Statistics in Climate Variability, Dry Spells, and Implications for Local Livelihoods in Semiarid Regions of Tanzania: The Way Forward

This research article published by Springer Nature Switzerland AG., 2016The Dodoma municipality, a semiarid region of Tanzania, is characterized by limited rains, lack of surface water sources, and a high frequency of extreme climate events, particularly droughts and floods. These disadvantaged settings make it vital to study long-term climate trends for signals and patterns of shifting climate regimes for integrity of local livelihood support systems, especially agriculture, recharge, and pasture developments. The area has fairly long climate records, some of which extend to about 100 years. This chapter presents detailed analysis of six climate parameters, namely, rainfall (R), atmospheric relative humidity (ARH), temperature (T), sunshine (S), radiation (RD), wind speed (WS), and evaporation (ET) records from three meteorological stations, namely, Hombolo Agrovet (HMS), Dodoma (DMS), and Makutupora (MMS). The parameters above were statistically and graphically analyzed in four time scales, namely, monthly, seasonal, annual, and time series. The results showed the area is characterized by slight spatial variability in R intensity and T magnitudes with HMS having higher T and rains than DMS and MMS. Further there are clear decreasing trends in ARH and R, while T, S, WS, ET, and RD parameters showed characteristic increasing trends. Thus, except for extreme rain events, particularly El Niño-Southern Oscillations (ENSO), which are characterized by abnormally increased R magnitudes, R intensity has generally decreased in which over the past 91 years, there has been a net R decrease of 54 mm out of annual rains of only about 550 mm/year. Compared to annual time step, however, monthly step reveals more silent features like shortening of the growing seasons. Similarly, the frequency and severity of drought episodes are increasing, all of which adversely impact agriculture, pasture development, and recharge. Similarly, disappearance of R in some months, shifting seasonality, and general declining R intensities and magnitudes are clearly observed. May rains have largely disappeared, while in January, February, March, and April rains have decreased and hence shortening the length of growing season. On the other hand, clear warming trends and declining ARH were also observed. Yet the area is marked by cyclic wetting and drying events where in recent years, drying cycles have been prolonged. However, there is more variability in the mean minimum temperature (MMT) than in mean maximum temperatures (MMMT) in all stations. Between 1961 and 2012, there has been a net 1.13 and 0.778 °C increases in annual MMT and MMMT in DMS, respectively. Like for R trends, silent features are more evident under monthly T data than annual time steps where it is clear that June had the highest increase in MMT (1.54 °C), while April had the least (only 0.662 °C). However, both trends have the potential of affecting major livelihood support systems particularly agriculture and pasture development, but also local groundwater recharge that is vital for the local economy. The study area therefore offers a rare opportunity to understand and manage changing climate regimes including on extent of dry spells and longevity of growing seasons. The changing climate trends consequently call for significant adaptation and mitigation strategies so that local activities adjust to the current climate regimes particularly on onset and end of rainfall seasons and recharge fluxes

Nutrients’ distribution and their impact on Pangani River Basin’s ecosystem – Tanzania

Research Articles published by Taylor & Francis GroupSurface and groundwater from Pangani River Basin (PRB) were sampled in dry and wet seasons, analysed for dissolved organic and inorganic nutrients (N, P, Si and Urea). There was spatial and seasonal nutrients’ variability, with enrichment of dissolved inorganic fractions accumulated from natural and anthropogenic sources. Silicates increased in dry season, whereas nitrate, ammonium, phosphate and urea increased in wet season; except for phosphate, other nutrients increased from upstream to the river mouth. High rate of chemical weathering possibly due to tropical climate and volcanic rocks has caused PRB to have higher concentration of silicates than average freshwater African Rivers. Contribution of PRB to the coast of Indian Ocean was 2.6, 39.0, 45.2, 67.4 and 5444.8 (mol/km2/yr) for nitrite, phosphate, ammonium, nitrate and silicates, respectively, which were lower than most of the tropical rivers in the world. Levels of nitrate and phosphate for most of the stations were higher than recommended levels for aquatic ecosystem health. Furthermore, observed hypoxia condition in some stations threatens aquatic life. This study recommends the efficient use of fertilizers to reduce nutrients’ uptake into the lakes and rivers so as to meet the recommended level for aquatic and human health

Sources and distribution of organic matter in northern Patagonia fjords, Chile (~44–47° S) : a multi–tracer approach for carbon cycling assessment

Author Posting. © The Author(s), 2010. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Continental Shelf Research 31 (2011): 315-329, doi:10.1016/j.csr.2010.05.013.We investigated the provenance of organic matter in the inner fjord area of northern Patagonia, Chile (~44–47° S), by studying the elemental (organic carbon, total nitrogen), isotopic (δ13C, δ15N), and biomarker (n–alkanoic acids from vascular plant waxes) composition of surface sediments as well as local marine and terrestrial organic matter. Average end–member values of N/C, δ13C, and δ15N from organic matter were 0.127 ± 0.010, –19.8 ± 0.3‰, and 9.9 ± 0.5‰ for autochthonous (marine) sources and 0.040 ± 0.018, –29.3 ± 2.1‰, 0.2 ± 3.0‰ for allochthonous (terrestrial) sources. Using a mixing equation based on these two end–members, we calculated the relative contribution of marine and terrestrial organic carbon from the open ocean to the heads of fjords close to river outlets. The input of marine–derived organic carbon varied widely and accounted for 13 to 96% (average 61%) of the organic carbon pool of surface sediments. Integrated regional calculations for the inner fjord system of northern Patagonia, which encompasses an area of ~ 4,280 km2, suggest that carbon accumulation may account for between 2.3 and 7.8 x 104 ton C yr–1. This represents a storage capacity of marine–derived carbon between 1.8 and 6.2 x 104 tons yr–1, which corresponds to an assimilation rate of CO2 by marine photosynthesis between 0.06 and 0.23 x 106 tons yr–1. This rate suggests that the entire fjord system of Patagonia, which covers an area of ~ 240,000 km2, may represent a potentially important region for the global burial of marine organic matter and the sequestration of atmospheric CO2.J. Sepúlveda was funded by a M.S. scholarship from the Graduate School at UDEC and by Fundación Andes through the Woods Hole Oceanographic Institution (WHOI)/UDEC agreement during a research visit at WHOI. This research was funded by the Ministerio de Hacienda de Chile and the Comité Oceanográfico Nacional (CONA) through the CIMAR–7 FIORDO Program (Grant C7F 01–10 to SP), CONICYT/NSF Grant 2001–120, Fundación Andes–Chile, and the Center for Oceanographic Research in the eastern South Pacific (COPAS) and COPAS Sur– Austral (PFB–31/2007)

