| Central Valley | |
|---|---|
| Great Central Valley, Great Valley, Golden Empire | |
 Typical flat farmland of the Central Valley as seen from the air | |
 United States Geological Survey map of their defined four major regions of the Central Valley | |
| Length | 450 mi (720 km) |
| Width | 40 to 60 mi (64 to 97 km) |
| Area | 18,000 sq mi (47,000 km2)[1] |
| Depth | 2,000 to 6,000 ft (610 to 1,830 m) |
| Geology | |
| Type | Alluvial |
| Age | 2–3 million years |
| Geography | |
| Location | California, United States |
| Population centers | Sacramento,Fresno,Bakersfield,Stockton andModesto |
| Borders on | Sierra Nevada (east),Cascade Range,Klamath Mountains (north),Coast Range,San Francisco Bay (west) andTehachapi Mountains (south) |
| Coordinates | 37°00′N120°18′W / 37°N 120.3°W /37; -120.3[2] |
| Traversed by | Interstate 5 andInterstate 80 |
| Rivers | Sacramento River,San Joaquin River andKings River |
TheCentral Valley is a broad, elongated, flatvalley that dominates the interior ofCalifornia, United States. It is 40–60 mi (60–100 km) wide and runs approximately 450 mi (720 km) from north-northwest to south-southeast, inland from and parallel to thePacific coast. It covers approximately 18,000 sq mi (47,000 km2),[1] about 11% of California's land area. The valley is bounded by theCoast Ranges to the west and theSierra Nevada to the east.
The Central Valley is a region known for itsagricultural productivity. It provides a large share of the food produced in California, which provides more than half of the fruits, vegetables, and nuts grown in the United States.[3] More than 7,000,000 acres (28,000 km2) of the valley are irrigated via reservoirs and canals.[4] The valley hosts many cities, including the state capitalSacramento, as well asRedding,Chico,Yuba City,Woodland,Davis,Roseville,Elk Grove,Stockton,Modesto,Merced,Fresno,Visalia,Porterville, andBakersfield.
The Central Valleywatershed comprises 60,000 square miles (160,000 km2), or over a third of California. It consists of three main drainage systems: theSacramento Valley in the north, which receives over 20 inches (510 mm) of rain annually; the drierSan Joaquin Valley in the south, and theTulare Basin and itssemi-arid desert climate at the southernmost end. TheSacramento andSan Joaquin river systems drain their respective valleys and meet to form theSacramento–San Joaquin River Delta, a large expanse of interconnectedcanals,stream beds,sloughs,marshes and peat islands. The delta empties intoSan Francisco Bay, and ultimately into the Pacific.[5] The waters of the Tulare Basin essentially never reach the ocean (with the exception ofKings River waters diverted northward for irrigation), though they are connected by man-madecanals to the San Joaquin.
The valley encompasses all or parts of 18 California counties:Butte,Colusa,Glenn,Fresno,Kern,Kings,Madera,Merced,Placer,San Joaquin,Sacramento,Shasta,Stanislaus,Sutter,Tehama,Tulare,Yolo andYuba.[6] The Central Valley has struggled to transform its economy beyond its role as an agricultural breadbasket. Although safety nets have drastically improved Central Valley poverty rates, without them the poverty level would drastically increase. But, the Central Valley still remains as one of the most impoverished regions of California.[7]
Air pollution is a major issue, but it is mostly an issue in the San Joaquin Valley, rather than the Sacramento Valley.[8]
Older names include "the Great Valley", a name still often seen in scientific references (notablyGreat Valley Sequence), as well as "Golden Empire", abooster name that is still referred to by some organizations (notablyGolden Empire Transit,Golden Empire Council).[citation needed]
Ideas about what constitutes the "Central Valley" can vary from person-to-person. While almost all authoritative sources and external observers consider theSacramento Valley to be part of the "Central Valley", many residents consider the Central Valley to consist of only theSan Joaquin Valley. This is perhaps due to significant landscape and cultural differences between the two; the San Joaquin Valley is poorer and drier with more fertile soil, while the Sacramento Valley is wetter with poorer soils.[9] The major presence of theSacramento River and itstributaries in the Sacramento Valley, with its high year-round flow and wide waterways, has been compared to the small and seasonal rivers of the San Joaquin basin; this also contributes to different identities between the two regions.[9]
Subregions and their counties commonly associated with the valley include:[6]
The four main population centers in the Central Valley area are roughly equidistant from each other. From south to north, they areBakersfield,Fresno,Sacramento andRedding.
