Selected Applications

1
Selected Applications of Seasonal Climate
Forecasting in Water Management

Niue 19 21 April 2005 Bureau of Meteorology -
AusAID project ENHANCED APPLICATIONS OF CLIMATE
PREDICTIONS IN PACIFIC ISLAND COUNTRIES
(PI-CPP) Ross James, Bureau of
Meteorology (Presentation prepared by Tony
Falkland)
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Outline of Presentation

• Scope
• Overview of water resources and uses
• Applications of seasonal climate forecasts
• Limitations in using seasonal climate forecasts
• Case examples

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Scope

• Water management
• Focus on water supply systems
• Forecasts
• Considering seasonal climate forecasts
• Not considering forecasts of weather / climate at
  other time scales such as
• Flood forecasting (short time scale)
• Cyclone warnings (short time scale)
• Longer-term climate variability (e.g. for design
  of larger water supply systems)

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Summary water other data for selected PICs

• Basic data

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Summary water other data for selected PICs
Water related data
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Hydrological cycle and processes

• Major hydrological processes are
• Precipitation (mainly rain also hail, dew,
  frost, snow)
• Surface retention (interception and depression
  storage)
• Infiltration
• Soil-water redistribution
• Evaporation transpiration
• (Evapotranspiration)
• Surface runoff
• Groundwater recharge
• Groundwater movement discharge (includes
  mixing with saltwater)

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Freshwater Resources of Small Tropical Islands

• Common, naturally occurring
• SURFACE WATER
• GROUNDWATER
• RAINWATER
• Less common or more expensive
• DESALINATION
• IMPORTATION
• USE of SEAWATER or BRACKISH WATER
• WASTEWATER REUSE

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Main Types of Water Resources

• High Island
• Surface Groundwater Resources

Low Island Groundwater Resources only
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Surface Water Resources

• RIVERS STREAMS
• surface
• subterranean (in karstic formations)
• SPRINGS
• on island
• at coastline
• submarine
• LAKES SWAMPS
• fresh
• brackish

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Groundwater Resources (HIGH ISLAND example)

• Example from the Hawaiian Islands - perched
  (horizontal)
• showing 3 types of groundwater aquifers -
  perched (vertical)
• - basal

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Groundwater Resources (LOW ISLAND example)

• Example of small coral island basal aquifer
  only
• from a typical atoll with thick (often called
  a freshwater lens)
• transition zone

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Water uses

• Water supply (most important use)
• Tourism (selected islands)
• Irrigated agriculture (limited)
• Hydropower (limited to some islands)
• Mining (limited to some islands)

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How can Seasonal Climate Forecasts (SCFs) help in
water management?

• SCFs can give probabilities of above average,
  average and below average rainfall and
  temperature
• Rainfall forecasts are particularly important.
  Rainfall is the main input in the hydrological
  cycle. Impacts on
• Soil moisture
• Streamflow
• Groundwater recharge
• Spring outflows
• Temperature forecasts are less important.
  Temperature is not the only factor influencing
  evapotranspiration (one of the main outputs in
  the hydrological cycle)

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Applications of seasonal climate forecasts to
water management

• (a) Forecasts of lower than normal rainfall
• Activate drought planning measures
• (b) Forecasts of higher than normal rainfall (and
  possible frequency of tropical cyclones)
• Enhance disaster planning and preparedness

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Applications (a) Drought planning

• Increase monitoring and surveillance of water
  resources
• Streamflows, water levels (reservoirs and
  groundwater)
• Groundwater salinity in coastal and small island
  aquifers
• Plan for emergency water supply measures.
  Examples are
• Barging of water (Fiji, Tonga)
• Desalination (Marshall Islands, Tuvalu)
• Temporary dug wells on beach below high tide in
  some islands
• Coconuts - substitute for freshwater (temporary
  use)
• Brackish or seawater - non-potable purposes
• Prepare to change water supply procedures, e.g.
• Use (more expensive) pumping rather than surface
  water sources
• Use more distant sources rather then closer, less
  expensive sources
• Accept higher groundwater salinity conditions
  during the drought

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Applications (a) Drought planning (contd)

