The Sangu river basin contributes to national economy significantly; however, exposures to water-related hazards frequently. As it is expected that water-related disasters will increase manifold in the future due to global warming, the Government of Bangladesh has formulated Bangladesh Delta Plan 2100 (BDP-2100) to enhanced climate resilience. Accordingly, this study assessed the hydro-meteorological characteristics of the Sangu River basin under changing climate. This study scientifically selected five General Circulation Models (GCMs) to include the model climate sensitivity and statistically bias-corrected their outputs. The Water and Energy Budget-based Rainfall-Runoff-Inundation (WEB-RRI) model was used to simulate the hydrological responses of the basin. The analysis of five GCMs under the Representative Concentration Pathway (RCP8.5) revealed that all selected GCMs estimate a 2-13% increase in annual rainfall and a 3-12% increase in annual discharge in the near-future (2025-2050), whereas four GCMs project an 11-52% increase in annual rainfall and a 7-59% increase in annual discharge in the far-future (2075-2100). The projected more frequent and intense increased extreme rainfall and flood occurrences in the future indicate an increase in flood disaster risk, whereas increased meteorological and hydrological drought in the future reflects a scarcity of water during dry periods. The number of projected affected people shows an increasing trend due to the increased inundation in the future. However, increasing trend of transpiration indicates agricultural productivity will increase in the future. Policymakers can utilize this evidence-based information to implement BDP-2100 and to reduce the disaster risks in the basin.

This study analyzes the potential response of the seasonal cycle of heatwave (HWDI), dry (CDD) and wet (CWD) spells indices over West Africa for the near (2031-2060) and the far (2071-2100) future periods, under RCP4.5 and RCP8.5 scenarios using CORDEX simulations. Although some relative biases during the historical period (1976-2005), the CORDEX simulations and their ensemble mean outperform the seasonal variability of the above indices over three defined sub-regions of West Africa (i.e., Guinea gulf, west and east Sahel). They have shown significant correlation coefficients and less RMSE. They project an increase in heatwave days for both near and far future periods over whole west Africa region under both RCP scenarios. In addition, the Sahel regions will face to a decrease in wet spells days from March to November, whereas, the Gulf of Guinea will face to a decrease during all the year, except CCCLM simulation which indicates an increase during the retreat phase of the monsoon (October to December). The results also have shown an increase in dry spells over Sahel regions, more pronounced during March-November period, whereas, over Guinea gulf, the increase is observed over the entire year. On the other hand, the months of increasing dry spells and decreasing wet spells coincide, suggesting that countries in these regions could be exposed simultaneously to dry season associated with a high risk of drought and heatwave under future climate conditions.

Addressing the impacts of climate change requires, first of all, understanding the mechanisms driving changes, especially at regional scale. In particular, policymakers and other stakeholders need physically robust climate change information to drive societal responses to a changing climate. In this study, we analyse the late 21st century precipitation projections (2071-2100) over the Congo Basin under Representative Concentration Pathway (RCP) 8.5, from the Rossby Centre Regional Climate Model (RCM) RCA4. In particular, we examine the impact of the RCM formulation (reduction of turbulent mixing) on future projections, by comparing the results of the modified version (RCA4-v4) with those of the standard version (RCA4-v1) used in CORDEX (Coordinated Regional climate Downscaling EXperiment). The two RCM versions are driven by two global climate models participating in the Coupled Model Intercomparison Project phase 5 (CMIP5). Results show that seasonal precipitation is largely affected by modifications in the atmospheric column moisture convergence or divergence, in turn, associated with dynamic and thermodynamic effects. Projected decreased precipitation in the dry seasons is associated with an increased moisture divergence, driven by dynamic effects (changes in circulation). Precipitation is projected to overall increase in the wet seasons, related to both dynamic and thermodynamic effects, but with larger thermodynamic contribution (changes in specific humidity). By comparing the two model versions, we found that the formulation strongly influences precipitation projections as well as the boundary conditions (driving GCM). This result could be very informative in view to ensure models fitness for the purpose of future projections for decision-makers.