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A global, monthly averaged time series of Sun-induced Fluorescence (SiF), spanning January 2007 to June 2015, was derived from Metop-A Global Ozone Monitoring Experiment 2 (GOME-2) spectral measurements. Far-red SiF was retrieved using the filling-in of deep solar Fraunhofer lines and atmospheric absorption bands based on the general methodology described by Joiner et al, AMT, 2013. A Principal Component (PC) analysis of spectra over non-vegetated areas was performed to describe the effects of atmospheric absorption. Our implementation (SiF KNMI) is an independent algorithm and differs from the latest implementation of Joiner et al, AMT, 2013 (SiF NASA, v26), because we used desert reference areas for determining PCs (as opposed to cloudy ocean and some desert) and a wider fit window that covers water vapour and oxygen absorption bands (as opposed to only Fraunhofer lines). As a consequence, more PCs were needed (35 as opposed to 12). The two time series (SiF KNMI and SiF NASA, v26) correlate well (overall R of 0.78) except for tropical rain forests. Sensitivity experiments suggest the strong impact of the water vapour absorption band on retrieved SiF values. Furthermore, we evaluated the SiF time series with Gross Primary Productivity (GPP) derived from twelve flux towers in Australia. Correlations for individual towers range from 0.37 to 0.84. They are particularly high for managed biome types. In the de-seasonalized Australian SiF time series, the break of the Millennium Drought during local summer of 2010/2011 is clearly observed.

International audience; Light use efficiency (LUE) models are widely used to simulate gross primary production (GPP). However, the treatment of the plant canopy as a big leaf by these models can introduce large uncertainties in simulated GPP. Recently, a two-leaf light use efficiency (TL-LUE) model was developed to simulate GPP separately for sunlit and shaded leaves and has been shown to outperform the big-leaf MOD17 model at six FLUX sites in China. In this study we investigated the performance of the TL-LUE model for a wider range of biomes. For this we optimized the parameters and tested the TL-LUE model using data from 98 FLUXNET sites which are distributed across the globe. The results showed that the TL-LUE model performed in general better than the MOD17 model in simulating 8 day GPP. Optimized maximum light use efficiency of shaded leaves (epsilon(msh)) was 2.63 to 4.59 times that of sunlit leaves (epsilon(msu)). Generally, the relationships of epsilon(msh) and epsilon(msu) with epsilon(max) were well described by linear equations, indicating the existence of general patterns across biomes. GPP simulated by the TL-LUE model was much less sensitive to biases in the photosynthetically active radiation (PAR) input than the MOD17 model. The results of this study suggest that the proposed TL-LUE model has the potential for simulating regional and global GPP of terrestrial ecosystems, and it is more robust with regard to usual biases in input data than existing approaches which neglect the bimodal within-canopy distribution of PAR.

Savannah regions are predicted to undergo changes in precipitation patterns according to current climate change projections. This change will affect leaf phenology, which controls net primary productivity. It is of importance to study this since savannahs play an important role in the global carbon cycle due to their areal coverage and can have an effect on the food security in regions that depend on subsistence farming. In this study we investigate how soil moisture, mean annual precipitation, and day length control savannah phenology by developing a lagged time series model. The model uses climate data for 15 flux tower sites across four continents, and normalized difference vegetation index from satellite to optimize a statistical phenological model. We show that all three variables can be used to estimate savannah phenology on a global scale. However, it was not possible to create a simplified savannah model that works equally well for all sites on the global scale without inclusion of more site specific parameters. The simplified model showed no bias towards tree cover or between continents and resulted in a cross-validated r2 of 0.6 and root mean squared error of 0.1. We therefore expect similar average results when applying the model to other savannah areas and further expect that it could be used to estimate the productivity of savannah regions.Figures

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.

Summary For instantaneous latent heat flux ( λE ) estimates from thermal remote sensing data to be useful in the hydrologic sciences, they require integration over longer time frames (e.g., months to years). This is not trivial because thermal remote sensing data acquired under cloud-free daytime conditions require upscaling to a monthly energy amount that is both relevant over cloudy periods and considers daytime and nighttime. Previous work has compared upscaling approaches, but as yet there is no authoritative comparison that does so under conditions relevant for thermal remote sensing. In this paper we describe, under the conditions relevant for thermal remote sensing, a generic framework for comparing any upscaling approach that assumes self-preservation. Then we use eddy-flux data from two sites in contrasting climates to systematically evaluate the accuracy of different upscaling proposals within the framework. We assumed that the instantaneous estimate of the latent heat flux measured by the eddy-flux technique would have been measured by a satellite sensor. We then scaled this estimate to a monthly period using four approaches and compared the result with the observed monthly integral. This design enabled us to isolate the accuracy of each upscaling method. The four methods upscaled λE by: (i) observed solar irradiance ( S ); (ii) modelled solar irradiance from a sine function ( S SIN ); (iii) modelled top-of-atmosphere solar irradiance ( S TOA ); and (iv) observed available energy ( A E ). We showed that upscaling λE using observed data ( S , A E ) resulted in underestimation of monthly evaporative energy, while the use of modelled data ( S SIN , S TOA ) led to overestimation, primarily due to the relationship between error and both the season (day-of-year) and cloud fraction. Of the two observed fluxes, upscaling with S resulted in lower overall errors than when using A E ( S bias: −1.11 M J m −2 d −1 or −16%; A E bias: −2.15 M J m −2 d −1 or −34%). Of the two modelled fluxes, upscaling with S TOA had lower errors than the widely used S SIN method ( S SIN bias: 1.03 M J m −2 d −1 or 14%; S TOA bias: 0.91 M J m −2 d −1 or 13%). We subsequently developed a simple procedure to minimise bias from all four upscaling approaches, and concluded that modelled data ( S TOA ) can be used to upscale λE to longer timescales for thermal remote sensing applications. This study developed the theory to minimise upscaling bias at two sites with contrasting climates, further work is needed to extend the approach to all global terrestrial climates.

Afforestation of agricultural land to mitigate climate change and other environmental degradation has been increasingly implemented around the world. However, the effects of afforestation on soil carbon and particularly nitrogen content remain unclear. We conducted a hierarchical Bayesian meta-analysis of published data on the effects of afforestation of pastures on soil carbon and nitrogen stocks in a Mediterranean climate. We found no evidence for substantial changes in soil carbon, nitrogen or C:N ratio across three decades of afforestation. However, a lack of data on the carbon content of the litter underestimates the potential for afforestation to sequester carbon in the soil. We investigated soil carbon content under remnant woodlands and found that it was higher than under the afforested pastures suggesting that afforestation has the potential to increase soil carbon over longer time scales. Targeted studies that measure carbon content and form within soils over an extended chronosequence are much needed to improve predictions of the potential for afforestation to increase soil carbon storage.

