This research aims to elucidate the linkages between seasonal-scale and multi-year drought. We examine the co-variability between decadal mean precipitation and the characteristics of extreme seasonal-scale precipitation deficits, which we define as meteorological drought. Specifically, we will explore the relationships between decades of very low and very high mean precipitation and how the nature of seasonal-scale meteorological drought, such as its frequency, severity and duration, changes in accordance with decadal mean precipitation. These changes will be contrasted against changes to seasons with extreme wet anomalies.

Using global precipitation data since 1960, this study will establish how the dry extremes of distributions of monthly-scale precipitation vary with mean precipitation on decadal time scales. One might expect that a decadal-scale mean precipitation deficit at some location would be reflected as a simple shift in the distribution of monthly rainfall totals. Such a shift would be manifest as a change to the frequency and intensity of meteorological drought e.g., an increase in the frequency of meteorological drought during drying decades. However, a concurrent change to variance and/or skewness could lead to quite different changes in the extremes of the precipitation distribution. This could conceivably lead to a situation where, for example, dry decades show few changes to the incidence or severity of meteorological drought but a significant decrease in the incidence and/or severity of very wet seasons. We expect that these characteristic changes to distributions of monthly precipitation will vary with location and season.

By examining aspects of the whole precipitation distribution, we can reveal how the nature of precipitation changes during multi-year, ‘megadrought’ conditions.