Every year the news media broadcasts dramatic scenes of wildfires burning California. Governor Jerry Brown has declared that
We’re facing a new reality in this state, where fires threaten people’s lives, their properties, their neighbourhoods, and of course billions and billions of dollars.
“With climate change, some scientists are saying southern California is literally burning up.
How frequent are droughts? What is the rainfall, year by year? Does the data back up Governor Brown’s claim?
A site called Los Angeles Almanac compiled rainfall totals for Los Angeles from 1877 through 2016 (a July 1 to June 30 year). They noted that:
Some earlier seasons (especially prior to 1941-1942) did not have complete data. In some cases, as many as 26 days or more were missing in the course of one month.
The trend line shows little change over the period 1941-2017. The drought of 2011-16 was severe enough to distort both the trend and the yearly average. The data does not demonstrate that rainfall shortfalls of similar sizes will frequently occur in the future.
What the data does show is that rainfall shortages over a three year period happen frequently in Los Angeles and have since records were first kept. It also shows that shortages are often followed by a year or more of higher than average rainfall.
I imported their data into a spreadsheet. Keeping in mind their caveat:
- The highest rainfall totals were in 1883-84 and 2004-05. In 83-84, a record 38.78 inches fell, while in 04-05 37.25 inches fell.
- In 2006-07, rainfall was at a record low, 3.21 inches. In 2001-02, the second lowest rainfall total was recorded, at 4.42 inches.
- The longest period of below average rainfall totals was 2011-2016. In those five years, the accumulated rainfall totals were 34.96 inches below average.
- The second worst period of below average rainfall totals was 1986-1990. It was another five year period, with a cumulative 26.71 inches below average.
- In the 140 years of data, there are 14 periods of three or more years with below average rainfall.
- In the 14 year period 1917-1931, there were 11 years with below average rainfall. In the seven year period 1958-1965, there were six years of below average rainfall.
| Period | Years | Shortfall |
|---|---|---|
| 2011-2016 | 5 | 34.96 |
| 1986-1991 | 5 | 26.71 |
| 1944-1950 | 6 | 26.37 |
| 1958-1961 | 3 | 25.64 |
| 1897-1900 | 3 | 23.69 |
| 1922-1925 | 3 | 20.12 |
| 2005-2008 | 3 | 19.99 |
| 1969-1972 | 3 | 16.99 |
| 1962-1965 | 3 | 14.25 |
| 1927-1931 | 4 | 11.54 |
| 1952-1955 | 3 | 10.86 |
| 1917-1920 | 3 | 10.33 |
| 1880-1883 | 3 | 8.61 |
What has changed, dramatically, is the population of Los Angeles County. From Los Angeles Almanac we learn that the population of the county in 1880 was 33,381. In 1900, it was 170, 298. By 1940, the population of the county had grown to 2,785,643.
By 1960, the population had more than doubled, to 6,039,834. Growth continued, and by 1990 the county held 9,818,605 people. The LA County government states that the 2016 population was 10,241,335.
It is fair to say that wildfires in Los Angeles County are more serious now than in the past. That point is demonstrated by the vastly increased population being exposed to the potential of wildfire. Ten million people need far more room than 33,000 or six million.
Is it climate change? The data does not support that hypothesis. Instead, the data suggests that the region routinely suffers periods of rainfall shortfalls followed by periods of higher than average rainfall. The key metric in the danger to property or persons from wildfires in Los Angeles may be the population increase, which has lead to more homes and businesses exposed to the dangers of wildfires.