Significantly wetter or drier future conditions for one to two thirds of the world's population

Future projections of precipitation are uncertain, hampering effective climate adaptation strategies globally. Our understanding of changes across multiple climate model simulations under a warmer climate is limited by this lack of coherence across models. Here, we address this challenge introducing an approach that detects agreement in drier and wetter conditions by evaluating continuous 120-year time-series with trends, across 146 Global Climate Model (GCM) runs and two elevated greenhouse gas (GHG) emissions scenarios. We show the hotspots of future drier and wetter conditions, including regions already experiencing water scarcity or excess. These patterns are projected to impact a significant portion of the global population, with approximately 3 billion people (38% of the world's current population) affected under an intermediate emissions scenario and 5 billion people (66% of the world population) under a high emissions scenario by the century's end (or 35-61% using projections of future population). We undertake a country- and state-level analysis quantifying the population exposed to significant changes in precipitation regimes, offering a robust framework for assessing multiple climate projections.

Impacts of climate change on nutrient and sediment loads from a subtropical catchment

Climate change is predicted to significantly alter hydrological cycles across the world, affecting runoff, streamflow, and pollutant loads from diffuse sources. The objectives of this study were to examine the impacts of climate change on streamflow, total nitrogen (TN), total phosphorus (TP), and total suspended sediment (TSS) loads in the subtropical Logan-Albert catchment, Queensland, Australia. We calibrated the Soil Water Assessment Tool (SWAT) against event monitoring data in the Logan and Albert rivers, respectively. Hydrological and water quality effects of an ensemble of 11 dynamically downscaled high-resolution climate models were assessed with SWAT under high (Representative Concentration Pathway 8.5 - RCP8.5) and intermediate (RCP4.5) emission scenarios. Streamflow decreased most in winter and spring and decreased least in summer. This followed the predicted seasonal changes for precipitation, although decreases tended to be amplified due to increasing evaporative loss. TSS, TN, and TP loads showed a similar pattern to streamflow, with the largest decreases predicted for the dry season under RCP8.5 by the 2080s. Annual TSS load decreased by 34.3 and 54.2%, TN load decreased by 29.8 and 30.5%, and TP load by 24.9 and 4.4% for the Logan and Albert sites, respectively. The results of this study indicate that for subtropical river-estuary systems, climate warming may lead to lower streamflow and contaminant loads, reduced flushing, and greater relative importance of point source loads in urbanising catchments.

Queensland’s multi-year Wet and Dry periods: implications for grazing enterprises and pasture resources

Year-to-year variability in rainfall has long been recognised as a major issue in managing livestock enterprises across Australia’s grazing lands. Extension products documenting rainfall variability have been developed over the last 30 years and have been keenly sought by producers and their advisors. This paper describes multi-year rainfall variability from 1889 to 2020 and provides the basis for classifying the 131 years of rainfall into 18 discrete Wet (7), Average (2) and Dry (9) periods as presented in the ‘Queensland’s Extended Wet and Dry Periods’ poster. The classification was consistent with: analysis of fluctuations and trends in the long-term time series of reported livestock numbers; drought declarations for government assistance; and documented periods of pasture resource degradation and recovery. Rainfall during the nine Wet and Average periods was +18% above the long-term average annual rainfall (LTAAR), in contrast to the Dry periods with −17% below LTAAR. Wet periods (including Average) were on average 7 years in duration, ranging from 5 to 9 years. Dry periods were on average 8 years in duration and ranged from 5 to 13 years. Detailed analysis of the effects of the El Niño Southern Oscillation (ENSO) phenomenon indicated that: (a) the Wet/Dry periods were dominated by different frequencies and amounts of rainfall in La Niña/El Niño years; (b) rainfall in ENSO neutral years was generally above and below average rainfall for the Wet or Dry periods respectively; (c) the frequency of ENSO year-types was less important than the overall rainfall surplus (or deficit) in La Niña (or El Niño) years within the Wet (or Dry) periods respectively; and (d) the timing of Wet and Dry periods was correlated with indices of quasi-decadal and inter-decadal variability in components (sea surface temperatures and atmospheric pressures) of the global climate system. Climatic risk assessment systems for grazing management at multi-year timescales are yet to be developed.

Heatwaves intensification in Australia: A consistent trajectory across past, present and future

Heatwaves are defined as unusually high temperature events that occur for at least three consecutive days with major impacts to human health, economy, agriculture and ecosystems. This paper investigates: 1) changes in heatwave characteristics such as peak temperature, number of events, frequency and duration over a past 67-year period in Australia; 2) projected changes in heatwave characteristics for this century in Queensland, northeast Australia; and 3) the avoided heatwave impacts of limiting global warming by 1.5 °C, 2.0 °C and 3.0 °C. The results reveal that heatwaves have increased in intensity, frequency and duration across Australia over the past 67 years, such intensification was particularly higher on recent decades. Downscaled future climate projections for Queensland suggest that heatwaves will further intensify over the current century. The projections also highlight that distinct climatic regions within Queensland may have different heatwave responses under global warming, where tropical and equatorial heatwaves appear to be more sensitive to elevated atmospheric CO₂ concentrations than temperate and arid regions. The results offer new insights to support climate adaptation and mitigation at regional scales. These findings are already being used by health and emergency services to inform the development of statewide policies to mitigate heatwave impacts.

Cascading effects of climate extremes on vertebrate fauna through changes to low-latitude tree flowering and fruiting phenology

Forest vertebrate fauna provide critical services, such as pollination and seed dispersal, which underpin functional and resilient ecosystems. In turn, many of these fauna are dependent on the flowering phenology of the plant species of such ecosystems. The impact of changes in climate, including climate extremes, on the interaction between these fauna and flora has not been identified or elucidated, yet influences on flowering phenology are already evident. These changes are well documented in the mid to high latitudes. However, there is emerging evidence that the flowering phenology, nectar/pollen production, and fruit production of long-lived trees in tropical and subtropical forests are also being impacted by changes in the frequency and severity of climate extremes. Here, we examine the implications of these changes for vertebrate fauna dependent on these resources. We review the literature to establish evidence for links between climate extremes and flowering phenology, elucidating the nature of relationships between different vertebrate taxa and flowering regimes. We combine this information with climate change projections to postulate about the likely impacts on nectar, pollen and fruit resource availability and the consequences for dependent vertebrate fauna. The most recent climate projections show that the frequency and intensity of climate extremes will increase during the 21st century. These changes are likely to significantly alter mass flowering and fruiting events in the tropics and subtropics, which are frequently cued by climate extremes, such as intensive rainfall events or rapid temperature shifts. We find that in these systems the abundance and duration of resource availability for vertebrate fauna is likely to fluctuate, and the time intervals between episodes of high resource availability to increase. The combined impact of these changes has the potential to result in cascading effects on ecosystems through changes in pollinator and seed dispersal ecology, and demands a focused research effort.