1. Loss of Heat Source: Tropical cyclones derive their energy from warm ocean waters. When they move over land, they lose this primary energy source. Evaporation from the ocean, which fuels the cyclone, ceases, leading to a decrease in storm intensity.

2. Increased Friction: On land, cyclones encounter surface friction from mountains, forests, and buildings. This friction disrupts the cyclone’s circulation and reduces its wind speeds, causing the storm to weaken.

3. Reduced Moisture Supply: Cyclones require high humidity to maintain their structure. Over land, the moisture supply is limited compared to the ocean. As a result, the storm’s convective activity diminishes, leading to weakening.

4. Terrain Disruption: Landforms like mountains can disrupt the storm’s structure by breaking up the wind patterns and rainfall distribution, further contributing to the cyclone’s dissipation.

Recent Example: Cyclone Amphan (2020) weakened as it moved inland after making landfall in West Bengal, illustrating the typical weakening process of tropical cyclones over terrestrial areas.

Conclusion: Tropical cyclones weaken upon reaching land due to the loss of their heat and moisture source, increased friction, and terrain disruptions. These factors contribute to the gradual dissipation of the storm’s intensity.