HYDROCLIMATIC VARIABILITY IN THE DWANGWA RIVER BASIN: ASSESSMENT OF LARGE-SCALE FORCING IMPACTS.

Abstract

The influence of the El Niño Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) persists as one of the drivers of climate variability worldwide. There are numerous studies on their evolution, triggering mechanisms, life cycles, and periodicities relating them to the local climate. This study was aimed at assessing the impact of ENSO and IOD on climate variability and river discharge in the Dwangwa Basin. It further assessed climate variability and the response of river discharge in relation to ENSO and IOD between 1985 and 2015. The direction and significance of trends in the rainfall data series were investigated using the non-parametric Mann Kendall test. The influence of ENSO and IOD was checked by correlating the October–January Nino 3.4 and IOD. Twenty-three years (1985–2008) of river discharge data were classified using Sea Surface Temperature (SST) anomaly data from the equatorial Pacific and Indian Ocean as occurring during an El Niño (warm event), La Nina (Cold event), Positive IOD (warm), and Negative IOD (cold). Correlations and responses were achieved using Pearson product moment and linear regression, respectively. The study found an insignificant (0.05%) negative trend annually in rainfall in the basin. Moreover, rainfall was negatively correlated with El Niño and positive IOD, though insignificant. The river is associated with a decrease in discharge during El Niño and Positive IOD. The opposite was noted during the cold (La Niña) and neutral phase. Study suggests that Dwangwa River Basin experience low rainfall when the SST are warmer in Pacific and Indian Ocean.