Estimated future global lightning strokes (2010-2100)

Estimated future lightning stroke density for FireMIP/ISIMIP Jed O. Kaplan, Alexander Koch, and Katie Hong-Kiu Lau Department of Earth Sciences, The University of Hong Kong jed.kaplan@arve-research.com Introduction This dataset contains scenarios of global lightning density (strokes km-2 day-1) for the period 2010-2100. The lightning density estimates are available on an unprojected global half-degree grid with monthly temporal resolution. Each pixel represents the monthly mean of daily lightning stroke density. The estimates of lightning density cover all global land and ocean areas. This dataset may be used in a range of applications, for example, to understand the influence of lightning on wildfire ignitions or atmospheric composition. Methods The estimate of lightning density is based on future climate simulations from an earth system model and an emprical relationship between Convective Available Potential Energy (CAPE) and lightning strokes based on the WWLLN Global Lightning Climatology and timeseries (WGLC) (Kaplan and Lau 2021, 2022). Future climate simulations performed with the UKESM1 earth system model for the 6th Coupled Model Intercomparison Project (CMIP6) provided the following meteorological outputs on pressure levels from the surface to the top of the troposphere required for calculating CAPE: air temperature (ta, K) air pressure (p, Pa) specific humidity (hus, kg kg-1). We derived dewpoint temperature (Td, K) based on ta and hus. CAPE was then estimated using the getcape.F (Version 1.02) code by George Bryan that is part of the NCAR CM1 atmosphere model . After experimenting with climate model output on different timesteps (6-hourly, daily, monthly) we decided to use daily mean values for calculating CAPE as it provided a reasonable balance of accuracy and computational time. The calculated CAPE values were linearly interpolated from the native UKESM grid resolution to a global half-degree grid using the CDO software We estimated lightning stroke density based on an emprical relationship between daily CAPE and observed lightning over the period 2015-2020. Lightning observations were provided by the WGLC. The relationship between CAPE and lightning is described by a linear regression on log(CAPE) vs. log(WGLC) for each gridcell and month of the year. Where