa and a similar resolution lake-level record for Lake Naivasha in Kenya have been in anti-phase for much of the last thousand years. A similar relationship is evident in the twentieth century meteorological record. The changes in rainfall in the two regions on multi-decadal to centennial scales have influenced both settlement patterns and livelihoods of Iron Age agriculturalists. The resulting latitudinal gradient of change may have been a significant factor in promoting southward migration of Sotho-Tswana speaking people from equatorial East Africa during the first few centuries of the last millennium and earlier. This would have occurred at times when environments in the north were deteriorating and those to the south were ameliorating.

Mangroves of Eastern Africa offer a diverse resource that can benefit the economy while protecting coastal environments. The greatest challenges to such regions come from increased tree cutting, charcoal and fuelwood harvesting, prawn aquaculture and ecosystem fragility. Management projects in Tanzania, Mozambique, and Kenya have produced useful data.

Coastal zones of East African countries offer considerable potential for economic growth, and management programs in this region have had varied success. Projects that focus on biodiversity protection that neglect local development succeed for a short while only, yet projects that utilize local and national ownership are successful in the long term. Private enterprise is the most important single factor that drives change in this region.

Most estimates of the cooling of tropical land areas at the last glacial maximum (LGM) are incompatible (1) with the much smaller decrease in sea-surface temperatures ([is less than or [...], Carbon-isotope values of bulk organic matter from high-altitude lakes on Mount Kenya and Mount Elgon, East Africa, were 10 to 14 per mil higher during glacial times than they are today. Compound-specific isotope analyses of leaf waxes and algal biomarkers show that organisms possessing [CO.sub.2]-concentrating mechanisms, including [C.sub.4] grasses and freshwater algae, were primarily responsible for this large increase. Carbon limitation due to lower ambient [CO.sub.2] partial pressures had a significant impact on the distribution of forest on the tropical mountains, in addition to climate. Hence, tree line elevation should not be used to infer palaeotemperatures.

Chloroplast DNA restriction-site variation was surveyed among 40 accessions representing all 11 species of giant senecios (Dendrosenecio, Asteraceae) at all but one known location, plus three outgroup species. Remarkably little variation (only 9 variable sites out of roughly 1000 sites examined) was found among the 40 giant senecio accessions, yet as a group they differ significantly (at 18 sites) from Cineraria deltoidea, the closest known relative. This pattern indicates that the giant senecios underwent a recent dramatic radiation in eastern Africa and evolved from a relatively isolated lineage within the Senecioneae. Biogeographic interpretation of the molecular phylogeny suggests that the giant senecios originated high on Mt. Kilimanjaro, with subsequent dispersion to the Aberdares, Mt. Kenya, and the Cherangani Hills, followed by dispersion westward to the Ruwenzori Mountains, and then south to the Virunga Mountains, Mt. Kahuzi, and Mt. Muhi, but with dispersion back to Mt. Elgon. Geographic radiation was an important antecedent to the diversification in eastern Africa, which primarily involved repeated altitudinal radiation, both up and down the mountains, leading to morphological parallelism in both directions. In general, the plants on a given mountain are more closely related to each other than they are to plants on other mountains, and plants on nearby mountains are more closely related to each other than they are to plants on more distant mountains. The individual steps of the geographic radiation have occurred at various altitudes, some clearly the result of intermountain dispersal. The molecular evidence suggests that two species are extant ancestors to other species on the same or nearby mountains.

