Glenorchy_Climate_Profile

Produced by Michael Grose, Antarctic Climate and Ecosystems Cooperative Research Centre, using material from the technical reports of the Climate Futures for Tasmania project 1 Local climate profile Glenorchy Municipality Past and current climate:  Glenorchy has a temperate, maritime climate with relatively mild winters and a relatively small annual temperature range compared to inland locations (average daily maximum temperatures are around 21.6 °C in January and 11.7 °C in July).  The municipality receives around 700 mm annual average rainfall, with no strong seasonal cycle (around 40-60 mm each month of the year). Rainfall can come from the regular westerly frontal rain systems that cross Tasmania, or from episodic systems from the north and east.  Year-to-year rainfall variability in this municipality shows some correlation with the El Niño Southern Oscillation in winter and spring (where El Niño winters are generally drier than average, La Niña winters are generally wetter than average), and some correlation with atmospheric blocking in summer and spring.  Long-term average temperatures have risen in the decades since the 1950s, at a rate similar to the rest of Tasmania (up to 0.1 °C per decade). Daily minimum temperatures have risen slightly more than daily maximum temperatures.  There has been a decline in average rainfall and a lack of very wet years in the municipality since the mid 1970s, and this decline has been strongest in autumn. This decline was exacerbated by the ‘big dry’ drought of 1995 -2009. Rainfall in the recent period since the end of the drought has been close to average. Future scenarios - from the Climate Futures for Tasmania project Fine-scale model projections of Tasmanian climate were made for two hypothetical but plausible scenarios of human emissions for the 21 st Century (taken from the special report on emissions scenarios (SRES) from the Intergovernmental Panel on Climate Change (IPCC)). The scenarios are of ongoing high emissions, A2, and one where emissions plateau and fall, B1. The climate response under the two scenarios is similar through the first half of the century, but the changes under the higher emissions scenario become much stronger than the lower scenario in the later half of the 21 st Century. 1. Temperature  Under the higher emissions scenario (A2), the municipality is projected to experience a rise in average temperatures of 2.6 to 3.3 °C over the entire 21 st Century. The rise in daily minimum temperature is expected to be slightly greater than daily maximum temperature, and fairly similar in the different seasons. Under the lower emissions scenario (B1), the projected change over the entire century is 1.3 to 2.0 °C. A time series of projected mean Tasmanian temperature is shown in Figure 1.  The projected change in average temperatures is similar to the rest of Tasmania, but less than the global average and significantly less than northern Australia and many regions around the world, especially the large northern hemisphere continents and the Arctic.

Produced by Michael Grose, Antarctic Climate and Ecosystems Cooperative Research Centre, using material from the technical reports of the Climate Futures for Tasmania project 2 Figure 1 . Tasmanian average temperature in observations (black) and model projections for the A2 scenario (red) and the B1 scenario (blue), all series are smoothed (11-year running average), shading shows the range of model projections. Changes under the higher scenario by the very end of the century are discussed in the examples below  The projected change in average temperature is accompanied by a change in the frequency, intensity and duration of hot and cold extremes of temperature. For Glenorchy under the A2 (higher) scenario by the end of the century the projections indicate: o The number of Summer Days (>25 °C) increases from 18 days per year, to around 40 days per year. o The temperature of very hot days increases by a similar amount as the average temperature: 2.5 to 3.5 °C, with some seasonal variation. o Frost risk days are currently infrequent, generally less than 10 days per year except for high altitude sites such as Collinsvale, and are projected to become rare events. o Warm spells (days in a row where temperatures are in the top 5% of baseline levels) currently last around 4 days, will last 2 to 6 days longer. Heat waves (>3 days over 28 °C) will occur every year or two. o The average hottest day of the year is high in the southeast compared to most places in Tasmania (up to 36 °C), this is projected to increase by up to 3 °C. 2. Rainfall, runoff and rivers  The climate response to rainfall and runoff is similar in nature between the two scenarios, but stronger by the end of the century under the A2 scenario. The general long-term influence of climate warming by the end of the century indicated by these model projections is that average annual rainfall in Glenorchy will increase slightly.