The table displays the counties of Central Valley and their respective population during the 2020 US Decennial Census. Total jobs for each county is from the U.S. Census Bureau, OnTheMap Application and LEHD Origin-Destination Employment Statistics (Beginning of Quarter Employment, 2nd Quarter of 2002–2020).
| County | Population | Jobs |
|---|---|---|
| Butte County | 211,632 | 73,219 |
| Colusa County | 21,839 | 7,834 |
| Fresno County | 1,008,654 | 374,478 |
| Glenn County | 28,917 | 9,314 |
| Kern County | 909,235 | 282,227 |
| Kings County | 152,486 | 43,542 |
| Madera County | 156,255 | 49,285 |
| Merced County | 281,202 | 74,470 |
| Placer County | 404,739 | 166,372 |
| Sacramento County | 1,585,055 | 669,429 |
| San Joaquin County | 779,233 | 247,406 |
| Shasta County | 182,155 | 61,665 |
| Stanislaus County | 552,878 | 184,916 |
| Sutter County | 99,633 | 29,951 |
| Tehama County | 65,829 | 17,735 |
| Tulare County | 473,117 | 157,971 |
| Yolo County | 216,403 | 106,643 |
| Yuba County | 81,575 | 16,937 |
| Total | 7,210,837 | 2,573,394 |
As of 2020, some 7.2 million people lived in the Central Valley; it was the fastest-growing region in California.[10] It includes 12Metropolitan Statistical Areas (MSA) and 1Micropolitan Statistical Area (μSA). Below, they are listed by MSA and μSA population. The largest city isFresno followed by the state capitalSacramento. The following metropolitan and micropolitan statistical areas are listed from largest to smallest:
| SMSA | Population |
|---|---|
| Sacramento Metropolitan Area | 2,527,123 |
| Fresno Metropolitan Area | 930,450 |
| Bakersfield Metropolitan Area | 839,361 |
| Stockton Metropolitan Area | 696,214 |
| Modesto Metropolitan Area | 518,522 |
| Visalia–Porterville Metropolitan Area | 449,253 |
| Merced Metropolitan Area | 259,898 |
| Chico Metropolitan Area | 220,266 |
| Redding Metropolitan Area | 177,774 |
| Yuba City Metropolitan Area | 167,497 |
| Hanford–Corcoran Metropolitan Area | 153,765 |
| Madera Metropolitan Area | 152,925 |
| Red Bluff Micropolitan Area | 63,601 |
After English andSpanish,Punjabi is the third most commonly spoken language in the Central Valley.[11] The valley has the largestSikh population in the nation.
The flatness of the valley floor contrasts with the rugged hills or gentle mountains that are typical of most of California's terrain. The valley is thought to have originated below sea level as an offshore area depressed bysubduction of theFarallon Plate into a trench farther offshore. The valley has no earthquake faults of its own but is surrounded by faults to the east and west.
The valley was enclosed by the uplift of theCoast Ranges, with its original outlet intoMonterey Bay. Faulting moved the Coast Ranges, and a new outlet developed near what is nowSan Francisco Bay. Over the millennia, the valley filled with the sediments of these same ranges, as well as the risingSierra Nevada to the east; that filling eventually created an extraordinary flatness just barely above sea level. Before California's flood control and aqueduct system was built, annual snow melt turned much of the valley into an inland sea.
The one notable exception to the flat valley floor isSutter Buttes, the remnants of an extinct volcano just to the northwest ofYuba City.
Another significant geologic feature of the Central Valley lies hidden beneath the delta. TheStockton Arch is an upwarping of the crust beneath the valley sediments that extends southwest to northeast across the valley.
The Central Valley lies within the California Trough physiographic section, which is part of the larger Pacific Border province, which in turn is part of thePacific Mountain System.[12][13]
Excessive groundwater pumping in Central Valley has caused measurable amounts ofland subsidence in recent years.[14]
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The Central Valley was formerly a diverse expanse of grassland, containing areas ofprairie, desert grassland (at the southern end),oak savanna,riparian forest,marsh, several types of seasonalvernal pools, and large lakes such as now-dryTulare Lake (once the largestfreshwater lake west of the Mississippi),Buena Vista Lake andKern Lake. However, much of the Central Valley environment has been altered by human activity, including the introduction ofexotic plants, notably grasses. The valley's grasslands, wetlands, and riparian forests constitute theCalifornia Central Valley grasslands, atemperate grasslands, savannas, and shrublandsecoregion. The foothill oak woodlands andchaparral that fringe the valley have been categorized as theCalifornia interior chaparral and woodlands ecoregion.[15]
The dominant grass of the valley wasNassella pulchra mixed with other species, but today only 1% of the grassland in the valley is intact. Grassland flowers includeCalifornia poppy (Eschscholzia californica),lupins, and purple owl's clover (Castilleja exserta), which can still be seen, especially inAntelope Valley in theTehachapi Mountains. Riverside trees include willows, western sycamore (Platanus racemosa), box elder (Acer negundo), Fremont cottonwood (Populus fremontii), and the endemic valley oak (Quercus lobata). Another endemic species is brittlescale (Atriplex depressa) which grows in saline and alkali soils.[16]
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The Central Valley was once home to large populations ofpronghorn antelope (Antilocapra americana),elk including the endemictule elk subspecies (Cervus elaphus nannodes),mule deer (Odocoileus hemionus),California ground squirrels,gophers, mice, hare, rabbits andkangaroo rats, along with their predators including theSan Joaquin kit fox (an endangered subspecies surviving on the San Joaquin Valley's hillsides). The valley's wetlands were an important habitat for winteringwaterbirds and migrating birds of other kinds. Reptiles and amphibians of the valley include the endemic San Joaquin coachwhip snake (Masticophis flagellum ruddocki),blunt-nosed leopard lizard (Gambelia sila),Gilbert's skink (Eumeces gilberti) and thewestern aquatic garter snake (Thamnophis couchii). Endemic invertebrates are present. The Central Valley is home to endemic fish species, including theSacramento pikeminnow,Sacramento perch,Sacramento blackfish, andSacramento splittail.
