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Climate Futures for Tasmania & ECOSYSTEMS CRC

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Climate Futures for Tasmania & ECOSYSTEMS CRC ACE CRC ANTARCTIC CLIMATE climate futures for tasmania & ECOSYSTEMS CRC water and catchments w s a nt ter e and catchm the summary formation for local commu limate in nities local c w s a nt ter e projecting future river flows and catchm Greenhouse emissions scenario Climate Futures for Tasmania used a five-step Projecting future river flows Climate Futures for Tasmania used the A2 (high process to model future river flows. The aim of the water and catchments component of Climate Futures for greenhouse emissions) scenario from the Tasmania was to project and analyse changes to runoff and river flows in Step 1 Outputs from six GCMs were Intergovernmental Panel on Climate Change’s Tasmania caused by rising greenhouse gases. dynamically downscaled to a Special Report on Emissions Scenarios for the 0.1-degree grid (10 km x 10 km) hydrological modelling. The A2 emissions Climate Futures for Tasmania has combined state-of-the-art regional climate using CSIRO’s Conformal Cubic scenario is the highest emissions scenario for modelling and hydrological models to project future catchment yields for Atmospheric Model (CCAM) for the which IPCC GCM projections were available, Tasmania. Six dynamically downscaled global climate models (GCM) were period 1961-2100. and best matches recent rates of greenhouse combined with runoff models to produce runoff projections to 2100. gas emissions. Step 2 Downscaled climate modelling outputs The runoff models used for the water and catchment analyses were originally were bias-adjusted to align them with Dynamical downscaling used for the CSIRO Tasmania Sustainable Yields project (TasSY). These runoff observations. Global climate model output, at a resolution models were calibrated to 90 catchments across Tasmania as part of TasSY. Step 3 Bias-adjusted climate modelling of 200 km to 300 km, is too coarse for Climate modelling outputs were used directly in the hydrological models and outputs were used as direct inputs to understanding changes in rainfall and were validated with direct measurements of stream flow. This validation showed the runoff models to simulate runoff for temperature at a catchment scale. In Climate Futures for Tasmania, GCM output was put that the models gave realistic simulations of river flows across Tasmania. all of Tasmania. through another climate model (CCAM) that River flows were projected to 2100 for 78 river catchments that cover more than Step 4 Runoff projections were fed through creates regional climate information. This 70% of the area of the state. The future operation of Tasmania’s hydro-electric the Temsim model (Tasmania’s hydro- process is called downscaling. The downscaling system and 14 major irrigation storages were also simulated. electric system) to generate power was carried out to a 0.1-degree (approximately station outflows. 10 km) grid. Step 1 Dynamically downscale Step 5 Runoff and power station outflows Bias-adjustment GCM projections with CCAM Step 2 were used as inputs to river models to All climate model simulations have a tendency Bias-adjust CCAM outputs simulate flows in 78 Tasmanian rivers. to under/over-estimate climate variables like Step 3 rainfall. When errors in climate model outputs Runoff modelling occur consistently and predictably they are Step 4 Temsim hydro-electric system modelling called biases. These biases have little impact on the climate trends or changes over the entire state, but they mean that the climate simulations are not compatible with the runoff models. Climate simulations were bias-adjusted to be used in the runoff models, a standard scientific method for handling consistent differences for loc between observations and simulations. For e information al communi l climat ties the runoff modelling, climate model outputs loca were carefully adjusted to be like observations from the SILO dataset. Step 5 River modelling Find the SILO dataset at: www.longpaddock.qld.gov.au/silo climate futures for tasmania w s a nt ter e rainfall and evapotranspiration and catchm Interpreting climate projections Using a range of climate models allows us to Water and catchments in Tasmania Changes to rainfall and understand uncertainty in the projections. evapotranspiration Runoff and river projections differ between Tasmanian rivers show a diverse range of hydrological characteristics, from different models. All the climate models used high-flowing mountain streams in the west to low-flowing streams in the Statewide annual rainfall is not projected to in Climate Futures for Tasmania are equally east. These differences in river flows reflect Tasmania’s rainfall. change markedly by the end of the century, however seasonal and spatial distributions of valid. Averaging projections from the six climate models is a useful way of summarising Tasmania has experienced a decline in rainfall since the mid-1970s in many rainfall are projected to change. Rain falling on changes. We call this average the central areas, leading to a decrease in runoff. the central highlands