Climate Change in Hawke's Bay

• By 2040, annual mean temperatures across Hawke’s Bay are projected to increase by 0.5-1.0 deg C. If no mitigating actions are taken, inland western Hawke’s Bay areas may see further increases of 1-1.5 deg C during summer and autumn.
• By 2090, projected annual mean temperature increases are 1.0-1.5 deg C where emissions reductions are taken, or could be up to 2.5-3.0 deg C where emission reductions are not taken, with inland, western areas potentially experiencing up to 4.0 deg C increase in summer averages.

• By 2040, frost days in the eastern half of Hawke’s Bay are projected to decrease by 1-5 days, with inland, higher elevation levels projected to decrease 5-10 days, with or without emissions reductions.
• By 2090, with emissions cuts, frost days in many locations are projected to decrease by 10-20 days, and without cuts, whilst much variation across Hawke’s Bay, higher elevations might see decreases in frost days of between 10-50.

• By 2040, heatwave days are projected to increase by 10-20 days per year for much of the region, without emissions cuts, this will be much more widespread.
• By 2090, projections are accentuated with cooler south-eastern areas of Hawke’s Bay also experiencing 10-20 heatwave days. Without emissions reductions, increases in some areas will reach 20-40 heatwave days per year.
• Further studies into extreme heat in New Zealand also identify the Napier and East Coast area as having high and very high risks associated with extreme heat. 

• The more significant changes are to seasonal rainfall patterns with an increasing number of extreme rainfall events being offset with longer dry periods. Overall, total annual rainfall levels will be similar.
• By 2040, seasonal variation will see a 5-10% increase in winter rainfall, with a similar decrease in spring. Without emissions cuts, it is projected seasonal variations will be slightly larger and/or more widespread throughout Hawke’s Bay.
• By 2090, without emission reductions, much stronger drying patterns are evident region-wide, with up to 15% increased rainfall in winter at high elevations.

• Aligned to changing rainfall patterns, the region will see increasing drought frequency, especially for southern Hawke’s Bay due to increased potential evapotranspiration deficit.
• Where emissions cuts are achieved, potential evapotranspiration deficits increase by 100-150mm, this becoming more widespread over time.
• Without emissions cuts, potential evapotranspiration deficits increase by up to 200mm by 2090, with the probability for extreme events (+300mm) and droughts more frequent and much more wide reaching.

In coastal areas, sea-level rise is already affecting human activities and infrastructure, they leave us more vulnerable to storms and tsunami. Other impacts include: 

• gradual inundation of low-lying marsh areas and adjoining dry land on spring high tides
• escalation in frequency of coastal flooding events
• exacerbated erosion of sand and gravel shorelines and unconsolidated cliffs
• increased incursion of saltwater in lowland rivers and nearby ground water aquifers, potentially raising water tables

These will all have implications for existing development in coastal areas and associated infrastructure.

Since NIWA prepared this report however, further analysis has been completed on sea-level rise and vertical land movement showing that sea level rise may happen much faster due to vertical land movement. Much of Hawke’s Bay’s coastline is slowly subsiding, which further exacerbates the implications of sea-level rise. This information can be found here.