Water Resources in Africa under Global Change: Monitoring Surface Waters from Space.

Abstract: The African continent hosts some of the largest freshwater systems worldwide, characterized by a large distribution and variability of surface waters that play a key role in the water, energy and carbon cycles and are of major importance to the global climate and water resources. Freshwater availability in Africa has now become of major concern under the combined effect of climate change, environmental alterations and anthropogenic pressure. However, the hydrology of the African river basins remains one of the least studied worldwide and a better monitoring and understanding of the hydrological processes across the continent become fundamental. Earth Observation, that offers a cost-effective means for monitoring the terrestrial water cycle, plays a major role in supporting surface hydrology investigations. Remote sensing advances are therefore a game changer to develop comprehensive observing systems to monitor Africa's land water and manage its water resources. Here, we review the achievements of more than three decades of advances using remote sensing to study surface waters in Africa, highlighting the current benefits and difficulties. We show how the availability of a large number of sensors and observations, coupled with models, offers new possibilities to monitor a continent with scarce gauged stations. In the context of upcoming satellite missions dedicated to surface hydrology, such as the Surface Water and Ocean Topography (SWOT), we discuss future opportunities and how the use of remote sensing could benefit scientific and societal applications, such as water resource management, flood risk prevention and environment monitoring under current global change. Article Highlights: The hydrology of African surface water is of global importance, yet it remains poorly monitored and understoodComprehensive review of remote sensing and modeling advances to monitor Africa's surface water and water resourcesFuture opportunities with upcoming satellite missions and to translate scientific advances into societal applications.

Longest sediment flows yet measured show how major rivers connect efficiently to deep sea.

Here we show how major rivers can efficiently connect to the deep-sea, by analysing the longest runout sediment flows (of any type) yet measured in action on Earth. These seafloor turbidity currents originated from the Congo River-mouth, with one flow travelling >1,130 km whilst accelerating from 5.2 to 8.0 m/s. In one year, these turbidity currents eroded 1,338-2,675 [>535-1,070] Mt of sediment from one submarine canyon, equivalent to 19-37 [>7-15] % of annual suspended sediment flux from present-day rivers. It was known earthquakes trigger canyon-flushing flows. We show river-floods also generate canyon-flushing flows, primed by rapid sediment-accumulation at the river-mouth, and sometimes triggered by spring tides weeks to months post-flood. It is demonstrated that strongly erosional turbidity currents self-accelerate, thereby travelling much further, validating a long-proposed theory. These observations explain highly-efficient organic carbon transfer, and have important implications for hazards to seabed cables, or deep-sea impacts of terrestrial climate change.

The efficacy of plain films vs MRI in the detection of scaphoid fractures.

An investigation was carried out to determine whether or not professionals perceived plain film radiography to be the 'gold-standard' in the detection of scaphoid fractures. Literature highlighted that plain film radiography was an unreliable method for detecting such fractures and that magnetic resonance imaging (MRI) should now be regarded as the new 'gold-standard'. Using a quantitative method, a total of 100 postal questionnaires were sent out to radiologists in 20 different imaging departments throughout the United Kingdom (UK) asking them their opinion on this controversial subject. In addition, the investigation looked into the use of MRI within each department in trying to determine whether or not it was surpassing plain film radiography as an established practice for detecting scaphoid fractures. Of the 100 questionnaires that were sent out, a total of 45 were returned from a total of 13 different departments. The results of this investigation conclude that plain film radiography is still used as a primary imaging modality to detect scaphoid fractures in all departments. There was much support for the use of plain film radiography with the modality being praised time and time again for its ease, 24-h availability, low cost and reproducibility. MRI was acknowledged as being superior in its capability to detect scaphoid fractures in comparison to plain films; its current use, however, is limited owing to high costs, lack of availability and long waiting lists. It would appear from this study that MRI is regarded as a useful modality in cases whereby plain film radiography fails to detect the presence or absence of a fracture in clinically positive patients, with great future potential.