TheGreat Valley Grasslands State Park preserves an example of the valley'snative grasshabitat, while oak savanna habitats survive nearVisalia. Areas of wetland and riverside woodland are found in the north, especially by the Sacramento River system, including theNature Conservancy'sCosumnes River Preserve just south of Sacramento, Gray Lodge Wildlife Area,Butte Sink Wildlife Management Area, and other patches in the delta area. Remaining vernal pools includePixley National Wildlife Refuge betweenTulare, California, and Bakersfield and Jepson Prairie Preserve in the delta. Large blocks of desert scrubland exist in the southern San Joaquin Valley and theCarrizo Plain, just outside the valley, but offering a similar landscape.
The wetlands have been the target of rescue operations to restore areas replaced by agriculture.[17]
These patches of natural habitat are disconnected, which is particularly damaging for wildlife that is used to migrating along the rivers. Agriculture, grazing land, and the draining of lakes and rivers have radically altered valley habitats. Most of the grassland has been overtaken by new species; most vernal pools have been destroyed, leaving only those on the higher slopes; the marshland has been drained, and the riverbank woodlands have nearly all been affected.[citation needed]
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The valley gives its name toValley fever, which is primarily a disease of the lungs that is common in the southwestern United States and northwestern Mexico. It is caused by thefungusCoccidioides immitis, which grows in soils in areas of low rainfall, high summer temperatures, and moderate winter temperatures. These fungal spores become airborne when the soil is disturbed by winds, construction, or farming. This illness frequently takes weeks or months to resolve. Occasionally Valley Fever is life-threatening or even fatal.
Due to the agricultural industry's significant presence in the Valley,pesticide drift and leaching have become concerns. Residents risk contamination when living in proximity to application sites.
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Air pollution is a growing problem that affects all of the citizens in the Central Valley. Some reasons of poor air pollution in the Central Valley are due to agriculture and its geographical features, increasing the stagnation of automobile and other particulate pollution.
Since the Central Valley consists mostly of farming land in a wide, flat valley, the emissions from the soil that is used for growing produce are released into the air. The soil exudesnitrous oxide, an odorless and colorless gas that can be harmful when exposed to it for a long period of time, and incorporates itself into the ozone layer located at ground level.[18] Production of nitrous oxide in California has shown that the addition of soil andfertilization can emit about 161,100 metric tons per year. Long term effects that nitrous oxide can have on a human being is loss of blood pressure, fainting, anemia, or lung cancer.
The physical geographical attributes can also contribute to the air pollution quality. The Central Valley is surrounded by mountain ranges which can capture the pollution coming from the agricultural farming, preventing it from dispersing from the other areas in California.[19]
The northern Central Valley has a hotMediterranean climate (Köppen climate classificationCsa); the more southerly parts inrainshadow zones are dry enough to be Mediterranean steppe or even low-latitude desert (BWh, as in areas aroundBakersfield). It is very hot and dry during the summer and cool and damp in winter when frequent ground fog known regionally as "tule fog" can obscure vision. Summer daytime temperatures frequently surpass 100 °F (38 °C), and commonheat waves might bring temperatures exceeding 115 °F (46 °C). Mid-autumn to mid-spring is therainy season—although during the late summer, southeasterly winds can bring tropical thunderstorms, mainly in the southern half of theSan Joaquin Valley but occasionally to theSacramento Valley. The northern half of the Central Valley receives greater precipitation than thesemidesert southern half. Frost occurs at times in the fall months, but snow is extremely rare.[21]
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Tule fog/ˈtuːliː/ is a thick groundfog that settles along the valley's length. Tule fog forms during the late fall and winter (California'srainy season), after the first significant rainfall. The official season is from November 1 to March 31. This phenomenon is named after the valley'stule grass wetlands (tulares). Auto collisions caused by the tule fog are the leading cause of weather-related casualties in California.
