Nigel J. Tapper

The sensitivity of Australian fire danger to climate change

Global climate change, such as that due to the proposed enhanced greenhouseeffect, is likely tohave a significant effect on biosphere-atmosphere interactions, includingbushfire regimes. Thisstudy quantifies the possible impact of climate change on fire regimes byestimating changes infire weather and the McArthur Forest Fire Danger Index (FDI), an index thatis used throughoutAustralia to estimate fire danger. The CSIRO 9-level general circulation model(CSIRO9 GCM)is used to simulate daily and seasonal fire danger for the present Australianclimate and for adoubled-CO2 climate. The impact assessment includes validation ofthe GCMs daily controlsimulation and the derivation of ‘correction factors’ which improve theaccuracy of the firedanger simulation. In summary, the general impact of doubled-CO2is to increase firedanger at all sites by increasing the number of days of very high and extremefire danger.Seasonal fire danger responds most to the large CO2-induced changesin maximumtemperature.

Impact of Increasing Urban Density on Local Climate: Spatial and Temporal Variations in the Surface Energy Balance in Melbourne, Australia

Variations in urban surface characteristics are known to alter the local climate through modification of land surface processes that influence the surface energy balance and boundary layer and lead to distinct urban climates. In Melbourne, Australia, urban densities are planned to increase under a new strategic urban plan. Using the eddy covariance technique, this study aimed to determine the impact of increasing housing density on the surface energy balance and to investigate the relationship to Melbourne’s local climate. Across four sites of increasing housing density and varying land surface characteristics (three urban and one rural), it was found that the partitioning of available energy was similar at all three urban sites. Bowen ratios were consistently greater than 1 throughout the year at the urban sites (often as high as 5) and were higher than the rural site (less than 1) because of reduced evapotranspiration. The greatest difference among sites was seen in urban heat storage, which was influenced by urban canopy complexity, albedo, and thermal admittance. Resulting daily surface temperatures were therefore different among the urban sites, yet differences in above-canopy daytime air temperatures were small because of similar energy partitioning and efficient mixing. However, greater nocturnal temperatures were observed with increasing density as a result of variations in heat storage release that are in part due to urban canyon morphology. Knowledge of the surface energy balance is imperative for urban planning schemes because there is a possibility for manipulation of land surface characteristics for improved urban climates.

Fire impacts on surface heat, moisture and carbon fluxes from a tropical savanna in northern Australia

Savannas form a large fraction of the total tropical vegetation and are extremely fire prone. We measured radiative, energy and carbon exchanges over unburned and burned (both before and after low and moderate intensity fires) open forest savanna at Howard Springs, Darwin, Australia. Fire affected the radiative balance immediately following fire through the consumption of the grass-dominated understorey and blackening of the surface. Albedo was halved following fire of both intensities (from 0.12 to 0.07 and from 0.11 to 0.06 for the moderate and low intensity sites, respectively), but the recovery of albedo was dependent on the initial fire intensity. The low intensity fire caused little canopy damage with little impact on the surface energy balance and only a slight increase in Bowen ratio. However the moderate fire resulted in a comprehensive canopy scorch and almost complete leaf drop in the weeks following fire. The shutdown of most leaves within the canopy reduced transpiration and altered energy partitioning. Leaf death and shedding also resulted in a cessation of ecosystem carbon uptake and the savanna turned from a sink to a source of carbon to the atmosphere because of the continued ecosystem respiration. Post-fire, the Bowen ratio increased greatly due to large increases in sensible heat fluxes. These changes in surface energy exchange following fire, when applied at the landscape scale, may have impacts on climate through local changes in circulation patterns and changes in regional heating, precipitation and monsoon circulation.

