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May 30, 2024 Feature

Climate Change in Unincorporated California: The Consequences of Limited Regulation for Land Use, Lodging, and Livelihoods in the Wildland Urban Interface

Lauren Ashley Week


Headlines ranking the largest wildfire to recently ravage the Western United States have unfortunately become a familiar feature of the annual news cycle. Throughout the summer and early fall of each year wildfire reporting consumes national media attention as flames simultaneously consume more land, more structures, and more lives. In Northern California in September 2020, a hazy, orange-tinted atmosphere loomed over the bridge spans and skyscrapers of San Francisco. News and social media channels filled their feeds with eerie shots captioned by astonished reactions and apocalyptic predictions. However, for scientists and activists the rust-hued skies symbolized an inevitable reality they had spent decades forewarning: climate change is an urgent crisis, and its consequences are not decades away but affecting cities and communities now.

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Although a massive fire set new records in California in 2021, the previous year is remembered in state history for more than orange skies. The year 2020 included a gigafire—a term coined to describe a blaze burning more than a million acres, on top of other record-breaking and worrisomely unusual statistics. Media outlets, government agencies, and climate experts emphasized the record-setting impacts of the 2020 season. First, the gigafire constituted the first fire of such a scale in the state’s modern history. Moreover, half of the ten largest fires since 1932 occurred that year, burning more than four million acres in total. The California Department of Forestry and Fire Protection (CAL FIRE) spent a staggering 1.23 billion dollars on fire suppression in 2020—its highest expenditure in recent memory and almost triple the fire budget of 2019. Alarmingly, multiple of the year’s wildfires erupted as late as December, illustrating the sad reality that, as a result of climate change, wildfire “season” persists all year. Lastly, with 7,778 structures razed, the year contained five of the most destructive wildfires since official state recordkeeping began.

In August 2020, the LNU Lightning Complex (LNU or Complex), a conglomeration of fires that forced my own family to evacuate from their Northern California home, made headlines as the state’s sixth largest. Although neither the most substantial, as measured by number of acres burned, nor the most destructive regarding number of buildings lost, the Complex serves as a case study for this paper due to its characteristics. Wildfires obviously do not discriminate based on manmade geographic boundaries or classifications; while some regions’ vegetation, terrain, and average weather have historically led to increased wildfire hazards, all locales—especially in the age of climate change—can face fire. Yet, throughout recorded history, wildfires have rarely occurred in urbanized areas. Instead of endangering officially incorporated cities, their flames targeted forests, grasslands, and prairies with natural, wild vegetation—hence the name wildfire. However, in recent years, more and more wildfires have encroached into developed lands. Specifically, blazes threaten the Wildland Urban Interface (WUI). As shown by Figure 1, the Complex intercepted the legally and technically defined WUI. Additionally, of the five largest fires that befell California in 2020, only the LNU directly abutted the boundary between incorporated (i.e., city) and unincorporated (i.e., county) territory.

This paper investigates the environmental consequences of climate change-induced wildfires in the WUI. It specifically examines how the significant overlap between unincorporated areas of California and the WUI creates extensive gaps in law and regulation that affect the natural environment and housing. Part I introduces the concept of the WUI and defines its three subcategories: (a) interface, (b) intermix, and (c) influence zone. Additionally, Part I describes how ever-increasing development in the WUI threatens land, lodging, and lives. Part II provides an overview of several existing legal frameworks meant to regulate climate change, wildfires, and the WUI at the federal, state, and local levels. Given this paper’s focus on the LNU, its examination of local law includes the land use regulations of Solano County—one of the five counties affected by the Complex. Part II also uncovers the gaps undermining these regimes. Finally, Part III offers potential solutions to help overcome the consequences of limited regulation in unincorporated California during the era of climate change. Furthermore, it considers the potential drawbacks of these solutions for a region equally affected by another crisis: access to affordable housing.

