Climate Change and the Baja California Peninsula: A Baja Working Group Report

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CLIMATE CHANGE and the

BAJA CALIFORNIA PENINSULA A Baja Working Group Report

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CLIMATE CHANGE AND THE BAJA CALIFORNIA PENINSULA A Baja Working Group Report

The goal of this document is to provide an overview of what we know from available downscaled climate knowledge for the Peninsula, where research is needed, and opportunities for working collaboratively to advance climate science and solutions. Suggested citation: Ezcurra, P., Lombardo, K., & Pairis, A. (2021). Climate Change and the Baja California Peninsula: A Baja Working Group Report. Climate Science Alliance.

We would like to thank the many contributors who led Case Study Perspectives, and those who helped review, revise, and improve this report: Rodrigo Beas-Luna, Pamela Castro, Michelle María Early Capistrán, Exequiel Ezcurra, Jeremy Long, Drew Talley, Kristin VanderMolen, and Alexandria Warneke. We would also like to thank the International Community Foundation for helping launch the Baja Working Group, and for co-leading the Climate Resilience Fellowship that helped this vision come to fruition. Special thanks to Erika Rosquillas Escalante and Ulises Pacheco Bardullas for their support in the Spanish translation of this report. Finally, thank you to all of the Baja Working Group for their enduring enthusiasm for working together to strengthen our binational natural and human communities. Design by Diane Terry, Climate Science Alliance Cover photos (from top to bottom): Michael Ready, Alejandro Arias, Michelle María Early Capistrán, Octavio Aburto, Drew Talley


CLIMATE C HANGE AND THE B AJ A CALIFOR NIA P E NINSULA | A B AJ A W ORK IN G G R O U P R E P O R T

TABLE OF CONTENTS Introduction

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The Baja California Peninsula

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About the Climate Science Alliance and the Baja Working Group

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Purpose Statement

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Anthropogenic Climate Change Drivers and Impacts

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Climate Change in the Baja California Peninsula

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Key Takeaways

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Temperature

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Precipitation

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Climate Change in the Pacific Ocean and the Gulf of California

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Sea Surface Temperature and Marine Heatwaves

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Tropical Cyclones

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Coastal Wind, Upwelling, and Fog

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Sea Level Rise

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Ocean Acidification

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Climate Impacts to Natural and Human Communities

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Wildfire Events

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Flora

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Reptiles

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Coasts and Oceans

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Human Communities

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Baja Working Group: Case Study Perspectives

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Conclusions and Next Steps

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Climate Knowledge Gaps and Next Steps

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Science Applications in the Community

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Baja Working Group: Shared Values

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Looking Ahead

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Reference List

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Photo by Alejandro Arias


The Baja California Peninsula

The Baja California Peninsula, as a bioregion, is unique in the world. The geography of the Peninsula and its nearby island archipelagos has created an ecosystem rich in endemic species (Escalante et al., 2007; Riemann & Ezcurra, 2005; Rojas-Soto et al., 2003). The surrounding waters are unparalleled in their biological richness, providing nourishment for the land and its people (Enríquez-Andrade et al., 2005; Lluch-Cota et al., 2010). The Peninsula is characterized by a long backbone of mountains, the Peninsular Ranges, which begin in Alta California and run all the way to the Cape Region. On the Pacific side of these ranges, the region is marked by vast plains like the Magdalena plains, the Vizcaíno plains, the Central Desert Mesas, and the San Quintín Valley. The Baja California Peninsula is made up of three distinct ecoregions: Mediterranean California, the Sonoran Desert, and the Sierra and Plains of El Cabo (Figure 1). Mediterranean California is characterized by mediterranean scrubs and winter rains, and this stretch in Baja California is the southernmost extent of the California Floristic Province. The California Floristic Province is considered one of the world’s top biodiversity hotspots— an area that is both high in endemism and under threat of habitat loss, and is the only instance of the mediterranean biome in all of Mexico (González-Abraham et al., 2015; Myers et al., 2000).

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Farther inland, east of the Sierra de Juarez mountain range, lies the Sonoran Desert. Made up predominantly of xerophilous scrubs, this habitat type begins in the southwest United States, covers the majority of the Peninsula, and extends into the state of Sonora. In general, the key physical climate features of deserts include extreme heat, low and erratic precipitation, and highly variable surface hydrology. And finally, the southernmost ecoregion, the Sierra and Plains of El Cabo is part of the Tropical Dry Forests biome, and is dominated by a seasonally dry tropical deciduous forest. The Baja California Peninsula and its three respective ecoregions has one of the lowest human footprint values in all of Mexico, likely because its unforgiving climate and geography have made it historically inaccessible (González-Abraham et al., 2015). That said, development in the northwest exploded during the 20th Century due to technological advancements, indicating that this region still faces the threat of development and degradation.

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Photo by Michael Ready

INTRODUCTION


INT R O D U C T I O N

Photo by Drew Talley

Figure 1. The three ecoregions of Northwestern Mexico. Data retrieved from The Human Footprint in Mexico Project (González-Abraham et al., 2010).

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About the Climate Science Alliance and Baja Working Group

The Climate Science Alliance (the Alliance) is a network dedicated to safeguarding natural and human communities in the face of a changing climate. The Alliance team works collaboratively to create partnerships, programs, and projects that increase awareness of the impacts of climate change, promote solutions, and facilitate actions. As part of this effort, the Alliance team facilitates boundary-spanning projects created and implemented through working groups of partners who share their skills and expertise to bridge the gap between research and application. One such working group is the Baja Working Group, established by the Alliance in 2019. This working group convenes scientists, resources managers, conservation groups, educators, philanthropists, and other stakeholders from both sides of the US-Mexico border to advance collaborative efforts that build resilience in terrestrial,

marine, and freshwater ecosystems, and in human communities in our shared ecoregion (Figure 2). The Baja Working Group acknowledges the profound connectivity between the Californias (Alta California in the United States and Baja California in Mexico). Through a holistic, ecosystem-based approach to addressing climate change for the cross-border region, this working group aims to collaborate in strengthening connectivity between researchers, communities, and ecosystems. Read more about, and connect with, the Baja Working Group at www.climatesciencealliance.org/bajaworking-group.

