This was the finding of a study conducted by University of the Philippines researchers on the environmental changes in the Pampanga delta, composed of Pampanga, Bulacan, and Bataan and the Caloocan City, Malabon City, Navotas, and Valenzuela area, the commonly flooded cities and towns in Metro Manila.
Because of the continuing sinking of the Pampanga peninsula, the flooding problem in the region has been worsening.
For instance, the flooding situation in San Fernando City and in Bacolor, Macabebe, Masantol, Minalin, and Sasmuan in the 1980s ranged from one to three feet in depth. In the 1990s, flooding depth averaged 3.4 feet and reached six feet during the typhoon season.
Floods have become more frequent, higher, longer lasting, and more widespread, according to a UP research titled "Net Sea Level Change in the Pampanga Delta: Causes and Consequences."
The other causes of flooding are decrease in flood plain areas owing to urban sprawl, flood control dikes, and fishponds; and global sea level rise and land subsidence, the least understood but the most important.
As explained by the researchers, land subsidence is the lowering of land owing to the natural compaction of underlying soil and sediments and compaction which is hastened by rapid withdrawal of groundwater.