The concept of enthalpy is the heat content.
When energy goes up in a substance or due to a chemical or physical reaction, temperature goes up as well. This results in enthalpy rising as well as it is the heat content in these reactions.
To put it into context:
In exothermic reactions where heat is released and work is being done on the surroundings (environment) and due to this content being released enthalpy as a result will go down.
A nuclear bomb exploding releases massive amounts of heat; the system is losing heat meaning enthalpy goes down.
Heat and enthalpy are directly related to each other, if heat goes down then enthalpy will go down, while the same applies if heat goes up then enthalpy will go up as well.