Water Resources Management in the

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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
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• 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.

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Map of the Philippines (upper left), Metro
Manila (upper right), the relative
locations (lower portion) of Pasig and
Marikina Rivers and Laguna de Bay.
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Basin maps top - Angat River Basin (A568
km2) bottom - Metro Manila and Laguna de
Bay Basins, A 4500 km2 900 km2 (lake)
3600 km2 (land) with annual isohyetal lines,
rainfall station locations and drainage
network.
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Rainfall pattern during El Niño episodes
Annual Rainfall Science Garden Mean
2418 mm (1961-2000) El Niño episodes
1982-1983 1970 mm, 1656 mm 1987-1988 1628 mm
(1987) 1997-1998 2141 mm (1997) UPLB
Mean 2010 mm (1977-2000) El Niño episodes
1982-1983 1373 mm, 1676 mm 1987-1988 1280 mm
(1987) 1997-1998 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.
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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.
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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
1997-1998.
This situation was most advantageous for the
traditional brackish-water aquaculture and
fisheries, but very disadvantageous for potential
water-supply and irrigation uses.
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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 1997-1999.
(a). Time series plots and (b). Scatter plots
and fitted regression lines of salinity
versus transparency and turbidity.
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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
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Mean annual basin rainfall 3155 mm. (for
years 1981- 2000) reservoir inflow 1724 MCM
(for years 1981 -1999). El Niño
episodes 1982-1983 basin rainfall 1430 mm,
1594 mm. reservoir inflow 1587 MCM, 1279
MCM 1987-1988 basin rainfall 3311 mm, 2831
mm. reservoir inflow 1311 MCM,2025
MCM 1997-1998 basin rainfall 2384 mm,2509 mm.
reservoir inflow 906 MCM,1800 MCM,
Impact of El Niño on water supply and irrigation
aa
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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).
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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 1997-2003.
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Summary of the history and pattern of decisions
for monthly releases of Angat Reservoir for
irrigation and water supply for the years
1997-2003, in terms of scatter plots and
regression curves.
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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 1997-1998 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 2001-2003. (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 .
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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.