A direct relationship between gross ecosystem productivity (GEP) measured by the eddy covariance (EC) method and Moderate Resolution Imaging Spectroradiometer (MODIS) vegetation indices (VIs) has been observed in many temperate and tropical ecosystems. However, in Australian evergreen forests, and particularly sclerophyll woodlands, MODIS VIs do not capture seasonality of GEP. In this study, we re-evaluate the connection between satellite and flux tower data at four contrasting Australian ecosystems, through comparisons of ecosystem photosynthetic activity (GEP) and potential (e.g. ecosystem light use efficiency and quantum yield) with MODIS vegetation satellite products, including VIs, gross primary productivity (GPPMOD), leaf area index (LAIMOD), and fraction of photosynthetic active radiation (fPARMOD). We found that satellite derived greenness products constitute a measurement of ecosystem structure (e.g. leaf area index – quantity of leaves) and function (e.g. leaf level photosynthetic assimilation capacity – quality of leaves), rather than productivity. Our results show that in primarily meteorological-driven (e.g. photosynthetic active radiation, air temperature and/or precipitation) and relatively aseasonal vegetation photosynthetic potential ecosystems (e.g. evergreen wet sclerophyll forests), there were no statistically significant relationships between GEP and satellite derived measures of greenness. In contrast, for phenology-driven ecosystems (e.g. tropical savannas), changes in the vegetation status drove GEP, and tower-based measurements of photosynthetic activity were best represented by VIs. We observed the highest correlations between MODIS products and GEP in locations where key meteorological variables and vegetation phenology were synchronous (e.g. semi-arid Acacia woodlands) and low correlation at locations where they were asynchronous (e.g. Mediterranean ecosystems). Eddy covariance data offer much more than validation and/or calibration of satellite data and models. Knowledge of the conditions in which flux tower measurements and VIs or other remote sensing products converge greatly advances our understanding of the mechanisms driving the carbon cycle (phenology and climate drivers) and provides an ecological basis for interpretation of satellite derived measures of greenness.

Leaf-level photosynthetic parameters of species in the closely related genera Eucalyptus and Corymbia were assessed along a strong rainfall gradient in northern Australia. Both instantaneous gas exchange measurements and leaf carbon isotope discrimination indicated little variation in intercellular CO2 concentrations during photosynthesis (ci) in response to a decrease in mean annual precipitation from not, vert, similar1700 mm to not, vert, similar300 mm. Correlation between stomatal conductance and photosynthetic capacity contributed toward the maintenance of relatively constant ci among the sampled leaves, when assessed at ambient CO2 concentration and photon irradiance similar to full sunlight. Leaf mass per area was the most plastic leaf trait along the rainfall gradient, showing a linear increase in response to decreasing mean annual precipitation. The maximum Rubisco carboxylation velocity, Vcmax, expressed on a leaf-area basis, showed a modest increase in response to decreasing rainfall. This modest increase in Vcmax was associated with the strongly expressed increase in leaf mass per area. These results suggest that variation in ecosystem-level gas exchange during the dry season in north-Australian savannas will likely be dominated by changes in leaf area index in response to increasing aridity, rather than by changes in photosynthetic performance per unit leaf area.

This paper compares estimates of Leaf Area Index (LAI) obtained from the MODIS (Moderate Resolution Imaging Spectroradiometer) collections 4.8 (MC4) and 5.0 (MC5) with ground-based measurements taken along a 900 km north–south transect through savanna in the Northern Territory, Australia. There was excellent agreement for both the magnitude and timing in the annual variation in LAI from MC5 and biometric estimates at Howard Springs, near Darwin, whereas MC4 overestimated LAI by 1–2 m2 m−2 for the first 200 days of the year. Estimates of LAI from MC5 were also compared with those obtained from the analysis of digital hemispherical photographs taken during the dry season (September 2008) based on algorithms that included random and clumped distribution of leaves. Linear regression of LAI from MC5 versus that using the clumping algorithm yielded a slope close to 1 (m = 0.98). The regression based on a random distribution of leaves yielded a slope significantly different from 1 (m = 1.37), with higher Mean Absolute Error (MAE) and bias compared to the clumped analysis. The intercept for either analysis was not significantly different from zero but inclusion of five additional sites that were visually bare or without green vegetation produced a statistically significant offset of +0.16 m2 m−2 by MC5. Overall, our results show considerable improvement of MC5 over MC4 LAI and good agreement between MC5 and ground-based LAI estimates from hemispherical photos incorporating clumping of leaves.

Savannas are highly significant global ecosystems that consist of a mix of trees and grasses and that are highly spatially varied in their physical structure, species composition, and physiological function (i.e., leaf area and function, stem density, albedo, and roughness). Variability in ecosystem characteristics alters biophysical and biogeochemical processes that can affect regional to global circulation patterns, which are not well characterized by land surface models. We initiated a multidisciplinary field campaign called Savanna Patterns of Energy and Carbon Integrated across the Landscape (SPECIAL) during the dry season in Australian savannas to understand the spatial patterns and processes of land surface–atmosphere exchanges (radiation, heat, moisture, CO2, and other trace gasses). We utilized a combination of multiscale measurements including fixed flux towers, aircraft-based flux transects, aircraft boundary layer budgets, and satellite remote sensing to quantify the spatial variability across a continental-scale rainfall gradient (transect). We found that the structure of vegetation changed along the transect in response to declining average rainfall. Tree basal area decreased from 9.6 m2 ha−1 in the coastal woodland savanna (annual rainfall 1,714 mm yr−1) to 0 m2 ha−1 at the grassland site (annual rainfall 535 mm yr−1), with dry-season green leaf area index (LAI) ranging from 1.04 to 0, respectively. Leaf-level measurements showed that photosynthetic properties were similar along the transect. Flux tower measurements showed that latent heat fluxes (LEs) decreased from north to south with resultant changes in the Bowen ratios (H/LE) from a minimum of 1.7 to a maximum of 15.8, respectively. Gross primary productivity, net carbon dioxide exchange, and LE showed similar declines along the transect and were well correlated with canopy LAI, and fluxes were more closely coupled to structure than floristic change.

Tropical savanna ecosystems are a major contributor to global CO2, CH4 and N2O greenhouse gas exchange. Savanna fire events represent large, discrete C emissions but the importance of ongoing soil-atmosphere gas exchange is less well understood. Seasonal rainfall and fire events are likely to impact upon savanna soil microbial processes involved in N2O and CH4 exchange. We measured soil CO2, CH4 and N2O fluxes in savanna woodland (Eucalyptus tetrodonta/Eucalyptus miniata trees above sorghum grass) at Howard Springs, Australia over a 16 month period from October 2007 to January 2009 using manual chambers and a field-based gas chromatograph connected to automated chambers. The effect of fire on soil gas exchange was investigated through two controlled burns and protected unburnt areas. Fire is a frequent natural and management action in these savanna (every 1-2 years). There was no seasonal change and no fire effect upon soil N2O exchange. Soil N2O fluxes were very low, generally between -1.0 and 1.0 mu g N m(-2) h(-1), and often below the minimum detection limit. There was an increase in soil NH4+ in the months after the 2008 fire event, but no change in soil NO3-. There was considerable nitrification in the early wet season but minimal nitrification at all other times. Savanna soil was generally a net CH4 sink that equated to between -2.0 and -1.6 kg CH4 ha(-1) y(-1) with no clear seasonal pattern in response to changing soil moisture conditions. Irrigation in the dry season significantly reduced soil gas diffusion and as a consequence soil CH4 uptake. There were short periods of soil CH4 emission, up to 20 mu g C m(-2) h(-1), likely to have been caused by termite activity in, or beneath, automated chambers. Soil CO2 fluxes showed a strong bimodal seasonal pattern, increasing fivefold from the dry into the wet season. Soil moisture showed a weak relationship with soil CH4 fluxes, but a much stronger relationship with soil CO2 fluxes, explaining up to 70% of the var

Savannas comprise a large proportion of the terrestrial land surface and are highly varied in their composition, structure and function. These characteristics alter land–atmosphere exchanges of heat, water, carbon dioxide and other trace gases, which feed back to the climate at multiple scales. Australian savannas provide significant ecosystem services and further systematic scientific study is needed to sustainably manage these ecosystems. We undertook an interdisciplinary research effort to understand the patterns and processes of carbon, water and energy cycles across northern Australian landscapes across scales from point to region. We quantified the land surface–atmosphere exchanges across the vast region of Australian savannas using a hierarchical, integrated measurement and modelling approach to determine regional greenhouse gas and water budgets. The research team comprised groups from seven institutions and four countries. The research effort comprised of a multi- year measurement and modelling endeavour and culminated in an intensive field program held in September 2008 (late dry season). The program aimed to improve our knowledge of the spatial and temporal variability of land–atmosphere exchanges and the processes driving them as well as our ability to remotely sense them and simulate them using land surface models, which are crucial components of Global Climate Models. We attempted to robustly integrate small scale processes, such as leaf photosynthesis to larger scales applicable to modelling and remote sensing for the savanna region. In this paper we provide the scientific background and our overall approach to the program with reference to the papers in this “Savanna Patterns of Energy and Carbon Integrated Across the Landscape” (SPECIAL) issue.