Watering our Cities: The capacity for Water Sensitive Urban Design to support urban cooling and improve human thermal comfort in the Australian context

Urban drainage infrastructure is generally designed to rapidly export stormwater away from the urban environment to minimize flood risk created by extensive impervious surface cover. This deficit is resolved by importing high-quality potable water for irrigation. However, cities and towns at times face water restrictions in response to drought and water scarcity. This can exacerbate heating and drying, and promote the development of unfavourable urban climates. The combination of excessive heating driven by urban development, low water availability and future climate change impacts could compromise human health and amenity for urban dwellers. This paper draws on existing literature to demonstrate the potential of Water Sensitive Urban Design (WSUD) to help improve outdoor human thermal comfort in urban areas and support Climate Sensitive Urban Design (CSUD) objectives within the Australian context. WSUD provides a mechanism for retaining water in the urban landscape through stormwater harvesting and reuse while also reducing urban temperatures through enhanced evapotranspiration and surface cooling. Research suggests that WSUD features are broadly capable of lowering temperatures and improving human thermal comfort, and when integrated with vegetation (especially trees) have potential to meet CSUD objectives. However, the degree of benefit (the intensity of cooling and improvements to human thermal comfort) depends on a multitude of factors including local environmental conditions, the design and placement of the systems, and the nature of the surrounding urban landscape. We suggest that WSUD can provide a source of water across Australian urban environments for landscape irrigation and soil moisture replenishment to maximize the urban climatic benefits of existing vegetation and green spaces. WSUD should be implemented strategically into the urban landscape, targeting areas of high heat exposure, with many distributed WSUD features at regular intervals to promote infiltration and evapotranspiration, and maintain tree health.

The status of the Indo-Pacific Warm Pool and adjacent land at the Last Glacial Maximum

Since the Climate: Long Range Investigation, Mapping and Prediction (CLIMAP) reconstructions for the Earth at the Last Glacial Maximum (LGM), there have been conflicting views on the extent of cooling of the oceans of tropical Australasia-here, referred to as the Indo-Pacific Warm Pool-in contrast with those temperatures registered on land. Based on sea-surface temperature (= SST) reconstructions for the Indo-Pacific Warm Pool, and on vegetation reconstruction for SE Asia as well as by considering the increase of land mass area engendered during low sea levels, we identify for the LGM a significant drop in precipitation in the Warm Pool region that would explain an increase in salinity while SST decreased by about 2 degreesC at the most. The latter would have caused a substantial decrease of large-scale atmospheric convection over the Indo-Pacific Warm Pool and suppressed deep atmospheric convection that would help maintain somewhat elevated SSTs. The drier atmosphere and diminished level of cloud cover would also have reduced nocturnal temperatures at elevation in the region and produced a steeper mean atmospheric lapse rate, forcing the tree line to drop and glaciers to be maintained down to much lower altitudes than today

The Maritime Continent Thunderstorm Experiment (MCTEX): Overview and some results

A description is given of the Maritime Continent Thunderstorm Experiment held over the Tiwi Islands (12°S, 130°E) during the period November–December 1995. The unique nature of regularly occurring storms over these islands enabled a study principally aimed at investigating the life cycle of island-initiated mesoscale convective systems within the Maritime Continent. The program objectives are first outlined and then selected results from various observationally based and modeling studies are summarized. These storms are shown to depend typically on island-scale forcing although external mesoscale disturbances can result in significant storm activity as they pass over the heated island. Particular emphasis is given to summarizing the environmental characteristics and the impact this has on the location of storm development and the associated rainfall distribution. The mean rainfall production from these storms is shown to be about 760 × 105 m3, with considerable variability. The mesoscale evolution is summ...

Central Australian cold fronts

Abstract This paper presents an observational study of the structure and behavior of cold fronts over central Australia during the late dry season, a time of year when the prefrontal convectively well-mixed layer is particularly deep. The study is based on the results of the Central Australian Fronts Experiments (CAFE) held in 1991. Three fronts were documented in unprecedented detail for the Australian region using a greatly enhanced surface-observing network and a boundary layer wind profiler, as well as serial upper-air soundings. Data on the surface energy balance were obtained also. A common feature of the fronts observed during CAFE was that they were dry. shallow (∼1 km deep), and moved into a deep (∼4 km) convectively well-mixed boundary layer. One of them initiated major dust storms across central Australia. A prominent feature of the fronts was the marked diurnal variation of their surface signature as they moved through the network. Noteworthy was the tendency during the night for the initiatio...

