Tropical cyclones in the South-West Indian Ocean : intensity changes, oceanic interaction and impacts

Includes abstract.Includes bibliographical references (p. 229-253).This study investigates the climatology, intensification and ocean atmosphere interaction in relation to the passage of tropical cyclones (TCs) in the South-West Indian Ocean (SWIO). A Climatology of TCs in the SWIO including landfall in the area of Mozambique and Madagascar was developed for the 1952-2007 and 1980-2007 periods

Unique relationship between tropical rainfall and SST to the north of the Mozambique Channel in boreal winter

In this study, we investigate a possible mechanism for the dichotomy in climatology of marine rainfall and sea surface temperature (SST) over a part of the Southwest Indian Ocean (SWIO) during boreal winter (January and February) with state-of-the-art satellite and reanalysis data sets. Rainfall to the north of the Mozambique Channel, bounded 10°–5°S and 40°–50°E, is found to be quite feeble despite being in the warm SST regime of up to 29–29.5 °C. The rainfall intensity is rather found to be highly associated with the atmospheric surface divergence. The vigorous rainfall is associated with the more convergence over the Intertropical Convergence Zone (ITCZ), while the weak rainfall is linked with the divergence to the north of the Mozambique Channel. The surface divergent flow to the north of the Mozambique Channel is associated with a deep southward penetration of the northerly Indian Winter Monsoon (IWM). Corresponding to the surface divergent field, a relatively high sea level pressure (SLP) compared to the SLP in the ITCZ, weak subsidence, and low-level stratiform clouds are formed to the north of the Mozambique Channel, despite the warm, tropical SST. These atmospheric conditions are most likely conductive to the inhibition of cumulus convection over the region and the unique relationship between rainfall and SST seems peculiar. Our analysis also shows that the rare occurrence of tropical cyclones over the area is attributed to a high-pressure surge and the associated positive surface vorticity (anti-cyclonic). This study suggests that the area to the north of the Mozambique Channel is dynamically interesting for climatological studies.acceptedVersio

Deep convection over Africa: annual cycle, ENSO, and trends in the hotspots

Africa is one of the three key regions of deep convection in the global tropics. There is a wealth of information on the intensity, variability and change of convection and associated rainfall in regions across the continent but almost all of this literature is regionally focused and confined to specific seasons. This fragmented approach precludes a continent-wide view of deep convection leaving the following key issues unanswered: When is deep convection the most wide-spread across Africa? Where on the continent is deep convection most active? Where does wide-spread convection have the most interannual variability? This paper confronts these questions using a satellite-derived integral of deep convection. At the continental scale, March exhibits the most extensive deep convection while the West African monsoon during June-July exhibits the least. El Niño generally suppresses pan-African convective activity while La Niña enhances this activity. These pan-African signals are largely determined by regional hotspots: the eastern Congo hosts the most persistent wide-spread deep convection, southeastern southern Africa displays the highest interannual variability, and regional highlands maintain local convective activity hotspots. Furthermore, pan-African annual mean convective activity has increase ∼10% between 1983 and 2015 with increases of >20% recorded in local hotspots. Results in this study provide a climatological baseline for both observational and model-based studies of African climates and offer insights into when African convection has the greatest potential impact on the general circulation