Savanna landscapes across north Australia are characterised by limited topographic variation, and in the Northern Territory, by a relatively constant decline in rainfall with distance inland. The North Australian Tropical Transect (NATT) traverses this 1000 km gradient of largely intact vegetation which provides an ideal ‘living laboratory’ and framework to investigate the influence of vegetation structural and floristic change and climate drivers on land–atmosphere exchange at a regional scale. We conducted a multidisciplinary program examining carbon, water and energy fluxes as a function of climate and vegetation change along a sub-continental environmental gradient. Initial findings are reported in this Special Issue. During the program, an intensive field campaign was undertaken during the dry season to characterise vegetation and soil properties of eight flux tower sites used to describe spatial and temporal dynamics of fluxes across this gradient. This paper provides an overview of the savanna landscapes of north Australia detailing vegetation structural and physiological change along this gradient. Above-ground woody biomass, stem density, overstorey LAI and canopy height declined along sites that spanned an 1100 mm annual rainfall gradient. Biomass ranged from 35 to 5 t C ha −1 with dry season LAI ranging from ∼1 to 0.05 across savanna sites both intact and cleared for grazing. Across open-forest and woodland savanna, basal area ranged from 9.7 to 5.3 m 2 ha −1 . While structural change was significant and correlated with rainfall, leaf scale physiological properties (maximal photosynthesis, V cmax , c i / c a , light use efficiency) of the dominant woody species showed little variation, despite the significant environmental gradient. It is likely that changes in structural properties dominate spatial patterns of flux as opposed to physiological plasticity or species differences along this gradient.

A soil–plant–atmosphere model was used to estimate gross primary productivity (GPP) and evapotranspiration (ET) of a tropical savanna in Australia. This paper describes model modifications required to simulate the substantial C4 grass understory together with C3 trees. The model was further improved to include a seasonal distribution of leaf area and foliar nitrogen through 10 canopy layers. Model outputs were compared with a 5-year eddy covariance dataset. Adding the C4 photosynthesis component improved the model efficiency and root-mean-squared error (RMSE) for total ecosystem GPP by better emulating annual peaks and troughs in GPP across wet and dry seasons. The C4 photosynthesis component had minimal impact on modelled values of ET. Outputs of GPP from the modified model agreed well with measured values, explaining between 79% and 90% of the variance and having a low RMSE (0.003–0.281 g C m � 2 day � 1 ). Approximately, 40% of total annual GPP was contributed by C4 grasses. Total (trees and grasses) wet season GPP was approximately 75–80% of total annual GPP. Light-use efficiency (LUE) was largest for the wet season and smallest in the dry season and C4 LUE was larger than that of the trees. A sensitivity analysis of GPP revealed that daily GPP was most sensitive to changes in leaf area index (LAI) and foliar nitrogen (Nf) and relatively insensitive to changes in maximum carboxylation rate (Vcmax), maximum electron transport rate (Jmax) and minimum leaf water potential (cmin). The modified model was also able to represent daily and seasonal patterns in ET, (explaining 68–81% of variance) with a low RMSE (0.038–0.19 mm day � 1 ). Current values of Nf, LAI and other parameters appear to be colimiting for maximizing GPP. By manipulating LAI and soil moisture content inputs, we show that modelled GPP is limited by light interception rather than water availability at this site.

The influence of synoptic-scale circulations on air quality is an area of increasing interest to air quality management in regards to future climate change. This study presents an analysis where the range of expected synoptic-scale circulation patterns over the region of Melbourne, Australia are determined and linked to regional air quality. A self-organizing map (SOM) has been applied to daily mean sea level pressure (MSLP) reanalysis to obtain twenty large-scale synoptic patterns in the Australian region. A time series of the occurrence of the synoptic archetypes was then employed within the framework of a generalized additive model (GAM) to identify links between synoptic-scale circulation and observed changes air pollutant concentrations. The GAM estimated shifts in pollutant concentration under the occurrence of each synoptic type after controlling for long-term trends, seasonality, weekly emissions, spatial variation, and temporal persistence. Results found the overall explanatory power of the synoptic archetypes in the models to be rather modest with 5.1% of the day-to-day variation in O3, 4.7% in PM10, and 7.1% in NO2 being explained. This indicates that synoptic-scale circulation features are not the primary driver of day-to-day pollutant concentrations. Nonetheless, further analysis of the partial residual plots identified that despite a modest response at the aggregate level, individual synoptic categories had differential effects on air pollutants. In particular, NO2 and O3 were 20% higher than average when synoptic conditions resulted in a northeasterly gradient wind over the Melbourne area. For PM10 maximum increases of up to 20% occurred when a strong anticyclonic system was centered directly over the Melbourne area. In sum, the unified approach of SOM and GAM provided a complementary suite of tools capable of identifying the entire range synoptic circulation patterns over a particular region and quantifying how they influence local air quality.

Urban land surface schemes have been developed to model the distinct features of the urban surface and the associated energy exchange processes. These models have been developed for a range of purposes and make different assumptions related to the inclusion and representation of the relevant processes. Here, the first results of Phase 2 from an international comparison project to evaluate 32 urban land surface schemes are presented. This is the first large-scale systematic evaluation of these models. In four stages, participants were given increasingly detailed information about an urban site for which urban fluxes were directly observed. At each stage, each group returned their models' calculated surface energy balance fluxes. Wide variations are evident in the performance of the models for individual fluxes. No individual model performs best for all fluxes. Providing additional information about the surface generally results in better performance. However, there is clear evidence that poor choice of parameter values can cause a large drop in performance for models that otherwise perform well. As many models do not perform well across all fluxes, there is need for caution in their application, and users should be aware of the implications for applications and decision making. Copyright  2010 Royal Meteorological Society

Terrestrial ecosystems are highly responsive to their local environments and, as such, the rate of carbon uptake both in shorter and longer timescales and different spatial scales depends on local environmental drivers. For savannas, the key environmental drivers controlling vegetation productivity are water and nutrient availability, vapour pressure deficit (VPD), solar radiation and fire. Changes in these environmental factors can modify the carbon balance of these ecosystems. Therefore, understanding the environmental drivers responsible for the patterns (temporal and spatial) and processes (photosynthesis and respiration) has become a central goal in terrestrial carbon cycle studies. Here we have reviewed the various environmental controls on the spatial and temporal patterns on savanna carbon fluxes in northern Australia. Such studies are critical in predicting the impacts of future climate change on savanna productivity and carbon storage.

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, a...

