Describing rainfall in northern Australia using multiple climate indices

Abstract

Abstract. Savanna landscapes are globally extensive and highly sensitive to climate change, yet the physical processes and climate phenomena which affect them remain poorly understood and therefore poorly represented in climate models. Both human populations and natural ecosystems are highly susceptible to precipitation variation in these regions due to the effects on water and food availability and atmospherebiosphere energy fluxes. Here we quantify the relationship between climate phenomena and historical rainfall variability in Australian savannas and, in particular, how these relationships changed across a strong rainfall gradient, namely the North Australian Tropical Transect (NATT). Climate phenomena were described by 16 relevant climate indices and correlated against precipitation from 1900 to 2010 to determine the relative importance of each climate index on seasonal, annual and decadal timescales. Precipitation trends, climate index trends and wet season characteristics have also been investigated using linear statistical methods. In general, climate index-rainfall correlations were stronger in the north of the NATT where annual rainfall variability was lower and a high proportion of rainfall fell during the wet season. This is consistent with a decreased influence of the IndianAustralian monsoon from the north to the south. Seasonal variation was most strongly correlated with the Australian Monsoon Index, whereas yearly variability was related to a greater number of climate indices, predominately the Tasman Sea and Indonesian sea surface temperature indices (both of which experienced a linear increase over the duration of the study) and the El Niño-Southern Oscillation indices. These findings highlight the importance of understanding the climatic processes driving variability and, subsequently, the importance of understanding the relationships between rainfall and climatic phenomena in the Northern Territory in order to project future rainfall patterns in the region.

Challenges and opportunities in land surface modelling of savanna ecosystems

“…This is further supported by more empirical studies involving fire exclusion experiments and showing similar tendencies towards woody dominance (Bond and Van Wilgen, 1996;Scott et al, 2012). Given that future climate projections point to predict higher temperatures and less precipitation for sub-tropical regions (Rogers and Beringer, 2017) the representation of short-and long-term impacts of fire on savanna structure and function in TBMs may be important in understanding how savanna landscapes may respond to changes in fire frequency and intensity .…”

“…Projected global increases in both temperature and the variability of precipitation patterns as a result of anthropogenic climate change are expected to lead to significant changes in the structure and diversity of global terrestrial ecosystems (IPCC, 2013;Rogers and Beringer, 2017). This will make modelling ecosystem distributions and biogeochemical fluxes under these transient conditions difficult, challenging TBMs in how they represent the response of the savanna ecosystem to structural shifts in vegetation through CO 2 fertilisation, increased rainfall seasonality, changes in vapour pressure deficiet and changing fire dynamics .…”

“…The response of savanna structure and function to changes in precipitation patterns is highly uncertain (Rogers and Beringer, 2017). Scheiter et al (2015) investigated the effect of variable rainfall seasonality, projecting modest to large increases in aboveground biomass for savannas in northern Figure 2.…”

“…Given their deeper root systems, tree growth persists longer into the dry season, providing an added period of resource acquisition at a time (Harris et al, 2014). The dataset has been clipped to the eco-floristic regions that approximate the global extent of savannas using the following plant functional types: tropical moist deciduous forest, tropical dry forest, sub-tropical dry forest and tropical shrubland (Ruesch and Gibbs, 2008). when grasses may be senescing.…”

Preface: OzFlux: a network for the study of ecosystem carbon and water dynamics across Australia and New Zealand

“…Bristow et al (2016) show in this special issue that clearing of woody vegetation from the tropical savanna results in carbon emissions double the size of that reported for savanna burning. Rainfall is an important driver of photosynthesis in Australian ecosystems, and fluctuations of rainfall and productivity in Australia have been associated with multiple climate indices Rogers and Beringer, 2017). Australia's climate has always been characterised by extreme, high-impact weather events such as cyclones, storms, fire…”