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NIWA Client Report: CVAS111 State of the Climate 2013 A snapshot of recent climate in New Zealand (2010-2012) NIWA Science and Technology Series No. 57 April 2013 Authors/Contributors: National Climate Centre Edited by Annette Semadeni-Davies with contributions from: Nicolas Fauchereau Petra Chappell Georgina Griffiths James Sturman Andrew Wilsman For any information regarding this report please contact: Andrew Tait, Principal Scientist National Climate Centre National Institute of Water & Atmospheric Research Ltd 301 Evans Bay Parade, Greta Point Wellington 6021 Private Bag 14901, Kilbirnie Wellington 6241 New Zealand Phone +64-4-386 0300 Fax +64-4-386 0574 Report date: February 2013 NIWA Project: CLVA1304 ISSN 1173-0382 Cover photo credits (clockwise from top right): Alan Blacklock, Dave Allen, Steve Le Gal, Steve Le Gal All photos downloaded from NIWA image library. © All rights reserved. This publication may not be reproduced or copied in any form without the permission of the copyright owner(s). Such permission is only to be given in accordance with the terms of the client’s contract with NIWA. This copyright extends to all forms of copying and any storage of material in any kind of information retrieval system. Whilst NIWA has used all reasonable endeavours to ensure that the information contained in this document is accurate, NIWA does not give any express or implied warranty as to the completeness of the information contained herein, or that it will be suitable for any purpose(s) other than those specifically contemplated during the Project or agreed by NIWA and the Client. Contents 1 Introduction ........................................................................................................ 5 1.1 Description of material ................................................................................. 5 2 Large-scale climate conditions during 2010-2012 ........................................... 6 2.1 ENSO .......................................................................................................... 6 2.2 IPO .............................................................................................................. 7 2.3 SAM ............................................................................................................ 8 3 Weather Patterns .............................................................................................. 10 4 Rainfall .............................................................................................................. 13 4.1 Rainfall in 2010, ........................................................................................ 13 4.2 Rainfall in 2011 ......................................................................................... 14 4.3 Rainfall in 2012 ......................................................................................... 16 5 Drought ............................................................................................................. 18 5.1 Soil moisture deficits 2010 ........................................................................ 18 5.2 Soil moisture deficits 2011 ........................................................................ 19 5.3 Soil moisture deficits 2012 ........................................................................ 19 6 Temperature ..................................................................................................... 21 6.1 Temperature in 2010 ................................................................................. 22 6.2 Temperature in 2011 ................................................................................. 25 6.3 Temperature in 2012 ................................................................................. 27 7 Sunshine hours ................................................................................................ 31 8 Wind .................................................................................................................. 33 9 End of summer snowline ................................................................................. 34 10 Significant weather events .............................................................................. 36 10.1 Events in 2010 .......................................................................................... 36 10.2 Events in 2011 .......................................................................................... 37 10.3 Events in 2012 .......................................................................................... 40 11 Extreme rainfall and temperature variability .................................................. 43 11.1 Extreme rainfalls – 2010-2012 compared to other years ........................... 43 11.2 Extreme temperatures – 2010-2012 compared to other years ................... 45 State of the Climate 2013 References ................................................................................................................. 46 National Climate Centre summaries cited in this report: ..................................... 46 Other references: ............................................................................................... 46 Appendix A Annual weather summary tables, 2010-2012 ........................... 48 Appendix B Monthly weather summary maps, 2010-12 .............................. 66 Reviewed by Approved for release by Andrew Tait David Wratt Principal Scientist Chief Climate Scientist ……………………………………… ……………………………… State of the Climate 2013 1 Introduction This report describes month-to-month and seasonal-scale variability in New Zealand climate over the three years 2010, 2011 and 2012. It is the second in a series of documents published every two to three years which describe recent climate fluctuations in New Zealand, and how they relate to the climate system at the broader scale across the Southern Hemisphere and the Globe. The report is intended to be a supplement to the State of the Climate 2010 (Renwick et al, 2010)1 which covered the years 2008 and 2009. For information on the context of New Zealand’s climate in the global setting and sources of data, please refer to this earlier document. 1.1 Description of material This report presents the observed fluctuations and extremes in New Zealand surface climate over the years 2010, 2011 and 2012 and is based on the annual climate summaries for these years. These summaries, along with detailed monthly, seasonal and annual statistical summaries of the climate can be found at: www.niwa.co.nz/our-science/climate/publications/all/cs2. Note that the annual summary for 2012 was released on 10 January 2013 and may yet be subject to change when climate data are reviewed in May 2013. Observed variability is put in the context of regional-scale variations in weather patterns, and into the context of hemispheric- and global-scale variations in climate. The report follows a similar structure to the State of the Climate 2010. It begins with a description of the large-scale climate patterns, their influence on New Zealand climate, and their recent variations. It then discusses rainfall patterns and drought occurrence, followed by temperature variations and frost occurrence. There is a section on extremes and significant weather events over the past three years, and a discussion of the state of snow and ice storage in the Southern Alps. Finally, there are two appendices which summarise observed climate for 2010-2012. 1 Available for download from the National Climate Centre (http://www.niwa.co.nz/climate/state-of-the-climate, date of last access 20 February 2013) 2 Date of last access 20 February 2013. Annual summaries are available back to 2000 while seasonal and monthly summaries are available from December 2001 State of the Climate 2013 5 2 Large-scale climate conditions during 2010-2012 The largest signal in the climate system on seasonal time scales is the changing of the seasons themselves, driven by the changing latitudinal distribution of solar heating as the Earth orbits around the Sun. After that, there are a number of modes of natural variability of the climate that involve exchanges of energy between different locations or different components of the system (e.g., atmosphere and ocean). These features are not driven by external influences such as solar heating changes, but are intrinsic to the climate system itself. The three main modes of natural climate variability that are relevant to New Zealand are the El Niño – Southern Oscillation (ENSO), the Interdecadal Pacific Oscillation (IPO) and the Southern Annular Mode (SAM). These modes were described in SOC 2010, what follows is an overview of their variations over the last three years. 2.1 ENSO The evolution of ENSO from mid-2009 to the end of 2012 is illustrated using the Southern Oscillation Index (SOI) in Figure 2-1. The SOI measures the difference in mean sea-level pressure between Tahiti (eastern Pacific) and Darwin (western Pacific), and thus indicates the strength of the trade winds. Stronger than normal trade winds are associated with a positive SOI (La Niña) and weaker than normal trades winds are associated with a negative SOI (El Niño). Figure 2-1: The Southern Oscillation Index (SOI) from mid-2009 to the end of 2012. Bars indicate monthly values and the black curve indicates values that have been lightly smoothed with a 3- month running mean. Values of +1 or more indicate the presence of La Niña conditions, while values of –1 or below indicate the presence of El Niño conditions. The start of 2010 was dominated by a moderate
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