Figure 2. Breakdown of the Baja Working Group as of 2021 by the sector that best represents each member’s affiliation (n=122).

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INT R O D U C T I O N

Purpose Statement

Southern California and Baja California are deeply connected in many ways. This trans-border region is connected geologically through the Peninsular Ranges, ecologically through their shared Mediterranean California and Sonoran Desert ecoregions, hydrologically via the California Current, the Colorado River, and various smaller watersheds, as well as economically and socially. Despite this, stark disparities remain in the availability of knowledge around downscaled climate change projections and their impacts. Often, research questions are geographically constrained by political boundaries. This is frequently due to a lack of available data, discrepancies between different datasets that makes them difficult to combine, or due to more research and funding occurring on the US side of the border.

In a 2018 synthesis of current knowledge of the most pressing climate change issues facing the US-Mexico border, the UC-Mexico Initiative’s Environment Working Group emphasized that the solution to these great challenges is to harness cross-border resources. Specifically, the Environmental Working Group recommended coordinated action among binational academic, nonprofit, government, and community volunteer sectors that would both build capacity and facilitate the exchange of information (Aburto-Oropeza et al., 2018).

Photo by Astrid Hsu

The US state of California has invested large amounts of time, research, and policy initiatives to create the California Climate Assessments, but much of the research and publicly available data end at the border. However, the

nature of much of this research lends itself to opportunities to go beyond the political border and embrace the connectivity of the Southern California–Northern Mexico region more broadly. Climate impacts and responses south of the border have direct consequences for Southern California, and as such, excluding the border region and areas south leads to an incomplete view of the state of climate in our ecoregion and limits opportunities to effectively prepare for the future.

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I NT R O DUCT I ON From the perspective of natural ecosystems, the US-Mexico socio-political border is an arbitrary marker, at least when the physical border wall does not get in the way (Flesch et al., 2010; Trouwborst et al., 2016). By sea, the iconic kelp forests of the Pacific extend as far down as the Vizcaíno Peninsula. On land, the Sonoran Desert begins in Southern California and Arizona and continues down into the states of Sonora and Baja California Sur, Mexico. Many of the plants and animals that depend on these ecosystems need to move and/or disperse across this boundary to maintain life history requirements and gene flow. If we are to maintain biodiversity and conserve species and habitats, we must work collectively to connect datasets and analyses when they apply south of the border and expand opportunities to amplify conservation research and actions. Otherwise, we will be left extrapolating and leveraging one-sided information—a practice that is detrimental to local ecosystem management, connectivity, and conservation.

The goal of this document is to provide an overview of what we know from available downscaled climate knowledge for the Peninsula, where research is needed, and opportunities for working collaboratively to advance climate science and solutions.

The role of the Baja Working Group is to put this advice into practice. Through the exchange of knowledge, building of an interdisciplinary network, and collaboration on climate resilience projects, this working group is dedicated to transformative adaptation not just for the cross-border region, but for the Peninsula as a whole, embracing the ecological and social connectivity that intertwines Alta and Baja California. In 2019, the Baja Working Group convened for the first time to discuss priority areas of focus for the Baja California Peninsula. Across the many areas of interest (e.g., species, ecosystems, land management, and human communities), one consistent theme emerged: the need for an assessment of the state of climate change knowledge for the region. This document is our initial step towards addressing that need. It aims to serve as a jumping off point towards understanding and addressing climate change impacts across the Baja California Peninsula to begin identifying priority areas for research and collaboration, and to serve as a foundation for launching collaborative efforts within the Climate Science Alliance Baja Working Group.

Photo by Octavio Aburto

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INT R O D U C T I O N

Anthropogenic Climate Change Drivers and Impacts

Anthropogenic climate change is leading to changes in the median temperature for many regions across the globe, as well as changes in temperature extremes (i.e., the minimum and maximum temperatures experienced in a region). Patterns in annual and seasonal precipitation are also changing in response to an altered climate. Together, these changes are predicted to have cascading impacts, such as altered regional water availability, increased flooding, drought

conditions, and increased stress on natural and human systems. This document focuses primarily on the projected changes in median and extreme temperatures and precipitation patterns for the Baja California Peninsula. Together, these two climate drivers have the most readily available and regionally downscaled projections for the region at this time.

Climate Change Scenarios The Intergovernmental Panel on Climate Change (IPCC) has set out two sets of emissions scenarios for use in projecting future climate changes. The first set is from the 2000 Special Report on Emissions Scenarios, and is referred to as SRES scenarios (Nakićenović & Swart, 2000). These were later superseded in the Fifth IPCC Assessment Report by a new set of scenarios termed Representative Concentration Pathways, or RCPs, which explicitly incorporated both carbon emissions controls as well as integrated assessment models (IPCC, 2013a). Although RCPs are presently the most common projection scenarios used, some sources for climate information in this report utilize SRES scenarios to project climate change for the Baja California Peninsula. For simplicity, we will utilize the terms high, intermediate, and low to describe either set of emissions scenarios. Table 1 below describes the four main RCP scenarios, and their SRES equivalents.

Emissions Scenario Description

Comparable SRES

8.5

High – worst-case scenario

A1 & A2

6.0

Intermediate – emission peak 2080

A1B

4.5

Intermediate – emission peak 2040

B1

2.6

Low – strong mitigation action

RCP Scenarios

Table 1. Emissions description for four different Representative Concentration Pathway (RCP) scenarios, and their closest SRES emissions scenario equivalents.

