Australia's Tinderbox Drought: An extreme natural event likely worsened by human-caused climate change

We examine the characteristics and causes of southeast Australia's Tinderbox Drought (2017 to 2019) that preceded the Black Summer fire disaster. The Tinderbox Drought was characterized by cool season rainfall deficits of around -50% in three consecutive years, which was exceptionally unlikely in the context of natural variability alone. The precipitation deficits were initiated and sustained by an anomalous atmospheric circulation that diverted oceanic moisture away from the region, despite traditional indicators of drought risk in southeast Australia generally being in neutral states. Moisture deficits were intensified by unusually high temperatures, high vapor pressure deficits, and sustained reductions in terrestrial water availability. Anthropogenic forcing intensified the rainfall deficits of the Tinderbox Drought by around 18% with an interquartile range of 34.9 to -13.3% highlighting the considerable uncertainty in attributing droughts of this kind to human activity. Skillful predictability of this drought was possible by incorporating multiple remote and local predictors through machine learning, providing prospects for improving forecasting of droughts.

Predicting resilience through the lens of competing adjustments to vegetation function

There is a pressing need to better understand ecosystem resilience to droughts and heatwaves. Eco-evolutionary optimization approaches have been proposed as means to build this understanding in land surface models and improve their predictive capability, but competing approaches are yet to be tested together. Here, we coupled approaches that optimize canopy gas exchange and leaf nitrogen investment, respectively, extending both approaches to account for hydraulic impairment. We assessed model predictions using observations from a native Eucalyptus woodland that experienced repeated droughts and heatwaves between 2013 and 2020, whilst exposed to an elevated [CO₂ ] treatment. Our combined approaches improved predictions of transpiration and enhanced the simulated magnitude of the CO₂ fertilization effect on gross primary productivity. The competing approaches also worked consistently along axes of change in soil moisture, leaf area, and [CO₂ ]. Despite predictions of a significant percentage loss of hydraulic conductivity due to embolism (PLC) in 2013, 2014, 2016, and 2017 (99th percentile PLC > 45%), simulated hydraulic legacy effects were small and short-lived (2 months). Our analysis suggests that leaf shedding and/or suppressed foliage growth formed a strategy to mitigate drought risk. Accounting for foliage responses to water availability has the potential to improve model predictions of ecosystem resilience.

Annual precipitation explains variability in dryland vegetation greenness globally but not locally

Dryland vegetation productivity is strongly modulated by water availability. As precipitation patterns and variability are altered by climate change, there is a pressing need to better understand vegetation responses to precipitation variability in these ecologically fragile regions. Here we present a global analysis of dryland sensitivity to annual precipitation variations using long-term records of normalized difference vegetation index (NDVI). We show that while precipitation explains 66% of spatial gradients in NDVI across dryland regions, precipitation only accounts for <26% of temporal NDVI variability over most (>75%) dryland regions. We observed this weaker temporal relative to spatial relationship between NDVI and precipitation across all global drylands. We confirmed this result using three alternative water availability metrics that account for water loss to evaporation, and growing season and precipitation timing. This suggests that predicting vegetation responses to future rainfall using space-for-time substitution will strongly overestimate precipitation control on interannual variability in aboveground growth. We explore multiple mechanisms to explain the discrepancy between spatial and temporal responses and find contributions from multiple factors including local-scale vegetation characteristics, climate and soil properties. Earth system models (ESMs) from the latest Coupled Model Intercomparison Project overestimate the observed vegetation sensitivity to precipitation variability up to threefold, particularly during dry years. Given projections of increasing meteorological drought, ESMs are likely to overestimate the impacts of future drought on dryland vegetation with observations suggesting that dryland vegetation is more resistant to annual precipitation variations than ESMs project.

Plant profit maximization improves predictions of European forest responses to drought

Knowledge of how water stress impacts the carbon and water cycles is a key uncertainty in terrestrial biosphere models. We tested a new profit maximization model, where photosynthetic uptake of CO₂ is optimally traded against plant hydraulic function, as an alternative to the empirical functions commonly used in models to regulate gas exchange during periods of water stress. We conducted a multi-site evaluation of this model at the ecosystem scale, before and during major droughts in Europe. Additionally, we asked whether the maximum hydraulic conductance in the soil-plant continuum k_max (a key model parameter which is not commonly measured) could be predicted from long-term site climate. Compared with a control model with an empirical soil moisture function, the profit maximization model improved the simulation of evapotranspiration during the growing season, reducing the normalized mean square error by c. 63%, across mesic and xeric sites. We also showed that k_max could be estimated from long-term climate, with improvements in the simulation of evapotranspiration at eight out of the 10 forest sites during drought. Although the generalization of this approach is contingent upon determining k_max , it presents a mechanistic trait-based alternative to regulate canopy gas exchange in global models.

