Was 2026 the Hottest Summer on Record in Arizona?
This year, the question I have heard most often is whether 2026 was the hottest one yet. Seven years of AZMet Yuma Valley data give a clear answer, and it is not the one most people expect.
No-Summer 2026 was not the hottest summer in this record. 2024 was. For an identical 75-day window in each year (1–27 June, all of July, and 1–17 August), the mean daily temperature was 92.3 °F in 2026 versus 93.0 °F in 2024. For daytime maximum, 2026 ranks third, behind 2020 and 2024, over the last 7 summers.
But that is not the end of the story, because the summer itself is not what made 2026 unusual. Three patterns matter more: The season started hot and stayed ahead. March 2026 ran 15.7 °F above the 2020–2025 mean for daily maximum temperature (Figure 1), the largest departure of any month in this seven-year record, more than twice the next largest (February 2026, +6.7 °F). Nights stayed warm. Night-time minimum temperature was above the six-year average in every month of 2026 with data (Figure 2), and August delivered the highest number of nights at or above 80 °F in this record. Heat units ran far ahead of recent years. By 31 July, 2026 had accumulated 3,943 °F-days (86/55 °F), which is 553 °F-days above the 2020–2025 mean (Figure 4) and 420 above the previous highest year.
What the data shows about summer 2026 temperatures
From Figure 1, the standout feature is March 2026, when maximum temperatures averaged 93 °F, exactly 12 °F higher than any other March in this record. Summer months, by contrast, sit inside the normal spread of the past seven years. Early-season heat matters because it accelerates plant growth, weed development, insect activity, soil drying, and residue breakdown before summer even begins.
Figure 1. Monthly mean daily maximum air temperature, AZMet Yuma Valley, 2020-2026. Aug. 2026=1-17 Aug. only; June 2024=1-27 only, with these shown as open markers.
Warm nights reduce the crop’s recovery time, as shown in Figure 2. Plants use night-time respiration to maintain living tissue, so when nights stay warm, more energy goes to maintenance, and less is available for growth, root development, and stress recovery. In 2026, every month with data ran above the six-year average for minimum temperature. That is not true of the maximum temperature line, where April was exactly at average, and May was 0.3 °F below it.
Figure 2. Monthly mean daily minimum (night-time) air temperature, AZMet Yuma Valley, 2020-2026. August 2026=1-17 only; June 2024=1-27 only, with these both shown as open markers.
As shown in Figure 3, August 1–17, 2026 was not the hottest daytime period among the seven years, but it was among the warmest at night. The mean daily maximum was 108.6 °F, and the mean daily minimum was 82.8 °F. The figure shows window averages; the daily record behind it carries the detail worth taking to the field. In 2026, 15 of those 17 nights never dropped below 80 °F, the highest count in this record, and 13 of them ran consecutively. 2024 matched that 13-night run and had a slightly higher average minimum (83.2 °F), so 2024 and 2026 are best described as the two warm-night years of this group rather than 2026 standing alone.
Figure 3. equal-window comparison, August 1-17 (n=17 d yr^-1), AZMet Yuma Valley.
By 31 July, 2026 had accumulated 553 °F-days more than the 2020–2025 mean, ahead of every other year by a wide margin from February onward.
Figure 4. Season-to-date accumulated heat units (86/55 degrees F), January 1st through July 31st. Aug 2026=1-17 only; June 2024=1-27 only.
Most of the extra heat arrived before June. March alone contributed 270 °F-days, nearly half the total surplus, and 89% of it was banked before 1 June. 2026 was not simply a hot summer; the season was running ahead before summer started.
Figure 5. Where the 2026 heat-unit surplus was banked (86/55 degrees F, by month). Dark bars signal January through May while grey bars are June and July.
Most of the extra heat arrived before June. March alone contributed 270 °F-days, nearly half the total surplus, and 89% of it was banked before 1 June. 2026 was not simply a hot summer; the season was running ahead before summer started.
Figure 6. Equal-window summer index, 1-27 June+1-31 July+1-17 August (75 d each year). June truncated to 27 d in all years so the incomplete June 2024 record does not bias the comparison. 95% Cl on any pairwise difference=+/-0.44 degrees F.
