Estimation of the return periods of maxima rainfall and floods at the Pra River Catchment, Ghana, West Africa using the Gumbel extreme value theory.

The Pra river catchment in Ghana is adversely affected by perennial flooding from high-intensity rainfall events. To aid in flood management at the catchment, the Gumbel extreme value distribution has been used to estimate the return periods of maxima rainfall, flood, and consecutive dry and wet days (CDD and CWD) for a period of 5 to 100 years. The results revealed an expected increase in maxima rainfall, CDD and CWD. Maxima rainfall favours the south of the catchment while the CDD decreases northward. Furthermore, an increase in the magnitude of CWD observed at the centre of the catchment had a maximum of approximately 30 days for the 100 year return period, while lower flood volumes had a higher recurrence of 50% to 100% for 1 to 2 year return periods. The inclusion of a projected increase in anthropogenic activities and climate factors at the catchment will slightly affect the magnitude of these variables for the various return periods. Nonetheless, the findings in this study will be of essential input to policy implementation of the Integrated Water Resource Management Plan for river catchments in Ghana, West Africa.

Radiation-induced reactive oxygen species partially assemble neutrophil NADPH oxidase.

Neutrophils are key cells from the innate immune system that destroy invading bacteria or viruses, thanks mainly to the non-mitochondrial reactive oxygen species (ROS) generated by the enzyme NADPH oxidase. Our aim was to study the response of neutrophils to situations of oxidative stress with emphasis on the impact on the NADPH oxidase complex. To mimic oxidative stress, we used gamma irradiation that generated ROS (OH•, O2•- and H2O2) in a quantitative controlled manner. We showed that, although irradiation induces shorter half-lives of neutrophil (reduced by at least a factor of 2), it triggers a pre-activation of surviving neutrophils. This is detectable by the production of a small but significant amount of superoxide anions, proportional to the dose (about 3 times that of sham). Investigations at the molecular level showed that this ROS increase was generated by the NADPH oxidase enzyme after neutrophils irradiation. The NADPH oxidase complex undergoes an incomplete assembly which includes p47phox and p67phox but excludes the G-protein Rac. Importantly, this irradiation-induced pre-activation is capable of considerably improving neutrophil reactivity. Indeed, we have observed that this leads to an increase in the production of ROS and the capacity of phagocytosis, leading to the conclusion that radiation induced ROS clearly behave as neutrophil primers.