New Zealand Seasonal Fire Danger Outlook

Transcription

1 New Zealand Seasonal Fire Danger Outlook ISSUE: South Island, December 2015 Summary The intention of these monthly outlooks is to provide a heads up on current and potential fire danger for the North and South Islands. It should be used as a prompt for local and regional discussions/debates on fire potential, and where things are at, where it is heading, and to drive awareness about what this might mean in your patch and for your neighbours. Current fire danger situation & outlook: Fire danger across most of the eastern South Island is high, but running about or below normal compared to the same time last year and during the super El Niño of 1997/98. Fire danger for the West Coast of the South Island is low but about normal for this time of year, and running about the same as last year and the 1997/98 El Niño. Fire dangers are expected to increase as is normal for this time of year as the summer builds. However, the strong El Niño conditions will continue to produce higher than normal fire dangers in parts of the South Island. Specific areas to watch are Marlborough, coastal Canterbury, inland South Canterbury, North and Central Otago, and central Southland. The climate outlook for the South Island is for a colder than normal second half of December, with higher rainfalls than normal in the west and below normal rainfall in the north and east. In particular, a dry December is expected for Tasman, Nelson and most of the eastern South Island. Further out, the outlook for January-February 2016 indicates continued cooler temperatures in most regions of the country, wetter than normal conditions to the west of the Southern Alps, and drier conditions in northern and eastern regions of both islands. El Niño conditions are expected to continue through to at least March/April 2016, with strength still predicted to be similar to 1997/98. Under El Niño, there is an increased likelihood of a dry summer in the north and east of both islands and, in the South Island, in particular for Nelson, Marlborough and coastal Canterbury. The three strongest previous El Niño events since 1950 (1972/73, 1982/83 and 1997/98) all produced very dry conditions (below 50% of normal summer rainfall) and, in turn, severe fire dangers to much of the northeastern South Island (based on average Monthly severity ratings observed during the 1997/98 El Niño). November 2015 December 2014 December 1997 Figure 1. Monthly Average Severity rating for: Current (left), last year (2014) (middle) and the super El Nino year (right).