Aerosols have been shown to affect the quantity and quality of solar radiation on the Earth’s surface. Savanna regions are subject to frequent burning and release of aerosols that may impact on radiation components and possibly vegetation productivity in this region. Therefore, in this study, we have analyzed the optical properties of aerosols (aerosol optical depth (AOD) and Angstrom coefficient) from the Atmospheric Radiation Measurement site in Darwin for the periods from April 2002 to June 2005 as measured by a multifilter rotating shadowband radiometer. The influence of aerosols and their effect on surface shortwave incoming solar radiation and savanna productivity were examined for the dry season using sky radiation collection of radiometers and eddy covariance measurements from the Howard Springs flux site. Results indicated that aerosol concentrations in the region were relatively low compared to other savanna regions with the maximum monthly average AOD over the period being the greatest in October (0.29 ± 0.003 standard error at 500 nm). The highest monthly average Angstrom exponent was also found in October (1.38 ± 0.008). The relatively low aerosol concentration in this region can be attributed to the mixture of smoke aerosols with humidity haze and local circulations. Over a range of AODs from 0.1 to 0.4, we found a modest increase in the fraction of diffuse radiation to total radiation from 11% to 21%. This small increase in diffuse fraction did not affect the carbon flux significantly. However, because the current range of AOD in the region is relatively low, the region could be sensitive to increases in aerosols and diffuse fraction in the future.

Urban planning is a useful method for improving local climate and human health in cities through purposefully modifying urban land surface characteristics. This can reduce the potential risks of elevated city temperatures due to the urban heat island (UHI). Unfortunately, simple tools are not readily available for urban planners to assess the climatological impacts of various urban development scenarios. Urban modelling could be developed into such a tool to achieve this. This study attempts to design and evaluate a suitable tool for application in Melbourne, Australia. The Air Pollution Model (TAPM) was chosen to assess the impact of a long-term urban planning strategy on local climate and the above canopy UHI in Melbourne. Improvements were made to TAPM by increasing the number of urban land-use classes in the model and creating a higher resolution land cover database focused on housing density. This modified version of TAPM showed a good performance in replicating the surface energy balance compared with an observational flux tower site in suburban Melbourne during summer. TAPM simulated a mean maximum UHI intensity of 3–4 °C at 2 a.m. in January. A future UHI scenario was then examined (year 2030) using an urban land cover database derived from plans in the Melbourne 2030 urban planning strategy. Results highlighted specific areas where planning intervention would be particularly useful to improve local climates, namely activity centres and growth areas. The appropriateness of the use of TAPM and climate models as a tool in urban planning is also discussed. Copyright © 2008 Royal Meteorological Society

Soils are responsible for storing up to 75% of forest carbon uptake making them extremely large carbon pools. However, soil carbon is eventually released to the atmosphere by below ground respiration, consisting of soil respiration (microbial activity) and root respiration, which is influenced by environmental climate variables (soil temperature and moisture), soil characteristics (chemical and physical properties) and stand characteristics (stand age). We investigated the impact of stand age of cool temperate mountain ash forests ( E. regnans ) in Wallaby Creek, Victoria on carbon cycling between the soil and atmosphere using a chronosequence of three sites of different ages (regrowth from bushfires in 1730, 1926 and 1983). Below ground respiration was measured between January (Summer) and May (Autumn) in 2005 across all three sites, with the highest rates found in the old growth forest (5.3 μmol CO 2 m −2 s −1 ) and with lowest rates in the youngest site (2.9 μmol CO 2 m −2 s −1 ). Within sites, below ground respiration rates increased with temperature, with Q 10 values ranging between 1.42 and 1.55. Rates were further influenced by soil moisture, and soil physical and chemical properties, including root biomass and levels of soil carbon. Litterfall was also measured and was highest at the youngest site (140 g biomass m −2 month −1 ) and lowest (92 g biomass m −2 month −1 ) at the old growth site. Greater understanding of forest carbon cycling will result in an improved understanding of forests and their influence on global warming.

Fire scars have the ability to radically alter the surface energy budget within a tropical savanna by reducing surface albedo, increasing available energy for partitioning into sensible and latent heat fluxes and increasing substrate heat flux. These changes have the potential to alter boundary-layer conditions and ultimately feedback to local and regional climate. We measured radiative and energy fluxes over burnt and unburnt tropical savanna near Howard Springs, Darwin, Australia. At the burnt site a low to moderate intensity fire, ranging between 1,000 and 3,500kW m −1 , initially affected the land surface by removing all understorey vegetation, charring and blackening the ground surface, scorching the overstorey canopy and reducing the albedo. A reduction in latent heat fluxes to almost zero was seen immediately after the fire when the canopy was scorched. This was then followed by an increase in the sensible heat flux and a large increase in the ground heat flux over the burnt surface. Tethered balloon measurements showed that, despite the presence of pre-monsoonal rain events occurring during the measurement period, the lower boundary layer over the burnt site was up to 2 ◦ C warmer than that over the unburnt site. This increase in boundary-layer heating when applied to fire scars at the landscape scale can have the ability to form or alter local mesoscale circulations and ultimately create a feedback to regional heating and precipitation patterns that may affect larger-scale processes such as the Australian monsoon.

Savannas comprise a large area of the global land surface and are subject to frequent disturbance through fire. The role of fire as one of the primary natural carbon cycling mechanisms is a key issue in considering global change feedbacks. The savannas of Northern Australia burn regularly and we aimed to determine their annual net ecosystem productivity (NEP) and the impact of fire on productivity. We established a long-term eddy covariance flux tower at Howard Springs, Australia and present here 5 years of data from 2001 to 2005. Fire has direct impacts through emissions but also has indirect effects through the loss of productivity due to reduced functional leaf area index and the carbon costs of rebuilding the canopy. The impact of fire on the canopy latent energy exchange was evident for 40 days while the canopy was rebuilt; however, the carbon balance took approximately 70 days to recover. The annual fire free NEP at Howard Springs was estimated at -4.3 t C ha(-1) yr(-1) with a range of -3.5 to -5.1 t C ha(-1) yr(-1) across years. We calculated the average annual indirect fire effect as +0.7 t C ha(-1) yr(-1) using a neural network model approach and estimated average emissions of fine and coarse fuels as +1.6 t C ha(-1) yr(-1). This allowed us to calculate a net biome production of -2.0 t C ha(-1) yr(-1). We then partitioned this remaining sink and suggest that most of this can be accounted for by woody increment (1.2 t C ha(-1) yr(-1)) and shrub encroachment (0.5 t C ha(-1) yr(-1)). Given the consistent sink at this site, even under an almost annual fire regime, there may be management options to increase carbon sequestration by reducing fire frequency.

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.

In this paper the authors explore the spatial and temporal patterns of lightning strikes in northern Australia for the first time. In particular, the possible relationships between lightning strikes and elevation, vegetation type, and fire scars (burned areas) are examined. Lightning data provided by the Bureau of Meteorology were analyzed for a 6-yr period (1998–2003) over the northern, southern, and coastal regions of the Northern Territory (NT) through the use of Geographical Information Systems (GIS) to determine the spatial and temporal characteristics of lightning strikes. It was determined that the highest densities of lightning strikes occurred during the monsoon transitional period (dry to wet) and during the active monsoon periods, when atmospheric moisture is highest. For the period of this study, lightning was far more prevalent over the northern region (1.21 strikes per km2 yr−1) than over the southern (0.58 strikes per km2 yr−1) and coastal regions (0.71 strikes per km2 yr−1). Differences in vegetation cover were suggested to influence the lightning distribution over the northern region of the NT, but no relationship was found in the southern region. Lightning strikes in the southern region showed a positive relationship with elevations above 800 m, but no relationship was found in the northern region, which could be due to the low-lying topography of the area. A comparison of lightning densities between burned and unburned areas showed high variability; however, the authors suggest that, under ideal atmospheric conditions, large-scale fire scars (>500 m) could produce lightning strikes triggered by either enhanced free convection or mesoscale circulations.