| Climate data for Sacramento, California (Sacramento Executive Airport), 1991–2020 normals, extremes 1941–present[a] | |||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Month | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | Year |
| Record high °F (°C) | 76 (24) | 78 (26) | 88 (31) | 95 (35) | 105 (41) | 115 (46) | 114 (46) | 112 (44) | 114 (46) | 104 (40) | 87 (31) | 74 (23) | 115 (46) |
| Mean maximum °F (°C) | 65.2 (18.4) | 71.1 (21.7) | 78.1 (25.6) | 87.4 (30.8) | 95.3 (35.2) | 103.1 (39.5) | 105.3 (40.7) | 104.1 (40.1) | 100.6 (38.1) | 91.8 (33.2) | 76.5 (24.7) | 65.1 (18.4) | 107.0 (41.7) |
| Mean daily maximum °F (°C) | 56.0 (13.3) | 61.3 (16.3) | 66.3 (19.1) | 72.1 (22.3) | 80.3 (26.8) | 87.9 (31.1) | 92.6 (33.7) | 91.9 (33.3) | 88.5 (31.4) | 78.8 (26.0) | 65.0 (18.3) | 56.0 (13.3) | 74.7 (23.7) |
| Daily mean °F (°C) | 47.6 (8.7) | 51.4 (10.8) | 55.4 (13.0) | 59.5 (15.3) | 66.1 (18.9) | 72.2 (22.3) | 75.9 (24.4) | 75.3 (24.1) | 72.5 (22.5) | 64.5 (18.1) | 53.9 (12.2) | 47.3 (8.5) | 61.8 (16.6) |
| Mean daily minimum °F (°C) | 39.2 (4.0) | 41.5 (5.3) | 44.5 (6.9) | 47.0 (8.3) | 52.0 (11.1) | 56.5 (13.6) | 59.2 (15.1) | 58.8 (14.9) | 56.5 (13.6) | 50.3 (10.2) | 42.7 (5.9) | 38.5 (3.6) | 48.9 (9.4) |
| Mean minimum °F (°C) | 29.1 (−1.6) | 31.7 (−0.2) | 35.1 (1.7) | 37.9 (3.3) | 44.1 (6.7) | 49.5 (9.7) | 54.1 (12.3) | 53.8 (12.1) | 49.6 (9.8) | 41.7 (5.4) | 32.7 (0.4) | 28.7 (−1.8) | 26.9 (−2.8) |
| Record low °F (°C) | 20 (−7) | 23 (−5) | 26 (−3) | 31 (−1) | 34 (1) | 41 (5) | 48 (9) | 48 (9) | 42 (6) | 35 (2) | 26 (−3) | 18 (−8) | 18 (−8) |
| Averageprecipitation inches (mm) | 3.66 (93) | 3.49 (89) | 2.68 (68) | 1.26 (32) | 0.75 (19) | 0.23 (5.8) | 0.00 (0.00) | 0.04 (1.0) | 0.09 (2.3) | 0.85 (22) | 1.66 (42) | 3.43 (87) | 18.14 (461) |
| Average precipitation days(≥ 0.01 in) | 10.0 | 9.1 | 9.0 | 5.1 | 3.6 | 1.1 | 0.1 | 0.2 | 0.7 | 3.1 | 6.1 | 9.6 | 57.7 |
| Averagerelative humidity (%) | 83.3 | 76.8 | 71.6 | 64.5 | 58.9 | 55.0 | 53.2 | 55.7 | 57.0 | 63.1 | 75.6 | 82.9 | 66.5 |
| Averagedew point °F (°C) | 39.4 (4.1) | 42.1 (5.6) | 42.8 (6.0) | 43.7 (6.5) | 46.9 (8.3) | 50.4 (10.2) | 53.1 (11.7) | 53.4 (11.9) | 50.9 (10.5) | 47.5 (8.6) | 43.7 (6.5) | 39.2 (4.0) | 46.1 (7.8) |
| Mean monthlysunshine hours | 145.5 | 201.3 | 278.0 | 329.6 | 406.3 | 419.5 | 440.2 | 406.9 | 347.8 | 296.7 | 194.9 | 141.1 | 3,607.8 |
| Percentagepossible sunshine | 48 | 67 | 75 | 83 | 92 | 94 | 98 | 96 | 93 | 86 | 64 | 48 | 81 |
| Source: NOAA (relative humidity, dew point and sun 1961–1990)[23][24][25] | |||||||||||||