Stable carbon and nitrogen isotope composition of organic matter in sediments of the Oman Margin

Stable isotopic compositions of carbon and nitrogen and organic carbon content of sediments ranging from the Pliocene to the Pleistocene-Holocene in age from the Oman Margin (ODP Sites 724 and 725) are reported. In general, the organic carbon content is greater than 2% at Site 724. Prior to the Pleistocene-Holocene at this site, sediments with higher content of organic matter were deposited owing to favorable preservation conditions and/or higher productivity. In the Pleistocene, lower amounts of organic matter have been preserved; this material generally has more enriched nitrogen isotopic compositions. This may indicate intensification of the Oxygen Minimum Zone and denitrification with the onset of the Pleistocene. A correlation of carbon isotope content of these sediments with oxygen isotope stages at Site 724 indicates an enrichment in 13C during glacial events. Based on the stable isotope evidence of both carbon and nitrogen, there does not appear to be major input of terrigenous-derived allochthonous material in this marine environment. The timing and extent of monsoon winds on the productivity of this region are not evident, but require further studies for collaborative interpretation of small-scale features in the isotopic and carbon content of this environment

Subsurface images of the Eastern Rift, Africa, from the joint inversion of body waves, surface waves and gravity: investigating the role of fluids in early-stage continental rifting

International audienceThe Eastern Rift System (ERS) of northern Tanzania and southern Kenya, where a cratonic lithosphere is in the early stages of rifting, offers an ideal venue for investigating the roles of magma and other fluids in such an environment. To illuminate these roles, we jointly invert arrival times of locally recorded P and S body waves, phase delays of ambient noise generated Rayleigh waves and Bouguer anomalies from gravity observations to generate a 3-D image of P and S wave speeds in the upper 25 km of the crust. While joint inversion of gravity and arrival times requires a relationship between density and wave speeds, the improvement in resolution obtained by the combination of these disparate data sets serves to further constrain models, and reduce uncertainties. The most significant features in the 3-D model are (1) P and S wave speeds that are 10–15 per cent lower beneath the rift zone than in the surrounding regions, (2) a relatively high wave speed tabular feature located along the western edge of the Natron and Manyara rifts, and (3) low (∼1.71) values of Vp/Vs throughout the upper crust, with the lowest ratios along the boundaries of the rift zones. The low P and S wave speeds at mid-crustal levels beneath the rift valley are an expected consequence of active volcanism, and the tabular, high-wave speed feature is interpreted to be an uplifted footwall at the western edge of the rift. Given the high levels of CO2 outgassing observed at the surface along border fault zones, and the sensitivity of Vp/Vs to pore-fluid compressibility, we infer that the low Vp/Vs values in and around the rift zone are caused by the volcanic plumbing in the upper crust being suffused by a gaseous CO2 froth on top of a deeper, crystalline mush. The repository for molten rock is likely located in the lower crust and upper mantle, where the Vp/Vs ratios are significantly higher

Lithospheric modification by extension and magmatism at the craton-orogenic boundary: North Tanzania Divergence, East Africa

We present a joint analysis of newly acquired gravity and teleseismic data in the North Tanzanian Divergence, where the lithospheric break-up is at its earliest stage. The impact of a mantle upwelling in more mature branches of the East African Rift has been extensively studied at a lithospheric scale. However, few studies have been completed that relate the deep-seated mantle anomaly detected in broad regional seismic tomography with the surface deformation observed in the thick Archaean Pan-African suture zone located in North Tanzania. Our joint inversion closes the gap between local and regional geophysical studies, providing velocity and density structures from the surface down to ca. 250 km depth with new details. Our results support the idea of a broad mantle upwelling rising up to the lithosphere and creating a thermal modification along its path. However, our study clearly presents an increasing amplitude of the associated anomaly both in velocity and density above 200 km depth, which cannot be solely explained by a temperature rise. We infer from our images the combined impact of melt (2-3 per cent), composition and hydration that accompany the modification of a thick heterogenous cratonic lithosphere are a response to the hot mantle rising. The detailed images we obtained in density and velocity assert that Archaean and Proterozoic units interact with the mantle upwelling to restrict the lithosphere modifications within the Magadi-Natron-Manyara rift arm. The composition and hydration variations associated with those units equilibrate the thermal erosion of the craton root and allow for its stability between 100 and 200 km depth. Above 80 km depth, the crustal part is strongly affected by intruding bodies (melt and gas) which produces large negative anomalies in both velocity and density beneath the main magmatic centres. In addition to the global impact of a superplume, the velocity and density anomaly pattern suggests a 3-D distribution of the crust and mantle lithospheric stretching, which is likely to be controlled by inherited fabrics and enhanced by lateral compositional and hydration variations at the Tanzanian craton-orogenic belt boundary