To avoid any risk of electrocution and damage to equipment due to an insulation fault or lightning discharge in the HV electrical network consisting mainly of HV transmission stations and lines, all equipment in these energy infrastructures must be earthed through an earth electrode which must maintain its performance over time following the recurrent flows of the shock wave.As this aggressive discharge flows to the ground, the resulting thermal effects can lead to ionization of the soil and reduce the performance of the earth electrode by changing the characteristics of the soil. This publication aims to establish the cause and effect relationship between the thermal effects due to the injected lightning current and the electrical characteristics of the ground through its resistivity.This analysis will allow energy infrastructure designers to take into account these performance changes when injecting lightning current and properly size the earth connections of HV substations.