Rei is overwhelmingly correct.
While Rei made one minor typographical error regarding Köppen climate codes, their factual claims regarding California geography, pistachio cultivation, precipitation levels, climate classification rules, and water usage are scientifically sound. Conversely, DamnOregonian’s rebuttals rely on fundamental misunderstandings of how climate classifications work, California's geography, and where pistachio agriculture takes place.
1. Where Pistachios Are Grown & Whether It Is a Desert
DamnOregonian’s claim: Pistachios are not grown in the desert, and the San Joaquin Valley is a Mediterranean climate where crops get "ample water."
Rei’s claim: Pistachios are overwhelmingly grown in the Tulare Basin lowlands (southern San Joaquin Valley), which receives 5–8 inches of rain annually—well within the standard definition of a desert.
The Facts:
California produces over 95% of U.S. pistachios[1][2][3]. The vast majority of production is concentrated in Kern, Fresno, Tulare, Kings, and Madera counties[3][4][5]. Kern County alone produces over a third of the state’s total crop.
These lowlands receive between 5 and 8 inches of precipitation per year[6] (Bakersfield averages ~6.5 inches[7], Lost Hills ~6.6 inches, and Kettleman City ~7.5 inches). For comparison, Phoenix, Arizona receives ~7.2 inches.
In biology and geography, this region is formally recognized as the San Joaquin Desert (established by Germano et al., 2011, and recognized by the USGS and conservation agencies)[8][9][10].
Without massive state and federal irrigation projects (the Central Valley Project, State Water Project, and groundwater pumping)[6][11][12], these orchards could not survive on local precipitation.
2. The Köppen Climate Classification Blunder
DamnOregonian's central argument relies on a flawed reading of the Köppen climate classification system:
DamnOregonian quoted Wikipedia’s description of Csa:
"Regions with this form of a Mediterranean climate experience average monthly temperatures in excess of 22.0 C... Point out where they mention rainfall."
Why DamnOregonian is wrong:
Köppen classifications are hierarchical, and Group B (Dry/Arid climates) takes precedence over Group C (Temperate/Mediterranean climates)[13].
To even consider whether a region belongs in Group C (Csa), the region must first fail the Group B aridity test[13].
The aridity threshold (P th) is calculated using mean annual temperature and the seasonality of precipitation[13][14]. Because the Central Valley gets most of its precipitation during winter, Köppen’s threshold formula is: P th =20×T Celsius
For Bakersfield (mean annual temperature ~18.5 C / 65.3 F), the threshold for aridity is 370 mm370 mm (~14.6 inches). Under Köppen, if an area receives less than half of the aridity threshold (P3. Native Range of Pistachios
Rei’s point: Pistachios (Pistacia vera) are native to the arid plateaus and steppes of Central Asia, northeastern Iran, and northern Afghanistan.
The Facts: Rei is correct. The modern commercial cultivar used throughout California (the "Kerman" cultivar) was collected in 1929 from the desert-adjacent Iranian Plateau by USDA botanist William E. Whitehouse[4][21]. The tree naturally adapted to thrive in hot, dry, rainless summers and survive on deep taproots in arid soils[4][21].
4. Rei's Only Minor Mistake
Rei wrote:
"southern San Joaquin Valley lowlands are a mix of BWh (Hot desert climate) and CWh (Cold desert climate)."
In the Köppen system, a cold desert climate is abbreviated BWk, not CWh[15][22]. Cwa and Cwb are temperate monsoon climates[14][22]. This was clearly a slip of the keyboard, as Rei correctly provided the definition ("Cold desert climate") in parentheses.
Conclusion
Rei is correct. The heart of California’s pistachio belt lies in the Tulare Basin / southern San Joaquin Valley, an arid desert and steppe landscape receiving only 5–8 inches of rain per year[6]. DamnOregonian's claim that this region is "not a desert" and that Köppen Mediterranean climates do not depend on rainfall criteria represents a complete misunderstanding of both climatology and local geography.
Sources
help
americanpistachios.org
agmrc.org
agwestfc.com
ca.gov
farmonaut.com
wikipedia.org
encountertravel.com.au
figshare.com
scienceforconservation.org
kglmeridian.com
nature.org
capitolweekly.net
climatezonemap.com
hardymaps.com
oregonstate.education
wikipedia.org
plantmaps.com
figshare.com
wikipedia.org
noaa.gov
californiacurated.com
worldbank.org