**5. Rainfall reconstructions**

Instrumental records of rainfall and temperature generally extend back only about 100 years in Australia. Reconstructions of past temperatures, extending back hundreds or thousands of years, are available for many parts of the world [49]. These are derived from palaeo data, including tree rings, corals, ice cores and stalagmites. Such reconstructions are much rarer for rainfall and, comparatively, few exist currently for Australia. However, it is important to consider the examples that exist as they enable episodes of droughts and flooding rains to be put into a wider context before asserting particular events are unprecedented, or ascribing them, with a high degree of certainty, to anthropogenic climate change.

Climate proxy data are ideally derived from sources that are located within, or in close proximity to, the region of interest. However, in cases where such proxy

records are unavailable, remote proxies can be considered as a possible alternative [50]. There are relatively few in situ rainfall-sensitive palaeoclimate proxy records in Australia providing continuous records of rainfall variability [51]. An alternative is to utilise records that are from the same continent, but external to the region of direct interest. For example, Ho et al. made use of three such records [52]. The first was a study by Lough [53], who found significant correlations between coral luminescence intensity recorded in coral cores from the Great Barrier Reef and summer rainfall variability in northeast Queensland, enabling the multi-century coral record to be used to reconstruct Queensland summer rainfall back to the eighteenth century. The second study used high-resolution (approximately annual) analysis of trace elements sensitive to moisture availability present in a stalagmite from the Wombeyan Caves in south-east Australia. McDonald [54] found this to correlate with periods of above or below average rainfall from 749 BCE (before the Common Era) to 2001 CE (Common Era). The third study generated a 350 year long rainfall reconstruction at Lake Tay in Western Australia, based on tree ring widths [55].

These three Australian palaeoclimate proxies of rainfall enabled the reconstructions of rainfall in the Murray Darling Basin of south-eastern Australia [49, 50] although all three lie outside the Murray Darling Basin. The results reveal several extended periods that are likely to have been drier than indicated by the instrumental record from approximately the last century. Extended dry periods include the midlate-1700s, 1500s, 1100s, 400s and 300 BCE. Comparisons between the reconstructed rainfalls and extreme instrumental rainfall indicated that the occurrence of extended periods wetter than the wettest decade in the instrumental record is also likely to have occurred in the mid-late-1800s and also around 1700. Multi-centennial wet epochs (or, at least, epochs without a multi-year drought) are also evident between 400–700 CE and 300 BCE–2100 CE. The reconstructions, therefore, confirm the occurrence during the last 2751 years of both wet and dry periods that have greater frequency, duration and severity than observations from the instrumental record.

O'Donnell [56] developed a 210-year tree ring-width chronology from *Callitris columellaris* from the Pilbara region of Western Australia. This was highly correlated with summer-autumn (December–May) rainfall across semi-arid northwest Australia. The reconstruction showed the periods of below average precipitation extending from one to three decades and the periods of above average precipitation which were often less than a decade. The results demonstrate that recent decades (1995–2012) have been unusually wet with average summer/autumn rainfall of 310 mm compared with the previous two centuries (average summer/autumn rainfall of 229 mm).

Freunmd et al. [57] used a diverse set of Southern Hemisphere palaeoclimate records to produce rainfall reconstructions for cool (April–September) and warm (October–March) seasons corresponding to eight regions across the Australian continent. They reported that trends towards wetter conditions in tropical northern Australia are highly unusual in the context of multi-century rainfall reconstructions. Cool season drying trends during the instrumental period in regions of southern Australia are very unusual, although not unprecedented, when compared with the past several centuries from 1600 CE.

Verdon-Kidd et al. [58] produced a 507 year reconstruction of rainfall for the monsoonal northwest of Australia, focussing on the site of Oenpelli in the Northern Territory. The study used remote proxies from Asia (tree rings), Australia (coral) and South America (tree rings) with an instrumental calibration period from 1900 to 1976. The rainfall reconstruction presented from 1470 CE suggests that the modern instrumental record on average represents a wetter climate than the preinstrumental period. Furthermore, the reconstructions display wet and dry periods of greater duration than evident from the instrumental record. Other recent studies

**9**

origin.

