Extreme monthly rainfall over Australia in a changing climate

Watterson, I. G.; Chua, Zhi‐Weng; Hope, Pandora

doi:10.22499/3.6604.003

Cited by 6 publications

(12 citation statements)

References 13 publications

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“…The analysis of extreme monthly precipitation previously applied to CMIP5 by Watterson et al . (2016) has been applied here to two 20‐year periods (starting with P1) of data from each of our CMIP6 simulations. At each model grid point, the top decile of monthly rain rate values in each of the four seasons is determined in each period.…”

Section: Analysis Of Atmospheric Moisturementioning

confidence: 99%

“…Correlations for pr and prw are also moderate, with both being broadly larger at warmer latitudes. The high r between the mean (pr) and high monthly (pr‐H) rain fields reflects a similar local ratio between the two statistics for most regions (Watterson et al ., 2016). The link between pr and conv is enhanced with the H composite.…”

Section: Relationships Between Rainfall and Moisture Variablesmentioning

confidence: 99%

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Analysis of CMIP6 atmospheric moisture fluxes and the implications for projections of future change in mean and heavy rainfall

Watterson

Keane

Ziehn

et al. 2020

Intl Journal of Climatology

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Motivated by the wide range of projections of regional rainfall (or precipitation, pr) based on the CMIP5 ensemble of global climate models, we investigate the atmospheric moisture budget of idealized rising-CO 2 (1pctCO2) simulations from 10 models submitted to CMIP6. We use the new CMIP6 standard variables, the vertically integrated eastward and northward moisture flux, and provide a multi-model assessment of these, their convergence (conv), along with water vapour path (prw). Seasonal climatologies of a 20-year base climate for pr, prw, flux, and conv match well those from the ECMWF's Reanalysis 5. In addition, composites 'H' of quantities for months in the top decile of monthly rainfall, calculated at each model grid point, produce a field of heavy rainfall, on average double that of the mean. Spatial correlation coefficients (r) between the pr and conv fields are typically .7 in each season. This rises to .9 for the corresponding H fields, due to the important link between moisture convergence and heavy rainfall. Fields of standardized change (Δ), or change per degree of global warming, were calculated. The ensemble-mean Δpr is only weakly correlated with the base climate pr, and likewise for conv. However, the prw change is highly correlated with the base prw, pointing to the importance of the "thermodynamic" change in that variable. Globally, the net Δconv is highly correlated with Δpr, around .9. This rises to .95 for the heavy-rain composites. Relationships between changes in pr and other components hold at grid points also, when the individual model results are correlated. Clearly, there is a dependence in the change in pr with that in conv, particularly for heavy rainfall. Assessment of a larger ensemble from CMIP6, using the new flux variables, would improve the evaluation of these processes, and potentially allow more confident projections in future rainfall changes.

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Section: Analysis Of Atmospheric Moisturementioning

confidence: 99%

Section: Relationships Between Rainfall and Moisture Variablesmentioning

confidence: 99%

Analysis of CMIP6 atmospheric moisture fluxes and the implications for projections of future change in mean and heavy rainfall

Watterson

Keane

Ziehn

et al. 2020

Intl Journal of Climatology

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“…They also found that persistence is enhanced following wetter months, thus, if monthly rainfall is projected to increase towards the end of the century, perhaps persistence will also increase. While extreme daily rainfall is projected to increase over Australia by the end of the century (CSIRO and Bureau of Meteorology 2015), with the wettest day of the year becoming wetter, there is not a clear signal that monthly rainfall will also increase (Watterson et al 2016). However, across southern Australia, where winter and spring mean rainfall are projected to decline, the reduction in the value of the top decile is less than for the median or lowest decile (Watterson et al 2016) indicating that there might be a relative increase in extreme monthly rainfall compared to a reducing mean.…”

Section: Introductionmentioning

confidence: 99%

“…While extreme daily rainfall is projected to increase over Australia by the end of the century (CSIRO and Bureau of Meteorology 2015), with the wettest day of the year becoming wetter, there is not a clear signal that monthly rainfall will also increase (Watterson et al 2016). However, across southern Australia, where winter and spring mean rainfall are projected to decline, the reduction in the value of the top decile is less than for the median or lowest decile (Watterson et al 2016) indicating that there might be a relative increase in extreme monthly rainfall compared to a reducing mean. The persistence of temperature anomalies is likely to be tied to both the rainfall persistence and the progression of evapotranspiration and soil moisture anomalies.…”

Section: Introductionmentioning

confidence: 99%

Persistence of cool conditions after heavy rain in Australia

Hope¹,

Watterson²

2018

JSHESS

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There is a general understanding that heavy rainfall will suppress subsequent near-surface temperatures. However, there have been few studies describing this effect. In this study the top 10 % of monthly rainfall, by season and by grid point over Australia is used to represent extended periods of heavy rainfall (termed 'very wet'). The corresponding daily maximum average monthly temperature (Tmax) during those months are shown to be cooler by at least 0.5 °C almost everywhere across Australia, in every season in both observation-based data and climate models. Cooler than average Tmax conditions are then evident for the following four months in some places, particularly following very wet months in winter. The average monthly daily minimum temperature (Tmin), unlike Tmax, is warmer than average during very wet months in winter,by up to 1.5 °C in the east of the continent in both observations and the model mean. Warmer Tmin conditions are also evident during very wet months in the south-east and across the south of the continent in other seasons, particularly in observations. Tmin is cooler than average in very wet months in summer elsewhere across the continent. In subsequent months, Tmin then tends to be cooler than average. It is suspected that increased cloud during the first month keeps Tmin warm, while wetter soils contribute to cooler Tmin during subsequent months. These results indicate that indeed heavy, extended rainfall can have a cooling influence on subsequent temperature, and, following winter, this can have an effect right through to the following summer. The Tmax anomalies at the end of the century under RCP8.5 are similar to those under the current climate, except in future there are relatively cooler conditions in the south during very wet months in winter and in the month following.

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“…While it represents a considerable challenge to provide robust results that are clearly communicated for stakeholders to use as part of their decision-making processes, these annual reports are increasingly showing their potential to help meet such growing needs. Extreme rainfall on a range of time scales is expected to become more extreme in a warmer world (e.g., Allan and Soden 2008;Held and Soden 2006) particularly at subdaily time scales (Westra et al 2014), but also on daily (CSIRO and Bureau of Meteorology 2015) and monthly time scales (Watterson et al 2016). Observed trends toward higher intensity rainfall have been found in many regions around the globe (Westra et al 2013).…”

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confidence: 99%