Surface runoff
The hydrographic system is divided into three primary drainage basins. First, the Pacific Ocean drainage basin covers 22% of the country and counts 18 watersheds. Some of the rivers in this zone transport volcanic sediments to be deposited along the coast and contributes to coastal flooding due to reduced depths of tidal marshes. Annual surface runoff in this basin is 25.5 km3. The Caribbean Sea drainage basin covers 31% of the country and has 10 watersheds. Average annual surface runoff in this basin is calculated at 31.9 km3. The Gulf of Mexico basin covers 47% of Guatemala and 10 watersheds. The rivers in this basin have the largest flows in the country and drain towards Mexico. Surface runoff in this basin is 43.3 km3.