| Climate data for Sacramento 5 ESE, California (Sacramento State[26]), 1991–2020 normals, extremes 1877–present | |||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Month | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | Year |
| Record high °F (°C) | 79 (26) | 80 (27) | 90 (32) | 98 (37) | 107 (42) | 112 (44) | 114 (46) | 112 (44) | 116 (47) | 102 (39) | 86 (30) | 72 (22) | 116 (47) |
| Mean maximum °F (°C) | 66.4 (19.1) | 72.5 (22.5) | 80.6 (27.0) | 89.5 (31.9) | 97.1 (36.2) | 104.4 (40.2) | 106.7 (41.5) | 105.5 (40.8) | 102.0 (38.9) | 92.3 (33.5) | 77.3 (25.2) | 65.9 (18.8) | 108.1 (42.3) |
| Mean daily maximum °F (°C) | 56.5 (13.6) | 62.2 (16.8) | 67.8 (19.9) | 73.5 (23.1) | 81.3 (27.4) | 89.0 (31.7) | 94.4 (34.7) | 93.5 (34.2) | 89.3 (31.8) | 78.9 (26.1) | 65.3 (18.5) | 56.4 (13.6) | 75.7 (24.3) |
| Daily mean °F (°C) | 48.8 (9.3) | 52.9 (11.6) | 57.2 (14.0) | 61.4 (16.3) | 67.7 (19.8) | 73.9 (23.3) | 77.9 (25.5) | 77.3 (25.2) | 74.0 (23.3) | 65.9 (18.8) | 55.3 (12.9) | 48.5 (9.2) | 63.4 (17.4) |
| Mean daily minimum °F (°C) | 41.1 (5.1) | 43.7 (6.5) | 46.7 (8.2) | 49.3 (9.6) | 54.0 (12.2) | 58.7 (14.8) | 61.4 (16.3) | 61.0 (16.1) | 58.8 (14.9) | 52.9 (11.6) | 45.3 (7.4) | 40.7 (4.8) | 51.1 (10.6) |
| Mean minimum °F (°C) | 32.5 (0.3) | 35.4 (1.9) | 38.8 (3.8) | 41.6 (5.3) | 47.2 (8.4) | 51.9 (11.1) | 55.9 (13.3) | 55.9 (13.3) | 52.4 (11.3) | 45.1 (7.3) | 36.2 (2.3) | 31.9 (−0.1) | 30.5 (−0.8) |
| Record low °F (°C) | 19 (−7) | 21 (−6) | 29 (−2) | 34 (1) | 37 (3) | 43 (6) | 47 (8) | 48 (9) | 44 (7) | 34 (1) | 27 (−3) | 17 (−8) | 17 (−8) |
| Averageprecipitation inches (mm) | 3.87 (98) | 3.63 (92) | 2.82 (72) | 1.44 (37) | 0.86 (22) | 0.21 (5.3) | 0.00 (0.00) | 0.02 (0.51) | 0.15 (3.8) | 0.93 (24) | 1.78 (45) | 3.49 (89) | 19.20 (488) |
| Average precipitation days(≥ 0.01 in) | 10.8 | 9.6 | 9.2 | 5.3 | 3.7 | 1.2 | 0.1 | 0.2 | 0.8 | 3.1 | 6.8 | 10.1 | 60.9 |
| Source: NOAA[23][27][28], Western Regional Climate Center[29] | |||||||||||||
| Climate data for Fresno, California (Fresno Airport), 1991–2020 normals,[b] extremes 1881–present[c] | |||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Month | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | Year |
| Record high °F (°C) | 78 (26) | 84 (29) | 91 (33) | 101 (38) | 110 (43) | 112 (44) | 115 (46) | 113 (45) | 114 (46) | 105 (41) | 90 (32) | 77 (25) | 115 (46) |
| Mean maximum °F (°C) | 68.1 (20.1) | 73.7 (23.2) | 81.9 (27.7) | 90.8 (32.7) | 99.0 (37.2) | 105.9 (41.1) | 107.7 (42.1) | 107.1 (41.7) | 103.1 (39.5) | 93.2 (34.0) | 79.6 (26.4) | 67.4 (19.7) | 109.2 (42.9) |
