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)

2. Outline of Presentation
Scope
Overview of water resources and uses
Applications of seasonal climate forecasts
Limitations in using seasonal climate forecasts
Case examples

3. Scope Water management Forecasts Focus on water supply systems
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)

4. Summary water & other data for selected PICs
Basic data

5. Summary water & other data for selected PICs
Water related data

6. 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)

7. 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

8. Main Types of Water Resources
High Island:
Surface & Groundwater Resources
Low Island: Groundwater Resources only

9. Surface Water Resources
RIVERS & STREAMS
surface
subterranean (in karstic formations)
SPRINGS
on island
at coastline
submarine
LAKES & SWAMPS
fresh
brackish

10. Groundwater Resources (HIGH ISLAND example)
Example from the Hawaiian Islands - perched (horizontal)
showing 3 types of groundwater aquifers - perched (vertical)
- basal

11. 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

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

13. 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)

14. 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

15. 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

16. Applications : (a) Drought planning (cont’d)
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

17. 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

18. 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)

19. 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

20. 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
Nuku’alofa, 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

21. 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

22. Groundwater pumping strategy for Home Island
Fresh groundwater occurs in the form of a freshwater lens (above saline water)

23. Groundwater pumping strategy for Home Island
Infiltration galleries (‘skimming wells’) are used to pump groundwater
Typical infiltration gallery details

24. 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)

25. 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

26. 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)
It is not an easy task to present the results of a statistical analysis and avoid that the audience is falling asleep. I hope I succeed in making it crisp and short. Here is the main message:
1 . Over the next 30 years we can produce enough food to feed 8100 million people. Food insecurity and rural poverty can be eradicated
2. To achieve this objective we can and must increase the effective irrigated area in developing countries by 34 percent
3. To do so, we need only 12 % more water if we use the means available to increase water use efficiency
How is this possible?

27. Groundwater pumping strategy for Home Island
Monthly groundwater salinity data at galleries:
1992 – present (13 years)

28. 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

29. 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

30. Groundwater pumping strategy for Home Island
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

31. 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
Possibly develop direct relationship between predictors (e.g. SSTs or SOI) and groundwater salinity

32. 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

33. 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
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)

34. 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)

35. 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.

36. 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.

37. (a) Rarotonga, Cook Islands
Use of Drought Indices
(a) Rarotonga, Cook Islands
Parakoti and Scott (2002)
Rarotonga’s 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.

38. (a) Rarotonga, Cook Islands (continued)
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, (values less than 600 are highlighted)

39. (a) Rarotonga, Cook Islands (continued)
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 Rarotonga’s 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)

40. (b) South Tarawa, Kiribati
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 )

41. (b) South Tarawa, Kiribati (continued)
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

42. (b) South Tarawa, Kiribati (continued)
Use of Drought Indices
(b) South Tarawa, Kiribati (continued)
Findings
The severity of the major 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)

43. 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

44. 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