Pricing the urban cooling benefits of solar panel deployment in Sydney, Australia

Cities import energy, which in combination with their typically high solar absorption and low moisture availability generates the urban heat island effect (UHI). The UHI, combined with human-induced warming, makes our densely populated cities particularly vulnerable to climate change. We examine the utility of solar photovoltaic (PV) system deployment on urban rooftops to reduce the UHI, and we price one potential value of this impact. The installation of PV systems over Sydney, Australia reduces summer maximum temperatures by up to 1 °C because the need to import energy is offset by local generation. This offset has a direct environmental benefit, cooling local maximum temperatures, but also a direct economic value in the energy generated. The indirect benefit associated with the temperature changes is between net AUD$230,000 and $3,380,000 depending on the intensity of PV systems deployment. Therefore, even very large PV installations will not offset global warming, but could generate enough energy to negate the need to import energy, and thereby reduce air temperatures. The energy produced, and the benefits of cooling beyond local PV installation sites, would reduce the vulnerability of urban populations and infrastructure to temperature extremes.

The plumbing of land surface models: is poor performance a result of methodology or data quality?

The PALS Land sUrface Model Benchmarking Evaluation pRoject (PLUMBER) illustrated the value of prescribing a priori performance targets in model intercomparisons. It showed that the performance of turbulent energy flux predictions from different land surface models, at a broad range of flux tower sites using common evaluation metrics, was on average worse than relatively simple empirical models. For sensible heat fluxes, all land surface models were outperformed by a linear regression against downward shortwave radiation. For latent heat flux, all land surface models were outperformed by a regression against downward shortwave, surface air temperature and relative humidity. These results are explored here in greater detail and possible causes are investigated. We examine whether particular metrics or sites unduly influence the collated results, whether results change according to time-scale aggregation and whether a lack of energy conservation in flux tower data gives the empirical models an unfair advantage in the intercomparison. We demonstrate that energy conservation in the observational data is not responsible for these results. We also show that the partitioning between sensible and latent heat fluxes in LSMs, rather than the calculation of available energy, is the cause of the original findings. Finally, we present evidence suggesting that the nature of this partitioning problem is likely shared among all contributing LSMs. While we do not find a single candidate explanation for why land surface models perform poorly relative to empirical benchmarks in PLUMBER, we do exclude multiple possible explanations and provide guidance on where future research should focus.

Factors that shape seed mass evolution

We used correlated divergence analysis to determine which factors have been most closely associated with changes in seed mass during seed plant evolution. We found that divergences in seed mass have been more consistently associated with divergences in growth form than with divergences in any other variable. This finding is consistent with the strong relationship between seed mass and growth form across present-day species and with the available data from the paleobotanical literature. Divergences in seed mass have also been associated with divergences in latitude, net primary productivity, temperature, precipitation, and leaf area index. However, these environmental variables had much less explanatory power than did plant traits such as seed dispersal syndrome and plant growth form.

Assessment of effects of chromated copper arsenate (CCA)-treated timber on nontarget epibiota by investigation of fouling community development at seven European sites

To assess the effect of the anti-marine-borer timber preservative CCA (a pressure-impregnated solution of copper, chromium, and arsenic compounds) on nontarget epibiota, fouling community development was investigated. Panels of Scots pine treated to target retentions of 12, 24, and 48 kg CCA per m3 of wood (covering the range of retentions recommended for marine use) plus untreated controls were submerged at seven coastal sites (Portsmouth, UK; La Tremblade [two sites], France; Ria Formosa, Portugal; Sagres, Portugal; Kristineberg, Sweden; Athens, Greece). The fouling community on the surfaces of the panels was assessed both qualitatively and quantitatively after 6, 12, and 18 months of exposure. Multivariate statistical methods were used to compare community structure between panel treatments. Panels treated to the three CCA loadings supported very similar fouling assemblages, which in most cases had higher numbers of taxa and individuals than assemblages on untreated panels. No detrimental effects on epibiota due to CCA preservatives were detected at any of the treatment levels at all seven exposure sites, suggesting that the range of environmental conditions at the sites had no bearing on preservative impact on fouling biota. Differences in community structure between CCA-treated and untreated panels may be due to enhanced larval settlement on CCA-treated timber by some species as a result of modifications to the surface properties of the timber by the preservative. Possible reasons for the higher numbers of certain species on the surface of CCA-treated panels are discussed.

An overview of the biology of the wharf borer beetle (Nacerdes melanura L., Oedemeridae) a pest of wood in marine structures

The UK distribution of N. melanura is reported, based on records from museum collections, government laboratories and a field survey of wooden marine structures and driftwood along the English and Welsh coastlines. The global distribution is also reported, based on a questionnaire survey. The life cycle of the wharf borer under different environmental conditions is described and the environmental conditions over the adult emergence period presented. The cellulase complex, xylanase and a range of dissacharases were present in the larval digestive tract when tunnelling archaeological oak.

Surfboard-riding injuries

The results of a study aimed at determining the nature, rate, and cause of traumatic surfing injuries by gathering injury data directly from surfers rather than by retrospective analysis of hospital or first-aid station records are reported. Three hundred and forty-six surfers of varying ages, experience, and competence reported 337 injuries sustained over a two-year period. The most common injuries requiring medical attention or resulting in inability to surf were lacerations (41%) and soft-tissue injuries (35%). The high incidence of back and shoulder sprains and strains has not previously been reported. As the rate of moderate and severe injuries among the sample was calculated to be 3.5 injuries per 1000 surfing days, and because more than 25% of the lacerations were caused by the sharp fin, or by the tail, or by the nose of the surfboard, some safety modifications in board design or structure may be necessary.