**2.2 Drought and climate change**

*Rainfall - Extremes, Distribution and Properties*

A book by McKernan entitled *Drought: The Red Marauder* [5] reveals a story as perceived by people who have experienced droughts in Australia throughout more than 200 years of European settlement. At any particular time, there is often a drought somewhere in continent of Australia. However, there is often a reluctance to acknowledge drought as a persistent aspect of Australian life and the arrival of drought is often greeted with surprise [5] with a tendency for each drought to be perceived as "the worst on record" [5]. Droughts are a recurrent and natural part of the Australian climate, with evidence of drought dating back thousands of years. However, deficiencies in our capability to adequately monitor, attribute, forecast and manage drought are exposed whenever a drought

For most Australian regions, individual climate drivers, associated with particular climate indices, generally account for less than 20% of monthly rainfall variability [7]. It is, therefore, unlikely that a single climate phenomenon is responsible for all drought events. It is probable that different periods of extended drought are driven by different and/or multiple combinations of

Three periods of prolonged droughts have occurred in south-east Australia during the period of instrumental records. These are known as the 'Federation drought' (1895–1902), 'World War II drought' (1937–1945) and the 'Big Dry' (1997–2010). Verdon-Kidd and Kiem [10] showed that these major droughts were related to the combinations of four principal climate drivers extending over the Pacific Ocean (El Nino Southern Oscillation: ENSO; Pacific Decadal Oscillation: PDO), the Indian Ocean (Indian Ocean Dipole: IOD) and the Southern Ocean (Southern Annular

Hiepp et al. [11] examined the relative contributions of four climate indices (ENSO, IPO, DMI and SAM) on rainfall in New South Wales. For the period 1948–2006, the study investigated the magnitude of the influence of each climate driver and its interaction on the rainfall at 15 locations distributed over NSW. It was reported that the influence of each driver at a particular site is different although some generalised patterns were evident. The results show that the ENSO has wide influence across over the entire state of New South Wales and is the primary climate driver of influence at 10 of the 15 sites analysed. The IPO (Interdecadal Pacific Oscillation) by itself does not have evidence for an influence on rainfall at any of the considered sites, but is influential when considered in combination with ENSO. Palmer et al. showed the importance of the IPO in modulating drought across Australia over past centuries [12]. Other investigations [13] have suggested that about half of Australian interannual-to-decadal precipitation variability may

McGree [14] examined rainfall data for 36 BOM stations from Queensland and the Northern Territory, representing north-eastern Australia. From this data, it was found that drought frequency, duration and magnitude was greater during 1981–2010 than during 1951–1980. The IPO and ENSO were the dominant drivers of drought occurrence over the period 1951–2010. The increase was not linear and was in a large part due to low-frequency variability, namely the positive phase of the IPO from 1977 to 1998. The switch to the negative phase of the IPO from 1999 resulted in a decade from 2000 with reduced drought activity. Carvalho et al. examined

**2.1 Drought frequency and relationship to climate indices**

originate from as far away as the Atlantic Ocean.

**2. Drought in Australia**

occurs [6].

climatic processes [8, 9].

Mode: SAM).

**4**

Although some reports [17] claim links between climate change and recent droughts in Australia with a high degree of certainty, an examination of the scientific literature would suggest a more cautious approach to stating unambiguous conclusions, due to the lack of rigorous evidence. Studies by Cai et al. [18] found that although climate models generally suggest that Australia's Millennium Drought was mostly due to natural multi-decadal variability, some late-twentieth-century changes in climate that influence regional rainfall are partially attributable to anthropogenic greenhouse warming. Cook et al. [19] examined the Millennium Drought during 2003–2009 and the record-breaking rainfall and flooding in austral summer 2010–2011 in eastern Australia. They found limited evidence for a climate change contribution to these events, but such analyses are restricted by the lack of information on long-term natural variability. Analysing a reconstruction of summer (December–January–February), they reported moisture deficits during the Millennium Drought fall within the range of the last 500 years of natural variability. van Dijik et al. [20] studied the Millennium Drought in southeast Australia (2001–2009). They found that prevailing El Nino conditions explained about two-thirds of rainfall deficit in east Australia, but the results for south Australia were inconclusive with a contribution from global climate change plausible, but unproven.

#### **2.3 Impacts of drought**

The impacts of droughts have been categorised as meteorological, hydrological, agricultural and socioeconomic [21]. Many of the reported studies have emphasised the impact of drought on agriculture, and this is a topic of current focus with drought in eastern Australia affecting many farming communities. Sheng and Xu [22] estimated that Millennium drought between 2002 and 2010 reduced agricultural total factor productivity by about 18% in Australia over the period.

Studies have been directed towards evaluating the impact of climate change on agricultural production in Australia. For example, drought frequently limits Australian wheat production, and the expected future increase in temperatures and rainfall variability will further challenge the productivity [23]. Relationships between wheat yields and climatic factors including rainfall are known to be complex and the subject of ongoing investigations [24]. Studies by Hunt et al. [25] show that the reduced yields of wheat associated with lower rainfall can be offset with adaptation through early sowing of the crop.

Feng [26] examined the impacts of rainfall extremes on wheat yield in semiarid cropping systems in eastern Australia and found that the frequent shortages of rainfall in eastern Australia created a greater threat to crop growth than excessive rainfall.

There are many impacts of droughts other than agriculture [20]. For example, droughts in Australia have had effects on wildlife populations including waterbirds [27, 28]. Studies have shown that droughts have an effect on mental health of the population, particularly in rural areas of Australia [29]. Li et al. investigated the ecological effects of extreme drought [30], including water acidification and eutrophication in the Lower Lakes (Lakes Alexandrina and Albert) in South Australia.