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I NT R O DUCT I ON

Importance of Regional Climate Information The Baja California Peninsula is not unfamiliar with the impacts of climate change, both on land and in the oceans. As scientists, policymakers, and the public work to understand how these changes will affect the region’s ecosystems and the communities that depend on them, the amount of readily available information at a regional scale will be a determining factor for the region’s adaptive capacity. The global drivers and impacts of climate change are well understood. They include warmer air temperatures, more extreme heat events, changes in precipitation frequency, intensity, and duration including heavy precipitation events punctuated by increased drought, and sea level rise (IPCC, 2013b). That said, it is also understood that these impacts are not uniformly distributed across the globe and will vary both spatially and temporally. Without regionally specific information, climate change projections serve a limited purpose for site-specific planning. For example, in Mexico the normal annual precipitation for the 1981–2010 period was 740 mm (de Anda Sánchez, 2020). However, the range across the country for that period varied between 29 and 4482 mm (Figure 3). To put it another way, the normal annual precipitation for the Baja California Peninsula (considered one hydrological region) was eleven times lower than that of Mexico’s hydrological administrative region XI (Chiapas and Tabasco). This spatial disparity in rainfall leads to differ-

ences in how regions across Mexico are impacted by changes in precipitation frequency or intensity. Drier areas are less adapted to intense rainfall events, but may better withstand certain degrees of drought compared to their tropical counterparts. Precipitation across Mexico varies not only spatially, but also temporally. During El Niño events, the Mexican Pacific northwest experiences increased winter rainfall while the southern tropical Pacific regions tend to increase in aridity. Conversely, La Niña periods create increased summer monsoon rainfall across the tropical south of the country (Caso et al., 2007). These patterns demonstrate how the same weather patterns can bring drastically different climatic conditions to different regions of Mexico at different times. The need for downscaled information does not stop with climate data. Other types of downscaled data, such as land-use data, vegetation change, and urban growth are critical baselines for evaluating potential impacts, such as range shifts for species (e.g., Cavanaugh et al. 2015; Riordan and Rundel 2014). As this document will demonstrate, all of these variations can happen at very small scales (e.g., see section “Extreme Temperatures in Urban Areas”). The more regionally downscaled climate projections and subsequent impacts are, the better the strategies for response to climate change for a region becomes—uncertainties decrease, and research, management, and education becomes more targeted and relevant (e.g., Jennings et al. 2018).

Figure 3. Distribution of the precipitation in Mexico during the period 1981-2010. Image borrowed from “Estadísticas del Agua en México” (CONAGUA, 2016).

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CLIMATE CHANGE IN THE BAJA CALIFORNIA PENINSULA Key Takeaways

Temperature

The Mexicali and Sierra de Guadalupe regions will experience the greatest increases in maximum temperatures. Increases in minimum temperatures will occur mostly along the central region, between south of Sierra de San Pedro Mártir along the western side of the Peninsular Ranges. Three of the four major cities in Baja California are projected to see significant increases in maximum temperatures, posing a risk to the most vulnerable members of these communities.

Photo by Michelle María Early Capistrán

Baja California will experience an overall warming trend across the Peninsula.

Photo by Michael Wall

Precipitation The Baja California Peninsula region is already experiencing conditions of water stress that will worsen over the next decade for demographic reasons, and climate change will only compound this trend.

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Precipitation (continued) Increased evapotranspiration can be expected with increasing temperatures, reducing water availability and soil moisture.

Rainfall in the state of Baja California shows high intra- and inter-annual variability, and decreases in precipitation will be strongest in winter, and will drive up evapotranspiration, decreasing moisture in the soils. The total area of very severe drought zones may increase for the state of Baja California Sur in the future.

Photo by Michael Wall

The Baja California Peninsula will observe a general decrease in average annual precipitation by mid-century, with a few exceptions.

Impacts to the Pacific Coast and Gulf of California The Pacific waters of the Peninsula will experience an increase in sea surface temperature between 1.0°C and 4.0°C. Marine heatwaves, particularly along the Pacific coast of the Peninsula, may become more frequent and more intense, negatively impacting the region’s kelp forest ecosystems. Data of cyclone origin in the northeast Pacific shows a significant shift in latitude for the past decade, and during warmer water cycles, cyclones exhibited higher intensity and also traveled farther.

Overall, there is limited local data on sea level rise for the Peninsula, and what assessments do exist are focused on urban regions, showing that the Pacific coast may be at greater risk compared to the Gulf coast. Overall, there is limited available information on climate change projections at regional scales for the Baja California Peninsula and its surrounding waters, and that which is available is not current.

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Photo by Rodrigo Beas-Luna

The Pacific coast of Baja California will experience an overall increase in upwelling.


CLIMATE CHANGE IN THE B AJ A CALIFOR NIA P EN I N S U L A

Temperature

Since 1970, all of Mexico has experienced anomalous warming caused by climate change, a trend that is projected to continue (Martínez-Austria, 2020). And although annual average temperatures are expected to increase across Mexico, the largest increases are expected to occur in the Mexican northwest (Magaña et al., 2012). In general, Baja California will experience an overall warming trend across the Peninsula. Ashraf Vaghefi et al. (2017) analyzed changes in temperature and precipitation patterns for the Peninsula under a high emissions scenario outcome by mid-century. Their findings show that temperature extremes will shift towards a warmer state overall. The trends for maximum temperature follow that of average annual temperature, with the majority of the Baja California Peninsula experiencing increases in maximum temperature between 2.0 and 2.5°C. Three exceptions to this are the narrow coastal strip just south of the US-Mexico border and the southern half of Baja California Sur, where the increase in maximum temperature will be slightly less (1–2°C), and the Mexicali and Sierra de Guadalupe regions, where increase in maximum temperatures will be greater (2.5– 3.0°C).

Baja California Since 1975, northwestern Mexico, including the state of Baja California, has seen significant increases of land surface temperature likely associated with greenhouse gas emissions (Karoly & Wu, 2005). These increases are expected to continue into the future. Under a high emissions scenario, average temperatures in the region may increase by over 1.5°C after 2040, and up to 5°C by 2100. Even in a low emissions scenario, projected changes still exceed 2°C by 2100 (Cavazos & Arriaga-Ramírez, 2012). Under a high emissions scenario, a 1°C increase in average temperature will also bring a 1 to 3°C increase in temperature extremes (SPA, 2012). Across scenarios, there is a noticeable divergence in temperature increases after 2050, where temperatures in the high emissions scenario rise dramatically, up to almost 5°C (Figure 4).

