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Climate Change and Variability - Tasman District

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This report describes the changes that may occur over the next century in the climate of the region administered by the Tasman District Council and describes some possible impacts of these changes. The pH of the oceans around New Zealand is predicted to decrease, in line with global trends.

The Physical Science Basis (IPCC Working Group I)

As the global average temperature increases, mid-latitude and humid tropical regions will experience more intense and frequent extreme precipitation events by the end of the 21st century. Global glacier volume (excluding Antarctic fringe glaciers) is projected to decrease by 15–85% by the end of the 21st century under various scenarios.

Impacts, Adaptation, and Vulnerability (IPCC Working Group II)

Even if emissions are stopped, most aspects of global climate change will persist for many centuries to come. Some unique and endangered systems, including ecosystems and cultures, are already at risk from climate change.

Mitigation of Climate Change (IPCC Working Group III)

In addition, climate change-related risks from extreme events, such as heat waves, extreme precipitation and coastal flooding, are already moderate/high with an additional 1°C of warming. Published information on the expected impacts of climate change on New Zealand has been summarized and reviewed in the Australasia chapter of the IPCC Working Group II assessment report (Reisinger et al., 2014).

Sectoral Impacts

Annual average rainfall is expected to decrease in the northeastern South Island and north and east of the North Island, and increase in other parts of New Zealand. Energy supply, demand and transmission: New Zealand's predominantly hydroelectric power generation is vulnerable to precipitation variability.

Spatial Patterns in Tasman’s Climate

Temporal Variability in Tasman’s Climate

Natural factors causing fluctuation in climate patterns over New Zealand

During the positive phase of the IPO, sea surface temperatures around New Zealand tend to be lower, and westerly winds stronger, with the opposite occurring in the negative phase. Negative values ​​indicate periods with more northeasterlies than normal in the northern regions of the country. The increase in temperatures across New Zealand around 1950 occurred shortly after the change from the positive to negative phase of the IPO.

In contrast, the negative phase of the SAM is associated with unsettled weather over New Zealand and stronger westerly winds, whereas winds and storms decrease towards Antarctica. 27 Figure 4-9: Time series of the southern annular mode from transient experiments forced with time-varying ozone-depleting substances and greenhouse gases.

Figure 4-8:  Percentage change in average annual rainfall, for the 1978-1998 period compared to the 1960- 1960-1977 period
Figure 4-8: Percentage change in average annual rainfall, for the 1978-1998 period compared to the 1960- 1960-1977 period

New Zealand Sea Level Trends and Variability

Gray shading indicates +/- one standard deviation of the three ensemble members around the ensemble mean. The long-term averages of the time series are arbitrary and have been set to zero for the period 1970-1975. Storm surge occurs due to a drop in atmospheric pressure (reverse barometric effect) and the influence of the wind on the.

Wave conditions also affect localized water levels where offshore of the breakwater area, water levels are set. The future climate of the Tasman District will be influenced by a combination of the effects of anthropogenic climate change (increased global greenhouse gas concentrations, Section 2) plus natural year-to-year and decade-to-decade variability resulting from "climate noise" and features such as the El Nino–Southern Oscillation (ENSO), the Interdecadal Pacific Oscillation (IPO), and the Southern Annular Mode (SAM), discussed in section 4 .

Table 4-1:  Historical relative sea-level rise rates.   Source: Hannah and Bell (2012)
Table 4-1: Historical relative sea-level rise rates. Source: Hannah and Bell (2012)

Tasman Climate Change Temperature Projections

Figures 5-3 and 5-4 show projected future warming of approximately 0.3°C per decade for the RCP8.5 scenario when averaged over 41 climate models. A slight acceleration of warming is predicted for the second 50 years of the 21st century compared to the first 50 years. The ensemble seasonal and annual mean projection (number outside parentheses) in Table 5-1 is the average temperature increase across the 23 models for RCP 2.6, 37 models for RCP 4.5, 18 models for RCP 6.0, and 41 models for RCP 8.5 analyzed by NIWA .