2 Regional Summaries Trends for DC, BUI and CDSR are located at the back of this report for key stations across the South Island. For those who are interested in tracking fire season trends for all your weather stations, and want to alter the graphs or check the raw data, please visit the link: dropbox.com/sh/h56ifyjel6rtid2/aadiizj4sokqrk_ PpbAC50ega?dl=0 Northern South Island: Nelson-Tasman Current fire severity low, but increasing around Nelson city area CDSRs about or above normal for this time of year, DCs about or above normal, BUIs about or below normal (suggesting frequent small amounts of rain sufficient to reduce DMC but not DC); Currently, this region is not yet as dry as 1997/98 Experienced below normal rainfalls right across the region Soil moisture lower than normal compared with historical average, similar to last year but perhaps not as dry around Nelson city; Soil moisture anomaly shows significantly drier than normal across eastern part of the region Expect fire dangers and fire climate severity to increase over the next months in parts of this region, especially around Nelson city/dovedale area Marlborough-Kaikoura Fire severity is much higher than normal for this time of the year Extreme values more widespread than last year, but not yet as widespread as 1997/98 CDSRs below normal for the Sounds, but above average for Blenheim plains south to Kaikoura BUIs also below average for the Sounds/western hills, and above average for Blenheim south to Kaikoura; The extent of elevated BUIs are not yet as widespread as 1997/98 DCs above average, in many cases significantly, for all stations; the values are higher than last year, and similar to 1997/98 DMCs higher than last year, but well below values seen in 1997/98 ISIs elevated, but similar to both last year and 1997/98; FWIs higher than last year, but not as widespread as 1997/98 Significantly below normal rainfall over the whole region, with the exception of the northernmost parts of the Sounds Soil moistures are well below average Expect fire dangers and fire severity to continue at above average levels across most of this region, and to reach levels similar to or even higher than seen in 1997/98 page: 2 Central South Island: West Coast Fire severity is low for this region, as would be expected under El Nino conditions bringing increased westerlies and rainfall on the westward side of the Alps CDSRs at or below normal BUIs normal or below normal DCs at or below normal Rainfall slightly normal across the southern parts of the region Soil moistures in coastal areas at normal levels, but soils further inland are drier Expect fire dangers to remain low for December North Canterbury (includes Selwyn, Christchurch, Waimakariri and Hurunui). Fire severity is higher than last year, and more widespread extending further inland than in 1997/98 CDSRs are above average, and close to or above levels reached at the same time of year in 1997/98 BUIs above average, and at or above levels seen in 1997/98 DCs are significantly above average, and at or above levels of 1997/98 for many of the stations Area of elevated DC values (in Fig. 4) are currently more localised than in 1997/98 Rainfall is below normal over the past month, but not severely so (compared with around Banks Peninsula/ coastal mid Canterbury) Soil moisture deficits are below average, particularly in coastal North Canterbury, but not as severe as last year The soil moisture anomaly map shows areas further inland are also significantly drier than normal Expect fire dangers and fire climate severity in coastal North Canterbury to continue at above average levels, but to also start to extend further inland as well South Canterbury (includes the Rakaia river south (i.e. Ashburton & SCRFA). Fire severities are higher for South Canterbury compared with last year, and are more widespread than last year or in 1997/98 CDSRs are above average, and similar to or in some cases (Ashburton Plains, Cannington) well above values seen in 1997/98 BUIs are at or above average; BUIs in coastal areas considerably more extreme than last year and than in 1997/98 DC values generally well above normal across most of the region, and at levels of or above those seen in 1997/98; Elevated DC values are not as widespread currently compared with the similar time last year DMC values similar to those seen in 1997/98, but not as high as last year, especially in the south of the district (Fig. 4) Rainfall is normal across inland parts of the district, but below average across the plains, especially in the coastal strip south of Banks Peninsula to Timaru Soil moistures across the region are significantly drier than the historical average, but not as dry as for the