Urban areas are significant contributors to global carbon dioxide emissions. Vehicle emissions and other anthropogenic related activities are a frequent source of CO2 to the atmosphere, contributing to global warming. Micrometeorological techniques used for observations in Northern Hemisphere cities have found that urban CO2 fluxes are consistently a source. This study investigates CO2 fluxes in an Australian city, adding to the global database of CO2 fluxes in a bid to aid in future development of planning policies concerning reductions in CO2 emissions. Using the eddy covariance approach, fluxes of CO2 were measured at a suburban site (Preston) in Melbourne, Australia from February 2004 to June 2005 to investigate temporal variability. A second site (Surrey Hills) with differing surface characteristics (in particular, greater vegetation cover) was also established in Melbourne and ran simultaneously for 6 months (February 2004–July 2004). Results showed that both sites were a net source of CO2 to the atmosphere. Diurnal patterns of fluxes were largely influenced by traffic volumes, with two distinct peaks occurring at the morning and evening traffic peak hours, with the winter morning peak averaging 10.9 μmol m−2 s−1 at Preston. Summer time fluxes were lower than during winter due to greater vegetative influence and reduced natural gas combustion. Vegetation limited the source of CO2 in the afternoon, yet was not enough to combat the strong local anthropogenic emissions. Surrey Hills showed higher fluxes of CO2 despite greater vegetation cover because of higher local traffic volumes. Annual emissions from Preston were estimated at 84.9 t CO2 ha−1 yr−1. Magnitudes and patterns of suburban CO2 fluxes in Melbourne were similar to those observed in Northern Hemisphere suburban areas.

Reliable estimation of evapotranspiration is important for many hydrological applications, including agriculture, climatology, and assessment of stormwater control measures. An automated chamber system was constructed to measure field evapotranspiration. The system consists of six chambers, sampled consecutively by means of a dynamic closed-chamber design, and is fully automated to allow replicable long-term measurements. However, the use of such a system is subject to measurement errors due to vapor adsorption along the sampling tubes and inappropriate internal ventilation. Because these issues are rarely addressed in the literature on flux chambers, a laboratory calibration was performed to estimate errors in evapotranspiration rates measured by the system. The effects of the sampling tube length and air mixing were investigated. A correction factor for evapotranspiration rates relative to the tube length was established. Appropriate air mixing induced by small fans ensured that the measured rates were representative of the internal conditions of the chambers. With appropriate internal ventilation and correction factors, the relative error of measurements was less than 5% for high evapotranspiration rates.

© 2014 The Authors. Global Change Biology Published by John Wiley & Sons Ltd. Savanna ecosystems comprise 22% of the global terrestrial surface and 25% of Australia (almost 1.9 million km2) and provide significant ecosystem services through carbon and water cycles and the maintenance of biodiversity. The current structure, composition and distribution of Australian savannas have coevolved with fire, yet remain driven by the dynamic constraints of their bioclimatic niche. Fire in Australian savannas influences both the biophysical and biogeochemical processes at multiple scales from leaf to landscape. Here, we present the latest emission estimates from Australian savanna biomass burning and their contribution to global greenhouse gas budgets. We then review our understanding of the impacts of fire on ecosystem function and local surface water and heat balances, which in turn influence regional climate. We show how savanna fires are coupled to the global climate through the carbon cycle and fire regimes. We present new research that climate change is likely to alter the structure and function of savannas through shifts in moisture availability and increases in atmospheric carbon dioxide, in turn altering fire regimes with further feedbacks to climate. We explore opportunities to reduce net greenhouse gas emissions from savanna ecosystems through changes in savanna fire management.

Shifts in the carbon balance of high-latitude ecosystems could result from differential responses of vegetation and soil processes to changing moisture and temperature regimes and to a lengthening of the growing season. Although shrub expansion and northward movement of treeline should increase carbon inputs, the effects of these vegetation changes on net carbon exchange have not been evaluated. We selected low shrub, tall shrub, and forest tundra sites near treeline in northwestern Alaska, representing the major structural transitions expected in response to warming. In these sites, we measured aboveground net primary production (ANPP) and vegetation and soil carbon and nitrogen pools, and used these data to parameterize the Terrestrial Ecosystem Model. We simulated the response of carbon balance components to air temperature and precipitation trends during 1981–2000. In areas experiencing warmer and dryer conditions, Net Primary Production (NPP) decreased and heterotrophic respiration (R H ) increased, leading to a decrease in Net Ecosystem Production (NEP). In warmer and wetter conditions NPP increased, but the response was exceeded by an increase in R H ; therefore, NEP also decreased. Lastly, in colder and wetter regions, the increase in NPP exceeded a small decline in R H , leading to an increase in NEP. The net effect for the region was a slight gain in ecosystem carbon storage over the 20 year period. This research highlights the potential importance of spatial variability in ecosystem responses to climate change in assessing the response of carbon storage in northern Alaska over the last two decades.

Surface energy exchanges were measured in a sequence of five sites representing the major vegetation types in the transition from arctic tundra to forest. This is the major transition in vegetation structure in northern high latitudes. We examined the influence of vegetation structure on the rates of sensible heating and evapotranspiration to assess the potential feedbacks to climate if high-latitude warming were to change the distribution of these vegetation types. Measurements were made at Council on the Seward Peninsula, Alaska, at representative tundra, low shrub, tall shrub, woodland (treeline), and boreal forest sites. Structural differences across the transition from tundra to forest included an increase in the leaf area index (LAI) from 0.52 to 2.76, an increase in canopy height from 0.1 to 6.1 m, and a general increase in canopy complexity. These changes in vegetation structure resulted in a decrease in albedo from 0.19 to 0.10 as well as changes to the partitioning of energy at the surface. Bulk surface resistance to water vapor flux remained virtually constant across sites, apparently because the combined soil and moss evaporation decreased while transpiration increased along the transect from tundra to forest. In general, sites became relatively warmer and drier along the transect with the convective fluxes being increasingly dominated by sensible heating, as evident by an increasing Bowen ratio from 0.94 to 1.22. The difference in growing season average daily sensible heating between tundra and forest was 21 W m � 2 . Fluxes changed non-linearly along the transition, with both shrubs and trees substantially enhancing heat transfer to the atmosphere. These changes in vegetation structure that increase sensible heating could feed back to enhance warming at local to regional scales. The magnitude of these vegetation effects on potential high-latitude warming is two to three times greater than suggested by previous modeling studies. # 2005 Elsevier B.V. All rights reserved.

