Why does rainfall decrease toward the southwestern plateau of Andhra Pradesh?

In Andhra Pradesh, annual precipitation is primarily driven by the southwest monsoon rains. While coastal areas receive approximately 40 to 47 inches (1,000 to 1,200 mm) of rainfall annually, the amounts decrease significantly toward the southwestern plateau, where the westernmost regions may receive only half that total.1

This decrease occurs because the Eastern Ghats and Western Ghats act as barriers to moisture-laden winds. The Western Ghats, in particular, intercept the heavy rainfall from the southwest monsoon on their seaward slopes, leaving the inland plateau area in a rain shadow where precipitation is much lighter. Consequently, as the monsoon winds move inland across the peninsula, the plateau region experiences a marked reduction in rainfall compared to the coastal plains and the windward mountain slopes.21