Similarly, with concerns to minimum temperatures, Ashraf Vaghefi et al. (2017) found an overall warming trend across the Peninsula, with minimum temperatures increasing by 1.0 to 2.5°C, mostly along the central region between south of Sierra de San Pedro Mártir along the western side of the Peninsular Ranges.

Figure 4. Projected temperature increases for Baja California by 2100 under a high (A1) and an intermediate (B1) emissions scenario. Borrowed from (SPA, 2012).

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CL I M AT E CH A N G E IN THE BAJ A C ALIFO RNIA P E NINSULA

Baja California Sur

Photo by Michael Wall

Temperature across the state of Baja California Sur will vary. The Gulf of California creates warmer conditions along the east coast of the state, while the California current creates cooler temperatures along the state’s western side. Historically, the maximum temperatures for the plains ranges between 40 and 44°C, while the minimum temperature ranges between 14 and 16°C (Ivanova & Gámez, 2013), although temperature extremes can reach freezing temperatures around the state’s mountain areas such as the Sierra de La Laguna or La Giganta. By the end of the current century, the mean air temperature for the state is projected to increase by around 2°C (Herrera Cervantes & Lluch-Cota, 2013).

Extreme Temperatures in Urban Areas García-Cueto et al. (2014) modeled temperature extremes under a high and a low emission scenario for four major cities in Baja California: Mexicali, Tecate, Tijuana, and Ensenada. Tables 2 and 3 summarize their main findings, including that while Mexicali has historically experienced the warmest maximum temperatures, Tecate will likely experience the largest increase in temperature over the next century. Their models also show that both Mexicali and Ensendada will experience significant warming of minimum temperatures by the end of the century (Table 3).

Maximum Temperature

Minimum Temperature

Mexicali

52.0 °C

-7.0 °C

Tecate

47.0 °C

-6.0 °C

Tijuana

45.0 °C

0.0 °C

Ensenada

43.5 °C

0.5 °C

City

Table 2. Extreme minimum and maximum temperatures for the four largest cities in the state of Baja California between 1950 and 2010. Adapted from (García-Cueto et al., 2014).

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CLIMATE CHANGE IN THE B AJ A CALIFOR NIA P EN I N S U L A

Maximum Temperature

Minimum Temperature

Mexicali

+2.5 °C

+11.8 °C

Tecate

+7.3 °C

Tijuana

+3.9 °C

+5.8 °C

City

Ensenada

Photo by Barbara Zandoval

Table 3. Estimated change in extreme minimum and maximum temperatures by 2110 with a 95% probability of being exceeded / not being exceeded, respectively, for the four largest cities in the state of Baja California. Adapted from (García-Cueto et al., 2014).

Changes in temperature extremes are particularly hard on both people and wildlife resulting in a myriad of impacts including, but not limited to, social, ecological, economic, and physiological stress. As three of the four major cities in Baja California are projected to see significant increases in maximum temperatures, this poses a risk to all communities with increased potential to impact those most vulnerable. Although most available research focuses on urban areas, some inferences can be made regarding the impacts to different ecosystems that surround these cities. Tijuana and Ensenada, for example, are found in the Mediterranean California ecoregion. Ensenada, in particular, appears to be sheltered from some of the most extreme increases in maximum temperatures—a sign that surrounding ecosystems may find refuge from extreme heat compared to those nearer to Tijuana.

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CL I M AT E CH A N G E IN THE BAJ A C ALIFO RNIA P E NINSULA

Precipitation

Photo by Drew Talley

As previously mentioned, the mean annual precipitation across Mexico is not evenly distributed across the country. In fact, most northern states, including those of the Baja region, receive less than 250 mm of precipitation per year (Raynal-Villasenor, 2020). Regardless of the potential impacts of climate change on water availability, the Baja California Peninsula region is already experiencing conditions of water stress that will worsen over the next decade, and climate change will only accelerate and compound this trend (MartínezAustria, 2020). Reductions in precipitation will lead to increased evapotranspiration, reducing water availability and soil moisture (de Anda Sánchez, 2020; Magaña et al., 2012). In comparison to historic patterns, under a high emissions scenario, Baja California will observe a general decrease in average annual precipitation by mid-century, with a few exceptions. This decrease will be most pronounced for the Sierra de San Pedro Mártir going east towards the state of Sonora, and for the entire southern half of the Peninsula, where precipitation may decline between 10-75% (Ashraf Vaghefi et al., 2017).

Baja California

Baja California experiences its greatest rainfall during winter months. However, the eastern portion of the state occasionally receives summer monsoon rains. In conjunction with temperature increases, under a high emissions scenario, the state of Baja California will also experience an up to 15% decrease in annual precipitation after 2030. By 2100, this scenario shows a decrease of 35% (SPA, 2012).

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Photo by Sula Vanderplank

For the State of Baja California, there is a projected winter and spring decline in precipitation of 15% after 2040 under a high emissions scenario. According to this research, the last two decades of this century will see a projected decrease in precipitation of 30%. In contrast, during the dry summer, Baja California may experience a small increase in precipitation of around 5% (Cavazos & Arriaga-Ramírez, 2012).

This rainfall pattern, however, shows high intra- and inter-annual variability. The projected decrease in precipitation will be strongest in winter, and will drive up evapotranspiration, decreasing moisture in the soils.

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CLIMATE CHANGE IN THE B AJ A CALIFOR NIA P EN I N S U L A

Baja California Sur Baja California Sur has a typical desert climate and is one of the most arid states in Mexico, with a low mean annual precipitation of around 180 mm per year (Ivanova & Gámez, 2013). This precipitation is not evenly distributed across space and time. Rainfall occurs predominantly in late summer and fall due to the occurrence of tropical cyclones, and the east coast receives half of the precipitation of the west coast of the state. Baja California Sur receives between 10 to 80% of its total annual rainfall from tropical cyclones (Figure 5). Although tropical cyclones contribute significantly to seasonal precipitation, they are rarely considered in seasonal climate forecasting (de Anda Sánchez, 2020).

