Twentieth century trends in moisture advection over Australia

We have examined some of the characteristics of moisture advection and its relation to precipitation over Australia. Seasonal extremes of moisture advection have changed considerably during the latter part of the 20th century. Analysis of its skewness reveals that the relative occurrence of these events has increased. A kurtosis analysis shows that there has been a geographical shift of where the largest impact has occurred. Moisture advection is significantly correlated to precipitation over large parts of Australia, most notably in the north and west. Changes in moisture advection show strong seasonality. Comparing two periods during the latter half of the 20th century, moisture advection was reduced over large parts of Australia, primarily in the east. However, moisture advection has increased over regions in the north and west of Australia during austral summer and autumn. Significant correlation patterns of moisture advection with precipitation have also changed over the twentieth century, partly as a result of changes in the advection of moisture by the atmosphere. The most noticeable change occurs during austral autumn, where the significant correlation of moisture advection with precipitation shifts from the east in the earlier period to the west at the end of the 20th century. A somewhat opposite change occurs during winter, although the shift occurs from the west to the southeast. Changes in the spatial extent of significant negative correlations between moisture advection and precipitation over parts of New South Wales occur during spring and summer. However, since this region gets most of its spring=summer precipitation through local convective events, this does not necessarily mean that moisture advection changes are the drivers of precipitation change in the region. Other regions that show negative correlations are found predominantly downwind of regions with high orography, where lee-winds result in adiabatic compression, restricting the occurrence of precipitation.