Climate Change and Tropical Total Lightning: Observations and Extrapolated Trends Based on 16 Years of TRMM LIS Observations

The International Panel on Climate Change (IPCC) assessment reports show that global warming will result in a future drier climate. They also show conflicting responses on the mean accumulated precipitation over the three major tropical zones of active convection: while southeast Asia, the Maritime Continent and east Africa show an increase in precipitation, South America show a major decrease. The heavy and very heavy events, on the other hand, show increased accumulated precipitation on warmer scenarios. Among these rainfall extremes, thunderstorms are major players and its associated lightning is a proxy for severe storms, a fact that recently motivated WMO to introduce lightning as a new essential climate variable.

On this subject, the Lightning Imaging Sensor (LIS) onboard of the Tropical Rainfall Measurement Mission (TRMM) has 16 years (1998-2013) of stable and continuous observations of total lightning along the tropics, making it possible to depict trends in convection and thunderstorm updraft over more than a decade. Here we address total lightning trends observed by LIS in different temporal (annual, seasonal and instantaneous) and spatial (large and regional) scales. Mean flash rates show no significant trends. On the other hand, instantaneous flash rates have systematic negative trends over most of the tropics (except southeast South America), and higher negative trends are observed at the extreme instantaneous values (higher-end of the orbit gridded flash rate distributions, or highest quantiles). It is also given a projected estimate for the future climate based on extrapolation of the trends found here, with special attention at the regional scales of places with most lightning occurrence (i.e., Earth’s lightning hotspots).