Aim Describe the spatial and temporal properties of transitions in the Arctic and develop a conceptual understanding of the nature of these spatial transitions in the face of directional environmental change. Location Arctic tundra ecosystems of the North Slope of Alaska and the tundra-forest region of the Seward Peninsula, Alaska Methods We synthesize information from numerous studies on tundra and treeline ecosystems in an effort to document the spatial changes that occur across four arctic transitions. These transitions are: (i) the transition between High-Arctic and Low-Arctic systems, (ii) the transition between moist non-acidic tundra (MNT) and moist acidic tundra (MAT, also referred to as tussock tundra), (iii) the transition between tussock tundra and shrub tundra, (iv) the transition between tundra and forested systems. By documenting the nature of these spatial transitions, in terms of their environmental controls and vegetation patterns, we develop a conceptual model of temporal dynamics of arctic ecotones in response to environmental change. Results Our observations suggest that each transition is sensitive to a unique combination of controlling factors. The transition between High and Low Arctic is sensitive primarily to climate, whereas the MNT/MAT transition is also controlled by soil parent material, permafrost and hydrology. The tussock/shrub tundra transition appears to be responsive to several factors, including climate, topography and hydrology. Finally, the tundra/forest boundary responds primarily to climate and to climatically associated changes in permafrost. There were also important differences in the demography and distribution of the dominant plant species across the four vegetation transitions. The shrubs that characterize the tussock/shrub transition can achieve dominance potentially within a decade, whereas spruce trees often require several decades to centuries to achieve dominance within tundra, and Sphagnum moss colonization of non-acidic sites at the MNT/MAT boundary may require centuries to millennia of soil development. Main conclusions We suggest that vegetation will respond most rapidly to climatic change when (i) the vegetation transition correlates more strongly with climate than with other environmental variables, (ii) dominant species exhibit gradual changes in abundance across spatial transitions, and/or (iii) the dominant species have demographic properties that allow rapid increases in abundance following climatic shifts. All three of these properties characterize the transition between tussock tundra and low shrub tundra. It is therefore not surprising that of the four transitions studied this is the one that appears to be responding most rapidly to climatic warming.

Land surface models (LSM) are designed to provide turbulent and radiative fluxes from the surface to the atmosphere that are in turn important in driving atmospheric models. The fluxes in land surface models are controlled by the surface properties and hence the correct parameterization of these properties and the processes that define them is vital in obtaining realistic fluxes. We investigate the sensitivity of turbulent fluxes predicted by the NCAR LSM to biotic surface parameters (roughness length, displacement height, leaf area index, rooting fraction with depth, albedo and minimum stomatal resistance). This is achieved using a multivariate reduced-form model that expresses the results of multiple realizations of the physical model as integrative response metrics such as summer ground, sensible and latent heat fluxes; average soil summer water content; and average soil temperature of the upper layer in each season. The sensitivity analysis shows that most response metrics were most sensitive to roughness length and displacement height. In summertime, leaf area index was important in determining summer ground heat flux, ground temperature and the timing of snow-free ground. This timing was also sensitive to albedo. Rooting fraction with depth was only important in determining summer soil water content. In general the NCAR LSM was more sensitive to a range of climate driven perturbations examined in a companion paper than to the range of biotic surface parameters chosen here.

The responses of high latitude ecosystems to global change involve complex interactions among environmental variables, vegetation distribution, carbon dynamics, and water and energy exchange. These responses may have important consequences for the earth system. In this study, we evaluated how vegetation distribution, carbon stocks and turnover, and water and energy exchange are related to environmental variation spanned by the network of the IGBP high latitude transects. While the most notable feature of the high latitude transects is that they generally span temperature gradients from southern to northern latitudes, there are substantial differences in temperature among the transects. Also, along each transect temperature co-varies with precipitation and photosynthetically active radiation, which are also variable among the transects. Both climate and disturbance interact to influence latitudinal patterns of vegetation and soil carbon storage among the transects, and vegetation distribution appears to interact with climate to determine exchanges of heat and moisture in high latitudes. Despite limitations imposed by the data we assembled, the analyses in this study have taken an important step toward clarifying the complexity of interactions among environmental variables, vegetation distribution, carbon stocks and turnover, and water and energy exchange in high latitude regions. This study reveals the need to conduct coordinated global change studies in high latitudes to further elucidate how interactions among climate, disturbance, and vegetation distribution influence carbon dynamics and water and energy exchange in high latitudes.

Reforestation has large potential for mitigating climate change through carbon sequestration. Native mixed-species plantings have a higher potential to reverse biodiversity loss than do plantations of production species, but there are few data on their capacity to store carbon. A chronosequence (5-45 years) of 36 native mixed-species plantings, paired with adjacent pastures, was measured to investigate changes to stocks among C pools following reforestation of agricultural land in the medium rainfall zone (400-800 mm yr(-1)) of temperate Australia. These mixed-species plantings accumulated 3.09 ± 0.85 t C ha(-1) yr(-1) in aboveground biomass and 0.18 ± 0.05 t C ha(-1) yr(-1) in plant litter, reaching amounts comparable to those measured in remnant woodlands by 20 years and 36 years after reforestation respectively. Soil C was slower to increase, with increases seen only after 45 years, at which time stocks had not reached the amounts found in remnant woodlands. The amount of trees (tree density and basal area) was positively associated with the accumulation of carbon in aboveground biomass and litter. In contrast, changes to soil C were most strongly related to the productivity of the location (a forest productivity index and soil N content in the adjacent pasture). At 30 years, native mixed-species plantings had increased the stability of soil C stocks, with higher amounts of recalcitrant C and higher C:N ratios than their adjacent pastures. Reforestation with native mixed-species plantings did not significantly change the availability of macronutrients (N, K, Ca, Mg, P, and S) or micronutrients (Fe, B, Mn, Zn, and Cu), content of plant toxins (Al, Si), acidity, or salinity (Na, electrical conductivity) in the soil. In this medium rainfall area, native mixed-species plantings provided comparable rates of C sequestration to local production species, with the probable additional benefit of providing better quality habitat for native biota. These results demonstrate that reforestation using native mixed-species plantings is an effective alternative for carbon sequestration to standard monocultures of production species in medium rainfall areas of temperate continental climates, where they can effectively store C, convert C into stable pools and provide greater benefits for biodiversity.

Simulating the gross primary productivity (GPP) of terrestrial ecosystems has been a major challenge in quantifying the global carbon cycle. Many different LUE models have been developed recently, but our understanding of the relative merits of different models remains limited. Using carbon dioxide flux measurements from 155 eddy covariance sites, we here assess the performance of seven LUE models (CASA, CFix, CFlux, EC-LUE, MODIS, VPM and VPRM) and compared the major model algorithms. Comparison between simulated GPP and estimated GPP from flux measurements showed that model performance differed substantially among ecosystem types. In general, most models captured well the pattern and magnitude of GPP for deciduous broadleaf forests and mixed forests, but performed less well in evergreen broadleaf forests and shrublands. During cloudy and overcast days, six out of seven LUE models significantly underestimated GPP because the impacts of diffuse radiation on light use efficiency were ignored. Among the seven models, CFlux and EC-LUE exhibited the lowest root mean square error at 80% and 75% sites respectively. Moreover, these two models showed higher performance for simulating the interannual variability of GPP. Two pairwise comparisons revealed the seven models differed substantially due to the differences in the algorithms describing the environmental regulation on GPP, particularly water stress. This analysis highlights the need to improve LUE model algorithms by integrating impacts of diffuse radiation on LUE and reliable water stress equations., JRC.H.7-Climate Risk Management

The position of the Arctic treeline has been associated with the preferred location of Arctic fronts that demarcate the boundary between Arctic and polar air masses. It has been argued that differences in summer energy balance, particularly in sensible heating, across treeline between forest and tundra may help determine the location of these frontal zones. Our observations of the energy balance at treeline show that the daily averaged summer heating contrast between treeline forest and tundra is an order of magnitude less than that previously proposed and that the influence on the atmosphere is confined to a shallow layer. In addition, maximum heating contrasts occurred in spring rather than in summer when the Arctic frontal zone is best expressed. Hence energy-balance contrasts at treeline are unlikely to be the major determinant of the position of the Arctic front.

