Gk Holz

Performance of downscaled regional climate simulations using a variable‐resolution regional climate model: Tasmania as a test case

[1] In this study we develop methods for dynamically downscaling output from six general circulation models (GCMs) for two emissions scenarios using a variable-resolution atmospheric climate model. The use of multiple GCMs and emissions scenarios gives an estimate of model range in projected changes to the mean climate across the region. By modeling the atmosphere at a very fine scale, the simulations capture processes that are important to regional weather and climate at length scales that are subgrid scale for the host GCM. We find that with a multistaged process of increased resolution and the application of bias adjustment methods, the ability of the simulation to reproduce observed conditions improves, with greater than 95% of the spatial variance explained for temperature and about 90% for rainfall. Furthermore, downscaling leads to a significant improvement for the temporal distribution of variables commonly used in applied analyses, reproducing seasonal variability in line with observations. This seasonal signal is not evident in the GCMs. This multistaged approach allows progressive improvement in the skill of the simulations in order to resolve key processes over the region with quantifiable improvements in the correlations with observations.

Effect of shadecloth tree shelters on cold-induced photoinhibition, foliar anthocyanin and growth of Eucalyptus globulus and E. nitens seedlings during establishment

The effects of shadecloth tree shelters on cold-induced photoinhibition, foliar anthocyanin and growth of Eucalyptus globulus Labill. and Eucalyptus nitens (Deane & Maiden) Maiden seedlings were assessed between planting (in early spring) and the age of 23 weeks. The experimental site was at 350 m above sea level (asl), which is considered marginal for establishment of E. globulus (but not E. nitens) plantations in Tasmania because of low mean minimum temperatures. Conditions within 3 weeks of planting induced severe photoinhibition in non-shaded seedlings. This was associated with increased anthocyanin and photodamage in non-shaded E. nitens and E. globulus. As a result, there was 20p mortality in non-shaded E. globulus. In contrast, shaded seedlings of both species had levels of photoinhibition and anthocyanin that were largely similar to those before planting and there was no photodamage. Levels of anthocyanin indicated that its synthesis responded to the severity of photoinhibition. Height growth and levels of mortality indicated that cold-induced photoinhibition, and not frost tolerance alone, determines the range of environments where E. globulus can be successfully planted. In contrast, the tolerance of E. nitens seedlings to cold-induced photoinhibition may be a factor in the demonstrated success of this species as a high-altitude plantation species.

Impact of climatic and soil conditions on environmental fate of atrazine used under plantation forestry in Australia.

We studied the leaching and dissipation of atrazine (2-chloro-4-ethylamino-6-isopropylamino-1, 3, 5-s-triazine) and its two principal metabolites (desethylatrazine and desisopropylatrazine) for more than two years through soil profiles at five forestry sites across Australia (representing subtropical, temperate and Mediterranean climatic conditions with rainfall ranging from 780 to 1536 mm yr(-1)). Following atrazine applications at local label rates, soil cores were collected at regular intervals (up to depths of 90-150 cm), and the residues of the three compounds in soil were analysed in composite samples using liquid chromatography. Bromide was applied simultaneously with atrazine to follow the movement of the soil water. While bromide ion rapidly leached through the entire profile, in most cases the bulk of atrazine, desethylatrazine and desisopropylatrazine remained in the top 45 cm of the soil profile. However, a small fraction of residue moved deeper into the soil profile and at a subtropical site (Toolara) trace levels (ng L(-1)) of atrazine and one of its metabolites (DEA) were detected in perched groundwater located at a depth of 1.8 m. Data on the total residues of atrazine in soil profiles from all sites except the Tasmanian site fitted a first-order decay model. The half-life of atrazine in surface soils at the subtropical sites (Toolara and Imbil) ranged from 11 to 21 days. Four separate applications of atrazine at Toolara resulted in a narrow range of half-lives (16 ± 3.6 days), confirming relatively rapid dissipation of atrazine under subtropical conditions (Queensland). In contrast, a prominent biphasic pattern of initial rapid loss followed by very slow phase of degradation of atrazine was observed under the colder temperate climate of Highclere (Tasmania). The data showed that while its 50% (DT(50)) loss occurred relatively rapidly (36 days), more than 10% of herbicide residue was still detectable in the profile even a year after application (DT(90) = 375 days). The rate of dissipation of atrazine at warm subtropical Queensland sites (Imbil and Toolara) was 2-3 times faster than sites located in colder climate of Tasmania. The marked contrast in DT(50) values between subtropical and temperate sites suggest that climatic conditions (soil temperature) is one of the key factors affecting atrazine dissipation. At the Tasmanian site, the combination of leaching of the herbicide in subsoil and slower microbial activity at cooler temperatures would have caused a longer persistence of atrazine.

Nitrogen fluxes in surface soils of young Eucalyptus nitens plantations in Tasmania

Nitrogen (N) fluxes in surface soils (0–10 cm) were measured by an in situ soil-core technique at 5 sites supporting 1- to 4-year-old Eucalyptus nitens plantations in Tasmania. Rates of net N mineralisation (NNM) ranged from 13 to 188 kg Nsha.year. The highest rate was from an ex-pasture site, which was almost double the highest rate of NNM measured on an ex-forest site. Although there was a tendency towards lower rates of NNM in uncultivated versus cultivated soils, and in the final versus previous year or two of measurement, these differences were not significant. Concentrations of mineral N, however, decreased at all study sites during the first 3–4 years, significantly at 4 of these sites. Within the errors of measurement, most N that was mineralised was also nitrified and leached. Seasonal patterns in NNM and concentrations of nitrate (NO3–) occurred only at one site, which also had the highest annual rate of NNM. The balance of mineral N remaining in surface soil each October was 2–17 kg Nsha. We concluded that there was little evidence of a decrease in rates of NNM between 1 and 4 years after planting, and that high rates of NNM at some sites were accompanied by high rates of leaching that limited the accumulation of mineral N. Sitespecific management of N fertiliser may be warranted to compliment the wide range of N availability in eucalypt plantations. mineralisation, nitrification, leaching, uptake, forests, Australia.