| Mean daily maximum °F (°C) | 55.4 (13.0) | 61.3 (16.3) | 67.5 (19.7) | 73.7 (23.2) | 82.7 (28.2) | 91.4 (33.0) | 97.7 (36.5) | 96.5 (35.8) | 90.7 (32.6) | 78.7 (25.9) | 64.9 (18.3) | 55.3 (12.9) | 76.3 (24.6) |
| Daily mean °F (°C) | 48.0 (8.9) | 52.3 (11.3) | 57.4 (14.1) | 62.3 (16.8) | 70.2 (21.2) | 77.6 (25.3) | 83.5 (28.6) | 82.2 (27.9) | 77.1 (25.1) | 66.7 (19.3) | 55.1 (12.8) | 47.5 (8.6) | 65.0 (18.3) |
| Mean daily minimum °F (°C) | 40.6 (4.8) | 43.3 (6.3) | 47.3 (8.5) | 50.9 (10.5) | 57.6 (14.2) | 63.9 (17.7) | 69.3 (20.7) | 67.9 (19.9) | 63.4 (17.4) | 54.6 (12.6) | 45.4 (7.4) | 39.8 (4.3) | 53.7 (12.1) |
| Mean minimum °F (°C) | 30.5 (−0.8) | 33.4 (0.8) | 37.2 (2.9) | 40.4 (4.7) | 47.7 (8.7) | 52.9 (11.6) | 60.1 (15.6) | 59.7 (15.4) | 53.8 (12.1) | 44.6 (7.0) | 34.7 (1.5) | 30.2 (−1.0) | 28.8 (−1.8) |
| Record low °F (°C) | 17 (−8) | 24 (−4) | 26 (−3) | 32 (0) | 36 (2) | 42 (6) | 50 (10) | 49 (9) | 37 (3) | 27 (−3) | 26 (−3) | 18 (−8) | 17 (−8) |
| Averageprecipitation inches (mm) | 2.16 (55) | 1.93 (49) | 1.90 (48) | 1.04 (26) | 0.42 (11) | 0.24 (6.1) | 0.03 (0.76) | 0.00 (0.00) | 0.05 (1.3) | 0.56 (14) | 0.87 (22) | 1.79 (45) | 10.99 (279) |
| Average precipitation days(≥ 0.01 in) | 7.7 | 8.5 | 7.2 | 4.5 | 2.7 | 0.7 | 0.3 | 0.1 | 0.6 | 2.2 | 4.7 | 7.3 | 46.5 |
| Averagerelative humidity (%) | 83.3 | 77.2 | 68.9 | 57.4 | 47.3 | 41.9 | 39.2 | 44.7 | 50.0 | 58.5 | 74.1 | 84.2 | 60.6 |
| Averagedew point °F (°C) | 39.4 (4.1) | 42.4 (5.8) | 43.2 (6.2) | 43.2 (6.2) | 45.3 (7.4) | 48.9 (9.4) | 52.3 (11.3) | 54.1 (12.3) | 51.6 (10.9) | 47.3 (8.5) | 43.2 (6.2) | 39.6 (4.2) | 45.9 (7.7) |
| Mean monthlysunshine hours | 141.5 | 196.9 | 286.2 | 335.5 | 398.9 | 412.2 | 428.2 | 399.6 | 345.9 | 302.3 | 189.9 | 127.1 | 3,564.2 |
| Percentagepossible sunshine | 46 | 65 | 77 | 85 | 91 | 94 | 96 | 95 | 93 | 87 | 62 | 42 | 80 |
| Source: NOAA (relative humidity, dew points and sun 1961–1990)[30][31][32] | |||||||||||||
Two river systems drain and define the two parts of the Central Valley. TheSacramento River, along with its tributaries theFeather River andAmerican River, flows southwards through the Sacramento Valley for about 447 miles (719 km).[33] In the San Joaquin Valley, theSan Joaquin River flows roughly northwest for 365 miles (587 km), picking up tributaries such as theMerced River,Tuolumne River,Stanislaus River andMokelumne River.[34] The Central Valleywatershed encompasses over a third of California at 60,000 square miles (160,000 km2), with 46 percent draining into the Sacramento River, 26 percent into the San Joaquin, and 27 percent into Tulare Lake.