Produced by Michael Grose, Antarctic Climate and Ecosystems Cooperative Research Centre, using material from the technical reports of the Climate Futures for Tasmania project 4 o Rainfall brought by rare extreme events will increase: a 200-year average recurrence interval (ARI) event is currently around 100 mm, and this is projected to increase 30-40%. More common ARI events (ARI-10, ARI-50) increase by a similar proportion.  Pan evaporation is projected to increase, by up to 19% under the A2 scenario by the end of the century, driven by the increases in temperature but also changes to relative humidity, wind speeds, cloudiness and radiation.  Changes to rainfall and evaporation lead to changes in water runoff and river flows. This in turn has impacts on the inflows into dams and water storages. Under the A2 scenario by the end of the century: o Average runoff is projected to increase in all seasons. o Proportional (%) increases in runoff are larger than the change to rainfall, some changes in runoff exceed 30% in some seasons. o High daily runoff amounts are projected to increase, including those that may lead to erosion or flooding, low daily runoff amounts are projected to stay much the same. o Average flows in the Derwent River are projected to increase slightly: the central estimate is 10% by the end of the century (flood flows see the section below). 3. Extreme sea level events High water events causing coastal inundation comes from a combination of sea level, tide, storm surge and wind waves. Sea level has been rising at a rate of 3.3 ±0.4 mm/year in the recent period, and are expected to continue rising with further climate warming. The upper range of model projections indicates a rise of up to 0.82 m global average sea level by 2100 under a high emissions scenario. The sea level rise varies in different locations, and for Tasmania the sea level rise for this scenario is close to the global average. In the east and southeast coasts of Tasmania, the very high tide height and the coastal surge contribute a roughly equal amount to high sea level events – the current 100-year storm tide event is around 0.9 to 1.4 m above average sea level. High storm heights in the southeast are generally brought by westerly cold frontal systems with a low-pressure system to the south of Tasmania. Changes to storm surges by the end of the century will not be as large as sea level rise. Accounting for all effects, the current 100-year event in Hobart is projected to be 1.87 m in 2090 under the high emissions scenario. This means that the current 100-year event would be approximately a 50-year event by 2030, and a 2 to 6-year event by 2090 under this scenario. These changes would have an influence on flooding and inundation in the estuary of the Derwent, within the Glenorchy municipality. 4. River floods – Derwent River Changes to design flood hydrographs were calculated for the 1:10, 1:50, 1:100 and 1:200 annual exceedance probability events for future periods using the climate model outputs and flood hydraulic models by partners at Entura consulting. Short duration events are projected to become more intense, so catchments with critical durations of less than 72 hours are projected to experience higher flood levels and faster flow responses. However, the Derwent River has a critical duration of more than 72 hours, so is not projected to see any significant increase in peak discharge, or in flood inundation caused by larger rain events for the Derwent River. However, sea level rise is a far more important consideration with inundation events in the estuary of the Derwent in Glenorchy (see above point).