Photo by Michael Wall

Climate change projections for the state predict a slight seasonal increase in rainfall during the summer-fall. Due to its naturally arid climate, Baja California Sur already demonstrates severe to extremely severe drought conditions. Modeling suggests that the very severe drought zones will increase in area in the future. Additionally, less frequent and more intense rainfall will lead to increased evapotranspiration from runoff towards the oceans (Ivanova & Gámez, 2013).

Figure 5. Mean contribution of tropical cyclones to a region’s mean annual precipitation for the period 1998-2013. Image borrowed from (Raynal-Villasenor, 2020).

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The narrow Baja California Peninsula stands between the Pacific Ocean on its west coast, and the Gulf of California to the east. Thus, the Peninsula is strongly influenced by marine conditions, and changes in sea surface temperatures, sea level, storm intensity and frequency, and ocean acidity threaten this delicate relationship. The health of the waters in this region are critically linked to the health of natural and human communities on land. The Pacific coast of the Baja California Peninsula plays an important role in the region’s eco-tourism and fishing industries. It is home to the Vizcaíno Bay—one of the largest bays in the Pacific—an area rich in marine life. A UNESCO world heritage site, Vizcaíno Bay serves as a breeding ground for seals and sea lions, whale sanctuary for the migratory gray whale, and as a shark nursery habitat (Oñate-González et al., 2017). Wetlands along the Pacific coast of the Peninsula are critical overwintering sites for birds, while the warm waters bring migratory Pacific gray whales who mate and calve in the San Ignacio Lagoon every winter. Many small-scale fishing communities thrive off the rich waters of the Pacific coast of the Peninsula.

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On the other side, the Gulf of California plays an equally vital part of the region’s economy and ecology. In addition to contributing up to 40% of total national marine catch for Mexico, the Gulf is also home to thriving local small-scale fisheries, which contribute significantly to the region’s subsistence and social identity (LluchCota et al., 2010). In terms of ecological value, the Gulf of California is one of the most productive and diverse marine ecosystems in the world, with a high level of endemism due in part to its complex geography and network of over 800 islands that create isolated habitats throughout the Gulf (Enríquez-Andrade et al., 2005). The coastal regions of Baja are as diverse as the oceans, and include mangroves, seagrass meadows, rocky and sandy beaches, rocky and coral reefs, bays, lagoons, coves, and estuaries (S. C. D. Castro et al., 2013). A changing climate, and warming ocean temperatures in particular, threatens to disrupt this ecosystem and the communities that depend on it. Anomalous warming in the Gulf has already been linked to declines to industrial fish catches and the reproductive success of seabirds—a proxy for overall ocean health (Lluch-Cota et al., 2010; Velarde et al., 2019).

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Photo by Michelle María Early Capistrán

CLIMATE CHANGE IN THE PACIFIC OCEAN AND THE GULF OF CALIFORNIA


C LIMATE C HANGE IN THE PACIFIC OCE AN AND THE GULF OF C A L I F O R N I A

Sea Surface Temperature and Marine Heatwaves

Sea surface temperature (SST) varies greatly between the Pacific coast and the Gulf coast of the Baja California Peninsula, with the Gulf seeing sustained higher temperatures, particularly in the spring and summer (A. T. Castro & Rodríguez, 2013).

Projected increases in sea surface temperature for the region, particularly in the months of October and November, favor the future intensification of tropical cyclones, and could also extend their season. This could be particularly troublesome for vulnerable areas with low recurrence intervals, such as Los Cabo and La Paz.

Photo by Drew Talley

Climate change projections show that by mid-century, sea surface temperatures will increase globally. The waters surrounding the Baja California Peninsula are no exception. Under an intermediate emissions scenario, the Pacific waters of the Peninsula will experience an increase in SST between 1 and 2°C. Under a high emissions scenario, this increase would be approximately twice that, between 1 and 4°C (Arellano & Rivas, 2019). In a report focused on the waters surrounding the state of Baja California Sur, Herrera Cervantes & Lluch-Cota (2013) found that sea surface temperature may increase by 2°C by 2100.

Marine heatwaves (MHWs), or periods of anomalous warm SSTs, are of additional concern—particularly along the Pacific coast of the Peninsula, which has experienced multiple heatwave events in the last decade. Although they are a naturally occurring phenomenon, evidence suggests that climate change is leading to more frequent and more intense MHWs (Fumo et al., 2020).

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CL I M AT E CH A N GE IN THE PAC IFIC O C EAN AND THE GULF OF CALIFOR NIA

Tropical Cyclones

Tropical cyclones are the primary source of precipitation for the state of Baja California Sur, and contribute to the recharging of the region’s aquifers. In a report on trends and potential effects of tropical cyclones, Vadillo & Vadillo (2013) found that data of cyclone origin in the northeast Pacific shows a significant shift in latitude for the past decade when compared to the 1970s and 1980s. They also observed that during positive Pacific Decadal Oscillation cycles (i.e., warmer waters), cyclones exhibited higher intensity and also traveled farther. Vadillo & Vadillo (2013) also found that the regions most vulnerable to tropical cyclones, based on their respec-

tive repeat intervals (in years), are the southernmost end of the Peninsula and the region near the town of Santa Rosalía in the Gulf of California (Figure 6). The weather events with the shortest repeat intervals (i.e., the ones that will occur with most frequency) are tropical depressions, tropical storms, and category 1 hurricanes. The projected extended season, combined with the intensification of tropical cyclones, could be particularly damaging for vulnerable areas with low recurrence intervals, such as Los Cabo and La Paz, but also has the potential to bring more precipitation to the region, which presently has an overextended water supply.

