In the second of a four-part series, Eloise Gibson looks at climate forecasters' needs.

Predicting booms and busts in rainfall that could lengthen the fire season and put pressure on city stormwater systems has been named as one of the top areas where climate scientists need to know more about our environment.

Rainfall, and making better overall predictions for cities and regions, was picked by Niwa principal climate scientist James Renwick as a key subject climate forecasters did not know enough about.

The head of Auckland University's Environment School, climate researcher Glenn McGregor, also picked rainfall as a major area in need of more research in New Zealand.

The problem was singled out by the journal Nature this month as one of four top areas of climate change uncertainty globally, with three others - regional predictions, the role of aerosols in warming and cooling, and palaeoclimate data.

Rainfall uncertainty could mean worse climate changes are in store than scientists think, because climate models tend to underestimate real changes in rainfall patterns.

Dr McGregor said clouds and rain were one of the harder climate processes to simulate, but modellers were working to improve their efforts.

To make matters harder, improving the models using data from past rainfall was being held back because there was not enough data tracking rainfall in some parts of the world - including some of those likely to be most affected by changes in drought patterns.

Aucklander Jim Salinger, the president of the World Meteorological Organisation's commission for agricultural meteorology, said diligent work by the DSIR in the 1930s meant New Zealand had good records going back over a long time.

For countries not so lucky, the Global Climate Observing System set up by the WMO in the early 1990s was intended to beef up the reliability of global climate records, he said.

But a report on the implementation of the system at the Copenhagen climate conference in December noted developing countries had made only limited progress filling in gaps in their observation networks, and some regions had gone backwards.

As the globe warms, rain is expected to come in heavier bursts - possibly meaning more erosion and run-off and potentially putting added pressure on city stormwater drains.

In 2007 the Intergovernmental Panel on Climate Change said production from agriculture and forestry was projected to decline by 2030 over parts of eastern New Zealand because of increased droughts and fire.

Western and southern parts of New Zealand close to major rivers, on the other hand, could benefit from more rain and a longer growing season.

The IPCC's summary for Governments predicted more frequent heavy rain, especially in the west, while eastern parts of the country and the Bay of Plenty and Northland could get severe droughts two to four times more often by the end of the century.

Solving the problem of uncertainty in local climate projections was an IPCC priority in its 2007 report.