The greatest warming is projected for summer or fall (depending on the RCP) and the least warming is projected for spring. Note that the temperature change of the mitigation scenario (RCP 2.6) for 2090 is smaller than the change for 2040, while all other emission scenarios show increased warming in 2090 compared to 2040.

Projections for Frosts and Hot Days under Climate Change

Numbers on the scale refer to the increase in the number of hot days, eg the coast adjacent to Tasman Bay is projected to experience an increase in the number of hot days by 50-60 days by 2090 under RCP8.5 (right bottom panel). The projected decrease in the number of cold nights in both 2040 and 2090 for both RCPs is more significant in the southeast of the Tasman district (at higher elevations). By 2090 under RCP8.5, the number of cold nights in the southeastern part of the district is expected to decrease by more than 90 nights per year compared to 1986-2005.

In 2090 under RCP8.5 along the coast and inland between Motueka and Nelson, the number of cold nights is expected to decrease by 20–30 nights per year compared to 1986–2005. The numbers on the scale refer to the decrease in the number of cold nights, e.g. the coast adjacent to Tasman Bay is expected to experience a decrease in the number of cold nights by 10–15 days in 2040 under RCP8.5 (top right panel).

Figure 5-5 shows the projected increase in the number of hot days per year at 2040 (2031-2050) and  2090 (2081-2100) relative to 1986-2005, for RCP4.5 and RCP8.5
Figure 5-5 shows the projected increase in the number of hot days per year at 2040 (2031-2050) and 2090 (2081-2100) relative to 1986-2005, for RCP4.5 and RCP8.5

Tasman Climate Change Precipitation Projections

The ensemble mean is often less than ±5%, with the model range (5th and 95th percentile values) varying between fairly large increases and decreases (>10%). For other seasons, the ensemble mean is often less than 5%, with the model range (5th and 95th percentile) varying from small decreases to large increases in precipitation. Note that Figures 5-13 through 5-16 show model variability at only two grid points (Appleby and Takaka), rather than a regional average (as is done for temperature).

While the ensemble averages show an increase in precipitation, there is some disagreement between the individual models about the direction and magnitude of the predicted precipitation changes - the scatter within each RCP color bar is quite large, ranging for example from a 20% decrease to more than 50% more winter rainfall for under RCP8.5 in 2090 (Figure 5-16). The model spread is much larger for Takaka than for Appleby for all RCPs in both 2040 and 2090.

Table 5-3 for Appleby and Table 5-4 for Takaka. The precipitation changes are relative to the baseline  period 1986-2005
Table 5-3 for Appleby and Table 5-4 for Takaka. The precipitation changes are relative to the baseline period 1986-2005

Scenarios for Changes in Extreme Rainfall

For the 2008 update of the Local Government Guidance manual (Ministry of the Environment, 2008a), NIWA has produced some updated guidance on changes in heavy rainfall to be used for "screening assessments"3 in New Zealand. An overview of the process for producing heavy rainfall statistics for screening analytics, with a detailed example of its application to Richmond, can be found in the appendix to this report. The recommendation in the Local Government Guidance manual is that if a screening analysis using statistics produced through this process indicates that changes in heavy rainfall could lead to problems for a particular asset or activity, further guidance should be sought with a scientific supplier for a more detailed risk analysis.

49 Table 5-7: Projected rainfall depth-duration-frequency statistics for Richmond in 2100 for a mid-range temperature scenario (2°C warming). Projected rainfall depth-duration-frequency tables for other locations in Tasman District can be produced using the HIRDS software package and the process illustrated in the Appendix and described in the revised Local Government Guidance Manual (Ministry for the Environment, 2008a).

Table 5-5:  Current rainfall depth-duration-frequency statistics for Richmond from HIRDS V3
Table 5-5: Current rainfall depth-duration-frequency statistics for Richmond from HIRDS V3

Evaporation, Soil Moisture, and Drought

Other parts of the Tasman District are unlikely to be as affected by climate change induced drought as the plains.