**Acknowledgements**

*Introductory Chapter: Australia—A Land of Drought and Flooding Rain*

extreme flooding and drought over past 2000 years [61].

using tree rings to reconstruct rainfall include Allen [59] for Arnhem Land in the Northern Territory of monsoonal Australia, and O'Donnell for Western Australia [60]. Evidence is also provided from sediments from northwest Australia periods of

A reconstruction of rainfall was produced by Tozer [62] for the Williams River catchment in subtropical eastern Australia (see map) extending over a period of 1013 years between 1000 and 2012 CE. Ho [50] relied on circulation teleconnections that strongly link climatic processes in one region to another. The remote proxies are calibrated with respect to an instrumental period, to develop palaeoclimate reconstructions. As no high-resolution palaeoclimate proxies were available corresponding to the Williams River catchment area, the study utilised the teleconnection between summer sea salt deposition recorded in ice cores from Law Dome in East Antarctica and rainfall variability in eastern Australia. It was found that both the dry and wet epochs persisted up to twice as long in the pre-instrumental compared

Documentary evidence can also be valuable in complementing palaeo reconstructions of rainfall. Fenby et al. [63, 64] considered 12 documentary-based rainfall chronologies for five subregions of south-eastern Australia (SEA) over the 1788–1860 period using a range of historical sources. This analysis identified 27 drought years in south-east Australia between 1788 and 1860 and 14 years of high rainfall in New South Wales (NSW) between 1788 and 1840. This study confirms that south-east Australia has experienced considerable rainfall variability that has influenced past Australian societies since the first European settlement in 1788. Of the droughts identified in this study, 1837–1841 was the longest and most widespread event influencing all subregions. The 1793–1809 period was particularly wet, with periods of heavy rainfall often resulting in devastating floods on the

This chapter provides some background to the available data and understanding of rainfall patterns experienced in Australia. Compared with many counties, Australia is fortunate in having a comparatively good set of rainfall records over the continent extending back about 100 years in many cases. The continent experiences extended episodes of drought and flooding rains. It is clear that these are related to multiple climate drivers that may extend widely over the globe, and are incompletely understood. Forecasting rainfall over the medium-to-long term remains problematical, and solutions may be found in advanced data analysis techniques such as machine learning rather than physical models. There remains a scarcity of rainfall reconstructions based on palaeo evidence enabling records to be extended back multiple centuries beyond the instrumental data. These are very important as they enable more recent episodes of drought and flooding rains to be placed into context. Without this, there is a tendency in the general community to believe that a particular event is unprecedented because something similar did not occur in recent decades. The reconstructions are also important from the perspective of assigning rainfall patterns to climate change and designating as natural or anthropogenic in

This work was supported by the B. Macie Family Foundation.

*DOI: http://dx.doi.org/10.5772/intechopen.89549*

with the instrumental period.

Hawkesbury River region of NSW.

**6. Conclusion**

*Introductory Chapter: Australia—A Land of Drought and Flooding Rain DOI: http://dx.doi.org/10.5772/intechopen.89549*

using tree rings to reconstruct rainfall include Allen [59] for Arnhem Land in the Northern Territory of monsoonal Australia, and O'Donnell for Western Australia [60]. Evidence is also provided from sediments from northwest Australia periods of extreme flooding and drought over past 2000 years [61].

A reconstruction of rainfall was produced by Tozer [62] for the Williams River catchment in subtropical eastern Australia (see map) extending over a period of 1013 years between 1000 and 2012 CE. Ho [50] relied on circulation teleconnections that strongly link climatic processes in one region to another. The remote proxies are calibrated with respect to an instrumental period, to develop palaeoclimate reconstructions. As no high-resolution palaeoclimate proxies were available corresponding to the Williams River catchment area, the study utilised the teleconnection between summer sea salt deposition recorded in ice cores from Law Dome in East Antarctica and rainfall variability in eastern Australia. It was found that both the dry and wet epochs persisted up to twice as long in the pre-instrumental compared with the instrumental period.

Documentary evidence can also be valuable in complementing palaeo reconstructions of rainfall. Fenby et al. [63, 64] considered 12 documentary-based rainfall chronologies for five subregions of south-eastern Australia (SEA) over the 1788–1860 period using a range of historical sources. This analysis identified 27 drought years in south-east Australia between 1788 and 1860 and 14 years of high rainfall in New South Wales (NSW) between 1788 and 1840. This study confirms that south-east Australia has experienced considerable rainfall variability that has influenced past Australian societies since the first European settlement in 1788. Of the droughts identified in this study, 1837–1841 was the longest and most widespread event influencing all subregions. The 1793–1809 period was particularly wet, with periods of heavy rainfall often resulting in devastating floods on the Hawkesbury River region of NSW.