Mosses dominate the surface cover in high northern latitudes and have the potential to play a key role in modifying the thermal and hydrologic regime of Arctic soils. These modifications in turn feed back to influence surface energy exchanges and hence may affect regional climate. However, mosses are poorly represented in models of the land surface. In this study the NCAR Land Surface Model (LSM) was modified in two ways. First, additional soil texture types including mosses and lichens were added to more realistically represent northern soils. Second, the LSM was also modified so that a different soil texture type could be specified for each layer. Several experiments were performed using climate data from an Arctic tundra site in 1995. The model was run for a homogeneous loam soil column and then also for columns that included moss, lichen, peat, and sand. The addition of a surface layer of moss underlain by peat and loam had a substantial impact on modeled surface processes. First, moss acted as an insulative layer producing cooler summer temperatures (6.9 8C lower at 0.5 m) and warmer winter temperatures (2.38C higher at 0.5 m) when compared with a homogenous loam soil column. Second, a soil column with a moss surface had a greater surface infiltration, leading to greater storage of soil moisture in lower layers when compared with a homogeneous loam column. Last, moss modulated the surface energy exchanges by decreasing soil heat flux (57% in July) and increasing turbulent fluxes of heat (67% in July) and moisture (15% in July). Mosses were also more effective contributors to total latent heating than was a bare loam surface. These results suggest that the addition of moss and the ability to prescribe different soil textures for different soil layers result in a more plausible distribution of heat and water within the column and that these modifications should be incorporated into regional and global climate models.

In an illustration of a model evaluation methodology, a multivariate reduced form model is developed to evaluate the sensitivity of a land surface model to changes in atmospheric forcing. The reduced form model is constructed in terms of a set of ten integrative response metrics, including the timing of spring snow melt, sensible and latent heat fluxes in summer, and soil temperature. The responses are evaluated as a function of a selected set of six atmospheric forcing perturbations which are varied simultaneously, and hence each may be thought of as a six-dimensional response surface. The sensitivities of the land surface model are interdependent and in some cases illustrate a physically plausible feedback process. The important predictors of land surface response in a changing climate are the atmospheric temperature and downwelling longwave radiation. Scenarios characterized by warming and drying produce a large relative response compared to warm, moist scenarios. The insensitivity of the model to increases in precipitation and atmospheric humidity is expected to change in applications to coupled models, since these parameters are also strongly implicated, through the representation of clouds, in the simulation of both longwave and shortwave radiation.

The development of tropical island thunderstorms in the maritime continent were investigated over the Tiwi Islands to the north of the Australian continent. A satellite cloud climatology was developed to examine these island thunderstorms, locally known as Hectors. During the pre-monsoon period of 1990 and 1991 Hectors were observed on 70% of days. These Hectors were observed to occur under two distinct environmental flow regimes. Under easterly flow, development occurred on the western end of the island and conversely under westerly flow, development occurred to the east. Hectors were also observed to have three distinct modes of development (Hector, suppressed and late developing) and one mode of non-development (non-Hector). Satellite cloud climatologies were developed and mean atmospheric characteristics were determined for each of these development modes. Hectors developed under conditions of moderate convective available potential energy, moderate shear and high moisture availability. Sub-cloud layer winds were also thought to contribute to the structure of the storm. Non-Hector and suppressed Hector days usually occurred after a previous convective disturbance such as a monsoon low or squall line and had typically low convective available potential energy and high values of convective inhibition. Conditions for late developing Hectors appeared to be conducive for thunderstorm development with high convective available potential energy and low values of convective inhibition. However, early initiation was suppressed by high shear conditions. Development in the late developing mode could be more intense than in other modes. Copyright © 2001 Royal Meteorological Society

Designed, green infrastructures are becoming a customary feature of the urban landscape. Sustainable technologies for stormwater management, and biofilters in particular, are increasingly used to reduce stormwater runoff volumes and peaks as well as improve the water quality of runoff discharged into urban water bodies. Although a lot of research has been devoted to these technologies, their effect in terms of greenhouse gas fluxes in urban areas has not been yet investigated. We present the first study aimed at quantifying greenhouse gas fluxes between the soil of stormwater biofilters and the atmosphere. N2O, CH4, and CO2 were measured periodically over a year in two operational vegetated biofiltration cells at Monash University in Melbourne, Australia. One cell had a saturated zone at the bottom, and compost and hardwood mulch added to the sandy loam filter media. The other cell had no saturated zone and was composed of sandy loam. Similar sedges were planted in both cells. The biofilter soil was a small N2O source and a sink for CH4 for most measurement events, with occasional large emissions of both N2O and CH4 under very wet conditions. Average N2O fluxes from the cell with the saturated zone were almost five-fold greater (65.6 μg N2O-N m(-2) h(-1)) than from the other cell (13.7 μg N2O-N m(-2) h(-1)), with peaks up to 1100 μg N2O-N m(-2) h(-1). These N2O fluxes are of similar magnitude to those measured in other urban soils, but with larger peak emissions. The CH4 sink strength of the cell with the saturated zone (-3.8 μg CH4-C m(-2) h(-1)) was lower than the other cell (-18.3 μg CH4-C m(-2) h(-1)). Both cells of the biofilter appeared to take up CH4 at similar rates to other urban lawn systems; however, the biofilter cells displayed occasional large CH4 emissions following inflow events, which were not seen in other urban systems. CO2 fluxes increased with soil temperature in both cells, and in the cell without the saturated zone CO2 fluxes decreased as soil moisture increased. Other studies of CO2 fluxes from urban soils have found both similar and larger CO2 emissions than those measured in the biofilter. The results of this study suggest that the greenhouse gas footprint of stormwater treatment warrant consideration in the planning and implementation of engineered green infrastructures.

Terrestrial plant productivity tends to increase under increasing but non-saturating photosynthetically active solar radiation when water, temperature and nutrients are not limiting. However, studies have shown that photosynthesis can also be higher under enhanced diffuse light despite a decrease in total irradiance. Clouds and atmospheric aerosols are two important variables that determine the total and proportion of diffuse light reaching the surface and thereby the rate of photosynthesis and carbon accumulation in plants. In addition to these factors, the response of plants to diffuse radiation is also dependant on plant characteristics such as functional types, leaf physiology, leaf area, leaf inclination, canopy structure and shape (i.e. clumping). Local environmental conditions (i.e. temperature, soil moisture, vapour pressure deficit, etc.) then modulate these plant responses. Changes in solar radiation as a consequence of clouds and aerosols thus can modify the carbon balance of terrestrial ecosys...

a b s t r a c t The regular monitoring of evapotranspiration from satellites has been limited because of discontinu- ous temporal coverage, resulting in snapshots at a particular point in space and time. We developed a temporal upscaling scheme using satellite-derived instantaneous estimates of evapotranspiration to produce a daily-sum evapotranspiration averaged over an 8-day interval. We tested this scheme against measured evapotranspiration data from 34 eddy covariance flux towers covering seven plant functional types from boreal to tropical climatic zones. We found that the ratio of a half-hourly-sum of potential solar radiation (extraterrestrial solar irradiance on a plane parallel to the Earth's surface) between 10:00 hh and 14:00 hh to a daily-sum of potential solar radiation provides a robust scaling factor to convert a half-hourly measured evapotranspiration to an estimate of a daily-sum; the estimated and measured daily sum evapotranspiration showed strong linear relation (r 2 = 0.92) and small bias (−2.7%). By com- parison, assuming a constant evaporative fraction (the ratio of evapotranspiration to available energy) during the daytime, although commonly used for temporal upscaling, caused 13% underestimation of evapotranspiration on an annual scale. The proposed temporal upscaling scheme requires only latitude, longitude and time as input. Thus it will be useful for developing continuous evapotranspiration estimates in space and time, which will improve continuous monitoring of hydrological cycle from local to global scales.