is projected to decrease estimate. by the end of the century in all seasons. An increase in rainfall in the east is projected to Results shown in this summary all use the Modelled Historical Runoff occur predominantly in summer and autumn. central estimate. When interpreting these Annual west coast rainfall shows little change results, it is important to remember that some overall, however west coast summer rainfall is climate models will project a drier future than projected to decrease and west coast winter the central estimate, and some will project a rainfall is projected to increase. wetter future. Water lost from the land surface is both evaporated and transpired by plants. In Potential Evapotranspiration Summer Autumn combination, this is called evapotranspiration. Potential evapotranspiration is projected 2070-2099 to increase in all regions of the state but Annual proportionately less in the east and more Evapotranspiration 1961-1990 Change in potential in the west. These differences are driven by evapotranspiration by changes to rainfall and solar radiation in 2070-2099 compared to 1961-1990. Evapo- Winter Spring summer, the season when most of the annual transpiration increases evapotranspiration occurs. proportionally more in the west. Percent change in potential evapotranspiration Runoff during the reference period (1961-1990) Rainfall Average annual and seasonal runoff modelled using climate model inputs to the Simhyd runoff model for the period 1961-1990. This period is used to represent historical runoff, and future changes are compared to this period. Tasmanian runoff distribution follows rainfall distribution, with very high runoff flowing from the western mountains, and much lower runoff in the east. Summer Autumn Annual Rainfall Change in annual and on for local seasonal rainfall by te informati communit l clima ies 2070-2099 compared loca to 1961-1990. Rainfall change varies between regions and Winter Spring between the seasons. 2070-2099 Percent change in rainfall climate futures for tasmania w s a nt ter e changes to runoff and catchm Changes to runoff Changes to Runoff Changes to runoff • Climate Futures for Tasmania has produced sophisticated projections of changes to Runoff is affected by changes to both Summer Autumn runoff and river flows for Tasmania to 2100 rainfall and evapotranspiration. Runoff in response to rising greenhouse gases. is also affected by changes to rainfall Annual intensity, because more intense rainfall • In a changing climate, seasonal runoff is usually leads to proportionately more projected to change differently in different runoff. This means that changes to runoff regions. are greater than changes to rainfall in many • Runoff is projected to decrease markedly in Winter Spring regions. For example, rainfall declines in the 2010-2039 the central highlands by 2100. central highlands by up to 15% by 2100, but runoff declines by more than 30% in parts • Runoff is likely to increase in the important of the central highlands. agricultural regions of the Derwent Valley and the midlands. The statewide annual runoff shows significant variation from decade to decade Summer Autumn throughout the 21st century. On average, statewide annual runoff is projected to Runoff in the lower Derwent Valley is increase by almost 560 GL (or about 1%) projected to increase, with increases of more Annual by 2100. Individual climate models project than 50% in some catchments. Annual (and increases in statewide annual runoff of up winter) runoff is projected to increase in the to 7085 GL (15%) or decreases up to 2110 lower South Esk River and lower Macquarie River catchments. Winter Spring GL (-4%) by 2100. 2040-2069 Changes to runoff by 2100 vary between Marked seasonal changes to runoff are regions. These patterns of change are projected to occur during the coming more important than the relatively small century. By 2100, little change is projected statewide changes. Annual runoff is for annual runoff on the west coast. However projected to decrease significantly by west coast runoff is projected to increase in 2100 in Tasmania’s central highlands, with winter but decrease significantly in summer Summer Autumn 30% less runoff in some areas. On average, and autumn. annual runoff in the eastern areas of the Annual state is generally projected to increase, particularly in the lowlands. Winter Spring 2070-2099 formation for local commu limate in nities local c Percent change in runoff Annual and Seasonal Runoff Annual and seasonal changes to runoff from the reference period (1961-1990) for three future periods: 2010-2039, 2040-2069, 2070-2099. Runoff changes vary between regions and between climate futures for tasmania the seasons. In many regions, runoff changes are proportionately larger than rainfall changes. w s a nt ter e changes to river flows and catchm Changes to river flows Irrigation Storages Changes to river flows • In a changing climate, some river flows Of the 78 rivers modelled, on average 32 will decrease and some will increase by are projected to have changes to annual 2100, and 32 of the 78 modelled rivers are flows of more than ±10% by 2100.
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