Equatorial African Lightning: Past. Present and Future

TL;DR

This study analyzes the past, present, and future of lightning activity in the Congo Basin, revealing counterintuitive trends and projecting significant weakening of lightning by 2100 under high emission scenarios.

Contribution

It provides a comprehensive analysis of lightning trends in the Congo Basin and introduces future projections based on climate model simulations under RCP 8.5.

Findings

Lightning rates peak during equinoctial months.

Lightning radiance decreases by ~1% annually.

Lightning is projected to weaken by ~50% by 2100.

Abstract

Lightning strikes are one of the leading causes of death among natural disasters in tropical regions. The Congo rainforests host the highest rates of lightning flashes in the world and the lightning properties in this region have a strong seasonality owing to the cross-equatorial movements of the Inter Tropical Convergence Zone (ITCZ) throughout the year. The Lightning Flash Rates (LFR) are found to peak during the Equinoctial months while lightning radiance assumes the strongest values during the Boreal Summer months. Across the Tropical Rainfall Measuring Mission (TRMM) duration, (1998-2015), annual LFR in the Congo rainforest increases steadily, however, the average and the peak lightning radiances decrease by ~1%/year and ~1.5%/year respectively which is counter-intuitive to the expected intensification in weather extremes in a warming climate. An in-depth analysis highlighted the influence of moisture convergence over the Congo Basin from the Atlantic as the primary contributor to lightning compared to the aerosol nucleation and thermodynamic instability effects during the boreal summers. Further, it has been proposed that in a gradually warming climate, the strength of the prevailing ITCZ over Sahel region has intensified thereby weakening the moisture ingress towards the Congo Basin, and this resulted in the observed reduction in lightning intensity in recent years. Consequently, the long-term projections of lightning properties from global model simulations revealed a prominent weakening in lightning (~50%) over the Congo Basin by the year 2100 assuming the Representative Concentration Pathways (RCP) 8.5 emission scenarios. Key Words: Lightning, LIS, Congo Basin, Sahel, Moisture Flux, Future projections.