Hydrokinetic Turbine Effects on Fish Swimming Behaviour

Hydrokinetic turbines, targeting the kinetic energy of fast-flowing currents, are under development with some turbines already deployed at ocean sites around the world. It remains virtually unknown as to how these technologies affect fish, and rotor collisions have been postulated as a major concern. In this study the effects of a vertical axis hydrokinetic rotor with rotational speeds up to 70 rpm were tested on the swimming patterns of naturally occurring fish in a subtropical tidal channel. Fish movements were recorded with and without the rotor in place. Results showed that no fish collided with the rotor and only a few specimens passed through rotor blades. Overall, fish reduced their movements through the area when the rotor was present. This deterrent effect on fish increased with current speed. Fish that passed the rotor avoided the near-field, about 0.3 m from the rotor for benthic reef fish. Large predatory fish were particularly cautious of the rotor and never moved closer than 1.7 m in current speeds above 0.6 ms-1. The effects of the rotor differed among taxa and feeding guilds and it is suggested that fish boldness and body shape influenced responses. In conclusion, the tested hydrokinetic turbine rotor proved non-hazardous to fish during the investigated conditions. However, the results indicate that arrays comprising multiple turbines may restrict fish movements, particularly for large species, with possible effects on habitat connectivity if migration routes are exploited. Arrays of the investigated turbine type and comparable systems should therefore be designed with gaps of several metres width to allow large fish to pass through. In combination with further research the insights from this study can be used for guiding the design of hydrokinetic turbine arrays where needed, so preventing ecological impacts

Renewable ocean energy in the Western Indian Ocean

Several African countries in the Western Indian Ocean (WIO) endure insufficiencies in the power sector, including both generation and distribution. One important step towards increasing energy security and availability is to intensify the use of renewable energy sources. The access to cost-efficient hydropower is low in coastal and island regions and combinations of different renewable energy sources will play an increasingly important role. In this study the physical preconditions for renewable ocean energy are investigated, considering the specific context of the WIO countries. Global-level resource assessments and oceanographic literature and data have been compiled in an analysis of the match between technology-specific requirements for ocean energy technologies (wave power, ocean thermal energy conversion (OTEC), tidal barrages, tidal current turbines, and ocean current power) and the physical resources in 13 WIO regions Kenya, Seychelles, Northern Tanzania and Zanzibar, Southern Tanzania, Comoros and Mayotte, Northern-, Central-, and Southern Mozambique, Western-, Eastern-, and Southern Madagascar, Reunion, and Mauritius. The results show high potential for wave power over vast coastal stretches in southern parts of the WIO and high potential for OTEC at specific locations in Mozambique, Comoros, Reunion, and Mauritius. The potential for tidal power and ocean current power is more restricted but may be of interest at some locations. The findings are discussed in relation to currently used electricity sources and the potential for solar photovoltaic and wind power. Temporal variations in resource intensity as well as the differences between small-scale and large-scale applications are considered

Simplified site-screening method for micro tidal current turbines applied in Mozambique

A variety of tidal current turbines (TCT) are emerging, the majority focussing on large-scale extraction of renewable energy at global tidal hot-spots. Concurrently, some turbines are small and may be suitable also for micro-scale applications (micro-TCT) in remote areas, such as decentralized electrification in countries where fuel-independent energy systems with high power predictability are particularly important. In shallow waters the force of tidal currents varies considerably over short distances and very site-specific measurements are important for assessment of localization, but are also expensive. For micro-TCT to be of interest site-screening and evaluation must be inexpensive, and low-cost methods are thus required. This study proposes a simplified tidal model that is calibrated to site-specific conditions by short-term observations using lightweight equipment. By measurements comprising down to 8% of the monthly tidal period the potential power output can be estimated, with uncertainty intervals up to +-20%, for currents applicable for micro-TCT. This site-screening method was tested at five sites in Mozambique where near-shore tidal currents were measured with lightweight current meters. At three of the sites, currents were estimated to exceed 1 m s-1 and power output was calculated based on technical assumptions for a micro-TCT device. Results are discussed from the perspective of micro-TCT development and decentralized remote area electrification

Climate variability, socio-economic conditions and vulnerability to malaria infections in Mozambique 2016–2018 : a spatial temporal analysis

