Distribution of lightning in relation to topography and vegetation cover over the dry and moist regions in the Himalayas

Abstract

The impacts of elevation, terrain slope and vegetation cover on lightning activity are investigated for contrasting environments in the north-east (NE) (21–$29{^{\circ }}\hbox {N}$; 86–$94{^{\circ }}\hbox {E}$) and the north-west (NW) (28–$36{^{\circ }}\hbox {N}$; 70–$78{^{\circ }}\hbox {E}$) regions of the Himalayan range. Lightning activity is more at a higher terrain slope/elevation in the dry NW region where vegetation cover is less, whereas it is more at a lower terrain slope/elevation in the moist NE region where vegetation cover is more. In the wet NE, 86% (84%) of the annual lightning flash rate density (LFRD) occurs at an elevation ${<} 500\ \hbox {m}$ (terrain slope ${<} 2\%$) and then sharply falls off at a higher elevation (terrain slope). However, only 49% (47%) of LFRD occurs at an elevation of ${<} 500\ \hbox {m}$ (terrain slope ${<} 2\%$) and then rather gradually falls off at a higher elevation (terrain slope) in the dry NW. The ratio of the percentages of LFRD and elevation points is much higher in the NW than in the NE above an elevation of ${\sim } 1000\ \hbox {m}$. The impacts of terrain slope and elevation in enhancing the lightning activity are stronger in the dry NW than in the moist NE. The correlation coefficient of the LFRD with the normalised difference vegetation index is higher in the NW than in the NE on both the regional and annual scales. Results are discussed as a caution in using any single climate variable as a proxy for projecting a change in the lightning–climate relationships in the scenario of global warming.