Lightning occurrences and intensity over the Indian region: Long-term trends and future projections

Abstract. Lightning activities constitute the major destructive component of thunderstorms over India. Hence, understanding the long-term variabilities of lightning occurrence and intensity and their inter-relation with various causative factors is required. Long-term (1998–2014) Tropical Rainfall Measuring Mission (TRMM) satellite-based lightning observations depict the most abundant lightning occurrences along the Himalayan foothills, the Indo-Gangetic plains and coastal regions, while the intensity of these lightning strikes are found to be strongest along the coastal regions and Bay of Bengal. In addition, both the lightning properties show a very strong intensification (~1–2.5 % annually) across all Indian regions during 1998–2014 with the maximum trends along the coasts. Accordingly, a detailed statistical dominance analysis is performed which reveals total column water vapor (TCWV) to be the dominant factor behind the intensification in lightning events, while instability, measured by the convective available potential energy (CAPE), and aerosols optical depth (AOD) jointly control the lightning frequency trends. An increase in surface temperatures has led to enhanced instability hence stronger moisture transport to the upper troposphere lower stratosphere regions especially in the along the coasts. This transported moisture helps deplete the ozone concentration leading to reduced temperatures and elevated equilibrium levels which finally results in stronger and more abundant lightning events as also evidenced from the trend analysis. Consequently, the relationship between lightning and its causative factors have been expressed in form of multi-linear regression equations which are then employed on multiple global circulation models (GCM) to understand the long-term impact of urbanization on lightning over a period of 1950–2100. The analysis reveals a uniform increase in lightning occurrences, and intensity from both urbanization scenarios; however, an accelerated growth is observed in the RCP8.5 projections after the year 2050 as also observed from the surface warming trends. As a result, lightning frequency and intensity values across the Indian region are expected to increase alarmingly by ~10–25 % and 15–50 %, respectively, by the end of this century with highest risks along the coasts and hence it requires immediate attention from policy makers.