Contrasting changes in hydrological processes of the Volta River basin under global warming

A comprehensive evaluation of the impacts of climate change on water resources of the West Africa Volta River basin is conducted in this study, as the region is expected to be hardest hit by global warming. A large ensemble of 12 general circulation models (GCMs) from the fifth Coupled Model Intercomparison Project (CMIP5) that are dynamically downscaled by five regional climate models (RCMs) from the Coordinated Regional-climate Downscaling Experiment (CORDEX)-Africa is used. In total, 43 RCM–GCM combinations are considered under three representative concentration pathways (RCP2.6, RCP4.5, and RCP8.5). The reliability of each of the climate datasets is first evaluated with satellite and reanalysis reference datasets. Subsequently, the Rank Resampling for Distributions and Dependences (R2D2) multivariate bias correction method is applied to the climate datasets. The bias-corrected climate projections are then used as input to the mesoscale Hydrologic Model (mHM) for hydrological projections over the 21st century (1991–2100). Results reveal contrasting dynamics in the seasonality of rainfall, depending on the selected greenhouse gas emission scenarios and the future projection periods. Although air temperature and potential evaporation increase under all RCPs, an increase in the magnitude of all hydrological variables (actual evaporation, total runoff, groundwater recharge, soil moisture, and terrestrial water storage) is only projected under RCP8.5. High- and low-flow analysis suggests an increased flood risk under RCP8.5, particularly in the Black Volta, while hydrological droughts would be recurrent under RCP2.6 and RCP4.5, particularly in the White Volta. The evolutions of streamflow indicate a future delay in the date of occurrence of low flows up to 11 d under RCP8.5, while high flows could occur 6 d earlier (RCP2.6) or 5 d later (RCP8.5), as compared to the historical period. Disparities are observed in the spatial patterns of hydroclimatic variables across climatic zones, with higher warming in the Sahelian zone. Therefore, climate change would have severe implications for future water availability with concerns for rain-fed agriculture, thereby weakening the water–energy–food security nexus and amplifying the vulnerability of the local population. The variability between climate models highlights uncertainties in the projections and indicates a need to better represent complex climate features in regional models. These findings could serve as a guideline for both the scientific community to improve climate change projections and for decision-makers to elaborate adaptation and mitigation strategies to cope with the consequences of climate change and strengthen regional socioeconomic development

137,138,139^{137,138,139}La(nn, γ\gamma) cross sections constrained with statistical decay properties of 138,139,140^{138,139,140}La nuclei

The nuclear level densities and $\gamma$-ray strength functions of $^{138,139,140}$La were measured using the $^{139}$La($^{3}$He, $\alpha$), $^{139}$La($^{3}$He, $^{3}$He$^\prime$) and $^{139}$La(d, p) reactions. The particle-$\gamma$ coincidences were recorded with the silicon particle telescope (SiRi) and NaI(Tl) (CACTUS) arrays. In the context of these experimental results, the low-energy enhancement in the A$\sim$140 region is discussed. The $^{137,138,139}$La($n, \gamma)$ cross sections were calculated at $s$- and $p$-process temperatures using the experimentally measured nuclear level densities and $\gamma$-ray strength functions. Good agreement is found between $^{139}$La($n, \gamma)$ calculated cross sections and previous measurements

Titan airglow spectra from Cassini Ultraviolet Imaging Spectrograph (UVIS): EUV analysis

peer reviewedaudience: researcher, professional, studentWe present the first UV airglow observations of Titan's atmosphere by the Ultraviolet Imaging Spectrograph (UVIS) on Cassini. Using one spectral channel in the EUV from 561-1182 Å and one in the FUV from 1115-1913 Å, UVIS observed the disk on 13 December, 2004 at low solar activity. The EUV spectrum consists of three band systems of N[SUB]2[/SUB] (b [SUP]1[/SUP]∏[SUB]u[/SUB], b' [SUP]1[/SUP]∑[SUB]u[/SUB] [SUP]+[/SUP], c[SUB]4[/SUB]' [SUP]1[/SUP]∑[SUB]u[/SUB] [SUP]+[/SUP] -> X [SUP]1[/SUP]∑[SUB]g[/SUB] [SUP]+[/SUP]), while the FUV spectrum consists of one (a [SUP]1[/SUP]∏[SUB]g[/SUB] -> X [SUP]1[/SUP]∑[SUB]g[/SUB] [SUP]+[/SUP]). Both the EUV and FUV spectra contain many N I and N II multiplets that are produced primarily by photodissociative ionization. Spectral intensities of the N[SUB]2[/SUB] c[SUB]4[/SUB]' [SUP]1[/SUP]∑[SUB]u[/SUB] [SUP]+[/SUP](v' = 0) -> X [SUP]1[/SUP]∑[SUB]g[/SUB] [SUP]+[/SUP](v'' = 0-2) progression from 950-1010 Å are resolved for the first time. The UVIS observations reveal that the c[SUB]4[/SUB]' [SUP]1[/SUP]∑[SUB]u[/SUB] [SUP]+[/SUP](0) -> X [SUP]1[/SUP]∑[SUB]g[/SUB] [SUP]+[/SUP] (0) vibrational band near 958 Å is weak and undetectable, and that N I multiplets near 953.2 and 964.5 Å are present instead. Magnetospheric particle excitation may be weak or sporadic, since the nightside EUV spectrum on this orbit shows no observable nitrogen emission features and only H Ly-β

Future shifting of annual extreme flows under climate change in the Volta River basin

Global warming is projected to result in changes in streamflow in West Africa with implications for frequent droughts and floods. This study investigates projected shifting in the timing, seasonality and magnitude of mean annual minimum (MAM) and annual maximum flows (AMF) in the Volta River basin (VRB) under climate change, using the method of circular statistics. River flow is simulated with the mesoscale hydrologic model (mHM), forced with bias-corrected climate projection datasets consisting of 43 regional and global climate model combinations under three representative concentration pathways (RCPs). Projected changes indicate that AMF increases between +1 % and +80 % across sub-basins, particularly in the near future (2021–2050), whereas MAM decreases between −19 % and −7 %, mainly from the late century (2071–2100), depending on RCPs. The date of occurrence of AMF is projected to change between −4 and +3 d, while MAM could shift between −4 and +14 d depending on scenarios over the 21st century. Annual high flows denote a strong seasonality with negligible future changes, whereas the seasonality of low flows has a higher variation, with a slight drop in the future