In the southern part of the San Joaquin Valley, thealluvial fan of theKings River and another from Coast Ranges streams have created a divide. The dry Tulare basin of the Central Valley receives flow from four major Sierra Nevada rivers, the Kings,Kaweah,Tule, andKern. This basin, usuallyendorheic, formerly filled during snowmelt and spilled out into the San Joaquin River. CalledTulare Lake, it is usually dry because the rivers feeding it have been diverted for agricultural purposes.[35]
Central Valley rivers converge in theSacramento-San Joaquin Delta, a network of marshy channels, distributaries, and sloughs that wind around islands mainly used for agriculture. There the rivers merge with tidewater, and eventually reach the ocean after passing throughSuisun Bay,San Pablo Bay, upperSan Francisco Bay, and finally theGolden Gate. Many of the islands lie below sea level because of intensive agriculture, and face a high risk of flooding, which would allow salt water to rush back into the delta, especially when too little fresh water is flowing in from the Valley.[36]
The Sacramento River carries far more water than the San Joaquin, with an estimated 22 million acre-feet (27 km3) of virgin annual runoff, as compared to the San Joaquin's approximately 6 million acre-feet (7.4 km3). Intensive agricultural and municipal water consumption decreased the rate of outflow to about 17 million acre-feet (21 km3) for the Sacramento and 3 million acre-feet (3.7 km3) for the San Joaquin. These figures vary widely from year to year. Over 25 million people, living in the valley and other regions of the state, rely on the water carried by these rivers.[37]
Sierra Nevada runoff provides one of California's largest water resources. The Sacramento River is the second largest river to empty into the Pacific from thecontiguous United States, behind only theColumbia River and greater than theColorado River.[38] Combined with the fertile and expansive area of the Central Valley's floor, the Central Valley is ideal for agriculture.[39]
The Central Valley is one of the United States' most productive growing regions. This is made possible by engineering the watercourses to prevent flooding during the spring snowmelt and drying up in the summer and autumn.[40] Many dams, includingShasta Dam,Oroville Dam,Folsom Dam,New Melones Dam,Don Pedro Dam,Hetch Hetchy Dam,Friant Dam,Pine Flat Dam andIsabella Dam, were constructed on the rivers, with many of them being part of theCentral Valley Project.[40] These dams impact physical, economic, cultural, and ecological resources: for example, enabling the development of its vast agricultural resources but leading to the loss of theChinook salmon.[41]
Post-World War II demand for urban development, most notably theSan Francisco Bay Area and theLos Angeles/Inland Empire/San Diego, required water resources. Moreover, agriculture in the southern Central Valley required far more water than was available locally. TheFeather River in the Sacramento Valley was looked to as a water source, leading to theCalifornia State Water Project. This transports water to the southern San Joaquin Valley and urban areas south of the Tehachapi Mountains.[42]
Runoff from the Sacramento and San Joaquin Rivers is intercepted in the delta through a series of pumps that divert water into theCalifornia Aqueduct, which runs south along the length of the San Joaquin Valley.[43] In parallel, pumps divert water into theDelta–Mendota Canal. The flow of the Sacramento River is further supplemented by a tunnel from theTrinity River (a tributary of theKlamath River, northwest of the Sacramento Valley) nearRedding.[44] Cities of theSan Francisco Bay Area, also needing water, built aqueducts from theMokelumne River andTuolumne River that run east to west across the middle part of the Central Valley.[45][46]
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Most valley lowlands are prone to flooding, especially in the oldTulare Lake,Buena Vista Lake, andKern Lake rivers. TheKings,Kaweah,Tule andKern rivers originally flowed into these seasonal lakes, which would expand each spring to flood large parts of the southern San Joaquin Valley. Farms, towns, and infrastructure in these lakebeds are protected with levee systems, while the risk of floods damaging properties increased greatly.
TheGreat Flood of 1862 was the valley's worst flood in recorded history, flooding most of the valley and putting some places as much as 20 feet (6.1 m) under water.
In 2003, it was determined that Sacramento had both the least protection against and nearly the highest risk of flooding. Congress then granted a $220 million loan for upgrades in Sacramento County.[47] Other counties in the valley that often face flooding areYuba,Stanislaus, andSan Joaquin.
A very strong positive correlation exists between rainfall and slow-movinglandslides in Northern California, especially in the Central Valley region. Changes in climate and precipitation levels have shown that consistent average rainfall has increased the number and intensity of landslides within the past 5–6 years. This information was shown in a study that focused on the behavior of these slow-moving landslides and how their nature changed with years of extreme average rainfall versus minimal average rainfall. In 2016, the average annual precipitation levels were lower because of a drought that was coming to an end at that time. The minimal rainfall in that year showed that 119 landslides had been moving. Comparatively, in 2017, there were very extreme levels of precipitation in the Central Valley, which cause 312 landslides to move that year.[48] Slow-moving landslides are impacted even if the intensity of the rainfall is not as severe.
Consistent, moderately intense rainfall increases the saturation of water in the ground. This over-saturation is what causes the movement of a slow-moving landslide, rather than the more quick-moving and rigorous landslides that also occur in this region of California. Quick-moving landslides are caused by very intense rain, or sometimes earthquakes, that make a greater difference in the land in a shorter amount of time. According to a survey paper written in 1988 about a storm that occurred in 1982 in the Central Valley region, rainstorms that can cause that type of landslide to happen about every 5 years. Landslides to higher degrees, such as the ones that happened due to the 1982 storm, only occur every 20 to 100+ years. This intense storm in the San Francisco Bay area caused a lot of damage as a result of moving debris and landslides. They caused damage to the land and put people living in these areas that are susceptible to these disasters in great harm. The aftermath of this storm involved millions of dollars in retributions to restore the land and surrounding areas. It also led people to make greater efforts into planning around the danger of these landslides, as in how to manipulate the land to accommodate the consequences.
