Steps toward "Useful" Hydroclimatic Scenarios for Water Resource Management in the Murray‐Darling Basin

Anthony S. Kiem and Danielle C. Verdon‐Kidd

There is currently a distinct gap between what climate science can provide and information that is practically useful for (and needed by) natural resource managers. Improved understanding, and model representations, of interactions between the various climate drivers (both regional and global scale), combined with increased knowledge about the interactions between climate processes and hydrological processes at the regional scale, is necessary for improved attribution of climate change impacts, forecasting at a range of temporal scales and extreme event risk profiling (e.g., flood, drought, and bushfire). It is clear that the science has a long way to go in closing these research gaps; however, in the meantime water resource managers in the Murray‐Darling Basin, and elsewhere, require hydroclimatic projections (i.e., seasonal to multidecadal future scenarios) that are regionally specific and, importantly, take into account the impacts, and associated uncertainties, of both natural climate variability and anthropogenic change. The strengths and weaknesses of various approaches for supplying this information are discussed in this paper.

Introduction

Traditionally, water resource managers have used empirical methods that assume stationarity to estimate the risk of climate‐related extremes (e.g., droughts, floods, and bushfires) that impact on water quantity, water quality, and/ or water resource–related infrastructure and management decisions. In other words, the observed history of climate extremes is analyzed under the assumption that the chance of an extreme event occurring is the same from one year to the next and that the future will look like the past (i.e., the stationary climate assumption). This assumption is flawed given that the physical mechanisms that actually deliver climate extremes have been ignored and also given that the impacts associated with anthropogenic climate change are not considered. Also ignored is the observed multiyear to multidecadal epochs of enhanced or reduced extreme event risk across eastern Australia, including the Murray‐Darling Basin. That is, the observations clearly show that the chance of drought or flood or bushfire is not the same from one year to the next. These studies demonstrate that the first step in any climate‐driven extreme risk assessment should be to understand the climate mechanisms that actually drive the periods of elevated risk. For example, numerous studies have shown that strong relationships exist between eastern Australian rainfall and streamflow and the global‐scale ocean‐atmospheric circulation process known as the El Niño–Southern Oscillation (ENSO). Previous work has also shown that, while ENSO is important, other climate phenomena also influence Australian climate on interannual to multidecadal timescales. On the basis of this research there is a clear need for an improved understanding into the multiple interactions between large‐ and local‐scale climate drivers and their influence on climate related risk.

Compounding the influence of natural climate variability, and the problems associated with the brevity (in climatological terms) of instrumental hydroclimatological records, there is also serious concern about how human‐induced climate change may increase the frequency and severity of extreme events, including droughts and floods, in the future. Accordingly, there have been attempts to utilize climate model outputs to determine how anthropogenic climate change may affect water resources and, on the basis of this information, to develop water resource management strategies to deal with the projected risks. However, the uncertainty associated with future climate projections is known to be significant and is magnified further when attempting to make inferences at the regional (i.e., catchment) scale (e.g., differentiating between coastal and inland processes). This is especially the case for precipitation. The uncertainty is so high that projections of future drought risk, on either the short (seasonal up to 5 years) or long (more than 10 years into the future) term, currently have limited practical usefulness for water resource managers and/or government policy makers.

Water resource planning must account for both natural climate variation and human‐induced climate change, since these factors will continue to influence Australia’s climate, even if immediate action is taken to curtail greenhouse gas emissions. Such considerations are needed to avoid overallocation of water resources and/or to ensure that economic activity based on utilization of water resources is not unnecessarily restricted. This paper aims to demonstrate the importance of understanding the hydroclimatic drivers that influence MDB water resources so that this information can be used to more realistically quantify climate‐related risk. The current limitations of climate models and the potential dangers associated with using them for something they were not designed for (i.e., regional‐scale water resources management) will also be examined. Finally, recommendations are given as to the steps required to enable provision of hydroclimatic scenarios that are useful for water resource management in the MDB.

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