I. The Wildland Urban Interface

An understanding of the WUI—an area that predominantly lies just outside the boundaries of existing cities—is required to accurately assess the impact of climate change in unincorporated California. This Part begins by reviewing the current legal and technical definitions of the WUI. Unfortunately, despite concerns surrounding the area’s increasing growth and continuing development, law as it currently exists, at both the federal and state levels, fails to adequately define the WUI. Thus, this Part continues by underscoring the societal and scientific consequences of attempting to ease the affordable housing crisis by building homes within this threatened and precarious land area. This provides needed context to fully capture the importance of the WUI, notwithstanding its limited recognition within federal and state as well as local regulatory schemes. This Part will also highlight the WUI’s intersection with unincorporated, and often underserved and understudied, communities. Ultimately, this geographic overlap results in regulatory gaps that threaten land use, lodging, and livelihoods, as will be illustrated in Part II.

A. Defining the Wildland Urban Interface

The national Healthy Forest Restoration Act (HFRA) offers the principal legal definition of the WUI. The Act incorporates an interagency notice which describes the WUI as an area “where humans and their development meet or intermix with wildland fuel,” making residents particularly susceptible to wildfires and subsequent loss. In California, despite its tumultuous history of wildfires, no state statute explicitly defines the WUI. Solano County’s local code also fails to offer a definition. However, as illustrated by the green shaded areas in Figure 1, CAL FIRE has developed a technical mapping technique to identify what areas constitute the WUI across the state. This technique assesses and conjoins a variety of land use characteristics including: (1) fire hazard severity, (2) vegetation cover, (3) number of unimproved parcels, and (4) housing density. The model relies on but adapts the HFRA definition to incorporate housing density thresholds in concurrence with the National Fire Plan. Thus, in California, while the term “WUI” maintains its focus on the convergence of man-made development and wild vegetation, it also integrates a more refined housing and population density lens.

B. Dividing the Wildland Urban Interface: Subcategories

Both the federal statutory and state technical definitions divide the WUI into three distinct subareas. Given this paper’s focus on California and the LNU, it will use the state’s three WUI subcategories: (a) interface, (b) intermix, and (c) influence zone. CAL FIRE defines the interface as an area of dense housing—ranging from at least one house per twenty acres to more than one house per acre—subject to extreme wildfire hazard due to its proximity to vegetation despite “not [being] dominated by wildland vegetation” within the area itself. To qualify as intermix, an area must (1) have a housing density of at least one house per twenty acres, or if a density of one house per every five acres or more exists, be dominated by wildland vegetation, (2) feature improved parcels only, and, obviously, (3) face moderate, high, or very high fire hazard. Lastly, situated up to one and a half miles away from either an interface- or intermix-designated area, the influence zone contains wildfire susceptible vegetation. Unlike the two former subcategories, no housing density or other requirements apply; however, this does not mean homes do not exist within the influence zone. While a multitude of studies and articles have investigated the WUI, the majority focus on the interface and intermix geographies and not the latter subcategory—the area with the highest overlap with unincorporated county territory as illustrated by Figure 2.

C. Developing the Wildland Urban Interface: Wildfires and Housing

Despite limited statutory recognition of the WUI, the California State Legislature has acknowledged that climate change-induced wildfires pose “catastrophic threats . . . to lives, property, and resources” within this technically defined area. The California Emergency Services Act further warns that “the proliferation of new homes in the [WUI] magnify this risk,” especially for the particularly vulnerable populations “that live in communities that face near-term public safety threats given their location,” i.e., in the difficult-to-reach, scattered structures of unincorporated California. Across the United States, over one-third of all homes have been built in the WUI. Furthermore, development in these fire-prone regions continues to increase. In 2010, researchers classified the WUI as the “fastest growing land use type” in the country. This trend has held over the past decade. A 2022 New York Times article reported that “more Americans than ever are moving to parts of the country more likely to burn.” Between 1990 and 2020, communities have added roughly ten million more homes in the WUI of the American West.

This form of development is particularly pronounced in California. With eleven million people living in a WUI-designated area, the state has the largest population facing an increased fire hazard due to the location of their homes. In total, as of 2022, over five million houses exist in California’s WUI. This equates to thirty-two percent of the state’s housing units. Given these statistics, the state also suffers from more wildfire-caused building destruction than all other states combined. Recent research found that homes located in the interface subcategory experience disproportionate losses; although only two percent of total burned area encompasses the interface, the area bears half of all burnt structures.

Despite the warranted media attention and academic research dedicated to the WUI, no existing analyses consider the potential consequences of climate change and wildfires on housing in the influence zone. Thus, using the LNU as a case study, this paper focuses on this overlooked subcategory. As illustrated by Figure 2, most structures damaged by the Complex were in this zone, not the interface or intermix. That is, the most impacted homes had addresses in unincorporated territory, not within official city boundaries.

