San Diego–Tijuana is an international transborder agglomeration, straddling the border of the adjacent North American coastal cities of San Diego, California, United States, and Tijuana, Baja California, Mexico. The 2020 population of the region was 5,456,577, making it the largest bi-national conurbation shared between the United States and Mexico, and the second-largest shared between the US and another country. The conurbation consists of San Diego County, (2020 population 3,298,634) in the United States and the municipalities of Tijuana (2020 pop. 1,922,523), Rosarito Beach (126,980), and Tecate (108,440) in Mexico. It is the third-most populous region in the California–Baja California region, smaller only than the metropolitan areas of Greater Los Angeles and the San Francisco Bay Area.
San Diego–Tijuana traces its European roots to 1542, when the land was explored by Portuguese explorers on behalf of the Spanish Empire. In 1601, it was mandated by the Spanish viceroy in Mexico City that safe ports be found, one of which would be San Diego Bay, for ships of the Manila galleon. During this mission, explorer Sebastián Vizcaíno was also told to map the California coast in great detail, leading to the further exploration of the modern-day site of San Diego–Tijuana.
The metropolitan region is host to 13 consulates for several countries. Over fifty million people cross the border each year between San Diego and Tijuana; it is the busiest land-border crossing in the Western Hemisphere. Since the implementation of the North American Free Trade Agreement (NAFTA) in 1994, San Diego–Tijuana has become a dominant commercial center in the United States and Mexico. The economic success of globalization has allowed San Diego–Tijuana to grow to the third richest region in the former Californias region, with a GDP of $136.3 billion in 2002. Tourism is a leading industry in the region and its coastal environs have been paramount factors in the growth of action sports–lifestyle companies; other key industries include military, biotech, and manufacturing. Since 2010, statewide droughts in California and in northern Mexico have further strained the San Diego–Tijuana binational region's water security.
History The Kumeyaay, referred to as Diegueño by the Spanish, are the original inhabitants of San Diego County and northern Baja California. The Kumeyaay lived in this region for over 10,000 years as hunter-gatherers and horticulturists. The boundaries of the Kumeyaay lands once extended from the Pacific Ocean, south to Ensenada, Baja California, east into the Imperial Valley and north to Warner Springs. The Luiseño, or Payómkawichum, also had a presence in modern-day North County San Diego.
Western exploration of the Californias dates back to the 16th century when in 1535 Hernán Cortés first visited the Baja California Peninsula in his search for Calafia. Subsequent exploration in 1542 by Juan Rodríguez Cabrillo brought the western explorers to what is now the California-Baja California region. Cabrillo first named San Diego, San Miguel. Initial expeditions by the west to the Californias were followed by pacification and conversion efforts by the Spanish Empire and the Catholic Church. The first Catholic religious order to visit the region was the Jesuits in 1683, followed by the Franciscans in 1768, and the Dominicans in the 1770s. The California mission system is a reminder of the Pacific Coast's colonial era.
In 1769 Father Junípero Serra founded San Diego after occupying the Kumeyaay village of Kosa'aay and created the first of the California missions, Mission San Diego de Alcalá. The Valley of Tijuana was explored the same year by Juan Crespí. In 1829 Santiago Argüello, a Californio and a major Mexican land grant ranchos owner, obtained ownership of a parcel of land known as Rancho Tía Juana and in 1889 was Tijuana officially founded on this parcel when descendants of Argüello and Agustin Olvera, an early Los Angeles pioneer, agreed to develop the city.
The metropolitan region was historically united as part of the province of Alta California under the Viceroyalty of New Spain. In 1821, Mexico won its independence from the Spanish crown and kept the area under the jurisdiction of Alta California. From the late 1860s Mission lands were granted as ranchos to Californio gentry. These distributions of lands accelerated after the Missions were secularized in 1833, ending the dominance of the Missions in the economy. San Diego Bay became a port of call for whalers and hide traders from the United States.
The region started depopulating, as settlements in the region began to be raided between 1836 and 1842 by the Kumeyaay resistance, with both Rancho Tía Juana (1839) and San Diego (~1840 & 1842) raided during that period.
In 1846, the Mexican–American War began and the United States continued to expand its borders under the doctrine of Manifest Destiny. As the war came to California, the Battle of San Pasqual was fought in the northern areas of modern-day San Diego. In 1848 the war ended with the Fall of Mexico City and boundaries were redrawn which created a border between San Diego and Tijuana, south of San Diego Bay. 1919 saw the implementation of Prohibition and the rapid growth of Tijuana tourism. Americans flocked to the city, which had become a major destination for the Hollywood elite, which led to the construction of the Agua Caliente Tourist Complex which in turn spurred the rise of hotels and overall growth in the city.
Urban landscape San Diego–Tijuana urbanity stretches along the coastline from the northernmost city of Oceanside to the southernmost city of Rosarito Beach. The urban area of San Diego–Tijuana is the 152nd most populous in the world and 21st most populous in North America, with a population of 5,330,000.
