When Rain Follows Fire

Chase Walz
Feb 20 · 5 min read

In the areas that have been plagued by fires, does rain bring relief…or another recipe for disaster?

Last year’s headlines were marred by stories of forest fires around the world. The 2018 California wildfires and Eastern Australia bushfires collectively devastated nearly four million acres. Yet, many will be surprised to know that while these fires have been contained and extinguished, the loss of life and property caused by these events has continued today.

The culprit?

Rain.

The conditions for forest fires — dry air, abundant tinder, and hot weather — often lead people to think that rain could be the miracle they need. In 2011, Texas Governor Rick Perry officially declared there to be three “Days of Prayer for Rain” as forest fires devastated the state. While opportune rainfall can slow down burns, it can also create new dangers. With ecosystems bared by fire and recovering plant life insufficient to soak up excess rainfall, flooding and mudslides add new dimensions to the destruction caused by wildfires.

Climate scientists have long theorized that our changing climate will include more extreme weather events such as forest fires and heavy precipitation. However, few have looked at what happens at the intersection of these two events. In today’s analysis, we will be looking at Los Angeles, USA and Townsville, Australia, two cities that have been in news for their forest fires and now heavy precipitation, to investigate what happens when storms come after fires.

From Ash to Mud

In order to understand the relationship between rainfall and newly charred land, we compared the level of precipitation in millimeters per day to the occurrence of mudslides and flooding in the region. In this analysis, precipitation in mm/day serves as our independent variable and the incidence of mudslides and flooding serve as our dependent variable.

To evaluate the levels of precipitation in these two distinct regions of the world, our Data Integration Engineer, Eneli Toodu employed three separate datasets to capture the nuances of each geography.

To generate a comparison baseline, we used the ERA5 dataset to create the ten-year yearly average from the hourly estimates of precipitation provided by the European Centre for Medium-Range Weather Forecasts. While these measurements are limited to a resolution of a 30km grid, their historical depth offers a balanced average to compare information across hemispheres.

For Los Angeles, we looked at the Gauge-Based Analysis Of Daily Precipitation dataset conducted by the National Oceanic and Atmospheric Administration (NOAA). The measurements are taken from water gauges at NOAA stations and then verified through the comparison to historical records and independent measurements taken by other nearby stations, radar/ satellite observations, and numerical model forecasts in order to provide the most accurate value.

For Australia, Eneli applied the Daily Rain, Temperature And Vapour Pressure For Australia dataset provided by the Australian Bureau of Meteorology. This data, which is produced automatically from real-time data with little quality control, sacrifice accuracy for timeliness. However, its high resolution and quick turnover allow us to capture the most recent weather events in detail. Using this data, she created the following graphic:

Drawing Connections

The first observation that can be drawn from the data is that the precipitation in both Townsville, Australia and Los Angeles, USA in the first week of February was historically unprecedented. In Townsville, rainfall was over 25 times the ten-year average. Rainfall totals for the Ross River dam catchment in Townsville were in “excess of one in 2,000 years rainfall event.” In Los Angeles, rainfall was over 15 times heavier than the ten-year average. In fact, Los Angeles had more rain in the first two months of 2019 than all of 2018.

Secondly, the proximity of the dates of heaviest rainfall provides insight into a broader climatic trend. In Los Angeles, the heaviest rainfall occurred on February 4th while in Townsville, the heaviest occurred on February 3rd. Only one day apart, two record-breaking storms hit areas that were recently plagued by wildfire. What unites these two cities nearly 11,622 km (7,222 mi) away is El Niño. The high temperatures caused by this climatic oscillation have been known to contribute to both the forest fires and storms that the two cities have experienced in the last year. Additionally, the fact that these events have gotten increasingly severe over the past half-century is one that should not be ignored.

Viewing these two observations in tandem, we expect to find soil destabilized by wildfires will mix with rainfall to produce significant mud and land movement. Recent headlines and reports from Townsville and Los Angeles support this prediction to an alarming extent. In Southern California, mudslides and floods have nearly crushed cars, wiped out highways, and carried away homes. Simultaneously in Eastern Australia, landslides and flooding have blocked roadways, prompted evacuations, and exacerbated property and other damages. From these two cities, it has become clear that heavy rainfall in former forest-fire afflicted areas heightens and contributes to further damage from both land slippages and flooding.

Through analyzing precipitation levels and the incidences of flooding and mudslides in Los Angeles and Townsville, it is evident that heavy rainfall in areas affected by forest fires can increase the disruption of human activity. When fires cull the plant life needed to soak in excess water and root the soil, water and land can pour out onto roadways and residences.

As extreme weather events become increasingly common, forest fires that quickly transition into floods are becoming less of a miracle of nature and more of an unwieldy series of events. It has become clear that these anomalous weather events are forming a pattern that will require cities to be prepared for future destructive weather incidences. With Datahub, activists, city planners, and companies can work together to analyze weather and environmental trends and increase preparedness for severe events like these.


Many of the datasets made available through the Planet OS Datahub have been at the request of our users. For those who require a consolidated, easy to use, resource for accessing large and complex material that the Datahub does not already offer, please reach out to the team and we will work toward bringing it onboard. For more information check out the Planet OS Datahub.

Planet OS (by Intertrust)

Provided by Intertrust Technologies

Thanks to Nishtha Sharma and Dashiell Pinger.

Chase Walz

Written by

Planet OS (by Intertrust)

Provided by Intertrust Technologies