What geographical feature is essential for irrigating rice fields in central Thailand?

The Chao Phraya River is the geographical feature that is essential for irrigating rice fields in central Thailand. This river system plays a critical role in the agriculture of the region, particularly for rice cultivation, which is a staple food and a key economic crop for Thailand. The river provides a reliable water source, especially during the dry season, ensuring that rice fields receive adequate irrigation. The extensive network of canals that branches off from the Chao Phraya also facilitates the distribution of water to various agricultural lands, making it vital for the productivity of rice farming in central Thailand.

The other rivers mentioned, such as the Mekong River, Red River, and Irrawaddy River, are important in their respective regions but do not have the same direct impact on the irrigation of rice fields in central Thailand. The Mekong, for instance, flows through northeastern Thailand and is not primarily utilized for rice irrigation in the central part of the country. Thus, the Chao Phraya River stands out as the crucial feature for this agricultural process.