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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 HighlightsThe 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

In the Sahelian semi-arid region, water resources, especially small waterbodies such as ponds, small lakes, and reservoirs in rural areas are of vital importance. However, because of their high number and the scarce in situ monitoring networks, these resources and their spatiotemporal variability are not well known at the regional scale. This study investigates the hydrological regime of 37 small waterbodies, located in Mali, Niger, and Burkina Faso in central Sahel. We propose a method based on remote sensing data only, which consists of combining water height data from Sentinel-3 Synthetic Aperture Radar Altimeter (SRAL) with water area data obtained with the Sentinel-2 MultiSpectral Instrument (MSI) to create a dense water height time series. Water height variations are then compared to the evaporation estimated by the Penman–Monteith method, using ERA5 reanalysis by the European Centre for Medium-Range Weather Forecasts (ECMWF) to infer water regimes during the dry season. Three main regimes stand out, namely a net water loss, mainly resulting from anthropogenic withdrawals, a net water supply occurring after the end of the rainy season through river network or water table exchange, and a balanced behaviour, where water losses during the dry season closely correspond to evaporation rates. Spatial patterns have been identified; in central Burkina Faso, most of the reservoirs show a net dry season water loss, which is explained by frequent irrigation, while reservoirs in northern Burkina Faso, generally show little water loss, indicating that water withdrawal is not significant in this area. Lakes located in the Inner Niger Delta in Mali and connected to the Niger River network generally show an important water supply, particularly at the beginning of the dry season. Lakes in Niger tend to show a weak signal toward water inflow that could be explained by exchange processes with the groundwater. These results show that satellite data are effective at estimating hydrological regimes and the anthropogenic impact on water resources at the large scale, including resources found in small waterbodies.

Background Recent cost studies related to infertility treatment have focused on assisted reproductive technologies. None has examined lower-intensity infertility treatments or analyzed the distribution of infertility treatment expenditures over time. The Purpose of the study was to analyse the size and distribution of infertility treatment expenditures over time, and estimate the economic burden of infertility treatment per 10,000 women aged 18 − 50 in France from a societal perspective. Methods We used French National individual medico-administrative database to conduct a self-controlled before-after analytic cohort analysis with 556 incidental women treated for infertility in 2014 matched with 9,903 controls using the exact matching method. Infertility-associated expenditures per woman and per 10,000 women over the 3.5-year follow-up period derived as a difference-in-differences. Results The average infertility related expenditure per woman is estimated at 6,996 (95% CI: 5,755–8,237) euros, the economic burden for 10,000 women at 70.0 million (IC95%: 57.6–82.4) euros. The infertility related expenditures increased from 235 (IC95%: 98–373) euros in semester 0, i.e. before treatment, to 1,509 (IC95%: 1,277–1,741) euros in semester 1, mainly due to ovulation stimulation treatment (47% of expenditure), to reach a plateau in semesters 2 (1,416 (IC95%: 1,161–1,670)) and 3 (1,319 (IC95%: 943–1,694)), where the share of expenses is mainly related to hospitalizations for assisted reproductive technologies (44% of expenditure), and then decrease until semester 6 (577 (IC95%: 316–839) euros). Conclusion This study informs public policy about the economic burden of infertility estimated at 70.0 million (IC95%: 57.6–82.4) euros for 10,000 women aged between 18 and 50. It also highlights the importance of the share of drugs in infertility treatment expenditures. If nothing is done, the increasing use of infertility treatment will lead to increased expenditure. Prevention campaigns against the preventable causes of infertility should be promoted to limit the use of infertility treatments and related costs.

BackgroundExit strategy after natalizumab cessation in multiple sclerosis (MS) is a crucial point because the risk of disease reactivation is high during this period. The objective of this observational study was to compare ocrelizumab to fingolimod after natalizumab cessation in patients with relapsing–remitting multiple sclerosis (RRMS).MethodsAll RRMS patients starting fingolimod or ocrelizumab within 6 weeks after natalizumab cessation were included. The primary endpoint was the annualized relapse rate (ARR) at 1 year.ResultsWe included 54 patients receiving fingolimod and 48 patients receiving ocrelizumab after natalizumab cessation. In multivariate analysis, ARR at 1 year was significantly lower in the ocrelizumab group than in the fingolimod group (0.12 ± 0.39 versus 0.41 ± 0.71, p = 0.026), i.e. a 70.7% lower relapse rate. The cumulative probability of relapses at 1 year was 31.5% (17/54 patients) with fingolimod and 10.4% (5/48 patients) with ocrelizumab, corresponding to a hazard ratio of 3.4 (95% confidence interval: 1.1–11, p = 0.04).ConclusionsOur results suggest ocrelizumab is potentially a better exit strategy than fingolimod after natalizumab cessation.

The Sentinel-3 Mission Performance Centre (S3MPC) is tasked by the European Space Agency (ESA) to monitor the health of the Copernicus Sentinel-3 satellites and ensure a high data quality to the users. This paper deals exclusively with the effort devoted to the altimeter and microwave radiometer, both components of the Surface Topography Mission (STM). The altimeters on Sentinel-3A and -3B are the first to operate in delay-Doppler or SAR mode over all Earth surfaces, which enables better spatial resolution of the signal in the along-track direction and improved noise reduction through multi-looking, whilst the radiometer is a two-channel nadir-viewing system. There are regular routine assessments of the instruments through investigation of telemetered housekeeping data, calibrations over selected sites and comparisons of geophysical retrievals with models, in situ data and other satellite systems. These are performed both to monitor the daily production, assessing the uncertainties and errors on the estimates, and also to characterize the long-term performance for climate science applications. This is critical because an undetected drift in performance could be misconstrued as a climate variation. As the data are used by the Copernicus Services (e.g., CMEMS, Global Land Monitoring Services) and by the research community over open ocean, coastal waters, sea ice, land ice, rivers and lakes, the validation activities encompass all these domains, with regular reports openly available. The S3MPC is also in charge of preparing improvements to the processing, and of the development and tuning of algorithms to improve their accuracy. This paper is thus the first refereed publication to bring together the analysis of SAR altimetry across all these different domains to highlight the benefits and existing challenges.