Global wildfires: perceptions vs realities
Sat 21 Sep 2019

Wildfires burning in the Amazon Basin and Indonesia as well as an unprecedented early and disastrous start to our Australian southern fire season has again focussed attention on their negative impacts.

The total number of wildfires globally is enormous. 18,959,413 fires have been detected for the year to today according to Global Forest Watch Fires (GFWF) based on data from the MODIS and higher resolution VIIRS satellites. This is their map showing fires burning in the last day. As is normal, the greatest number lie in the tropical band across central Africa, especially the Congo, Angola and Zambia. Africa accounts for around 70% of global fires annually. 

Russia, driven by the fires in Siberia, comes second in number of fire alerts this year, Brazil third and Australia fourth, with most fires in the NT and WA. Indonesia doesn't appear in the year-to-date top ten, yet, because it has only been in the past month that the worst fires since 2015 have burned for agricultural clearing in Sumatra and additionally escaped into peatlands in Kalimantan. [Guardian, NOAA, NASA]

Global fire season comparison, 2001 to 2019, using MODIS data only (therefore fewer fires identified than when combined with VIIRS data). GFWF

It's interesting to compare global fire seasons using satellite data between 2003 and 2019. The lowest two lines, for 2001 and 2002, can be ignored as those were years that government agencies were setting up to use MODIS as a tool for identifying fires and issuing alerts. The remaining 17 years cluster far more closely together than you'd expect, showing that fires globally are a common and steady phenomenon, not varying greatly in number from year to year. Comparing years to today's date, 2019 sits at 12th out of 17 — so below average — in terms of number of fires identified.

While many developed nations, eastern Australia, western USA and southern Europe in particular, regard fire as an enemy, for much of the world's population it has long been a part of life and an indispensable agricultural tool to clear land or nourish the soil. Lightning from dry thunderstorms has started fires in grasslands and forests for aeons before humans arrived, so many ecosystems are dependent on regular burning to maintain their biodiversity and natural habitats.

It's surprising to learn that, despite global heating, the area burnt globally by fires, as distinct from the number of fires, has decreased by 25% since 2003 according to Yale Environment based on NASA data. This study in Nature Geoscience went much further back and examined charcoal records in sediments over the past 2,000 years. It concluded that global burning has dropped sharply since about 1870, and attributed that to the global expansion of intensive grazing and agriculture and improvements in fire management.

The increasingly apocalyptic reporting of fires is driven by their increased intensity helped by global heating as well as urban sprawl that sees increasing settlement in forest and grassland areas on the edges of cities and in regional areas. However, it is more complex than that. This detailed study by Doerr and Santin, published by the Royal Society, explains the paradox of why we see wildfires as an increasingly severe problem while the evidence says that the global area burned has declined in the past few decades. It is a compelling read and brings some balance to many exaggerated wildfire perceptions.

  An unusually warm night in SE Australia
Sat 21 Sep 2019

Overnight Friday into Saturday 20/21 Sep was an unusually warm night given that it came in the NW stream ahead of a pretty inconsequential cool change.

Sixteen new provisional September high minimum temperatures were set stretching from the NSW Central West Plains to the TAS East Coast. All except three of them are from AWSs with short 15 to 25 year histories. Lake Cargelligo Airport, with a 50-year history, added a remarkable 3.4° to its previous record (but see note in records below) while Essendon Airport in Melbourne's north, also with a half-century history, added just 0.1°. Rutherglen Research is the outstanding one, though. Daily records there go back to 1912 providing 101 complete years of observations. Saturday morning's minimum of 18.7 breaks the previous September record of 17.8 set on 28 Sep 1928, so a significantly warm September night in the vineyards. The full list of new records is here.

One of the great pities of the shift to Automatic Weather Stations in Australia during the 1990s and 2000s has been the loss of continuity with older, often very long records at most locations across the country. AWSs have been put in places where there weren't manual stations previously, or have been moved to a location not comparable with the old manual station. Forbes, Cowra and Young are classic examples where the manual station was in town (usually at the Post Office), with records back to 1873, 1907 and 1907 respectively, while the AWS is in a different environment at the airport 5 to 10km out of town.

Of course, the AWS era has led to huge improvements in monitoring the weather with readings taken as often as every minute and usually of a higher quality than in the manual observer era. However, although airports are better, more representative, locations for measuring most weather elements now due to urbanisation of the earlier station areas, it still makes meaningful comparisons with significant events more than a quarter of a century ago difficult.

Haiti: heavy rain brings flooding. Sat 21 Sep 2019 Heavy rain on Haiti, off the eastern tip of Cuba, has caused severe flooding with 2 deaths and 4 missing reported so far. 300 houses are flooded, 30 destroyed and 55 damaged while there has been significant damage to infrastructure and agriculture. [Reliefweb]