HWF (sum of days satisfying definition criteria)

1. HWF (sum of days satisfying definition criteria) KEY OBJECTIVE To define a framework in which heatwaves/warm spells can be measured, giving justice to the geographical regions affected, the communities impacted, and the climatic fields involved. • Global (warm spells) Global (heatwaves) • Australia (heatwaves) • INTRODUCTION • Due to a wide range of impacted sectors (e.g. Coumouand Rahmstorf, 2012), the definition of a heatwave remains is very broad in describing a period of consecutive days where conditions are excessively hotter than normal. • This has resulted in a plethora of metrics that seek to measure heatwaves, however are generally only suited to a specific sector or study (e.g. Matzarakis and Mayer, 1997; Deo et al., 2007). • This inconsistency creates great difficulty in ascertaining observed changes in heatwaves. • Annual warm spells (which include non-summertime events) may also be of interest and need to be measured appropriately CTX90pct • DATA • Australia: • AWAP gridded dataset of daily Tmin and Tmax at 0.5o X 0.5o resolution (Jones et al., 2009). • Time period 1951-2008. • All data consistent through space and time. • 5-month summer (i.e. heatwaves only) • Global: • Updated HadGHCND (Donat and Alexander, 2012) daily Tmin and Tmax at 3.75ox2.5o resolution. • Time period 1951-2011. • Grid points included with at least 65% of data for the entire period, 5% of which is after 2000. • 5-month summer for heatwaves (Austral=Nov-Mar; Boreal=Jun-Sep); all months for warm spells. CTN90pct Closing the Gap on Measuring Heat Waves and Warm SpellsSarah E. Perkins1,2 and Lisa V. Alexander1,21. Climate Change Research Centre, University of New South Wales, Sydney, Australia. 2. ARC Centre of Excellence for Climate System Science, University of New South Wales, Sydney, Australia. Email: Sarah.Perkins@unsw.edu.au EHF • INDICES • A wide range of indices published in the scientific literature employed for heatwave/warm spell measurement were surveyed (see Perkins and Alexander, 2012). • By balancing a range of “definitions” and “components”, the framework seeks to satisfy the requirements • of many users, as well as enabling the measurement of events from a climatological standpoint. • Definitions – a heatwave/warm spell exists when at least 3 consecutive days satisfy the below criterion: • 1) CTX90pct: Tmax exceeds the calendar day 90th percentile, based on a 15-day moving window. • 2) CTN90pct: Tmin exceeds the calendar day 90th percentile, based on a 15-day moving window. • 3) EHF: Positive Extreme Heat Factor based on average temperature, derived from: • EHI(accl.) = (Ti+ Ti−1 + Ti−2)/3 − (Ti−3 + …+ Ti−32)/30 • EHI(sig.) = (Ti+ Ti−1 + Ti−2)/3 − T95 • EHF = max[1,EHI(accl.)]x EHI(sig.) • Where Ti = (Tmaxi+Tmini)/2; • T95=95th percentile of time period • Aspects (annually per definition): • HWN: Total number of events. • HWD: Length of longest event. • HWF: Sum of days satisfying definition criteria. • HWM: Average magnitude of all events. • HWA: Hottest day of hottest event. • Trends estimated by Sens’ Kendall slope method, • significant at 5% level. days/decade %/decade • Globally averaged trends • (trends in bold are significant, averaged across all regions with data) Warm Spells HWD Length (days) HWA Magnitude (degrees C/ degrees C2 Globally averaged time series of CTX90pct, CTN90pct and EHF warm spell HWA (top) and HWD (bottom). • HWA (amplitude of hottest event) • Australia (heatwaves) Global (warm spells) • CONCLUSIONS • Increasing trends in HWF are driving increases in HWN and HWD. • Small-scale differences in changes of event magnitude (HWA, HWM). • Tmin (night-time) events increasing fastest, agreeing with other studies. • Warm spell trends larger than heatwaves – non-summertime events driving this • annual trend more than summertime only events. • Qualitatively, all definitions agree on changes of aspects. • Framework allows for a consistent measure of events, while permitting the user to • “cherry pick” the most appropriate definitions/aspects for their purpose. CTX90pct CTN90pct For more information please see: Perkins, S.E., Alexander L.V. and Nairn J.R., 2012. Increasing intensity, frequency and duration of observed global heatwaves and warm spells. GRL, doi:10.1029/2012GL053361 Perkins, S.E. and Alexander L.V., 2012. On the Measurement of Heatwaves, submitted to J. Climate. REFERENCES Coumou, D. and Rahmstorf, S., 2012: A decade of weather extremes. Nature Climate Change, DOI: 10.1038/NCLIMATE1452 Donat, M. G., and Alexander L.V., 2012:The shifting probability distribution of global daytime and night-time temperatures, GRL, DOI:10.1029/2012GL052459. Deo, R. C., McAlpine C. A., Syktus J., McGowan, H. A. and Phinn, S., 2007: On Australian heatwaves: time series analysis of extreme temperature events in Australia, 1950-2005. L. Oxley and D. Kwasiri (eds), Proceedings of the International Congress on Modelling and Simulation.Modelling and Simulation Society of Australia and New Zealand. Jones, D. A., Wang W. and Fawcett R., 2009: High-quality spatial climate data-sets for Australia. Australian Meteorological and Oceanographic Journal, 58, 233-248. Matzarakis, A. and Mayer, H. 1997: Heat stress in Greece. Int. J, Biometeorol., 41, 34-39. EHF Degrees C (C2 for EHF)/decade Degrees C/decade