The highest population densities are located in the San Diego neighborhoods of University City, La Jolla, Mission Valley, Pacific Beach the downtown San Diego district of the East Village among others, and areas of Tijuana. An area of 116 census tracts in the North County region of the conurbation has a population of 615,092 and a per capita income of $44,131 which is about 50 percent more than that of California and the entire United States.U.S. Census Bureau. American Community Survey, 2011 American Community Survey 5-Year Estimates, Tables B01003 and B19025. U.S. Census website . Retrieved October 26, 2013. This area contains nearly all of the area located in the cities of Carlsbad, Encinitas, Solana Beach, and Del Mar. A part of this region are the communities of Rancho Santa Fe, Carmel Valley and La Jolla which have consistently been among the ranks of some of the richest neighborhoods in the United States.
Outside of the urban centers, older regions of San Diego County south of the San Diego River, as well as La Jolla and Pacific Beach, are built on a street grid. Suburban growth north of the San Diego river were built as master planned suburban communities on top of mesas with the "city of villages" concept in mind, built around car-dependency. Tijuana's suburban landscape is made up densely packed low-density mixed land uses, with patches of street grids east of the city and more organic growth influenced by topography. Cities like Tecate and Rosarito are built on street grid systems.
Geography
The metropolitan region is situated along the Pacific coast, on the border between the United States and Mexico. The region lies just south of Orange County and west of Imperial County, and shares borders with Greater Los Angeles. The area has a varied topography with over seventy miles of coastline and snow-capped mountains that rise to the northeast, in San Diego County. The terrain includes flood plains, canyons, steep hills, and mesas. The region has its eastern terminus in the Colorado Desert and Imperial Valley regions, where another conurbation – Mexicali–Calexico – is formed. The urbanized area where San Diego and Tijuana meet is known as San Ysidro on the American side of the border and Colonia Federal/Colonia Libertad on the Mexican side. East from the coast , the Tijuanense boroughs of Mesa de Otay and Centenario are heavy urbanized whereas the corresponding American area of Otay Mesa is composed of primarily dispersed industrial and distribution facilities. At the Pacific Ocean region of the border, the border is urbanized on the Mexican side while the adjacent American side is in Tijuana River National Estuarine Research Reserve, and thus not urbanized.
According to the U.S. Census Bureau, San Diego County has a total area of , of that of it is land and of it (7.20%) is water. The area of Tijuana Municipality is ; the municipality includes part of the Coronado Islands, located off the coast of the municipality in the Pacific Ocean. This combined area, with the additional areas of Tecate, , and Rosarito Beach, , place the area of San Diego–Tijuana at .
San Diego is by far the most populated county though population density is much higher in the immediate border area adjacent to the south in Baja California than it is in San Diego County. Urban growth is currently developing regions to the east of Tijuana Municipality and south of Rosarito Beach, where developers are building many new residential communities while in San Diego it is observed to the northeast along the Interstate 15 corridor to Temecula and Murrieta.
Greater Ensenada is more frequently than not considered part of the region given its proximity and inter-connectivity with the metropolitan area. While it is from the cities of San Diego and Tijuana respectively, recent developments between the port city and Rosarito Beach including upscale, Americanized subdivisions and resorts such as Punta Azul, Baja Mar, and La Salina have greatly increased the urbanity of the corridor between Rosarito Beach and Ensenada. Transportation infrastructure increasingly binds the region, as the under-construction Ensenada International Airport is expected to serve as the third major airport of the metropolitan region, offering flights to Europe, South America, and East Asia.
Climate
San Diego–Tijuana straddles a Mediterranean climate and semi-arid climate area. The Mediterranean climate is characterized by generally warm, dry summers on the near coastal regions with a slight temperature increase westward, and relatively cool, mild, wet winters; this is the climate that dominates northern San Diego–Tijuana. In southern San Diego–Tijuana, the semi-arid climate is observed, though characteristics of the Dry-Summer Subtropical Mediterranean climate are present, with most of the annual precipitation falling in the winter. The Peninsular Ranges assist in containing moisture to the coastal areas and create a rain shadow to the east as they are west-facing mountains.
The climate of the area often varies significantly due to the abundance of microclimates characterizing the region. San Diego–Tijuana's topography, bays, coastal hills, mountains, canyons and gorges maintain their own climates while being relatively near to each other. During the May gray and June gloom seasons, a dense cloak of coastal clouds, known as marine layer, covers the coastal areas, keeping the area cool and moist to up to inland. This coastal cloud cover is frequently observed reaching as far inland as Poway and in some cases, San Diego Country Estates. Yet once outside this cloud, the weather in sharp contrast can be warm and sunny. In some cases, June gloom lasts into July, creating cloudy skies over the coastal regions for entire days.