3 same time last year; The soil moisture anomaly map shows levels are well below normal for this stage of the year, particularly closer to the coast Expect fire dangers and fire severity to continue to increase over most of this region, with the possible exception of areas closest to the Alps, and to reach levels at least as severe as seen in 1997/98 Lower South Island: Otago Fire severities across North and Central Otago are extreme, but similar to those last year and in 1997/98 CDSRs are generally above average, in some cases significantly so (Central Otago Tara Hills, Wanaka, Clyde/Butchers Dam/Cromwell, North Otago Bucklands, Danseys Pass, Oamaru, Windsor), and at or above levels seen in 1997/98; CDSRs about average in South Otago BUI values across the region are currently only average, or even below average for this time of year, but about the same as in 1997/98 DCs across North Otago, and some Central Otago stations, are above average; other around normal; However, all are significantly lower than last year, and than 1997/98 DMCs also lower than last year, but similar to or higher than in 1997/98 Rainfall across the region is about normal, or slightly lower in some areas Soil moisture deficits in inland areas are elevated, and greater for the same time in 1997/98, but below levels seen last year; The soil moisture anomaly map shows soil dryness is about normal or slightly drier than usual Expect fire dangers over much of the region over the next few months to be about or slightly above normal, But expect fire dangers to reach more extreme levels than normal in North Otago and parts of Central Otago Southland Fire severity across much of the region is about normal, but higher than normal in a zone extending from central Southland to the central south coast; it is similar or slightly higher than last year, but generally higher than for 1997/98 CDSRs are generally about average, with exception of central Southland (Lumsden, Gore) where values are well above average and the highest on record for this time of year BUIs across all stations are about average, although in some cases (e.g. Lumsden) only as a result of rain in recent weeks reducing otherwise very elevated values DC values are about or below average, with the exception of Lumsden where values are elevated well above normal and near the highest on record for this time of year Rainfall across the region are currently around normal, with the exception of the central Southland area where values were lower than normal Soil moisture levels, for the most part, are around the historical average, but drier than normal in inland central Southland; The soil moisture anomaly map emphasises the drier than normal conditions in central parts of the region, but also in the northeast Expect fire dangers to be higher than normal in central Southland, as well as possibly in the northeastern coastal area as the dry conditions seen to the north in Otago and Canterbury extend further south Pacific Islands: Chatham Island Currently, the Chathams are experiencing low fire danger and severity. Expect fire danger to increase as conditions continue to dry out over summer. The drought indices are currently high, and are trending just above the historical average for this time of the year. BUI values for Chatham Island Aero is currently trending just below average for December, but historically the values continue to increase until early February. The cumulative Fire Severity Rating is trending above average for this time of the year. Current temperatures for December are below normal (based on a three year historical average from the Chatham Island Aero station). Total rainfall for the month of November was just above normal, currently for December the total rainfall amount is well below the historical average EXPECTED CLIMATE OUTLOOK: Over the last few months, the strength of the 2015 El Nino has been comparable to the 1997/98 and the 1982/83 events. International guidance indicates that El Niño will continue (100% probability) over the next three months. The event may well be approaching its peak. Climate models have the event continuing through the following season, March-May 2016, and a rapid return to ENSOneutral status by winter in June-August Note that El Niño events are typically (but not always) associated with more south-westerlies in spring followed by stronger and/or more frequent westerly winds over summer. Such a circulation pattern usually leads to cooler conditions in most regions of the country, wetter than normal conditions to the west of the Southern Alps and drier conditions in northern and eastern regions of both Islands. Predictions for the next three months (December 2015 February 2016) broadly reflect these typical impacts. In particular, the three previous strongest El Niño events since 1950 (1972/73, 1982/83 and 1997/98) all show very dry conditions (below 50% of the normal rainfall over summer) in northeast parts of the country: eastern Northland, Coromandel, coastal Bay of Plenty, southern Hawke s Bay and coastal Wairarapa, and Marlborough. It s important to remember that once El Nino begins to weaken, i.e. sea surface temperatures cool in the central and eastern equatorial Pacific, the impacts in New Zealand will persist well beyond into the autumn season. On average, New Zealand experiences at least one ex- page: 3

4 tropical cyclone passing within 550km of the country every year. For this tropical cyclone season (November April 2016), the risk for New Zealand is slightly higher than normal. The first Tropical Cyclone of this season (TC Tuni) formed late in November, tracking between Samoa and Niue before weakening. The 2015/16 Tropical Cyclone season is expected to be an active one in the tropics north of New Zealand. If an ex-tropical cyclone comes close to the country, the current background climate conditions suggest it has an equal probability of passing east or west of Auckland city. Significant rainfall, damaging winds and coastal impacts can occur leading up to and during these episodic events. Last month (November): For the second month in a row, Highs prevailed over the Tasman Sea and across much of New Zealand With frequent northwesterly winds over the lower South Island. It continued to be extremely dry in Marlborough, with Blenheim recording its driest November on record (4.8mm). It was also very dry for Nelson and Canterbury Temperatures were well below average for most of November, until northwesterlies delivered a run of hot days to eastern areas during the last week. This month (December): December starts very warm, notably so for the South Island. However, the second week turns unusually cold for the time of the year right across New Zealand. Temperatures for the second half of the month look likely to continue a touch cooler over the southern South Island Below normal December rainfall is forecast for the north and east of both Islands. A wetter than usual December is predicted along the West Coast of the South Island. Closer to normal December rainfall is signalled for Southland. Bottom line: A drier than usual December is signalled for the north and east of both Islands. Further ahead: December February 2016 Temperatures are most likely to be: equally likely to be average (35% chance) or below average (40% chance) for Nelson, Marlborough, Buller equally likely to be near average (40% chance) or below average (45% chance) for West Coast, Alps and foothills, inland Otago, Southland near average (45% chance) for Coastal Canterbury, east Otago Rainfall is most likely to be: normal (40% chance) or below normal (40% chance) for Nelson, Marlborough, Buller equally likely to be near normal (40% chance) or above normal (40% chance) for West Coast, Alps and page: 4 Figure 7. Outlook for December February 2016, air temperature (top), rainfall (middle), available soil moisture (below). Source: NIWA