• Increase water conservation measures (especially
  urban areas)
• Advise communities of possible need for water
  restrictions
• Advise householders to conserve rainwater for
  essential needs
• Commence use of water from special communal
  storages (e.g. Funafuti, Tuvalu).
• Increase leakage control measures
• Plan for alternative electricity sources where
  hydropower is used
• Advise communities in advance
• Possible need for additional funds to run diesel
  powered stations

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Applications (b) Disaster planning preparedness

• Increase surveillance of weather conditions
• Ensure measures in place for possible increased
  flooding
• Assess vulnerability of critical areas (e.g.
  urban areas, water supply infrastructure)
• Check/update existing plans operational
  procedures
• Undertake road and bridge maintenance
• Check/clear floodways upstream of critical areas
• Ensure capability to disseminate warnings in a
  timely manner
• Plan for gauging of streams in high flow
  conditions
• Need to check equipment, transport access
• Need for appropriately trained personnel
• Ensure sufficient funds are available for
  contingencies

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Limitations of seasonal climate forecasts

• Not applicable to short-term forecasting
• Flood forecasting (except higher rainfall
  forecasts may indicate greater risk of floods)
• Cyclone warnings (except that frequency of
  cyclones may vary)
• Not applicable to water supply schemes that
  account for longer-term climate variability
• Many large water supply/resource systems are
  designed using sustainable yield principles
  (which take account of seasonal fluctuations in
  climate)

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Case examples

• Groundwater pumping strategies to cope with
  droughts
• Home Island, Cocos (Keeling) Islands
• Assessment of streamflow conditions
• Australia
• Hawaiian Islands
• Use of Drought Indices (using rainfall data where
  there is insufficient water resources data)
• Rarotonga, Cook Islands
• South Tarawa, Kiribati

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Groundwater pumping strategies (to cope with
droughts)

• Two main approaches
• Fixed pumping rates
• Based on estimation of sustainable yield
• Used where consequences of failure are high
• Seasonal forecasting is not applicable as pump
  rates do not vary
• Examples include groundwater pumping systems for
• South Tarawa, Kiribati
• Nukualofa, Kingdom of Tonga
• Variable pumping rates
• Based on rainfall index and/or groundwater
  salinity
• Has application for seasonal forecasting
• Example
• Water supply to Home Island, Cocos (Keeling)
  Islands

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Groundwater pumping strategy for Home Island,
Cocos (Keeling) Islands

• Coral atoll in Indian Ocean (territory of
  Australia)
• Groundwater supplied to 500 people on Home Is
• Example of variable pumping rates

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Groundwater pumping strategy for Home Island

• Fresh groundwater occurs in the form of a
  freshwater lens (above saline water)

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Groundwater pumping strategy for Home Island

• Infiltration galleries (skimming wells) are
  used to pump groundwater

Typical infiltration gallery details
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Groundwater pumping strategy for Home Island

• Sustainable yield (safe pumping rate) of the
  freshwater lens
• 150 kilolitres per day (kL/day)
• estimated using groundwater model using
• data from multi-level monitoring boreholes
• recharge estimates based on daily rainfall
  readings and evaporation estimates

Layout of Galleries and Boreholes (Main Lens)
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Groundwater pumping strategy for Home Island

• Regular monitoring of groundwater salinity and
  rainfall
• Daily Rainfall and volumes of water pumped from
  each gallery
• Monthly Groundwater salinity data from 9
  galleries every month (7 in main lens and 2 in
  northern lens)
• Quarterly Groundwater salinity v depth data from
  18 boreholes

Daily-read raingauge
Borehole monitoring
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Groundwater pumping strategy for Home Island

• Daily rainfall data
• Home Island 1987 present (18 years)
• West Island (Bureau of Meteorology stn) 1952
  present (53 years)

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Groundwater pumping strategy for Home Island

• Monthly groundwater salinity data at galleries
• 1992 present (13 years)

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Groundwater pumping strategy for Home Island

• Quarterly groundwater salinity data from
  boreholes
• Late 1987 2004 (17 years)
• Fresh groundwater indicated to base of red line
  (EC 2,500 µS/cm)

