New normal? Historical context of recent global tropical cyclone inactivity

1. 2B.7 New normal? Historical context of recent global tropical cyclone inactivity Ryan N. Maue National Research Council AMS 30th Conference on Hurricanes and Tropical Meteorology April 16, 2012

2. Thoughts • What is normal for global tropical cyclone (TC) activity? • How do we quantify TC activity with our current best-track [quality]? What’s our record book? • For climatology (change), what is important? ratios, counts, integrated metrics, SST impacts…etc. • What are the relevant metrics ? • Landfalls

3. Best Track Data: IBTrACS-All v03r03 includes global RSMCs + other centers NHC HURDAT + JTWC 1981-2012 best tracks & operational Pre-1981, combination of available data, muchless reliable, e.g. UCAR ds824.1 (clear underestimate?) Frequency  Counts Accumulated Cyclone Energy (Bell et al. 2000) Only 34-knots + maximum one-minute sustained, tropical phase TCs Analogous to Power Dissipation Index (V 3 PDI, Emanuel 2005) Global Tropical Cyclone Database CONTINUED REANALYSIS Knapp et al. (2010) BAMS

4. Historical Declines in TC Activity Dramatic Downturns Recent Marks Calendar Year 2010 saw 69 TCs globally, fewest since 1977. 75 in 2011. Northern Hemisphere in 2010 saw 46 TCs, fewest since 1977. Global and Hemispheric TC Accumulated Cyclone Energy since 2007 has plumbed record lows • With many metrics, global TC activity has decreased markedly since 2006. • Frequency and integrated metrics such as ACE and PDI have reached near-record lows (Maue, 2011) • Has continued into 2012, with no end in sight?

5. TS | Hurr | Major Global: 75 | 39 | 21 Northern Hemisphere: 54 | 27 | 16 Southern Hemisphere: 18 | 9 | 3 October 2011 - April 2012 2011 Global TC Activity: Frequency

6. Global Tropical Cyclone Frequency 12-month Running Sums TC (34 knots +) & HURR (64 knots +) April 2011 – March 2012 = 74 TC | 38 HURR January 1, 2011 – December 31, 2011: 75 | 39 μ = 87 | 47 Linear Trends [66,107], [28,63]

7. Global Tropical Cyclone Frequency 24-month Running Sums TC (34 knots +) & HURR (64 knots +) April 2010 – March 2012 = 140 TC | 77 HURR TS Hurr Linear Trends January 1, 2010 – December 31, 2011: 144 | 78 μ = 174 | 95

8. Global Tropical Cyclone Frequency 12-month Running Sums HURR (64 knots +) & MAJOR HURR (96 knots +) Linear Trend

9. [knots2] Global Tropical Cyclone ACE 24-month Running Sums | January 1970 - March 2012 Global NH

10. Global Tropical Cyclone ACE [knots2] Calendar Sums: Global & Northern Hemisphere ++++ 1970 – 2011 July-June offset yearly sums: Southern Hemisphere +++ 1971 - 2012

11. Historical global tropical cyclone landfalls: 1970-2010

12. Historical global tropical cyclone landfalls: 1970-2010

13. Relevant metric: global major hurricane landfall$ …this subset of storms is a function of “climate” Weinkle et al. (in press, J Climate)

14. Historical global tropical cyclone landfalls Weinkle et al. (in press, J. Climate) Over 1970 to 2010 the globe averaged about 15 TC landfalls per year Of those 15, about 5 are intense (Category 3, 4 or 5)  1978 had the fewest with 7 2011 tied for second place for the fewest global landfalls with 10 (and 3 were intense, tying 1973, 1981 and 2002) 1999 had the most intense TC landfalls with 9 1981 had the fewest intense TC landfalls with zero There have been only 8 intense TC landfalls globally since 2008 (2009-2011), very quiet but not unprecedented (two unique 3-year periods saw only 7 intense landfalls) The US is currently in the midst of a record streak without an intense hurricane landfall (Wilma 2005) http://rogerpielkejr.blogspot.com

15. Moving forward into the 2020s… Frequency ΔTC activity 2024 – 1970? “Normal” ?

16. Moving forward into the 2020s… Integrated Metric (ACE) ΔTC activity 2024 – 1970? “Normal” ?

17. Moving forward into the 2020s… Best metrics to measure TC climatology – what is normal? Best metrics to measure climate change impacts on TCs? ? IPCC SREX (2012): “The present period of quiescence, as well as the period of heightened activity leading up to the high point in 2005, does not clearly represent substantial departures from past variability. (Maue, 2009)” Global tropical cyclone frequency: annual mean ~ 87, range from 66-107. Is the recent downturn a regional or global phenomena -- represent a climate shift to a colder Pacific (-PDO)? Active North Atlantic vs. inactive North Pacific. How long is this going to last? Impacts on landfalls in the future?

18. IPCC, 2012: Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation. A Special Report of Working Groups I and II of the Intergovernmental Panel on Climate Change (Field et al. 2012) In summary, there is low confidence that any observed long-term (i.e., 40 years or more) increases in tropical cyclone activity are robust, after accounting for past changes in observing capabilities. The uncertainties in the historical tropical cyclone records, the incomplete understanding of the physical mechanisms linking tropical cyclone metrics to climate change, and the degree of tropical cyclone variability provide only low confidence for the attribution of any detectable changes in tropical cyclone activity to anthropogenic influences. There is low confidence in projections of changes in tropical cyclone genesis, location, tracks, duration, or areas of impact. Based on the level of consistency among models, and physical reasoning, it is likely that tropical cyclone related rainfall rates will increase with greenhouse warming. It is likely that the global frequency of tropical cyclones will either decrease or remain essentially unchanged. An increase in mean tropical cyclone maximum wind speed is likely, although increases may not occur in all tropical regions.