Long-term drought risk assessment in the Lachlan River Valley – a paleoclimate perspective

Abstract

The frequency and severity of droughts during the past two decades in eastern Australia have caused water resource managers to question the suitability of current drought management practices. For example, water accounting schemes in NSW (and elsewhere) use an estimate of the “worst drought in 100 years” for resource assessment, which is based solely on the instrumental record. However, inflows during the most recent drought (2002–2007) were lower than those recorded in the last 100 years for some of the catchments in NSW. This resulted in an overestimate of expected inflows and critically low storage volumes (ie. failure of the system). It is clear that hydrological drought risk would be better assessed by extending the records beyond the single 100 year instrumental record, so as to capture a larger spectrum of climatic variability. Incorporating paleoclimate information on the major climate drivers for the region may provide the critical insight required to achieve this goal. In this paper, proxy climate records derived from paleoclimate data are used to investigate the long-term behaviour of the Interdecadal Pacific Oscillation (IPO) and the El Niño/Southern Oscillation (ENSO). This information is then used to develop a stochastic framework for generating rainfall replicates to be used in assessing long-term hydrologic drought risk for water resource management in NSW. Importantly, the rainfall replicates demonstrate that this region may have experienced meteorological droughts of longer duration than has been recorded by the instrumental record. This result highlights the possibility that current management practices may fail to meet needs in the future, if history were to be repeated.