Appendix – details of climate projections Greenhouse gas emissions have an influence on the Earth’s climate system, along with other human activities such as the emission of ozone-depleting substances, emission of aerosol (particles) and changing the land cover (e.g. deforestation). Sophisticated model simulations can be used to project the likely effect of these influences into the future given our current state of knowledge. It is impossible to predict exactly what future human emissions will be, so models are run under a set of plausible hypothetical emissions scenarios. A model simulation shows the likely effect if we follow that scenario, so it is not a single ‘prediction’ of the future. The simulat ion can’t include the effect of things that are impossible to predict (such as major volcanic eruptions). The Climate Futures for Tasmania project produced a set of climate projections at the regional scale for Tasmania. Two emissions scenarios were considered – one of ongoing high emissions (SRES A2), and one where emissions plateau and fall (SRES B1). The climate response under the two scenarios is similar through the first half of the century, but the changes under the higher emissions scenario become much stronger than the lower scenario in the latter half of the 21 st Century. Climate warming causes many complex changes to the earth’s climate system. These changes include alterations to ocean currents, average atmospheric circulation and ocean-atmosphere cycles such as the El Niño Southern Oscillation. Projected effects that are relevant to Tasmania include a continued extension of the East Australia Current bringing warmer waters off the east and northeast coast of Tasmania, a pole-ward shift of the subtropical ridge of high pressure and shifts in the mid- latitude westerlies (the ‘Roaring 40s’), and a change in remote climate drivers such as atmospheric blocking, the El Niño Southern Oscillation and the Southern Annular Mode. The position of Tasmania adjacent to the Southern Ocean means that the effect of climate warming is not as severe as other more continental regions. The results presented in this report were made using established methods, including:  Extreme value distribution fitting in a generalized Pareto distribution to calculate the average recurrence intervals (ARIs).  Hydrology runoff models developed and calibrated for the Tasmanian Sustainable Yields project to estimate the runoff, river flows and inflows to storages.  Standard agricultural indices such as the Utah model to calculate chill hours and standard equations and a 10 °C threshold to calculate Growing Degree Days. All information is drawn from the Climate Futures for Tasmania Technical reports please see these reports for more details, and to cite in other written work. Reference list Bennett JC, Ling FLN, Graham B, Grose MR, Corney SP, White CJ, Holz GK, Post DA, Gaynor SM & Bindoff NL 2010, Climate Futures for Tasmania: water and catchments technical report, Antarctic Climate and Ecosystems Cooperative Research Centre, Hobart, Tasmania Corney SP, Katzfey JJ, McGregor JL, Grose MR, Bennett JC, White CJ, Holz GK, Gaynor SM & Bindoff NL 2011, Climate Futures for Tasmania: climate modeling technical report, Antarctic Climate and Ecosystems Cooperative Research Centre, Hobart, Tasmania Entura Consulting, 2010, Climate Futures for Tasmania Flood inundation mapping, Entura Consulting Technical report, 23 Dec 2010 Grose MR, Barnes-Keoghan I, Corney SP, White CJ, Holz GK, Bennett JC, Gaynor SM & Bindoff NL 2010, Climate Futures for Tasmania: general climate impacts technical report, Antarctic Climate and Ecosystems Cooperative Research Centre, Hobart, Tasmania Holz GK, Grose MR, Bennett JC, Corney SP, White CJ, Phelan D, Potter K, Kriticos D, Rawnsley R, Parsons D, Lisson S, Gaynor SM & Bindoff NL 2010, Climate Futures for Tasmania: impacts on agriculture technical report, Antarctic Climate and Ecosystems Cooperative Research Centre, Hobart, Tasmania McInnes KL, O’Grady JG, Hemer M, Macadam I, A bbs DJ, White CJ, Bennett JC, Corney SP, Holz GK, Grose MR, Gaynor SM & Bindoff NL In Press, Climate Futures for Tasmania: extreme tide and sea level events technical report, Antarctic Climate and Ecosystems Cooperative Research Centre, Hobart, Tasmania White CJ, Sanabria LA, Grose MR, Corney SP, Bennett JC, Holz GK, McInnes KL, Cechet RP, Gaynor SM & Bindoff NL 2011, Climate Futures for Tasmania: extreme events technical report, Antarctic Climate and Ecosystems Cooperative Research Centre, Hobart, Tasmania The material in this report is based on computer modelling projections for climate change scenarios and, as such, there are inherent uncertainties involved. While every effort has been made to ensure the material in this report is accurate, Antarctic Climate & Ecosystems Cooperative Research Centre (ACE) provides no warranty, guarantee or representation that material is accurate, complete, up to date, non-infringing or fit for a particular purpose. The use of the material is entirely at the risk of a user. The user must independently verify the suitability of the material for its own use. To the maximum extent permitted by law, ACE, its participating organisations and their officers, employees, contractors and agents exclude liability for any loss, damage, costs or expenses whether direct, indirect, consequential including loss of profits, opportunity and third party claims that may be caused through the use of, reliance upon, or interpretation of the material in this report.