By: John Bradley
The L.A. wildfires reignited my wonder about extreme weather on the west coast. Some scientists consider land use change to be of equal importance with greenhouse gas emissions as causes of climate change. The climate science blogs discussed below illustrate tragic examples of how long-term bad land use contributes locally, or at distance, to propagation of wildfires.
First is a big picture graphic of how global land use has changed over several centuries. The second section is how land use change in the Great Basin of Utah and Nevada has had an outsized impact on LA fires, hundreds of miles away. The third section is how the pattern of land use, climate change and wildfires is replicating itself along the Pacific Coast from California to Chile.
Global Land Use Change
Anatasia Makarieva, a Russian physicist and climate researcher, shared this graphic in her recent blog Warming, Cooling, or We just don’t know?. The chart shows the replacement of primary ecosystems by human modified land use (data from Hurtt et al. 2011). Since 1800, the area occupied by primary ecosystems which evolved naturally over millennia has halved.
The two articles discussed below elaborate on how land use changes, such as deforestation, urbanization and water diversion including aquifer depletion, have contributed to climate change, especially aridification of whole regions and extreme weather swings. The typical pattern discussed for the Mediterranean basin (Spain) and Southern California is that land use changes result in reduced rainfall and evolve into an extreme weather pattern of drought, wildfires, and flooding.
The L.A. Fires and The Impact of the Great Basin
(From Alpha Lo, Taming the Hot Dry Winds)
The Santa Ana Winds that amplify the L.A. fires originate in the Great Basin of Nevada and Utah. It is a vast area between the Sierra Nevada and Wasatch mountain ranges and includes the major metropolitan areas of Las Vegas, Reno and Salt Lake City. The population growth, urbanization, and various land use changes have made the basin hotter and drier and more susceptible to climate change.
The Santa Ana winds that fueled and spread the wildfires on the coast are affected by the extensive land use changes that occur in the Great Basin. These land use changes involve aspects of water management throughout the watersheds - diversion of surface water, depletion of aquifers, soil degradation which reduces water retention due to agriculture practices and landscaping, less moisture added to the atmosphere via transpiration due to changes in vegetation cover, invasive species, loss of biodiversity, deforestation, and wildfires. These factors contribute to the Santa Ana winds being hotter, drier and stronger. Increased warming in the Mojave Desert contributes adversely to L.A.’s wildfires. Mountain forests that might serve as windbreaks are less effective due extensive harvesting of trees by the logging industry. As Alpha Lo notes, “all these factors connect and California is caught in a vicious cycle of drought, fire and floods.” He discusses the need for vast eco-restoration, lest this region go the “the way of the Fertile Crescent in the Middle East, when desertification followed human mismanagement, or the way of the African Sahel in the mid 1900s when desertification followed the removal of trees.” While these parallels seem extreme, the climate science is the same.
To me, these fires and their connection to distant land use changes are a sobering illustration of the interdependence of local and distant ecologies, and how unrelated land use changes can contribute to a systemic climate disturbance with an amplifying effect.
The Repetition of Land Degradation, Rain Loss, and Climate Change on the Pacific Coasts Science blogger Rob Lewis (The Climate According to Life) has summarized some important climate science drawn from the Mediterranean. His article Did Southern California once have Summer Rains? focuses on the similarities in geography and climate change patterns between the Pacific coast of the Americas and the Mediterranean. In the 1980’s, the Mediterranean Center for Environmental Studies (CEAM) investigated the loss of summer rains on the Iberian Peninsula, and concluded that land use changes were a primary cause. The moist sea breezes from the Mediterranean Sea did not have enough moisture to condense into clouds and rain so they needed to pick up additional moisture and aerosols from the forests and vegetation on the Spanish mainland. For ages, as moist air would rise up the mountains, the air cooled and condensed to rain. However, due to recent centuries of land use change, deforestation for industry, development, agriculture and other purposes, the vegetation no longer supported this process and the insufficiently moist air moved on into the higher atmosphere. Interestingly, the CEAM scientists predicted that this additional high atmospheric moisture would be blown inland over northern and central Europe and result in catastrophic flooding. This of course is precisely what has occurred in recent decades. Interestingly, Millan Millan, the scientist director of CEAM, predicted a similar fate for Southern California when he visited San Diego in 1995. When land use is changed with deforestation, urbanization, expanded agriculture, tourism, timber harvesting, the water cycle is disrupted and the summer rains are reduced.
Regarding Southern California, Lewis describes the historic landscape under indigenous (Tongva) stewardship - a wet landscape with marshes, meadows, oak groves, flower fields and a population, all a sustainable ecology enduring 2,500 years. In the 18th century, disease and Spanish colonization started far-reaching change. Mexican independence transferred land control to white rancheros and not the Tongvas peoples. In short, the 19th and 20th centuries brought about vast economic development with urbanization, cattle grazing, agriculture and deforestation. Vast flowered meadows were converted to invasive European grasses and in suite, new industries replaced the old. The once sustainable ecologies were replaced with concrete, industry, insufficient biodiversity and an increasingly arid landscape, setting the stage for the weather extremes such as wildfires seen in recent decades, and droughts and flooding.
Lewis also describes the replication of this development/degradation process and the loss of rains through Mexico and South America. The recurring pattern is droughts, wildfires, and flooding, which are increasingly attributable to the patterns of land use change discussed above.
Lewis also reports on the fate of a small Tongva Conservancy in LA that was in the path of the Eaton fire. In just a few years, the Tongva removed many invasives and stewarded an old Oak Grove. Although several buildings were burned, the vegetation survived the fire.
These articles are a small sample highlighting that land use change is of equal importance with greenhouse gas emissions. An important remedy is to restore the planet's biodiversity as well as reducing GHG emissions. There is increasing evidence that the water cycle may be just as important as the carbon cycle. There is well established science that to regenerate our ecologies, water and soil play crucial roles. Looking at the land use change factors contributing to California weather extremes help us understand the complexity of our climate predicament.
References:
Haines, CA, (2022) Greenhouse Gases: True, but Not the Whole Truth. Journal of Sustainability Education.
Anatasia Makarieva’s recent blog Warming, Cooling, or We just don’t know?
Alpha Lo - https://climatewaterproject.substack.com/p/taming-the-hot-dry-winds-that-cause Alpha Lo is a researcher, writer, educator and activist focusing on the water cycle and eco-restoration. He is the founder of the Climate Water Project
Rob Lewis (The Climate According to Life), recent blog: Did Southern California once have Summer Rains?
World Resources Institute “Not just carbon” , 2023
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