An expert discussion document on drought and climate change highlights the urgent need for future national planning to improve water storage and look at a range of options to mitigate the effects of the more severe droughts, IrrigationNZ says.

"More frequent droughts and more variable rainfall will affect both urban and rural communities and will mean that we will need to rethink how we manage water in the future," says IrrigationNZ chief executive Andrew Curtis.

"For example, with less rainfall forecast over summer in western areas of New Zealand, there will be more demand for water storage from both councils and farmers to provide a reliable water supply.

"To adequately prepare for the future New Zealand needs to capture more of its plentiful water from rain and ice melt. Hopefully the issues highlighted in this document will lead to action to avoid our regions being crippled from future droughts," Curtis says.

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The document highlights that having been historically 'water-rich', New Zealand is not well-prepared to cope with a future that will involve more droughts.

"Much of our irrigation in drier areas is on a run-of-river basis, a model extremely vulnerable to drought given environmental obligations," the report says.

"New Zealand's dependence on agricultural exports and urban reservoirs may yet be a recipe for drought vulnerability. Changing drought risk will have an impact on our society in many ways including on water supply, wastewater, stormwater and primary production among others."

Curtis says it's positive the Government is looking at how water services will be delivered in the future.

"The next step is to develop a national approach to plan for improved water storage for both urban and rural communities.

"Local and regional water storage infrastructure can be expensive to design and construct but the need for this investment will become more critical in the future.

"We will also need new infrastructure in regions where this hasn't previously been required as rainfall and river flows change."

Curtis says the recent decision by Tasman District Council to proceed with constructing a new dam to supply residents, businesses and growers with water is the kind of investment that will increasingly be needed in the future.

"The project is critical to avoid severe water restrictions for urban and rural water users, and also provide for environmental river flows," he adds.

Curtis says that improving water use efficiency will also continue to be a priority.

"Farmers are already investing in more efficient irrigation systems and New Zealand has very efficient systems operating by world standards.

"Regional councils are continuing to require that farmers adopt more efficient irrigation systems and irrigation schemes are also modernising their networks to install piped systems which reduce water loss.

"Urban areas are also looking at programmes to improve and encourage water use efficiency."

KEY POINTS

* NIWA projections indicate droughts are expected to become more severe in most areas and more frequent in already drought-prone regions.

* Seasonal rainfall patterns will also change, according to the Ministry for the Environment. For example, in spring, there may be less rain in eastern and northern regions and more rain in summer in eastern areas while western areas will experience drier summers.

* Droughts in New Zealand were estimated by Treasury to cost $720 million from 2007-17, significantly higher than for flood-related insurance claims over the same period.