Borehole, HI1 (centre of main lens) salinity
monitoring data
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Groundwater pumping strategy for Home Island

• Rainfall index and groundwater salinity updated
  each month
• Rainfall index based on previous 12 months
  rainfall decay factor of 0.9
• Groundwater salinity from blended water (from all
  galleries) and a critical (No 1) gallery

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Groundwater pumping strategy for Home Island

• Pumping strategy
• Pump at sustainable rate when dry conditions
  apply
• Allow pumping at higher rates during other times
• The table below shows pumping rates for
  different conditions of a rainfall index
  groundwater salinity at main tank
• Procedure each month
• Rainfall index is updated groundwater salinity
  is checked
• Pumping rates at galleries are set according to
  the climate condition (based on worst of
  rainfall index and groundwater salinity criteria)
• At present, the strategy is based on historical
  data and not on forecasts

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Groundwater pumping strategy for Home Island

• Seasonal climate forecasts could be used to
  forecast pumping conditions
• To do this, options are
• Update rainfall index with rainfall estimate
  based on rainfall forecast
• Update groundwater salinity based on forecast
  rainfall using relationship between rainfall
  index and groundwater salinity
• Example of relationship
• between rainfall index
• and groundwater salinity

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Applications to other islands

• The same or similar type of approach could be
  used in other islands
• Which use groundwater pumping systems
• Where monitoring data is available for daily
  rainfall, daily pumping volumes and groundwater
• On Home Island, groundwater salinity is the key
  parameter. In other islands, groundwater level
  and/or salinity could be used

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Assessment of Streamflow Conditions (a) Australia

• Chiew and McMahon (2003)
• Study of teleconnections between ENSO indicators
  and monthly rainfall / streamflow
• Examined data from 284 catchments for period
  1901-1998
• Investigated potential for forecasting rainfall
  and streamflow several months ahead using
• Lag correlations between ENSO indicators (the SOI
  and a Multivariate ENSO Index, MEI) and rainfall
  / streamflow. The lag was one season.
• Serial correlations in rainfall and in streamflow
  (statistical properties of each variable)

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Assessment of Streamflow Conditions (a) Australia
(continued)

• Main Findings
• Forecasting of streamflows in parts of Australia
  is feasible for selected times of the year.
• Using ENSO indicators
• Moderate to high correlation with spring summer
  (Sept Feb) streamflow
• Reasonable correlation with autumn (April-June)
  streamflow
• The serial correlation in streamflow can also be
  used for forecasting
• Similar results to lag correlations for
  streamflow with ENSO indicators.
• Strongest for spring, summer and winter,
  particularly in southern Australia.
• Comment
• Further work is being done on this topic
• Potential to apply these procedures in Pacific
  Island countries (provided there is sufficient
  streamflow data)

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Assessment of Streamflow Conditions (b) Hawaiian
Islands

• Oki (2004)
• Analysis of long-term flows trends in 5 islands
  (Kauai, Oahu, Molokai, Maui and Hawaii)
• Data from 16 stream-gauging stations. Length of
  records varied from 36 to 91 years, with average
  60 years.

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Assessment of Streamflow Conditions (b) Hawaiian
Islands (continued)

• Main Findings
• Short-term variability in streamflow is mainly
  related to seasons and ENSO. It may also be
  partly affected by the phase of the Pacific
  Decadal Oscillation (PDO).
• Streamflow in Jan - March quarter tends to be low
  following El Niño episodes and high following La
  Niña episodes.
• ENSO is more strongly related to rainfall and
  direct runoff than groundwater storage and
  baseflow.
• From 1913 to 2002, baseflows generally decreased.
  Consistent with a long-term downward trend in
  annual rainfall.
• Conclusions
• Further study required into
• The physical causes for the variations in
  streamflow.
• Whether regional climate indicators can
  successfully be used to predict streamflow trends
  and variations.
• To allow for ongoing study, the network of
  stream-gauging stations should be maintained.