Narrowband spectral indices have largely been used for the estimation of biochemical attributes of vegetation. However, most of the proposed indices were developed using a limited number of species and locations. In this study, a strong precipitation gradient in northern savannas of Australia was used to develop narrowband spectral indices for the estimation of leaf chlorophyll content and verify the spatial generality of the indices when applied to different species from different environmental conditions. Simple ratio indices (SRI) and normalized difference indices (NDI) were developed for samples taken from seven study sites along the transect. The results showed a limited transferability of the indices along the transect. Therefore, there is a need for more site-specific indices for large scale estimation of chlorophyll in the study area.

International audience; We propose the Breathing Earth System Simulator (BESS), an upscaling approach to quantify global gross primary productivity and evapotranspiration using MODIS with a spatial resolution of 1-5 km and a temporal resolution of 8 days. This effort is novel because it is the first system that harmonizes and utilizes MODIS Atmosphere and Land products on the same projection and spatial resolution over the global land. This enabled us to use the MODIS Atmosphere products to calculate atmospheric radiative transfer for visual and near infrared radiation wave bands. Then we coupled atmospheric and canopy radiative transfer processes, with models that computed leaf photosynthesis, stomatal conductance and transpiration on the sunlit and shaded portions of the vegetation and soil. At the annual time step, the mass and energy fluxes derived from BESS showed strong linear relations with measurements of solar irradiance (r(2) = 0.95, relative bias: 8%), gross primary productivity (r(2) = 0.86, relative bias: 5%) and evapotranspiration (r(2) = 0.86, relative bias: 15%) in data from 33 flux towers that cover seven plant functional types across arctic to tropical climatic zones. A sensitivity analysis revealed that the gross primary productivity and evapotranspiration computed in BESS were most sensitive to leaf area index and solar irradiance, respectively. We quantified the mean global terrestrial estimates of gross primary productivity and evapotranpiration between 2001 and 2003 as 118 +/- 26 PgC yr(-1) and 500 +/- 104 mm yr(-1) (equivalent to 63,000 +/- 13,100 km(3) yr(-1)), respectively. BESS-derived gross primary productivity and evapotranspiration estimates were consistent with the estimates from independent machine-learning, data-driven products, but the process-oriented structure has the advantage of diagnosing sensitivity of mechanisms. The process-based BESS is able to offer gridded biophysical variables everywhere from local to the total global land scales with an 8-day interval over multiple years.

Australian tropical savannas occur at annual rainfalls greater than 600 mm and extend from the Gulf of Carpentaria in north Queensland, across the northern half of the Northern Territory (NT), to the Kimberly region of northwest Western Australia. This is a savanna biome of almost 2 million km2 and one of the world’s most ecologically intact savanna regions (Mackey et al., 2007). Australian savanna ecosystems experience one of the most seasonal of the world’s savanna climates (Prior and Bowman, 2005) with 90–95% of rainfall between November and April (Figure 3.1). This seasonality is driven by the annual movement of the Intertropical Convergence Zone, which drives the Australian summer monsoon. Soils of the region are ancient, highly weathered, and leached and are dominated by low-nutrient Kandosol (equivalent to Palexeralf using U.S. Taxonomy) and affiliated types. Soil and climate characteristics are generally unsuitable for broad-acre cropping, and grazing is the dominant land use with some horticulture. In the Northern Territory and Kimberly region, indigenous lands and conservation CONTENTS

[1] Evaporation from the land surface, averaged over successive 8 day intervals and at 0.05° (∼5 km) spatial resolution, was calculated using the Penman-Monteith (PM) energy balance equation, gridded meteorology, and a simple biophysical model for surface conductance. This conductance is a function of evaporation from the soil surface, leaf area index, absorbed photosynthetically active radiation, atmospheric water vapor pressure deficit, and maximum stomatal conductance (gsx). The novelty of this paper is the use of a “Budyko-curve” hydrometeorological model to estimate mean annual evaporation rates and hence a unique value of gsx for each grid cell across the Australian continent. First, the hydrometeorological model was calibrated using long-term water balances from 285 gauged catchments. Second, gridded meteorological data were used with the calibrated hydrometeorological model to estimate mean annual average evaporation () for each grid cell. Third, the value of gsx for each cell was adjusted to equate calculated using the PM equation with from the hydrometeorological model. This closes the annual water balance but allows the PM equation to provide a finer temporal resolution for evaporation than is possible with an annual water balance model. There was satisfactory agreement (0.49 < R2 < 0.80) between 8 day average evaporation rates obtained using remotely sensed leaf area indices, the parameterized PM equation, and observations of actual evaporation at four Australian eddy covariance flux sites for the period 2000–2008. The evaporation product can be used for hydrological model calibration to improve runoff prediction studies in ungauged catchments.

Understanding the relationships between climate and carbon exchange by terrestrial ecosystems is critical to predict future levels of atmospheric carbon dioxide because of the potential accelerating effects of positive climate-carbon cycle feedbacks. However, directly observed relationships between climate and terrestrial CO2 exchange with the atmosphere across biomes and continents are lacking. Here we present data describing the relationships between net ecosystem exchange of carbon (NEE) and climate factors as measured using the eddy covariance method at 125 unique sites in various ecosystems over six continents with a total of 559 site-years. We find that NEE observed at eddy covariance sites is (1) a strong function of mean annual temperature at mid-and high-latitudes, (2) a strong function of dryness at mid-and low-latitudes, and (3) a function of both temperature and dryness around the mid-latitudinal belt (45 degrees N). The sensitivity of NEE to mean annual temperature breaks down at similar to 16 degrees C (a threshold value of mean annual temperature), above which no further increase of CO2 uptake with temperature was observed and dryness influence overrules temperature influence.

International audience; Micrometeorological measurements of nighttime ecosystem respiration can be systematically biased when stable atmospheric conditions lead to drainage flows associated with decoupling of air flow above and within plant canopies. The associated horizontal and vertical advective fluxes cannot be measured using instrumentation on the single towers typically used at micrometeorological sites. A common approach to minimize bias is to use a threshold in friction velocity, u*, to exclude periods when advection is assumed to be important, but this is problematic in situations when in-canopy flows are decoupled from the flow above. Using data from 25 flux stations in a wide variety of forest ecosystems globally, we examine the generality of a novel approach to estimating nocturnal respiration developed by van Gorsel et al. (van Gorsel, E., Leuning, R., Cleugh, H.A., Keith, H., Suni, T., 2007. Nocturnal carbon efflux: reconciliation of eddy covariance and chamber measurements using an alternative to the u*-threshold filtering technique. Tellus 59B, 397–403, Tellus, 59B, 307-403). The approach is based on the assumption that advection is small relative to the vertical turbulent flux (FC) and change in storage (FS) of CO2 in the few hours after sundown. The sum of FC and FS reach a maximum during this period which is used to derive a temperature response function for ecosystem respiration. Measured hourly soil temperatures are then used with this function to estimate respiration RRmax. The new approach yielded excellent agreement with (1) independent measurements using respiration chambers, (2) with estimates using ecosystem lightresponse curves of Fc + Fs extrapolated to zero light, RLRC, and (3) with a detailed process-based forest ecosystem model, Rcast. At most sites respiration rates estimated using the u*-filter, Rust, were smaller than RRmax and RLRC. Agreement of our approach with independent measurements indicates that RRmax provides an excellent estimate of nighttime ecosystem respiration