Wind

Climate Change and Sea Level

This requires a broader consideration of the possible impacts or consequences of sea level rise on a specific decision or issue. An assessment of the potential impacts of a range of possible higher sea level rises (particularly where impacts are likely to be major or where additional future adaptation options are limited). On the open coast of Tasman Bay, sea level rise will not significantly alter the tidal range.

What will change significantly with accelerated sea level rise are the occurrences of high tides exceeding a certain height (above present mean sea level) (Figure 5-19). 55 An example of the impact of future sea level rise on tidal frequency at Tarakohe and Little Kaiteriteri is shown in Figure 5-19.

Figure 5-18 shows Wellington and Auckland annual mean sea level measurements spliced with  global-mean sea-level rise projections for two of the RCPs (RCP2.6 and RCP8.5) from IPCC (2013)
Figure 5-18 shows Wellington and Auckland annual mean sea level measurements spliced with global-mean sea-level rise projections for two of the RCPs (RCP2.6 and RCP8.5) from IPCC (2013)

Climate Change Impacts on Other Coastal Hazard Drivers

For each plot, the black line shows the percentage of high tides that exceed certain levels above mean sea level for today's sea levels. Exceeding 99th percentile wave heights and storm surges were determined for today's scenarios and for each of the climate change scenarios, enabling the calculation of an approximate scaling factor for large events (99th percentile ). Values ​​based on percent change from today's WASP simulations and the median of future climate change projections projected by WASP, at 99%.

Because the astronomical tide accounts for a larger proportion of the total storm height than the weather-induced storm surge, a 6.4 percent increase in storm surge caused a 1.3 percent increase in storm surge levels due to climate change. In summary, the WASP climate change scenarios suggest that climate change will cause about a 2% increase in extreme storm surge height and extreme significant wave height by the end of the 21st century.

Ocean acidification

The reader is referred to Robinson et al. 2014) for more information on how to use the Coastal Calculator with regard to sea level rise. Colored symbols are the anomalies and gray symbols the observed data, with the annual trends (year-1) shown (Bates et al., 2014). There is evidence of an increase in bacterial enzyme activity under increased dissolved CO2, which increases oxygen removal and decreases carbon uptake in the ocean (Burrell, 2015, Maas et al., 2015).

Similar effects were found for growth and shell area of ​​flat oysters (Cummings et al., 2013, Cummings et al., 2015). This is consistent with the observed negative effects of ocean acidification on the function and metabolism of Antarctic bivalves (Bylenga et al., in press, Cummings et al., 2011).

Figure 5-20:  Change in ocean surface pH.Time series (model averages and minimum to maximum ranges and  (b) maps of multi-model surface ocean pH for the scenarios RCP2.6, RCP4.5, RCP6.0 and RCP8.5 in 2081-2100
Figure 5-20: Change in ocean surface pH.Time series (model averages and minimum to maximum ranges and (b) maps of multi-model surface ocean pH for the scenarios RCP2.6, RCP4.5, RCP6.0 and RCP8.5 in 2081-2100

Considering both Anthropogenic and Natural Changes

Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change.

Contribution of Working Group III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change.

Figure 5-23 should not be interpreted as a set of specific predictions for individual years
Figure 5-23 should not be interpreted as a set of specific predictions for individual years

Figure

Figure 4-1 shows the spatial variation in annual average temperature over the Tasman region
Figure 4-3:  Homogenised annual temperature time series for Nelson from 1909 to 2014.   A number of  climate stations surrounding Nelson (including Appleby) are compiled into this long-term series
Figure 4-8:  Percentage change in average annual rainfall, for the 1978-1998 period compared to the 1960- 1960-1977 period
Table 4-1:  Historical relative sea-level rise rates.   Source: Hannah and Bell (2012)
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References

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