Background: Temperature, precipitation, relative humidity (RH), and Normalized Different Vegetation Index (NDVI), influence malaria transmission dynamics. However, an understanding of interactions between socioeconomic indicators, environmental factors and malaria incidence can help design interventions to alleviate the high burden of malaria infections on vulnerable populations. Our study thus aimed to investigate the socioeconomic and climatological factors influencing spatial and temporal variability of malaria infections in Mozambique. Methods: We used monthly malaria cases from 2016 to 2018 at the district level. We developed an hierarchical spatial–temporal model in a Bayesian framework. Monthly malaria cases were assumed to follow a negative binomial distribution. We used integrated nested Laplace approximation (INLA) in R for Bayesian inference and distributed lag nonlinear modeling (DLNM) framework to explore exposure-response relationships between climate variables and risk of malaria infection in Mozambique, while adjusting for socioeconomic factors. Results: A total of 19,948,295 malaria cases were reported between 2016 and 2018 in Mozambique. Malaria risk increased with higher monthly mean temperatures between 20 and 29°C, at mean temperature of 25°C, the risk of malaria was 3.45 times higher (RR 3.45 [95%CI: 2.37–5.03]). Malaria risk was greatest for NDVI above 0.22. The risk of malaria was 1.34 times higher (1.34 [1.01–1.79]) at monthly RH of 55%. Malaria risk reduced by 26.1%, for total monthly precipitation of 480 mm (0.739 [95%CI: 0.61–0.90]) at lag 2 months, while for lower total monthly precipitation of 10 mm, the risk of malaria was 1.87 times higher (1.87 [1.30–2.69]). After adjusting for climate variables, having lower level of education significantly increased malaria risk (1.034 [1.014–1.054]) and having electricity (0.979 [0.967–0.992]) and sharing toilet facilities (0.957 [0.924–0.991]) significantly reduced malaria risk. Conclusion: Our current study identified lag patterns and association between climate variables and malaria incidence in Mozambique. Extremes in climate variables were associated with an increased risk of malaria transmission, peaks in transmission were varied. Our findings provide insights for designing early warning, prevention, and control strategies to minimize seasonal malaria surges and associated infections in Mozambique a region where Malaria causes substantial burden from illness and deaths

Applications of Satellite-Derived Ocean Measurements to Tropical Cyclone Intensity Forecasting

Sudden tropical cyclone (TC) intensification has been linked with high values of upper ocean heat content contained in mesoscale features, particularly warm ocean eddies, provided that atmospheric conditions are also favorable. Although understanding of air-sea interaction for TCs is evolving, this manuscript summarizes some of the current work being carried out to investigate the role that the upper ocean plays in TC intensification and the use of ocean parameters in forecasting TC intensity

KwaZulu-Natal coastal erosion events of 2006/2007 and 2011: A predictive tool?

Severe coastal erosion occurred along the KwaZulu-Natal coastline between mid-May and November 2011. Analysis of this erosion event and comparison with previous coastal erosion events in 2006/2007 offered the opportunity to extend the understanding of the time and place of coastal erosion strikes. The swells that drove the erosion hotspots of the 2011 erosion season were relatively low (significant wave heights were between 2 m and 4.5 m) but of long duration. Although swell height was important, swell-propagation direction and particularly swell duration played a dominant role in driving the 2011 erosion event. Two erosion hotspot types were noted: sandy beaches underlain by shallow bedrock and thick sandy beaches. The former are triggered by high swells (as in March 2007) and austral winter erosion events (such as in 2006, 2007 and 2011). The latter become evident later in the austral winter erosion cycle. Both types were associated with subtidal shore-normal channels seaward of megacusps, themselves linked to megarip current heads. This 2011 coastal erosion event occurred during a year in which the lunar perigee sub-harmonic cycle (a ±4.4-year cycle) peaked, a pattern which appears to have recurred on the KwaZulu-Natal coast. If this pattern proves true, severe coastal erosion may be expected in 2015. Evidence indicates that coastal erosion is driven by the lunar nodal cycle peak but that adjacent lunar perigee sub-harmonic peaks can also cause severe coastal erosion. Knowing where and when coastal erosion may occur is vital for coastal managers and planners