Assessment of the hydrological impacts of El Niño and La Niña on selected watersheds in the Philippines

Abstract

The direction and magnitude of the impacts of El Niño and La Niña on the water budget of watersheds in the Philippines were assessed with particular focus on runoff. The WatBal and BROOK 5 models were chosen because of their simple structures and the availability of the database required to run these models. The expected decrease in rainfall due to El Niño was not observed in all 4 watersheds. Likewise, the expected increase in rainfall due to La Niña did not occur in all the watersheds. However, rainfall variability during the El Niño and La Niña episodes was markedly different from rainfall variability during the normal years. Concerning runoff, decreasing patterns in the predicted values were observed during El Niño years but no clear runoff pattern was observed during the La Niña years probably due to the variation in the intensity of La Niña episodes. Although both WatBal and BROOK 5 showed acceptable estimates of runoff in more than one watershed, they were unable to estimate the variability of actual runoff. Modification of BROOK 5 can be pursued in relation to the evaluation of land use parameters. The use of distributed instead of lumped parameters could help to improve the accuracy of results obtained through the use of water budget models.

Source or Periodical Title

Philippine Agricultural Scientist

ISSN

317454

Page

158-171

Document Type

Article

Subject

BROOK 5, El Niño, Hydrologic models, La Niña, Runoff, WatBal, Water, Water budget, Watershed

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