II. Existing Legal Frameworks and Their Gaps

As climate change continues to exacerbate wildfires in the Western United States it becomes a question of not if but when WUI-sited homes, especially those within the influence zone, will confront fire. Unfortunately, as this Part will illustrate, existing legal frameworks fail to protect the land area, homes, and communities most at risk, i.e., those in unincorporated jurisdictions. This Part begins with a broad-level overview of American land use and planning institutions. It then turns to specific examples of existing laws aimed at managing construction in the WUI at the federal, state, and local levels. Finally, this Part identifies and analyzes the institutional and regulatory gaps that keep land, lodging, and lives at risk.

A. Understanding Institutional Challenges: The Federalist System

The United States’ federalist system reduces the federal government’s ability to dictate land use patterns. Under federalism, the three national branches and fifty individual states all exist as sovereign entities. The Constitution then grants certain authorities to the federal government and the rest to the sovereign states. Decisions surrounding land use constitute a police power, i.e., an authority not listed in the Constitution and thus reserved for state control.

Yet a majority of state governments do not directly regulate land use. In fact, every American state has adopted a zoning enabling act, which delegates land use and planning authority to local governments. Although municipalities are “creatures of the state,” and not their own sovereigns under federalism, such delegation has consolidated a vast amount of planning power at the local level. California is no exception. This leaves the responsibility of managing the risks associated with developing housing in the WUI to local governments; however, as will be discussed in Part II.D.1., unincorporated areas such as Solano County have done relatively little to confront the wildfire-related challenges faced by communities in the influence zone.

B. Considering Limited Federal Law

Unfortunately, limited federal law meaningfully regulates the WUI as well. This subpart further describes and assesses the HFRA—the sole federal statute to directly regulate the WUI. This subpart then introduces the federal government’s most recent attempt to address climate change: the Inflation Reduction Act (IRA). Both acts offer funding opportunities to at-risk communities; however, both programs also lead to tensions and gaps.

1. Healthy Forest Restoration Act

Although the HFRA provides the primary legal definition of the WUI, it does relatively little to regulate the problem of increasing development near wildlands. An unsuccessful search for terms such as “housing” and “development” (the latter as used to refer to the built environment) within the HFRA reveals the law’s lacking regulatory framework. Community Wildfire Protection Plans (CWPPs), authorized by the HFRA, constitute the most meaningful attempt at protecting the WUI and its communities. CWPPs are stakeholder-driven planning documents aimed at (1) identifying treatments to mitigate hazardous fuel sources and (2) providing recommended strategies to reduce structure ignitability. Once communities complete CWPPs they become eligible for federal funding earmarked for hazardous fuel reduction efforts.

Thus, although the HFRA permits continued construction in the WUI, it does offer proactive financial support to minimize such structures’ wildfire vulnerability. Besides decreasing the physical and emotional damage associated with wildfires by making WUI-sited homes less susceptible to fire in the first place, CWPP-associated funding can also help reduce federal expenditures. As noted by land use law professor Stephen R. Miller, “while [ninety-one] percent of federal appropriations for wildfire management are allocated to protect federal lands, it is increasingly evident that federal funds are being used to protect private homes and other structures ‘adjacent to federal lands,’” i.e., in the WUI. This use creates a dilemma: although the HFRA does not regulate development in the WUI directly—instead local governments retain this authority—the federal government “bears the greatest burden in protecting those developments from wildfire.”

2. Inflation Reduction Act

Although the IRA does not explicitly reference the WUI, it does constitute the “most aggressive action [that the federal government has] taken to confront the climate crisis.” Particularly relevant for this paper, the IRA creates a funding program facilitated by the U.S. Department of Housing and Urban Development (HUD) to provide loans and grants to communities for the purpose of addressing the intersection of affordable housing and climate change issues. Examples include projects that improve energy efficiency, enhance air quality, produce low-emission buildings materials, or address climate resiliency.

