1. Water Resources Management in the Philippines during El Niño Episodes
Leonardo Q. Liongson
National Hydraulic Research Center
University of the Philippines
Diliman, Quezon City, Philippines
FIJI-2003
International Conference on
Managing Water Resources under Climatic Extremes
and Natural Disasters
The Outrigger Hotel, Sigatoka, Fiji
27 October – 31 October 2003

2. To present the main impacts of recent El Niño episodes
Aims of the paper :
To present the main impacts of recent El Niño episodes
to the water resources situation in the Metro Manila and
Laguna de Bay Basins in Luzon island, in terms of the
rainfall magnitudes and distributions and the consequent
streamflow values and lake and reservoir water levels
attained in affected areas.
To describe the effects on water quality indices such as
lake salinity, transparency and turbidity.
To present hydrological and water-quality data time-series
and their statistical correlations.
To analyze the management options which were exercised
by the state under the El Niño conditions of water scarcity
for allocation to various multipurpose uses.
Outline:
1. Introduction
2. Rainfall pattern during El Niño episodes
3. Impact of El Niño on aquaculture and fisheries
4. Impact of El Niño on water supply and irrigation
5. Conclusion and recommendations

3. Map of the Philippines (upper left),
Metro Manila (upper right),
&
the relative locations (lower portion)
of Pasig and Marikina Rivers
and Laguna de Bay.

4. Basin maps: top - Angat River Basin (A=568 km2) ; bottom -
Metro Manila and Laguna de Bay
Basins, A = 4500 km2
= 900 km2 (lake) km2 (land)
with annual isohyetal lines, rainfall station
locations and drainage network.

5. Rainfall pattern during El Niño episodes
Annual Rainfall
Science Garden
Mean = mm ( )
El Niño episodes:
: mm, 1656 mm
: mm (1987)
: mm (1997)
UPLB
Mean = mm ( )
: 1373 mm, 1676 mm
: 1280 mm (1987)
: 1355 mm (1997)
Monthly and annual time-series of rainfall data at Science Garden station,
Quezon City, Metro Manila and at UPLB, Los Baños station.

6. aquaculture and fisheries
Impact of El Niño on
aquaculture and fisheries
Small fisherman engaged
in open lake fishing.
Fish pens (top) &
Fish cages (bottom)
used for aquaculture in Laguna de Bay.

7. aquaculture and fisheries
Impact of El Niño on
aquaculture and fisheries
Rainfall (in drought conditions),
lake stage (severe drawdown),
&
salinity (maximized conditions)
during the El Niño
months of
This situation was most advantageous
for the traditional brackish-water aquaculture
and fisheries, but very disadvantageous for
potential water-supply and irrigation uses.

8. aquaculture and fisheries
Impact of El Niño on
aquaculture and fisheries
Monthly measurements of salinity, transparency
and turbidity at Laguna de Bay West-Bay-I
station during the years
(a). Time series plots and
(b). Scatter plots and fitted regression lines
of salinity versus transparency and turbidity.

9. Impact of El Niño on water supply and irrigation
Angat
Reservoir
Water-supply sources
of Metro Manila
from Angat Reservoir
in the north
to Novaliches Reservoir
and water treatment plants
to the south.
Novaliches
Reservoir
Metro Manila

10. Impact of El Niño on water supply and irrigation
Mean annual
basin rainfall = 3155 mm.
(for years )
reservoir inflow = 1724 MCM
(for years ).
El Niño episodes:
basin rainfall =
1430 mm, 1594 mm.
reservoir inflow =
1587 MCM, MCM
3311 mm, 2831 mm.
1311 MCM,2025 MCM
2384 mm,2509 mm.
906 MCM,1800 MCM,
Impact of El Niño on water supply and irrigation aa

11. Scatter plots and regression lines for:
(a). Current reservoir inflow, Q(t),
versus previous inflow, Q(t-1),
&
(b). Residual error, e(t), versus
basin rainfall, P(t).

12. Monthly plots of
Angat Reservoir
monthly inflows,
releases for
irrigation & water supply,
and
ending water surface elevation,
together with
the lower rule curve,
for the years

13. Summary of the history and pattern of decisions for monthly
releases of Angat Reservoir for irrigation and water supply for the
years , in terms of scatter plots and regression curves.

14. Conclusion:
(a). Inspite of the observed unpredictability and low correlation of rainfall
in many parts of the Philippines with respect to sea surface temperatures
(SST Index), whenever El Niño episodes did indeed happen, remarkable
localized cases of prolonged drought conditions had registered in terms of
the secondary effects of increased salinity and transparency (and decreased
turbidity) in Laguna de Bay, and the reduced inflows and excessive drawdown
of Angat Reservoir water level below the lower rule curve.
(b). The occurrence of El Niño episodes such as in had tested the
resolve and will of the state to enforce the provision of the Water Code,
which places higher priority to releases for water supply, to the extent of reducing
the release for irrigation down to zero for extended period of time. With this
conscious policy, reductions in irrigation releases have been made for briefer
periods during mild El Niño events in the years
(c). The prolonged drought conditions and the highly localized rainfall variations
during El Niño episodes pose serious challenges to the capability of local experts
to model and forecast reliable rainfall and streamflow amounts, given already
the spatial inadequacy in hydrometric networks, shortness of most hydrologic
records, and the lack of understanding of the meteorological phenomena .

15. Thank you. Recommendations:
(a). More and closer cooperation between meteorologists, hydrologists, and
other natural scientists and engineers in order to exchange ideas, data and
research results to better understand the El Niño and La Niña phenomena
and be able to translate the acquired knowledge to better-informed decisions,
strategies and programs of actions in water resources management.
(b). Encourage and support cooperative hydrological research and development,
in workable local, regional or international groupings, to bridge the gaps in the
theory and practice related to predicting rainfall during El Niño episodes and
how this effort relate to modeling (use of global circulation models, rainfall
forecasting, rainfall-runoff modeling, streamflow forecasting), as well as tackle
the related practical and technical issues of hydrometry, data archiving, software
tools, data sharing and research dissemination with publications, conferences
and the Internet.
Thank you.