Exploring post 2011-12 drought in the Murray-Darling Basin

Abstract

Drought, defined as rainfall deficiency, a familiar phenomenon in the Murray-Darling Basin, (the Basin) presents a risk to ecosystems, agriculture, industry and communities. The Millennium Drought from 1998 to 2009, with a peak from 2001 to 2009 (Bureau of Meteorology, 2015), was one of the longest and most severe droughts in the observed recorded history of the Basin. However, the Basin has experienced new intense drought conditions post 2011-12. In this paper, we use various climatic and hydrological variables including rainfall, soil moisture and streamflow to assess the severity of the drought in the Basin. Storage volumes and water market prices provide an indication of the impact of the drought on water availability. Low rainfalls since 2012-13 led the Basin into drought. The contributing factors are a mixture of consistently rising temperatures and deficits in rainfall resulting in below average streamflows and declining groundwater and storage levels. During the July 2013 to June 2019 period; fifty per cent of the whole Basin experienced either severe or serious rainfall deficiencies. As a consequence, in the last 24-month period, soil moisture deficiencies were more than that during the most deficient 24-month period during the Millennium Drought. During the post 2011-12 period, 90 per cent of the gauges in Namoi, Gwydir and Border Rivers catchments of the northern Basin-recorded very-much-below-average flows. The impact of drought on water availability is apparent from the total accessible storage volume across the Basin, which has declined to below 40 per cent by the end of 2018-19. In the northern Murray-Darling Basin, storage volume declined to nine per cent, a level as low as observed during the Millennium Drought. Water market activity in the Basin is greatly influenced by the availability of water. During the low water availability years from 2012-13 to 2018-19 the demand for water rose and the price started to increase. In 2018-19, competition for very limited seasonally allocated water increased markedly, pushing the price up to record levels. Given the drought, prices for high reliability long-term water entitlements also hit unprecedented levels in 2018-19. Consumptive water use in the Basin declined when water availability was low and showed increased dependency on groundwater. The post 2011-12 drought in the Murray-Darling Basin has in many ways been no less severe than the Millennium Drought; rather it can be considered as being more intense in many parts, especially in the north, even though up to the end of 2018-19 it may not have run its full course.