Although many researchers attribute access to nature, related recreational amenities, and aesthetic values as primary motivators for increasing development in the WUI, academics also blame the affordable housing crisis for causing environmentally worrisome outer fringe construction, especially in California. As noted by urban planning scholar Karen Chapple, most new housing construction in the state occurs in the periphery of existing urban areas because “that’s where land is cheap.” Furthermore, as evidenced by the example provided in Part II.D.1., the relative lack of land use regulations in unincorporated counties allows for essentially unchecked construction in the WUI. This also makes housing more affordable; in contrast to incorporated cities with restrictive land use regulations and expensive permitting procedures, rural, unincorporated areas offer less burdensome and more cost-effective development options. This creates a disconnect: the areas that allow for the most affordable housing also present the biggest climate risks. This reality limits the potential of the IRA’s funding program.

C. Summarizing State Approaches

Even though California has taken more legislative and regulatory steps to safeguard homes and other resources in the WUI than its Western neighbors, no state-level policy directly limits or prohibits development in the interface, intermix, or influence zones. Instead, the state regulates building materials and requirements via its Building Standards Code, as discussed in this subpart. Another mechanism for regulating the WUI at the state level is the California Environmental Quality Act (CEQA). Unfortunately, as discussed in this subpart, both regulatory schemes fail to fully protect WUI-sited communities.

1. California Building Standards Code

Overall, California has adopted “some of the strictest rules in the country for new homes in high-risk fire areas,” such as the WUI. Legal strategies include state-level building regulations originally adopted in 2008 that require use of fire-resistant materials and defensible space—i.e., buffers between structures and wild vegetation. Additionally, new developments must provide evacuation routes. Such stringent state requirements have had positive results. An analysis of the impact of the 2018 Camp Fire found that most homes built after the implementation of the building codes escaped damage, whereas only eighteen percent of older housing survived. Despite such progress, a major gap persists, as the state building requirements only apply to new construction. Thus, millions of homes remain vulnerable. Considering that over ninety-two percent of housing was built before 2008 in unincorporated Solano County, the state law most likely had limited effect in safeguarding homes during the Complex.

2. California Environmental Quality Act

CEQA—the state’s much more extensive version of the National Environmental Policy Act (NEPA)—also affects development within the WUI. By requiring an analysis of significant environmental impacts of government-approved projects, like housing construction permits, CEQA could potentially limit or at least mitigate further WUI development. Over the past decade, the state has built more housing outside the WUI than within it. However, it is unclear whether this trend is explained by regulatory frameworks like CEQA, the myriad state housing laws passed in recent years, changing attitudes towards wildfire risk, or something else. Moreover, state supreme court case law has significantly limited the effect of CEQA in reviewing and restricting WUI development. In 2015, the court held that “the risks to a new project from the environment are not the kinds of impacts that CEQA covers.” Thus, CEQA analysis cannot include an assessment of fire hazard on new housing, even if built in the WUI. Do other regulatory tools exist for CEQA to meaningfully limit housing construction in the influence zone?

Parallel to the dilemma surrounding federal funding for firefighting that Professor Miller identified, protecting homes in the WUI also overwhelms and burdens CAL FIRE. According to a 2015 audit conducted by the USFS, fighting fires in the WUI costs $1,695 per acre. This staggering expenditure is double the per acre cost of fighting traditional forest fires and is thirty times more expensive than the expense of putting out fires in undeveloped grasslands. As illustrated by Figure 3, due to the amount of homes located in the WUI in California, fire-suppression costs in the state surpass both Oregon and Washington, two other Western states severely threatened by climate change-induced wildfires. Beyond the environmental impact of wildfires, this cost assessment could potentially trigger CEQA. As codified in California Public Resources Code Section 21001, the state legislature passed the environmental review statute to require governmental agencies to consider ecological and economic factors. However, despite this legislative intent, Section 15131 of the CEQA Guidelines—the regulatory complement to the statute—disallows economic effects from being treated as a “significant effect.” Thus, CEQA still falls short.

Figure 3. Fire Suppression Costs Versus Number of Buildings Destroyed for Twenty Most Expensive Fires in Each State

D. Critiquing the Lack of Local Law: Land Use in Unincorporated Solano County

Lastly, this subpart will reveal the largest gap for communities in the influence zone: the limited nature of local land use law in unincorporated areas. Considering this paper’s use of the LNU as a case study, this subpart reviews Solano County’s code. Specifically, it assesses the International Wildland-Urban Interface Code (IWUIC).

