Sensitivity of the orographic precipitation across the Australian Snowy Mountains to regional climate indices

Abstract

The wintertime (May–October) precipitation across south-eastern Australia, and the Snowy Mountains, was studied for 22 years (1995–2016) to explore the sensitivity of the relationships between six established climate indices and the precipitation to the orography, both regionally and locally in high-elevation areas. The high-elevation (above 1100 m) precipitation records were provided by an independent network of rain gauges maintained by Snowy Hydro Ltd. These observations were compared with the Australian Water Availability Project (AWAP) precipitation analysis, a commonly used gridded nationwide product. As the AWAP analysis does not incorporate any high-elevation sites, it is unable to capture local orographic precipitation processes. The analysis demonstrates that the alpine precipitation over the Snowy Mountains responds differently to the indices than the AWAP precipitation. In particular, the alpine precipitation is found to be most sensitive to the position of the subtropical ridge and less sensitive to a number of other climate indices tested. This sensitivity is less evident in the AWAP representation of the high-elevation precipitation. Regionally, the analysis demonstrates that the precipitation to the east of the Snowy Mountains (the downwind precipitation) is weakly correlated with the upwind and peak precipitation. This is consistent with previous works that found that the precipitation in this downwind region commonly occurs from mechanisms other than storm systems passing over the mountains.