1. Between 1985 and 1991, bush encroachment was serious in Lake Manyara National Park, northern Tanzania. Shrub cover increased by c.20%. The increase was independent of initial (1985) shrub cover. 2. Since 1987 there has been a steep decline in the number of African elephant in the Park due to poaching. Elephant density decreased from about 6 km to the -2 to about 1 km to the -2. However, shrub establishment, as determined from counting tree-rings, preceded poaching. 3. Shrub establishment in two areas of the Park coincided with anthrax epidemics that drastically reduced the impala population. In the northern section of the Park this was in 1984, in the southern section in 1977. 4. The diameter increment of Acacia tortilis was 5.24 mm year to the -1, irrespective of the size of the trees. Size measurements indicated an even-aged stand of Acacia established in 1961, which coincided with another anthrax outbreak among impala. 5. Size measurements of old Acacia tortilis trees indicated another even-aged stand established at the end of the 1880s. The size of trees of this stand was not significantly different from a stand in Tarangire National Park, nor from a stand near Ndutu (on the boundary between Serengeti National Park and Ngorongoro Conservation Area), also northern Tanzania. All three stands are likely to have originated from bush establishment caused by the rinderpest pandemic at the end of the 1880s. 6. It is suggested that seedling establishment of Acacia is a rare event under the prevailing conditions of high browsing pressures by ungulates such as impala. Punctuated disturbances by epidemics among these ungulates create narrow windows for seedling establishment, which may explain the occurrence of even-aged stands.

Diatom assemblages, geochemistry and magnetic minerology of radio carbon dated sequences of sediments from Lake Magadi in the East African rift indicate large climatic changes. Records indicate an abrupt cooling phenomenon, interrupted in the last glacial period, at about 11,000 years before 1990s. The interrupting abrupt cooling period is known as Younger Dryas, which is identified in marine and ice-core records all over the world, especially in Europe. In some places, the climatic changes are recorded by the salinity of lakes and reduction in water levels.

Several analyses are conducted to explain the various effects of the droughts and land desertification practices on the Agricultural Drought Framework, which is observed in the semiarid East African regions. It is shown that an increase in the usage of rainwater can be extremely beneficial, as it can lead to better productivity and food security in the country.

The evidence on the climatic history of East Africa over the past two centuries comprises historical accounts of lake levels, observations and analyses of glacier variations, wind and current observations in the Indian Ocean, as well as raingauge measurements. East Africa experiences its rainy seasons in boreal spring and autumn, centered around April-May and October-November; the spring rains being more abundant and the autumn rains more variable. Rains tend to be abundant/deficient with slow/fast westerlies (UEQ) and Eastward Equatorial Jet (EEJ) in the upper hydrosphere of the equatorial Indian Ocean. A drastic climatic dislocation took place during the last two decades of the 19th century, manifest in a drop of lake levels, onset of glacier recession, and acceleration of UEQ and EEJ. The decades immediately preceding 1880 featured high lake stands, extensive glaciation, and slow UEQ and EEJ, as compared to the 20th century. The onset of glacier recession in East Africa after 1880 contrasts with a start of ice shrinkage in New Guinea and the Ecuadorian Andes around the middle of the 19th century. The regional circulation regime characterized by slow UEQ and EEJ in the decades prior to 1880 was conducive to extensive ice cover along with high lake stands in East Africa, and this may account for the onset of glacier recession much later than in the other mountain regions of the equatorial zone. The evolution of East African climate over the first half of the 19th century merits further exploration.

Variations in the temporal and spatial distribution of solar radiation caused by changes in Earth's orbit provide a partial explanation for observed long-term fluctuations in African lake levels. The understanding of causal links between insolation changes and lake-level fluctuations is essential for the design of models predicting future changes in the hydrological budgets and water supply in Africa. Here we present a record of climate change in East Africa between 175 and 60 ka. This time span includes the last interglacial (the Eemian, 130-117 ka), which may provide the closest analogue to the present interglacial. Assessments of the nature and timing of East African climate changes are based on lake-level fluctuations of Lake Naivasha (Kenya) inferred from sediment characteristics, diatom assemblages, and [sup.40]Ar/[sup.39]Ar dating. Our results show dramatic alternation between deep, freshwater and shallow, highly alkaline lake conditions. The Lake Naivasha record demonstrates that periods of increased humidity in East Africa mainly follow precessional insolation forcing in spring, causing more intense April-May rains every 23 k.y. Keywords: East Africa, lake sediments, Milankovitch, climate.

The regular 'polka-dot' arrangement of termite mounds in East Africa boosts ecosystem productivity, researchers say. Robert Pringle at Harvard University in Cambridge, Massachusetts, and his team found that plants grow [...]

On 12 August 1986, a deadly cloud of C[O.sub.2] and water mist was released from Lake Nyos, Cameroon, and killed more than 1700 people by asphyxiation as it spilled into [...]