Beneficial impacts of climate change on pastoral and broadacre agriculture in cool-temperate Tasmania

Abstract. Although geographically small, Tasmania has a diverse range of regional climates that are affected by different synoptic influences. Consequently, changes in climate variables and climate-change impacts will likely vary in different regions of the state. This study aims to quantify the regional effects of projected climate change on the productivity of rainfed pastoral and wheat crop systems at five sites across Tasmania. Projected climate data for each site were obtained from the Climate Futures for Tasmania project (CFT). Six General Circulation Models were dynamically downscaled to ∼10-km grid cells using the CSIRO Conformal Cubic Atmospheric Model under the A2 emissions scenario for the period 1961–2100. Mean daily maximum and minimum temperatures at each site are projected to increase from a baseline period (1981–2010) to 2085 (2071–2100) by 2.3–2.7°C. Mean annual rainfall is projected to increase slightly at all sites. Impacts on pasture and wheat production were simulated for each site using the projected CFT climate data. Mean annual pasture yields are projected to increase from the baseline to 2085 largely due to an increase in spring pasture growth. However, summer growth of temperate pasture species may become limited by 2085 due to greater soil moisture deficits. Wheat yields are also projected to increase, particularly at sites presently temperature-limited. This study suggests that increased temperatures and elevated atmospheric CO2 concentrations are likely to increase regional rainfed pasture and wheat production in the absence of any significant changes in rainfall patterns.

Indices of soil nitrogen availability in five Tasmanian Eucalyptus nitens plantations

Several soil analyses were used to estimate available N in surface soils (0–10 cm) over a 2-year period at 5 sites that supported 1- to 4-year-old Eucalyptus nitens plantations, and once in subsoils (10–120 cm) at 3 of these sites. Soils were derived from basalt (1 site previously pasture, 1 Pinus radiate, and 2 native forest) or siltstone (previously native forest). Soil analyses examined were total N, total P, total C, anaerobically mineralisable N (AMN), hot KCl-extractable N (hot KCl-N), and NH4+ and NO3– in soil solution and KCl extracts. AMN, KCl-extractable NH4+ and NO3–, and soil solution NH4+ and NO3– varied considerably with time, whereas hot KCl-N, total N, total P, and total C were temporally stable except for a gradual decline in total C with time at one site. Only total P was correlated with net N mineralisation (NNM) across all sites (r2 = 0.91, P < 0.05, n = 5). At 2–3 years after planting, soil solution and KCl-extractable NO3– dropped below 0.1 mm N and 1 μg N/g soil, respectively, at sites with NNM ≤24 kg N/ha.year (n = 3). Sites with NNM ≤24 kg N/ha.year also had ≤0.8 Mg P/ha. Although concentrations of indices of soil N availability decreased with depth, the contribution of subsoil (10–120 cm depth) to total profile N availability was estimated to be at least twice that of the top 10 cm. At an ex-pasture site, high concentrations of mineral N were found at 75–105 cm depths (KCl-extractable N, 289.3 μg N/g soil; 2.8 mm mineral N in soil solution), which may have become available to plantations as their root systems developed.

Improved regional climate modelling through dynamical downscaling

Coupled Ocean-Atmosphere General Circulation Models (GCMs) provide the best estimates for assessing potential changes to our climate on a global scale out to the end of this century. Because coupled GCMs have a fairly coarse resolution they do not provide a detailed picture of climate (and climate change) at the local scale. Tasmania, due to its diverse geography and range of climate over a small area is a particularly difficult region for drawing conclusions regarding climate change when relying solely on GCMs. The foundation of the Climate Futures for Tasmania project is to take the output produced by multiple GCMs, using multiple climate change scenarios, and use this output as input into the Conformal Cubic Atmospheric Model (CCAM) to downscale the GCM output. CCAM is a full atmospheric global general circulation model, formulated using a conformal-cubic grid that covers the globe but can be stretched to provide higher resolution in the area of interest (Tasmania). By modelling the atmosphere at a much finer scale than is possible using a coupled GCM we can more accurately capture the processes that drive Tasmanias weather/climate, and thus can more clearly answer the question of how Tasmanias climate will change in the future. We present results that show the improvements in capturing the local-scale climate and climate drivers that can be achieved through downscaling, when compared to a gridded observational data set. The underlying assumption of this work is that a better simulated current climatology will also produce a more credible climate change signal.

Assessing rainfall trends and remote drivers in regional climate change projections: The demanding test case of Tasmania

Understanding and modelling Tasmanian rainfall variability and making future projections of Tasmanian rainfall are challenging tasks. Tasmania has spatially and temporally complex rainfall patterns. Rainfall variability is influenced by a complex suite of remote drivers and these influences vary by season. The Climate Futures for Tasmania high-resolution model simulations project small changes to annual rainfall averaged over Tasmania, but larger changes to the spatial patterns and seasonality of rainfall. A case study of changes to summer rainfall under a high greenhouse gas emission scenario is shown here. The projected summer decrease in rainfall in the western rainfall region is consistent with the southerly movement and intensification of the subtropical ridge as well as an enhancement of the high phase of the Southern Annular Mode. The increase along the east coastal strip is consistent with an increase in blocking in the Tasman Sea as well as an increase in sea surface temperature, relative humidity and convective rainfall. We propose that projections of rainfall for places like Tasmania are strengthened through dynamical downscaling and also the analysis of the rainfall mechanisms within the model at all length scales.