Demographic, seasonal, and spatial differences in acute myocardial infarction admissions to hospital in Melbourne Australia

BackgroundSeasonal patterns in cardiac disease in the northern hemisphere are well described in the literature. More recently age and gender differences in cardiac mortality and to a lesser extent morbidity have been presented. To date spatial differences between the seasonal patterns of cardiac disease has not been presented. Literature relating to seasonal patterns in cardiac disease in the southern hemisphere and in Australia in particular is scarce. The aim of this paper is to describe the seasonal, age, gender, and spatial patterns of cardiac disease in Melbourne Australia by using acute myocardial infarction admissions to hospital as a marker of cardiac disease.ResultsThere were 33,165 Acute Myocardial Infarction (AMI) admissions over 2186 consecutive days. There is a seasonal pattern in AMI admissions with increased rates during the colder months. The peak month is July. The admissions rate is greater for males than for females, although this difference decreases with advancing age. The maximal AMI season for males extends from April to November. The difference between months of peak and minimum admissions was 33.7%. Increased female AMI admissions occur from May to November, with a variation between peak and minimum of 23.1%. Maps of seasonal AMI admissions demonstrate spatial differences. Analysis using Global and Local Morans I showed increased spatial clustering during the warmer months. The Bivariate Morans I statistic indicated a weaker relationship between AMI and age during the warmer months.ConclusionThere are two distinct seasons with increased admissions during the colder part of the year. Males present a stronger seasonal pattern than females. There are spatial differences in AMI admissions throughout the year that cannot be explained by the age structure of the population. The seasonal difference in AMI admissions warrants further investigation. This includes detailing the prevalence of cardiac disease in the community and examining issues of social and environmental justice.

Biomass burning and resulting emissions in the Northern Territory, Australia

The extent of biomass burning in the Northern Territory, Australia, during 1992 (a year of low fire activity) was estimated using NOAA-AVHRR satellite imagery and was subsequently used to calculate the emission of gaseous compounds from biomass burning for that year. A total of 73,729 km2 was determined to have been burnt, representing 5.5% of the total Northern Territory area. The extent of biomass burning in different vegetation units in the Northern Territory was also estimated with eucalypt communities comprising 72% of the total area burnt. An estimated 29.5 x 106 tonnes of biomass was consumed by burning, resulting in the production of an estimated : 1. 11.3 Tg C as carbon dioxide, 2. 1.02 Tg C as carbon monoxide, (3) 5.23 x 10-3 Tg C as total particulate matter, 4. 26.1 x 10-3 Tg N as nitrous oxides, 5. various other trace gases. The calculated release of CO2 in this study accounts for only 41% of the estimated Australian contribution to global emmissions from biomass burning, indicating that the Australian contribution may be overestimted.

Changing Urban Climate and CO2 Emissions: Implications for the Development of Policies for Sustainable Cities

Current planning strategies for future urban development often target issues such as housing, transport, water and infrastructure; but very few strategies comprehensively consider the urban climate and its interaction with the built environment. By drawing on recent research conducted in Melbourne, Australia, this article demonstrates the importance of incorporating urban climate understanding and knowledge into urban planning processes to better develop cities that are more sustainable. Melbourne currently experiences the effects of a modified urban climate, with research demonstrating that during the night, urban areas are often warmer than surrounding rural landscapes: an effect known as the ‘urban heat island’. Recent studies also suggest that continuing current patterns of development without intervention would produce degraded urban climates with further exacerbated urban temperatures. With the urgency regarding the enhanced greenhouse effect, the urban heat island is an extremely important issue, as the growing urban population could be further exposed to elevated temperatures. Given our improved understanding of the interactions between the built environment and urban climates, those involved in urban planning and development should begin to adopt this knowledge. Many opportunities exist to intentionally modify the built environment (e.g. cool roofs; water-sensitive urban design) to minimise the risks of developing unfavourable urban climates.