5 foothills, inland Otago, Southland equally likely to be in the near normal range (40% chance) or below normal (35% chance) range for Coastal Canterbury, east Otago Soil moistures are most likely to be: below normal (45% chance) for Nelson, Marlborough, Buller in the above normal range (45% chance) for West Coast, Alps and foothills, inland Otago, Southland equally likely to be near normal (40% chance) or below normal (45% chance) for Coastal Canterbury, east Otago Current weather situation: For the second month in a row, Highs prevailed over the Tasman Sea and across much of New Zealand, with frequent northwesterly winds over the lower South Island. It continued extremely dry in Marlborough, with Blenheim recording its driest November on record (4.8mm). It was also rather dry in Nelson and Canterbury, and parts of inland South Canterbury and Southland (see Fig. 8). Temperatures were well below average for most of November, until northwesterlies delivered a run of hot days to eastern areas during the last week. Over most of the South Island, soil moisture levels continue to be much drier than normal compared with the historical average, following a pattern similar to that for the same time last year (Fig. 9). High soil moisture deficits that are well above average are present in Marlborough, coastal Canterbury, the Mackenzie Basin and Central Otago. However, with the exception of the Canterbury Plains area, these deficits were also present last year. The map of soil moisture anomaly (Fig. 8) shows the anomaly or difference from normal levels for the same time of year. This better represents areas where soil dryness is above (or below) average. This shows that soil are drier than normal across virtually the entire South Island, with the exception of coastal portions of the West Coast, Fiordland and Southland. Severely to extremely drier than normal soils for this time of year exist in parts of Nelson, Marlborough, Canterbury (especial central Canterbury) and inland Southland. Figure 8. Top: Rainfall deciles for November 2015 (data from 1972). Bottom: Soil Moisture Anomaly as of 10/12/2015 Source: NIWA Historical Figure 9. Soil moisture deficits as of (left), the same time last year (middle), and historical average (right). Source: NIWA page: 5

6 FWI values November 2015 December 2014 December 1997 BUI values November 2015 December 2014 December 1997 ISI values November 2015 December 2014 December 1997 Figure 2. Current Monthly Average for the: Fire Weather Index (top), Buildup Index (middle) and Initial Spread Index (below). Figure 3. Average Monthly values of Fire Weather Index (top), Buildup Index (middle) and Initial Spread Index (below); for the previous year (2014) and during the 1997/98 super El Nino year. page: 6

7 DC values November 2015 December 2014 December 1997 DMC values November 2015 December 2014 December 1997 FFMC values November 2015 December 2014 December 1997 Figure 4. Current Monthly Average for the: Drought Code (top), Duff Moisture Code (middle) and the Fine Fuel Moisture Code (below). Figure 5. Average Monthly values of Fire Weather Index (top), Buildup Index (middle) and Initial Spread Index (below); for the previous year (2014) and during the 1997/98 super El Nino year. page: 7