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Use of Drought Indices (a) Rarotonga, Cook Islands

• Parakoti and Scott (2002)
• Rarotongas water supply
• 12 stream water intakes around the island
• Difficult to meet water demand plus leakage
  during drought periods
• Streamflow records
• Relatively short (approx. 4-5 years) at 3
  catchments.
• Not long enough to correlate with ENSO
  indicators.

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Use of Drought Indices (a) Rarotonga, Cook
Islands (continued)

• A Drought Index developed to monitor drought
  onset severity
• Based on monthly rainfall
• Several methods investigated
• Selected Weighted Sum Drought Index approach
  using previous 10 months of data and factors
  decreasing from 0.9 to 0.1

Weighted Sum Drought Index, 1929-2002 (values
less than 600 are highlighted)
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Use of Drought Indices (a) Rarotonga, Cook
Islands (continued)

• The Drought Index is currently used as a
  monitoring and not a predictive tool
• At onset of droughts, main drought management
  strategies are
• Water restrictions
• Short-term emphasis on leakage control measures
• Additional drought management strategies are
• Introduce water conservation measures (e.g. dual
  flush cisterns, use of grey water for garden
  watering)
• Design and install roof catchment systems
• Require greater public and political awareness of
  Rarotongas water resources
• Potential developments
• Update Drought Index each month with SCFs of
  rainfall (e.g. using estimates of monthly
  rainfall based on forecast rainfall - high,
  medium or low)
• When sufficient streamflow data is available
  correlate streamflow with seasonal climate
  predictors (SOI and SSTs)

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Use of Drought Indices (b) South Tarawa, Kiribati

• White et al (1999)
• Study of drought and its impact on water
  supplies
• Domestic groundwater wells
• Public groundwater system using infiltration
  galleries on two islands (Bonriki and Buota)
• Rainwater tanks
• Tarawa and other atolls in Kiribati experience
• Highly variable rainfall closely related to
  ENSO cycles
• Severe droughts associated with La Niña episodes
  (e.g. 1998-2000)

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Use of Drought Indices (b) South Tarawa, Kiribati
(continued)

• Drought Index based on Decile Method
• rainfalls expressed as percentile rankings of
  rainfall, accumulated over time periods ranging
  from 6 months to 5 years
• Following categories identified when the
  accumulated rainfall drops
• Warning of onset of severe dry period below 40
  percentile level
• Severe drought below 10 percentile level
• Drought Index ranking 6 months Drought
  Index ranking 5 years

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Use of Drought Indices (b) South Tarawa, Kiribati
(continued)

• Findings
• The severity of the major 1998-2000 drought in
  South Tarawa was ranked against other historical
  droughts, as follows
• Rainwater tanks worst on record for 4 months,
  lowest 2 for 6 months
• Domestic wells lowest 3 for 12 month period
• Public water supply system lowest 17 for 5 year
  period
• The 5 year rainfall accumulation times for large
  freshwater lenses is consistent with the
  residence time for freshwater in the lens.
• Further work is required re appropriate
  percentile levels for onset of drought and
  severe drought
• Potential developments
• Update Drought Index each month with seasonal
  rainfall forecasts (as for Rarotonga)
• Possibly use ENSO indicators to forecast
  groundwater salinity (collected since 1980)

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Water Resources Data Requirements

• Long-term, good-quality water resources data sets
  (preferably greater than 30 years) are required
  by models (e.g. SCOPIC) to develop direct
  relationships between climate predictors (e.g.
  SOI or SSTs) and water resources parameters.
• Most Pacific Island countries do not have
  long-term water resources data sets
• Need for ongoing water resources data collection
  programs. e.g.
• Streamflows spring flows
• Groundwater levels and salinity

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Conclusions

• Seasonal climate forecasting can be applied to a
  variety of water resources and water supply
  systems provided that suitable monitoring data is
  available.
• The main application is in the area of drought
  forecasting and related management strategies.
• SCFs have limitations in water resources
  applications (not apply to short and long term
  time scales of relevant hydrological processes)
• Further development work required to apply SCFs
  to specific water sector issues.
• Long-term, good quality water resources data is
  essential for analysing relationships between
  climatic and water resources data.
• Need for continued operation (and expansion) of
  water monitoring networks.
• Thank you