Multiscale Drivers of Rainfall Variability in Wa, Northern Ghana: Relative Roles of Oceanic Teleconnections and Local Atmospheric Controls.

Abstract

Rainfall variability in northern Ghana has significant implications for rain-fed agriculture and climate risk management. This study investigates the multiscale drivers of rainfall variability in Wa over the period 1960-2020, distinguishing between largescale oceanic teleconnections and local atmospheric controls. A key contribution of this study is the development of a comparative multiscale framework that isolates and quantifies the individual and combined influence of remote oceanic forcing and local atmospheric processes on rainfall variability. Monthly rainfall variability, trends, and interannual fluctuations were first quantified using the coefficient of variation, Mann-Kendall trend analysis, Sen’s slope estimator, and change-point detection. To attribute drivers, three regression models were developed: (i) teleconnection indices only, (ii) local ERA5 atmospheric variables only, and (iii) a combined model incorporating both predictor sets. Rainfall exhibited the highest relative variability during the onset and cessation months. It is revealed that interannual variability has significantly declined since 1990, while significant negative trends are confined to March and July. Regression results show that teleconnection indices explain 8.6% of rainfall variance, whereas local atmospheric variables explain 30.2%. The combined model provides the highest explanatory power (41.1%), indicating that large-scale oceanic variability exerts a statistically significant but secondary influence relative to local thermodynamic and cloud-related processes. The findings demonstrate that rainfall variability in Wa is primarily governed by local atmospheric conditions, with large-scale SST anomalies modulating the background monsoon environment. These results highlight the importance of integrating both remote and local predictors to improve seasonal rainfall prediction, climate risk assessment, and agricultural planning in northern Ghana.