Influence of the 2015–2016 El Niño on the record‑breaking mangrove dieback along northern Australia coast

This study investigates the underlying climate processes behind the largest recorded mangrove dieback event along the Gulf of Carpentaria coast in northern Australia in late 2015. Using satellite derived fractional canopy cover (FCC), variation of the mangrove canopies during recent decades are studied, including a severe dieback during 2015–2016. The relationship between mangrove FCC and climate conditions is examined with a focus on the possible role of the 2015–2016 El Niño in altering favorable conditions sustaining the mangroves. The mangrove FCC is shown to be coherent with the low-frequency component of sea level height (SLH) variation related to the El Niño Southern Oscillation (ENSO) cycle in the equatorial Pacific. The SLH drop associated with the 2015–2016 El Niño is identified to be the crucial factor leading to the dieback event. A stronger SLH drop occurred during austral autumn and winter, when the SLH anomalies were about 12% stronger than the previous very strong El Niño events. The persistent SLH drop occurred in the dry season of the year when SLH was seasonally at its lowest, so potentially exposed the mangroves to unprecedented hostile conditions. The influence of other key climate factors is also discussed, and a multiple linear regression model is developed to understand the combined role of the important climate variables on the mangrove FCC variation

Climate drivers of the 2015 Gulf of Carpentaria mangrove dieback

ESCC Hub researchers investigated the oceanic and atmospheric conditions leading up to the major mangrove dieback in late 2015 to identify potential stressors that contributed to the tree deaths. They found that it was most likely a result of a combination of very dry conditions and lower than average sea level. In combination, it appears that these conditions were unprecedented since at least 1971, and linked to the strong El Niño of 2015/16. More detailed attribution studies are necessary to determine what role, if any, human-induced climate change played in the 2015 dieback event. This would help inform natural resource policy-makers, planners and associated decision-makers about the causes of such events and how they may change into the future

Dynamics and predictability of El Nino-Southern Oscillation: an Australian perspective on progress and challenges

Many scientific challenges remain for managing the risk of future ENSO impacts in countries like Australia that are strongly affected by ENSO event diversity

Subseasonal to Seasonal Climate Forecasts Provide the Backbone of a Near-Real-Time Event Explainer Service

The Bureau of Meteorology serves the Australian community to reduce its climate risk and is developing a suite of tools to explain the drivers of extreme events. Dynamical sub-seasonal to seasonal forecasts form the backbone of the service, potentially enabling it to be run in near real time

The weather and climate of Australia at the Last Glacial Maximum

© 2005 Dr. Pandora HopeThe global climate has experienced four glacial cycles in the last 420,000 years, with each cycle characterised by a prolonged period of cooling culminating in maximal glaciation followed by a brief warm period. The most recent period of maximal glaciation is termed the Last Glacial Maximum (LGM) and occurred about 21,000 years ago. We currently live in one of the warm periods. The global climate is changing, and it is becoming more important to understand the extremes of the climate system and how well our modelling capability can capture those extremes. There has been a modelling intercomparison project established to examine how global general circulation models compare in simulating past climates, including the LGM. Analysis and comparison of these model results has been presented for many parts of the globe, but there has not been a comparison of the different model results over the Australian region. This thesis aims to fill that gap and explore the simulated LGM weather and climate of Australia and its drivers in more detail. Comparison with proxy evidence is also undertaken, and inconsistencies seen in the literature addressed. The Australian climate at the LGM was believed to be generally cooler, drier and possibly windier from proxy evidence in the literature. In the comparison done here the mean temperature and precipitation fields from most models show cooler and drier conditions, with some seasonal variability, but there are some strong outliers. It was found that the differences were not dependent on model resolution, but that the surface parameterisations were highly important for these fields. The shifts in the circulation were examined both in the model results and with a study of the non-linear link between the wind, surface moisture and dunes, which are a proxy for past winds. All the models simulate a southward shift in the westerlies in the Australian region. This is strongly driven byte prescribed sea-surface temperatures. Australia's current wind regime is conducive to dune building. However, the binding effect of soil moisture (or vegetation) is strong enough to limit present day movement, whereas in the drier climate at the LGM there was a capacity for sand movement. The analysis of dune orientations did not produce conclusive evidence for how the westerlies might have shifted at the LGM. An apparent enigma in the proxy evidence at the LGM is the high lake levels in Australia’s south east, while most inland lakes were dry. Previous authors believed that the precipitation was still low, but the high lake levels were driven by lowered potential evaporation. The hydrological cycle was generally depressed in the LGM simulations, but the potential for evaporation remained high. Thus an alternative hypothesis is posed based on increased run off due to a known shift in the vegetation types and a lag in the timing of the run off due to snowmelt. The analysis here shows that our capacity to simulate climates quite different from the present is still developing, but that model results can help explain apparent inconsistencies in the reconstruction of past climates from proxies

Atmospheric trends explained by changes in frequency of short-term circulation patterns

Abstract The circulation of the atmosphere is subject to natural and anthropogenic forcings that alter the energy balance of the climate system. In each hemisphere the zonally averaged atmospheric circulation can be represented by a single overturning cell if viewed in isentropic coordinates, highlighting the connections between tropics and extratropics. Here we present clusters of the meridional atmospheric circulation based on reanalysis data. Our results reveal preferred global circulation regimes with two clusters in each solstice season. These clusters show strong trends in their occurrence in the last two decades of the 20th century coincident with the depletion of the low-stratospheric ozone over Antarctica. We hypothesize that a change in the occurrence of short-term circulation regimes may lead to some long-term atmospheric trends. Finally, we show a strong coupling between the atmospheric circulation in boreal and austral winters and propose a mechanism linking anomalies in both seasons to the stratospheric ozone that requires confirmation with modelling experiments