Wet season rainfall onset and flash drought: The case of the northern Australian wet season

Abstract

In this paper, we report on the frequency of false onsets of wet season rainfall in the case of the Northern Australian wet season and investigate the role of largescale tropical climate processes such as the El Niño-Southern Oscillation, Indian Ocean Dipole (IOD) and Madden-Julian Oscillation. A false onset occurs when a wet season rainfall onset criterion is met, but follow-up rainfall is not received for weeks or months later. Our analysis of wet season rainfall data from 1950 through 2020 shows a false onset occurs, on average, between 20 and 30% of wet seasons across all of northern Australia. This increases at a regional and local level such as at Darwin, the Northern Territory (NT), and parts of Queensland's north coast to over 50%. Seasonal climate influences, such as a La Niña pattern and a negative IOD that typically expedite the wet season rainfall onset, also increase the likelihood of a false onset over northern Australia. Our analysis also finds that periods of false onsets can sometimes, but not always, coincide with periods of rapid soil moisture depletion. The false rainfall onsets that develop into flash drought can be potentially disruptive and costly and are of potential significance for agriculture and fire management in northern Australia, and in other monsoonal climates that also typically experience a slow build-up to the seasonal monsoon. In conclusion, effective rainfall indicates that many seasons experience 'false onsets' with dry conditions after early rainfall. We propose that false onsets are a physical characteristic of the climate of northern Australia which occurs with relatively high frequency. In addition, these false onsets may sometimes co-occur with a flash drought.

Improved Understanding of Flash Drought from a Comparative Analysis of Drought with Different Intensification Rates

“…Contrary to the previous common perception that flash droughts are rare events, they occur more frequently than the other two types. Some previous studies seem to provide similar evidence of frequent, rapid drops in soil moisture and high frequency of flash drought [12,16,33]; here, our results reinforce the conclusion that the rapid transition from an energy-limited to a water-limited condition is a prevalent phenomenon in most of the regions. Note that our definition of the flash drought was more restrictive than previous studies.…”

“…However, in some hotspots, flash drought can occur twice or even three times a year, leading to a debate about whether it can be considered a drought if the criterion is met so frequently. One undeniable fact is that the frequent, rapid changes in soil moisture evidenced by the rapid transitions from an energy-limited environment to a water-limited environment are part of the climatology of the locations at least [33].…”

Developing Psychological Resilience to the Impact of Drought

“…Projections show an exacerbation in the occurrence and severity of drought in the future in the Northern Territory, Australia [ 24 , 25 ]. For instance, Wang et al [ 26 ] found drought severity increased from 44.26 cm/month to 52.19 cm/month in 2006–2009 and 2018–2020, respectively, and predicted an increased severity due to changes in El Niño and the Indian Ocean Dipole.…”