8 Background info on FWI codes and indices: Fine Fuel Moisture Code (FFMC) - An indicator of the relevant ease of ignition and flammability of fine fuels Difficult Moderately easy Easy Very easy 92 + Extreme easy Duff Moisture Code (DMC) - A rating of the average moisture content of loosely compacted organic soil layers (duff/ humus) of moderate depth, and medium-sized woody material Little mopup needs Moderate Difficult Difficult & extended 41 + Difficult & extensive Drought Code (DC) - A rating of the average moisture content of deep, compact, organic soil layers, and a useful indicator of seasonal drought effects on forest fuels and amount of smouldering in deep duff layers and large logs Little mopup needs Moderate Difficult Difficult & extended Difficult & extensive Initial Spread Index (ISI) - Combines the effect of wind speed and the FFMC, providing a numerical rating of potential fire spread rate. 0-3 Slow rate of spread 4-7 Moderate fast 8-12 Fast Very fast 16 + Extremely fast Buildup Index (BUI) - Combines the DMC and DC, and represents the total amount of fuel available for combustion Easy control Not difficult Difficult Very difficult 60 + Extremely difficult Fire Weather Index (FWI) - Combines the ISI and BUI to indicate the potential head fire intensity of a spreading fire (on level terrain). 0-5 Low fire intensity 6-12 Moderate High Very High 30 + Extreme page: 8 Daily Severity Rating (DSR) - a numerical rating of the daily fire weather severity at a particular station, based on the FWI. It indicates the increasing amount of work and difficulty of controlling a fire as fire intensity increases. The DSR can be averaged over any period to provide monthly or seasonal severity ratings. DSR values: Monthly Severity Rating (MSR) - is the average of the DSR values over the month. DSR and MSR captures the effects of both wind and fuel dryness on potential fire intensity, and therefore control difficulty and the amount of work required to suppress a fire. It allows for comparison of the severity of fire weather from one year to another. 0-1 Low fire behaviour potential 1-3 Moderate fire potential 3-7 High to very high fire potential 7 + Represents extreme fire behaviour potential Tracking trends in BUI, DC and CDSR: Comparisons of fire dangers for individual indicator stations for different regions are shown overleaf, highlighting where current Buildup Index (BUI), Drought Code (DC) and Cumulative Daily Severity Rating (CDSR) values sit in comparison with previous fire seasons. The graphs display: Bold black line is the current fire season Blue bold line is the previous fire season Bold red line is the average Light grey lines are historical fire seasons We ve also colour coded the 97/98 El Nino season orange (if your weather station goes back far enough). Acknowledgements: Fire Danger interpretation was from information gathered from the Average Monthly Maps for: Severity Rating, FWI, BUI, ISI, DC, DMC, FFMC. These maps were obtained from the National Rural Fire Authority Fire Weather System powered by Eco Connect. Information on the Expected Climate Outlook was gathered from: MetService, Rural Monthly outlooks: NIWA, Seasonal Climate outlook: Front Cover Image: Unknown Wildfire, John Foley (MKRFA). If you are keen to submit a weather and fire related photo that will appear on the front page, please a high resolution image(s) with details on the location and the photographer s name and organisation. to: Veronica.Clifford@scionresearch.com

9 Figure 10. Comparisons for Chatham Islands Aero (Wellington) of Drought Code (top), Buildup Index (middle) and Cumulative Daily Severity Rating (below) page: 9

10 page: 10 Figure 11. Comparisons for Awatere weather station (Marlborough) of Drought Code (top), Buildup Index (middle) and Cumulative Daily Severity Rating (below)

11 Figure 12. Comparisons for Hira weather station (Nelson) of Drought Code (top), Buildup Index (middle) and Cumulative Daily Severity Rating (below) page: 11

12 page: 12 Figure 13. Comparisons for Westport station (West Coast) of Drought Code (top), Buildup Index (middle) and Cumulative Daily Severity Rating (below)

13 Figure 14. Comparisons for Balmoral weather station (Canterbury) of Drought Code (top), Buildup Index (middle) and Cumulative Daily Severity Rating (below) page: 13

14 page: 14 Figure 15. Comparisons for Darfield weather station (Canterbury) of Drought Code (top), Buildup Index (middle) and Cumulative Daily Severity Rating (below)

15 Figure 16. Comparisons for Tekapo station (South Canterbury) of Drought Code (top), Buildup Index (middle) and Cumulative Daily Severity Rating (below) page: 15

16 page: 16 Figure 17. Comparisons for Wanaka weather station (Otago) of Drought Code (top), Buildup Index (middle) and Cumulative Daily Severity Rating (below)

17 Figure 18. Comparisons for Lumsden station (Southland) of Drought Code (top), Buildup Index (middle) and Cumulative Daily Severity Rating (below) page: 17