This is where the early heat shows up most clearly for field management. In panel (a), March 2026 averaged 73 °F at 4 inches, the warmest March in the record by 6 °F, and a level the recent record does not usually reach until April (the 2020–2025 April average is 72 °F). Interpolating the six-year baseline, that temperature is not normally reached until about 18 April, so 2026 was running roughly 35 days ahead at this depth by early spring. July and August at 4 inches (98 and 99 °F) were second only to 2020. Panel (b) tells a different story at 20 inches: warm through spring, then at or slightly below the 2020–2025 mean from May onward, so the summer heat signal stayed concentrated near the surface.
Figure 7. Soil temperature at two depths, AZMet Yuma Valley, 2020-2026. Aug 2026=1-17 only, designated by open marker. Data from AZMet Yuma Valley monthly summaries.
How does temperature impact water management?
In a hot year, the first reaction is often to assume the crop simply needs more water. Irrigation decisions should not be based on temperature alone. Crop water demand depends on reference ET, solar radiation, wind, humidity, crop stage, soil moisture, and root-zone conditions.
The 2026 data show exactly why this matters. Heat units were far ahead of recent years (Figure 4), but standardized reference ET through 31 July was only about 5% above the six-year average, 50.8 inches against a 2020–2025 mean of 48.3 inches, second behind 2022. A record heat-unit year did not produce a record water-demand year. Temperature and evaporative demand are not interchangeable, and 2026 is a clean illustration of the gap.
One practical note on which ETo number to use: AZMet reports both a legacy AZMet ETo and a standardized ASCE Penman–Monteith ETo. The legacy value runs roughly 6–10% higher in every year of this record (5.9% in 2026, 10.2% in 2020). If your crop coefficients were developed against the standardized reference, pairing them with the legacy AZMet column will over-apply water.
This matters most before produce season. If fields dry faster than expected, stand establishment becomes less uniform. If irrigation is over-applied, water moves nutrients below the root zone and complicates salinity management. In Yuma, irrigation is not only about replacing crop water use; it also controls salt movement, nutrient placement, and early root-zone conditions.
How does temperature impact IPM?
Heat also changes pest timing. Many insects develop faster as temperature accumulates, so the heat-unit surplus in 2026 is an IPM signal (Figures 4 and 5). When the season runs ahead, pest development may run ahead of the calendar too
That does not mean every pest problem will be worse. It means scouting should be timed to field conditions, crop stage, and heat accumulation rather than to planting date alone. Warm conditions can accelerate insect generations, speed weed growth, and drive movement from surrounding vegetation or summer crops into fall vegetable fields.
Warm nights matter here as well. Figures 2, 3, and 6 all point to elevated nighttime temperatures in 2026, and sustained warm nights keep plants under stress and may reduce their capacity to recover from daytime heat, insect feeding, or disease pressure. Crop stress belongs in the scouting picture: weak plants, uneven stands, field edges, and areas with poor water movement will usually show problems first.
I should be plain about what this section is. The thermal data are measured; the pest-timing implication is an inference from how insect development responds to accumulated heat. It is a reason to start looking earlier, not a forecast. Check it against your own trap counts and scouting records.
How does temperature impact the soil and root zone?
Soil does not respond to heat separately from water. High temperatures increase soil evaporation, speed residue breakdown, affect microbial activity, and change nutrient cycling. These processes are useful when they stay synchronized with crop demand and create problems when moisture, nitrogen availability, and residue decomposition drift out of step.
Figure 7 puts numbers on this for 2026. Soil at 4 inches was the warmest in the record for January, February, March, and April, and March reached a temperature the recent record does not normally see until April. For fields coming out of cover crops, fallow, or heavy residue before vegetable planting, that means biological and chemical processes were running ahead of schedule well before the main summer period.
Warm surface soils dry quickly, can concentrate salts near the seed line, and increase stress during germination. That is critical for fall vegetable establishment, where uniform moisture and salinity control determine stand quality. A field may look ready from the surface while the seed zone and root zone still carry heat, salts, or uneven moisture. Worth noting that the 20-inch record stayed near or below average from May onward; surface conditions and root-zone conditions were not telling the same story in 2026, which is an argument for measuring rather than assuming.
Summer 2026 was hot but not record-setting; it ranks second of the past seven summers, behind 2024. What set 2026 apart was everything that happened before June: the warmest January, February, and March in this record for air temperature, the warmest January through April at 4-inch soil depth, and a heat-unit surplus that was 89% complete before summer began. Yuma growers have built their success by responding to heat with precision and experience: better irrigation timing, stronger scouting, and careful root-zone management before produce season begins.