Figure 6. Each map shows the recurrence interval (in years) of tropical cyclones across the Baja California Sur region from tropical depressions (top left) to category 4 hurricanes (bottom right). Adapted from (Vadillo & Vadillo, 2013).

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C LIMATE C HANGE IN THE PACIFIC OCE AN AND THE GULF OF C A L I F O R N I A

Coastal Wind, Upwelling, and Fog

The west coast of the Baja California Peninsula contains the southernmost extent of the California Current System, creating a strong eastern boundary current along the coastline. These currents are responsible for the process of upwelling, by which cold, nutrient-rich waters come up to the surface, creating highly productive coastal environments. To assess how climate change would impact upwelling along the Pacific side of the Baja California Peninsula, Arellano & Rivas (2019) compared the dampening impact of increasing sea surface temperatures with the amplifying impacts of intensification of alongshore winds in two future climate change scenarios, RCP6.0 (intermediate) and RCP8.5 (high). What they found was that, by mid-century, the region would experience an overall increase in chlorophyll-a concentration—a proxy for increased upwelling. This occurred in both scenarios, but was stronger in the high emissions scenario, and indicates that the effect from offshore winds would counteract the effects from temperature stratification. The impact, however, will be lower during summer, when sea surface temperatures are highest.

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Photo by Drew Talley

The coastal regions of mediterranean climates are defined by the presence of an atmospheric “marine layer” along the coast, formed by coastal low clouds and fog, which help reduce air temperature and provide additional moisture. There is limited regional research available on the status of coastal low clouds and fog for Baja California, how climate change may impact it, or how it may help buffer against climate impacts (Jennings et al., 2018).

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CL I M AT E CH A N GE IN THE PAC IFIC O C EAN AND THE GULF OF CALIFOR NIA

Sea Level Rise

Sea levels are rising globally and this, assuming no adaptive measures are taken, will lead to a range of impacts including coastal flooding and erosion that will be magnified by more intense storm events and storm surge. Coastal erosion (particularly in regions below 2 m in elevation), will submerge existing wetlands, estuaries, and human communities, resulting in impacts to infrastructure, people, ecosystems, and economies.

Photo by Michelle María Early Capistrán

The rate and extent of these impacts, however, is not uniform across the globe. As with other climate drivers, regionally specific data on sea level rise (SLR) is needed to improve research efforts and local management of the

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coastal areas. Herguera & Ortiz (2009) have highlighted the limited local data on sea level rise around Baja California. Although the available data are too limited to test statistical significance, they found a positive trend of sea level increasing by ~2 mm per year for the last few years, matching the rate detected for nearby San Diego, California. One regional sea level rise report for the northern state of Baja California assessed possible vulnerability to sea level rise for different coastal areas of the state based on a 1 m and a 2 m sea level rise scenario. Table 4 below summarizes some of those projected impacts for key areas of the state (see section 2.5.5 of SPA (2012) for a comprehensive description of areas and impacts). These impacts are for a median rise in sea level, but this range can vary by up to 1.5 m daily depending on tides, and even double during climatic events such as storms or hurricanes (SPA, 2012). It is worth noting that for both the Guerrero Negro and Colorado River Delta regions, the 1 m and 2 m SLR scenarios are identical—an unlikely result considering these areas are geographically flat expanses, and would be expected to be highly sensitive to flooding. This highlights the need for further research that can make more detailed projections. Another regional sea-level rise report for Baja California Sur focused on vulnerability to urban regions, and found that due to flatter geography, the Pacific coast is at greater risk compared to the Gulf coast which has more pronounced relief (S. C. D. Castro et al., 2013). This study, however, assessed vulnerability based primarily on human-centered factors (e.g., population, infrastructure, tourism) and less so on ecological factors, only taking into account designated protected areas. Future work could focus on conducting these same downscaled analyses with other ecological factors included.

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C LIMATE C HANGE IN THE PACIFIC OCE AN AND THE GULF OF C A L I F O R N I A

1m sea level rise

2m sea level rise

Tijuana and Rosarito Beaches

Inundation of 1/5 to 1/3 of the existing beach

Inundation of 1/3 to 2/3 of the existing beach

Mission Beaches

Inundation and erosion of 1/3 to 2/3 of the beach

Inundation and erosion of 2/3 or more of the beach

Port of Ensenada

145,000-162,000 m2 lost to flooding

231,000-282,000 m2 lost to flooding

Ensenada Beaches

155,000-175,000 m2 lost to flooding. Erosion could lead to loss of protective dunes

Accelerated loss of protective dunes

San Quintín Lagoon

Could expand by almost 50%, reaching a submerged area nearing 42 km2

Could expand by an additional 8 km2

Guerrero Negro-Ojo de Liebre Lagoon Complex

Extension of area by a factor of 3 to 4

Extension of area by a factor of 3 to 4

Los Angeles Bay

Loss of stretches of beach due to permanent flooding

Loss of stretches of beach due to permanent flooding

Colorado River Delta

Significant flooding of the delta, around 700 km2, with likely saltwater intrusion to subterranean aquifers

Significant flooding of the delta, around 700 km2, with likely saltwater intrusion to subterranean aquifers

Region PACIFIC COAST

GULF OF CALIFORNIA

Table 4. Impacts to coastal regions of Baja California under 1 and 2m sea level rise scenarios. Adapted from (SPA, 2012).

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CL I M AT E CH A N GE IN THE PAC IFIC O C EAN AND THE GULF OF CALIFOR NIA

Ocean Acidification

ocean acidification both along the Pacific coast of Baja California and the Gulf of California is needed. Given the numerous emerging ocean acidification studies on the pacific coast of the US, there is a strong foundational baseline of information which should make it easier to expand and build on understanding of impacts south of the border.

