Climate Sense

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Seasonal climate outlooks for

assistance in water management

Charles Pearson, National Institute of Water and Atmospheric Research, New Zealand

ater managers and engineers make use of climate

information and predictions at a range of temporal

and spatial scales, and also use their own tech-

niques to account for climate variability. In the longer term,

the impacts of global warming will be of significant interest

to water managers, as will improved short- and medium-term

climate and hydrological predictions. For the short (seasonal)

to medium (interannual) term, some knowledge of climatology

and climate variability is useful for water managers, engineers

and decision makers.

Some national hydrological services are now taking advantage of

regular climate outlook information to produce regular seasonal

hydrological predictions. The predictions can be particularly useful

for the freshwater sector, for such uses as irrigation scheduling,

water resources management, water supply, hydropower opera-

tions and hazard mitigation (floods and droughts). Typical water

variables predicted, based on good climate data and predictions

(air temperature and rainfall) and good hydrological data, include

soil moisture, likely mean river flows and groundwater and lake

levels for the season ahead.

These predictions rely upon good communications and data

transfer between national hydrological and climate services.

Typically the predictions are made by consensus among expe-

rienced hydrologists. As with climate predictions, hydrological

predictions rely upon international collaboration to extend predic-

tions to regional bases. The advent of increased monitoring during

the International Hydrological Decade (1965-74) and a number

of regional Hydrological Cycle Observation Systems projects, led

by the World Meteorological Organization (WMO), are enabling

regions and countries to validate hydrological predictions with

reliable data.

Many water resource managers use their own techniques to

account for climate variability, on seasonal and longer times-

cales. For example, in designing a flood protection scheme, a

water engineer will estimate the flood frequency for a river loca-

tion, estimating the flood peak flow magnitude of a given risk of

occurrence. If the protection scheme has a design life of 50 years

ahead, then engineers are aware that climate change, variability

and upstream land use change all have potential to impact upon

the occurrence of flood peaks.

Some national and international meteorological and clima-

tological services produce climate information and predictions

ahead for one to three months and beyond for their country and

surrounding region. Information produced includes status of rain-

fall and air and sea temperatures for the immediate past period,

and predictions of rainfall and air temperatures for a

season ahead. In some cases, hydrological agencies

engage with climatological counterparts to produce

corresponding downstream predictions of terrestrial

hydrological variables such as soil moisture, river

flow, lake and groundwater storages.

Climate information is produced from good quality

climate data records, and timely extraction of the data

into information on the status of current conditions.

Tabular and mapped information can be produced on

air temperatures, rainfall and precipitation, sunshine,

solar radiation, barometric pressure and sea surface

temperatures.

Climate prediction relies upon global signals such as

the status of the El Niño Southern Oscillation (ENSO)

and the Interdecadal Pacific Oscillation, and their

implications (from previous records and science) at

regional and country scales. Local scientific knowledge

on circulation and seasons, and developed statistical

prediction tools such as similar past analogous situ-

ations and regression schemes, are used to predict

climate variables one to three months in advance. Over

ten global climate models provide predictions on the

state of Pacific sea surface temperatures and ENSO up

to nine months ahead.

Typically, climatologists take into account all avail-

able information to form a consensus view to predict

seasonal outlooks of variables such as air temperatures

and rainfall.

Hydrological information can be generated from

hydrological monitoring networks. It is necessary to

know the initial status of water fluxes and storages

before making predictions.

New Zealand’s National Climate Centre has

predicted ahead three monthly rainfall, air temper-

atures, soil moisture levels and streamflows for

six defined regions of the country since 1999. The

predictions are published in a monthly newsletter

The Climate Update

(now Web-based), and dissemi-

nated through media releases. Users of the predictions

include the agricultural and horticultural sectors,

hydropower and irrigation companies, and local

government bodies responsible for water resource and

hazard management.

The method used to translate these predictions into

on the ground soil moisture and river flow predictions

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