1. International Wildland-Urban Interface Code

A search for “wildland urban interface” in the Solano County zoning ordinance yields one result. The only mention of the WUI is the county’s adoption, by reference, of the IWUIC. While the IWUIC is extensive, its regulations parallel the California Building Standards Code, as it revolves around construction standards, such as defensible space and ignition-resistant building materials. The IWUIC also only applies to new construction, creating the same gaps as discussed earlier in Part II.C.1. Nowhere in the Solano County land use regime is development in the WUI restricted. Further, nothing in the existing legal framework—at the federal, state, or local levels—addresses the particular issues and wildfire hazards faced by communities and homes in the influence zone.

III. Summary of Proposed Solutions

With the institutional and regulatory gaps currently plaguing the intersection of the influence zone and unincorporated jurisdictions outlined, this Part now offers potential solutions. First, it discusses how small amendments to existing federal funding programs can better safeguard communities at risk of climate change-induced wildfires. This Part then proposes a more substantial but not unprecedented solution involving state police powers. Finally, this Part discusses the most direct fix: increasing development regulation in Solano County and other unincorporated areas. To conclude, this Part also considers the potential drawbacks of each of these solutions, with special consideration of how new or additional regulations can affect housing supply and affordability.

A. Fixing Funding: Federal Solutions

Both the HFRA and IRA rely on funding schemes to combat the pressing and intersecting issues of climate change, wildfires, and housing. Neither of these regimes directly regulates development in the WUI and likely cannot due to the American system of federalism. However, the federal legislature could amend these programs to indirectly dictate WUI land use patterns. For example, HFRA funding is currently reliant on communities adopting CWPPs. Although CWPPs already have specific requirements—mostly surrounding land management and building standards—the statute could require additional prerequisites for funding, such as having communities incorporate, or at least recommend, potential land use restrictions on WUI development within CWPPs. Similarly, the IRA funding program managed by HUD would benefit from amended statutory language. At present, this loan and grant program only vaguely references “climate resiliency” as a goal. Instead, language specifically encouraging non-WUI development could be adopted.

Unfortunately, these solutions, especially the recommended IRA amendment, conflict with affordable housing goals. As noted above, the HUD funding program aims to address the housing crisis. Any additional requirements could potentially restrict access to much needed grants and loans. Furthermore, communities may want to use funding received from HUD to build in unincorporated areas, i.e., in the WUI, where land is cheap. At the same time, rural areas do not benefit from economies of scale; they often disallow large-scale, multifamily housing developments, which translates to higher per unit construction costs in these areas.

Solano County offers a pertinent example. As evidenced by the county’s zoning map in Figure 4, only two neighborhoods allow dense housing (as demarcated by the deeper red parcels). This limit potentially explains the disparity between the build price of a single family home and an apartment in unincorporated Solano. As documented in the county’s state-mandated Housing Element, the total cost of a new detached home is $328,002. In contrast, each multifamily unit can be completed for $124,949. Ultimately, considering high construction costs, the savings in land prices may be negligible. Either way, unincorporated counties desperately need affordable housing. Solano County, for example, lacks over three hundred homes for lower-income community members. Any additional regulation may impede housing progress for these individuals and families.

Figure 4. Solano County Zoning Map

B. Furthering Control: State Solutions

Although California’s state building requirements have been somewhat successful in diminishing wildfire consequences for structures and homeowners in the WUI, its regulatory regime fails to cover most of California’s housing stock. Instead of only regulating building materials and standards for new construction, the state should pursue legislation that directly controls land use and imposes tighter restrictions on development in fire-prone regions. Although the state has delegated most zoning and land use authority to local governments, the state legislature can also take these police powers back. Given the dire status of the affordable housing crisis, precedent already exists for this solution; California state laws have completely suspended cities’ residential zoning ordinances to spur construction of units. Other state-passed housing laws have similarly infringed and superseded local zoning authority. The state already requires local governments to account for the risk of fire when developing their general plans. Instead of requiring municipalities to simply consider wildfire hazards, why not completely prevent cities and counties from allowing development in interface, intermix, and influence zones?