## **6. Conclusion**

*Rainfall - Extremes, Distribution and Properties*

records are unavailable, remote proxies can be considered as a possible alternative [50]. There are relatively few in situ rainfall-sensitive palaeoclimate proxy records in Australia providing continuous records of rainfall variability [51]. An alternative is to utilise records that are from the same continent, but external to the region of direct interest. For example, Ho et al. made use of three such records [52]. The first was a study by Lough [53], who found significant correlations between coral luminescence intensity recorded in coral cores from the Great Barrier Reef and summer rainfall variability in northeast Queensland, enabling the multi-century coral record to be used to reconstruct Queensland summer rainfall back to the eighteenth century. The second study used high-resolution (approximately annual) analysis of trace elements sensitive to moisture availability present in a stalagmite from the Wombeyan Caves in south-east Australia. McDonald [54] found this to correlate with periods of above or below average rainfall from 749 BCE (before the Common Era) to 2001 CE (Common Era). The third study generated a 350 year long rainfall reconstruction at Lake Tay in Western Australia, based on tree ring widths [55]. These three Australian palaeoclimate proxies of rainfall enabled the reconstructions of rainfall in the Murray Darling Basin of south-eastern Australia [49, 50] although all three lie outside the Murray Darling Basin. The results reveal several extended periods that are likely to have been drier than indicated by the instrumental record from approximately the last century. Extended dry periods include the midlate-1700s, 1500s, 1100s, 400s and 300 BCE. Comparisons between the reconstructed rainfalls and extreme instrumental rainfall indicated that the occurrence of extended periods wetter than the wettest decade in the instrumental record is also likely to have occurred in the mid-late-1800s and also around 1700. Multi-centennial wet epochs (or, at least, epochs without a multi-year drought) are also evident between 400–700 CE and 300 BCE–2100 CE. The reconstructions, therefore, confirm the occurrence during the last 2751 years of both wet and dry periods that have greater frequency,

duration and severity than observations from the instrumental record.

O'Donnell [56] developed a 210-year tree ring-width chronology from *Callitris columellaris* from the Pilbara region of Western Australia. This was highly correlated with summer-autumn (December–May) rainfall across semi-arid northwest Australia. The reconstruction showed the periods of below average precipitation extending from one to three decades and the periods of above average precipitation which were often less than a decade. The results demonstrate that recent decades (1995–2012) have been unusually wet with average summer/autumn rainfall of 310 mm compared with the previous two centuries (average summer/autumn

Freunmd et al. [57] used a diverse set of Southern Hemisphere palaeoclimate records to produce rainfall reconstructions for cool (April–September) and warm (October–March) seasons corresponding to eight regions across the Australian continent. They reported that trends towards wetter conditions in tropical northern Australia are highly unusual in the context of multi-century rainfall reconstructions. Cool season drying trends during the instrumental period in regions of southern Australia are very unusual, although not unprecedented, when compared

Verdon-Kidd et al. [58] produced a 507 year reconstruction of rainfall for the monsoonal northwest of Australia, focussing on the site of Oenpelli in the Northern Territory. The study used remote proxies from Asia (tree rings), Australia (coral) and South America (tree rings) with an instrumental calibration period from 1900 to 1976. The rainfall reconstruction presented from 1470 CE suggests that the modern instrumental record on average represents a wetter climate than the preinstrumental period. Furthermore, the reconstructions display wet and dry periods of greater duration than evident from the instrumental record. Other recent studies

**8**

rainfall of 229 mm).

with the past several centuries from 1600 CE.

This chapter provides some background to the available data and understanding of rainfall patterns experienced in Australia. Compared with many counties, Australia is fortunate in having a comparatively good set of rainfall records over the continent extending back about 100 years in many cases. The continent experiences extended episodes of drought and flooding rains. It is clear that these are related to multiple climate drivers that may extend widely over the globe, and are incompletely understood. Forecasting rainfall over the medium-to-long term remains problematical, and solutions may be found in advanced data analysis techniques such as machine learning rather than physical models. There remains a scarcity of rainfall reconstructions based on palaeo evidence enabling records to be extended back multiple centuries beyond the instrumental data. These are very important as they enable more recent episodes of drought and flooding rains to be placed into context.

Without this, there is a tendency in the general community to believe that a particular event is unprecedented because something similar did not occur in recent decades. The reconstructions are also important from the perspective of assigning rainfall patterns to climate change and designating as natural or anthropogenic in origin.

### **Acknowledgements**

This work was supported by the B. Macie Family Foundation.

*Rainfall - Extremes, Distribution and Properties*