Out of the past twenty-two years,[when?] California has experienced significant drought conditions for thirteen years. From 2000 to 2018 was the second driest period that California has ever experienced. The driest three-year period ever in California was from 2012 to 2014. Three-quarters of the state of California is experiencing extreme drought conditions. There are also multiple types of droughts such as agricultural droughts, meteorological droughts, snow droughts, and hydrological droughts. All of these droughts affect California in different ways. Droughts can damage forests and can cause wildfires. Droughts cause forests to become dry which causes trees to die. Dead trees result in wildfires. The U.S. drought monitor is released every Thursday, showing which parts of the U.S. are in a drought. It started in 2000, and since then the longest duration of a drought in California lasted a total of 376 weeks. It started on December 11, 2011, and ended on March 5, 2019. The most intense period captured on the drought monitor was on the week of July 29, 2014. It showed that 58.41% of California's land was affected by a drought. In 2014–2015, farm-related losses in California totaled $5 billion and 20,000 farmers also lost their jobs.[citation needed]
Agriculture is the primary industry in most of the Central Valley. A notable exception is the Sacramento area, which hosts a large and stable workforce of government employees. Despite state hiring cutbacks and the closure of several military bases, Sacramento's economy has continued to expand and diversify and now more closely resembles that of the San Francisco Bay Area. Primary sources of population growth are Bay Area migrants seeking lower housing costs, augmented by immigration from Asia, Central America, Mexico, Ukraine, and the rest of the former Soviet Union.[6] The Central Valley's high rates ofpoverty,asthma, andair pollution have impeded the Valley from transforming its economy into relevance beyond its role as an agricultural breadbasket.[49]
The Central Valley is one of the world's most productive agricultural regions.[50][5] More than 230 crops are grown there.[5] On less than 1 percent of the total farmland in the United States, the Central Valley produces 8 percent of the nation's agricultural output by value: US$43.5 billion in 2013.[51] California's farms and ranches earned almost $50 billion in 2018.[52] The valley's productivity relies on irrigation from surface water andbadly depleted underground aquifers.[53] About one-sixth of the US' irrigated land is in the Central Valley.[54]
Virtually all non-tropical crops are grown in the Central Valley, which is the primary source for produce throughout the United States, including tomatoes, grapes, cotton, apricots, and asparagus.[55] Six thousandalmond growers produced more than 600 million pounds (270×10^6 kg) in 2000, about 70 percent of the world's supply and nearly 100 percent of domestic production.[56][57]
The US' top four counties in agricultural sales are in the Central Valley (2007 Data).[6][58]
| County | Sales |
|---|---|
| Fresno County | $3.731B |
| Tulare County | $3.335B |
| Kern County | $3.204B |
| Merced County | $2.330B |
Early farming was concentrated close to the Sacramento-San Joaquin Delta, where the water table was high year-round and water transport was readily available. Subsequent irrigation projects brought many more parts of the valley into productive use.[59] The even largerCalifornia State Water Project was formed in the 1950s and construction continued over the following decades.
In the 1960s, farm labor leadersCesar Chavez andDolores Huerta organizedMexican American grape pickers into aunion, theNational Farmworkers Association (NFWA), to improve their working conditions. This organizing took place primarily in the Central Valley because of the extensive agriculture, especially in and aroundDelano.[60]
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The state water project'sOroville Dam in the Sacramento Valley provides water and power for theCalifornia Aqueduct in the San Joaquin Valley. The aqueduct runs from Clifton Court Forebay in the Delta southwards across theTransverse Ranges. The Central Valley Project includes numerous facilities betweenShasta Dam in the north and Bakersfield in the south.Pacific Gas and Electric,Western Area Power Administration, andSouthern California Edison built an interconnectedelectric grid connecting the north and south ends of the Central Valley.
Central Valley, which is two valleys: the San Joaquin to the south and Sacramento to the north. All told,[ sic] the Central Valley is about 450 miles long, from Bakersfield up to Redding, and is 60 miles at its widest, between the Sierra Nevada to the east and the Coast Ranges to the west.
About 6.5 million people live here, making it the state's fastest-growing region, according to the 2010 U.S. Census. Between 1990 and 2009, the population here grew 44 percent (compared with 24 percent growth statewide).
Community members have also raised funds to support billboards drawing attention to India's protests throughout the Central Valley, where Punjabi is the third-most spoken language, after English and Spanish.
{{cite web}}: CS1 maint: archived copy as title (link)The state's 6,000 growers produce more than 600 million pounds a year, more than 70 percent of the world's supply and virtually 100 percent of domestic production.
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