Conversely, extensive research identifies rising regulatory costs—i.e., building and land use codes—as the culprit behind delayed (and overly expensive) housing, especially in California. According to a report prepared by McKinsey, a shortage of roughly two million homes burdens California’s housing market. If the state absolutely restricts development in the WUI, or even just in the influence zone, can this demand be met? This perceived tension obscures the capability of state-level regulation of the WUI. Overwhelmingly, planners, conservationists, climate change scientists, and even environmental groups responsible for delaying housing projects in the past, argue that infill and density promote ecofriendly lifestyles and afford environmental benefits. Infill, which is new construction in underutilized or vacant urban areas, protects greenfield and open space—that is, the influence zone—by reducing the need to develop such natural land areas. Simultaneously, housing density, especially when coupled with transit-oriented development, minimizes greenhouse gas emissions and further reduces urban sprawl into the WUI. Infill and density also increase the availability of affordable housing. Considering these co-benefits, the goals of safeguarding against wildfire destruction and housing affordability can coexist.

C. Fighting Fire Directly: Local Solutions

Infill and density mean mostly building in incorporated California. Thus, this solution does not protect or promote the interests of unincorporated areas and the existing residents that call them home. While the most obvious solution for counties is to restrict housing construction in the WUI, at the same time, many people choose, or are forced, to live in such areas due to lack of local regulation and the associated savings in housing costs. Despite this, the LNU illustrates the grave consequences of limited regulation in unincorporated California: 363,220 acres burned, 1,491 structures decimated, a further 232 damaged, and eleven people killed or injured. To better safeguard land, lodging, and lives in the era of climate change, direct legal action by unincorporated places in California is necessary. County zoning codes can balance wildfire risk with affordable housing needs by allowing for and promoting denser multifamily housing near city boundaries, i.e., in the interface and intermix areas, while also increasing land use restrictions against construction in the influence zone. The interface—in line with its existing technical definition—should allow for the highest density housing, e.g., apartment complexes. The intermix should focus on less intensive multifamily projects, such as duplexes, triplexes, and accessory dwelling units. While farms that feature housing and other structures will and can continue to exist in rural California, counties should adopt development restrictions that prevent large-scale subdivision development and other single family uses not tied to agriculture in the influence zone.


Although no new records have been set since the 2021 season, climate change-induced megafires still pose risks to California’s land, structures, and communities. The threat of destruction and loss is especially significant for individuals and families living within the intersection of the influence zone and an unincorporated jurisdiction. As shown in Part II, existing federal, state, and local laws fail to fully safeguard rural communities and their property, homes, and livelihoods. At the federal level, funding opportunities still allow for development in the WUI and potentially even incentivize it due to vague climate resiliency standards. Within the state statutory and regulatory context, the commendable California Building Standards Code still leaves many homes unprotected, while state supreme court precedent minimizes the potential of CEQA to limit environmentally worrisome WUI construction. Lastly, the limited nature of local land use and zoning law in unincorporated jurisdictions, as epitomized by Solano County’s ordinances, creates the largest gap: no direct regulation of development in the most vulnerable subarea of the WUI, i.e., the influence zone.

To overcome these gaps, this paper offers three potential solutions. In regard to the HFRA and IRA loan and grant programs, small amendments adding additional requirements for federal funding could help disincentive construction in the most fire-prone regions while still spurring more resistant and resilient development. Due to the dire status of the affordable housing crisis in California, the state legislature has already established a precedent of withdrawing previously delegated local land use powers. Building upon this practice, the state can adopt legislation that imposes tighter restrictions or outright prohibits housing construction in fire-prone zones. Finally, counties across California should consider adopting local land use ordinances that balance housing supply and affordability needs with wildfire risk. One means to achieve this equilibrium is by dictating zoning by WUI subcategory. Counties such as Solano can upzone the interface and intermix. At the same time, unincorporated jurisdictions should adopt laws and policies that inhibit further development of the influence zone. If adopted in a way that still considers the impact of regulation on housing supply and affordability, these solutions can help safeguard California’s most vulnerable land, lodging, and lives.

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    Lauren Ashley Week

    Hawai‘i State Judiciary

    Judicial Law Clerk, Civil and Environmental Court, Hawai‘i State Judiciary; Juris Doctor and Master of Urban and Regional Planning, University of Michigan, 2023; Bachelor of Arts, University of California, Berkeley, 2014.