Photo by Octavio Aburto

Excess carbon dioxide in the ocean, taken up from the atmosphere, has led to a decrease of 0.1 units in the pH of the ocean, and could continue to decrease pH by 0.4 units by the end of this century. In Mexico, studies of carbonate systems are rare. One study for the north Pacific indicates that the depth of corrosive water for calcium carbonate is decreasing at a rate of 1m per year (SPA, 2012). More information on

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Photo by Octavio Aburto

CLIMATE IMPACTS TO NATURAL AND HUMAN COMMUNITIES The climatic drivers described above will have innumerable impacts on natural and human communities in the region. Temperature increases, more variability in extreme events, prolonged drought, among others, will alter ecosystems and their functions in myriad ways. Below, we describe a few examples of how these drivers will impact people and places, the potential consequences of those impacts, and highlight areas for future research.

Wildfire Events

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Photo by Juan Carlos Velázquez Padilla

The Baja California Peninsula is a wildfire hotspot, particularly along the mediterranean shrubland of the upper peninsula (Zúñiga-Vásquez et al., 2017). The Baja California forests, specifically the Sierra San Pedro Mártir in Ensenada, are uniquely pristine and have been proposed as reference ecosystems for restoration and management of other similar forests. Within this ecosystem, fire suppression policies are causing increases in forest fuels and are believed to be the cause of recent increases in high severity burn areas (Rivera-Huerta et al., 2016). How climate change and associated increased heat and drought may impact wildfires in Baja California is an area ripe for future research.

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CL I M AT E I M PA CT S TO NATU RAL AND HU MAN COMMUNITIE S

The Baja California Peninsula is home to ~10% of Mexico’s cacti, and about three quarters of those are endemic to the region (Benavides et al., 2021). In an assessment of climate change impacts on the distribution of endemic cacti of the Baja California Peninsula, Benavides et al. (2021) found that, under various migration scenarios, many currently threatened species with a tropical affinity and globose growth may end up as “winners”, while non-threatened species of arid and mediterranean systems come out “losing.” In a more conservative, no migration scenario, nearly 20% of the endemic cacti of the region are expected to lose over 50% of their existing distribution range. Mangrove ecosystems may also come out as winners in these scenarios. Decreases in minimum temperatures removes physiological barriers to northward migration of mangrove populations, and data from the Atlantic coast suggests coastal warming will allow various North American mangrove species to migrate over 100 km northward (Cavanaugh et al., 2014, 2015). This phenomenon, however, has not been studied in the unique desert ecosystem of Baja California, and thus the same may not be true for mangrove in the Peninsula. Additionally, sea level rise rates may impact mangroves’ ability to adapt to changing climates, and the negative effects of this are poorly understood. California sage scrub, a vegetation type that begins in Alta California and whose southern extent is the northern Pacific region of Baja California, could experience range contraction due to projected climate change—though this result is highly dependent on dispersal assumptions (Riordan & Rundel, 2014). As warmer, drier conditions cause mediterranean-type climate to contract, the coastal sage scrub of Baja California may become threatened, an effect compounded by increased landuse change. Contraction of sage scrub will also have an impact on wildlife connectivity and movement. Many mammal and bird species rely on intact vegetation corridors for life history requirements and gene flow (Stallcup et al., 2015).

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Photo by Michael Wall

Flora

Reptiles The desert ecosystem of Baja California makes it a key habitat zone for many reptile species. The California-Mexico biogeographic region is expected to lose 14% of its reptile species, some endemic, within the next 50 years (Aburto-Oropeza et al., 2018). A study of Mexican lizards suggests that “lizards have already crossed a threshold for extinctions caused by climate change” (Sinervo et al., 2010). More detailed studies of risk to local populations could allow for targeted management.

Coasts and Oceans The possible increase in coastal upwelling along the Pacific coast of the Peninsula alleviates one potential threat to kelp forest ecosystems (see previous section, “Coastal Wind, Upwelling, and Fog”), but there are many other climatic factors to consider. Marine heatwaves, for example, have negative effects on the kelp forest ecosystems of Baja California—the southernmost extent of Pacific kelp forests—and cause shifts in species distributions (Arafeh-Dalmau et al., 2019; Lonhart et al., 2019). In general, there is more available information on climate projections and impacts for the Pacific coast waters compared to the Gulf.

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CLIMATE IMPACTS TO NATUR AL AND HUMAN CO M M U N I T I ES An analysis of susceptibility of different fish species in Baja California Sur to shifts in temperature showed that goby family (Gobiidae) is most likely to be impacted, followed by blennies (Chaenopsidae) and croakers (Sciaenidae) (Reyes-Bonilla et al., 2013). Reyes-Bonilla et al. (2013) also found that an increase in sea surface temperature of 2°C could put 50% or more of the resident fish species of Cabo Pulmo and La Paz under thermal stress. Meanwhile, the Pacific regions of Bahía Magdalena and Punta Eugenia would be in the thermal range for these traditionally southern Gulf species. Similar thermal stress would be felt for marine invertebrate species, particularly around Cabo Pulmo, where a 2°C increase in sea surface temperature would put over 80% of species under thermal stress. This same study found that fish species vulnerability to thermal stress around Baja California Sur is much greater in the Gulf coast than the Pacific coast.

Photo by Michael Ready

Species on the coasts, such as the northern elephant seal (Mirounga angustirostris) are also feeling the impacts of both warming sea and land temperatures. Northern elephant seal colonies in Baja California have been declining for over three decades, and as they are protected and relatively unthreatened, it is hypothesized that this decline is most likely due to increasing

temperatures and more exposure to heat stress leading to a shrinking of their natural range (García-Aguilar et al., 2018). In the Gulf of California, the Pacific sardine (Sardinops sagax) is an essential fishery species, contributing to well over half of total catch for the region (Arreguín-Sánchez et al., 2017). A population that is highly temperature-driven, the Pacific sardine is at risk of decreased distribution under even the most conservative warming scenarios as early as 2021, and may experience an over 95% habitat reduction under worse scenarios (PetatánRamírez et al., 2019). There are cascading implications from the loss of sardines, a species foundational in the food web, and for its ecosystem services (e.g., tourism from predator populations like dolphins). This effect has already been observed during past crashes in populations (e.g., Velarde et al., 2004).

Human Communities Baja California has various large metropolitan areas, but also many smaller human communities both along the coast and into the mountains. People across the region will be impacted by changing climates in various ways. For example, water availability will be impacted as changes in temperature and precipitation directly impact groundwater availability having cascading effects that lead to more extreme air temperatures, and drought impacts to agriculture or sea surface temperatures impacts to fisheries. No two urban or rural communities will feel the effects of a changing climate in the same way. It is critical that strategies to address climate change impacts be created in consultation with communities directly. Effective and implementable solutions are dependent on engaging and learning from the people who live and work in these places. It is critical that activities to respond to climate related impacts are based on the expertise and experiences of local community members to ensure their perspectives, local knowledge, and vision is incorporated into resilience planning and long term stewardship of strategies and actions.

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CL I M AT E I M PA CT S TO NATU RAL AND HU MAN COMMUNITIE S

Baja Working Group: Case Study Perspectives The Baja Working Group represents a diversity of disciplines and perspectives from both sides of the border. As such, members contributed individual perspective pieces on their core area of expertise and weighed in on how climate change may impact their work, and what the key needs are to address these impacts. These perspectives cover a variety of topical areas (e.g., sea turtles, extreme heat impacts to human communities, mangroves, intertidal systems, and more), and demonstrate the range of expertise our group represents, as well as many areas ripe for collaboration and future work. You can read all of these perspectives on our website by visiting www.climatesciencealliance.org/2021-baja-report.

Anthropogenic impacts on marine subsidies to coastal ecosystems

Baja California Wetlands

Climate change mitigation and adaptation actions in the Sierra de San Pedro Mártir

East Pacific green turtle (C. mydas) population dynamics in the context of climate change

From Soil to Sky: Monitoring mangroves in a changing climate

Identifying opportunities and challenges for protecting against extreme heat in Southern California-Baja California border communities

MexCal: Monitoring and enhancing the resilience of temperate social-ecological systems

Monitoring ecological dynamics and climate change impacts in the rocky intertidal of the Californias

Spatial Subsidy in Insular Systems

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CONCLUSIONS AND NEXT STEPS Climate Knowledge Gaps and Next Steps

Based on the available information on various climate change projections for the Baja California Peninsular region, we conclude three high priority areas that merit immediate actions. First, downscaled information overall is quite limited across the region, most notably around wildfires, coastal fog, sea level rise, and ocean acidification. Second, the information that is available is outdated, sometimes using data over a decade old. And third, as is repeatedly pointed out in the Case Study Perspectives, long-term monitoring is another critical missing component. Long-term datasets can complement the existing shorter-term research to create baselines, identify refugia, and adapt management plans to changing needs. Making progress on these fronts requires incentives, and cross-boundary collaboration, as the data and know-how to do this work already exists.

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CON C LUSI ON S A N D NEXT STEPS

Science Applications in the Community

Photo by Drew Talley

As a working group that includes practitioners, educators, artists, and community members with a passion for science dissemination and for the conservation of communities and of natural areas, a key part of our efforts includes looking beyond the research. Climate change impacts need to be well understood not only by scientists, but also by the larger community. With every project we undertake, we ask, how does this information support communities and outreach efforts around climate education? Education and community outreach efforts should be informed by up-to-date and locally relevant science. That science needs to be accessible in a way that allows for community involvement in the advancement of climate adaptation.

Case Study: Climate Kids Mexico

Photo by Martha Aidé Escalante Garcia

Part of the community-building efforts of the Climate Science Alliance, Climate Kids is a series of community-level collaborative projects that provide youth education on climate change through science activities, storytelling, and art. Each Climate Kids project brings together local artists, scientists, educators, and storytellers to engage students of all socioeconomic levels and inspire them to become environmental stewards. One such project is Climate Kids - Mexico.

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Climate Kids - Mexico is a collaborative partnership that began with Baja Working Group member Profesora Aidé Escalante piloting a unique approach to training high school students to deliver the Climate Kids program in elementary and middle school classes in Tijuana. The program has since expanded, with much support from Working Group member Anna Lucia López Avedoy, to additional schools and partner programs across northern Baja and is having a positive impact in the community through its environmental stewardship activities, workshops, and outreach.

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CONCLUSIONS AND N EX T S T EP S

Baja Working Group: Shared Values

The following four tenets were identified as focus areas for the Baja Working Group that represent our shared values. These tenets will help us frame projects for the working group, and ensure we are working towards established goals and leveraging existing projects and partners to complement efforts. The Baja Working Group is action-oriented, and shared collaborations going forward will be informed by these tenets.

1. Research priorities a. Identify both short- and long-term research needs for the Baja California Peninsular region, and surrounding waters b.

Identify opportunities to advance collaborative research efforts

2. Community engagement a. Connect regionally specific science and scientists to youth and community programming b.

Promote youth engagement in science-based projects, internships, mentorship opportunities

3. Information sharing a. Increase visibility of the working group members and their projects related to climate change adaptation science and solutions b.

Promote relevant organizations and communicate research findings and projects within and outside the working group

4. Binational cooperation a. Convene to maintain and build collaborative and cooperative partnerships b.

Seek funding for collaborative projects associated with the key tenets

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CON C LUSI ON S A N D NEXT STEPS

Looking Ahead

collaboratively to advance climate science and solutions for the region. If you are interested in contributing additional information, a case study perspective, or joining the Baja Working Group, we are an ever-growing collaborative that is always open to new voices and ideas. Contact us at info@climatesciencealliance.org to get involved.

Photo courtesy of A La Natouraleza

This report is meant to be a snapshot of existing publicly available climate information specific to the Baja California Peninsula. It is our hope that in the future we can provide updated versions, as our understanding of climate change impacts and solutions unfold. This was a needed first step that has truly highlighted the vast information gap when it comes to regional climate impacts for this region of Mexico. That said, it also highlights a profound opportunity to work

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Reference List

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