Thermal imaging shows the city is 7°C warmer than surroundings at night. But the effect reverses during day due to irrigation creating an 'urban cool island' in summer.
A Tale of Two Islands
In most cities, a well-documented phenomenon called the Urban Heat Island (UHI) effect occurs. Paved surfaces and buildings absorb more of the sun's energy than natural landscapes. This stored heat radiates out after sunset, making cities significantly warmer than their rural surroundings. Tashkent is no exception at night. Satellite thermal data shows that the city can be 7-8°C (12-14°F) warmer than the adjacent countryside. Impervious surfaces like roads and buildings, which cover approximately 78% of the city, are the primary causes of this nighttime warming.
During the day, however, Tashkent performs a surprising thermal reversal. In the hot, arid summer, the city becomes cooler than the surrounding parched farmlands. This creates an "urban cool island" (UCI). The cause is water. Tashkent, an ancient oasis, is interlaced with a network of irrigation canals, some over a thousand years old, that divert water from the Chirchiq River. This water supports extensive green spaces—parks, gardens, and many trees lining the streets.
The Cooling Power of Water
The daytime cooling mechanism is a process called evapotranspiration. When water from irrigation evaporates from the soil and transpires from the leaves of plants, it consumes thermal energy and cools the surrounding air. The dry, non-irrigated agricultural land outside the city has very little surface moisture. It heats up quickly and intensely under the summer sun, which shines in famously clear skies for most of the season. Inside the city, the large-scale, human-made oasis effectively "sweats," keeping daytime temperatures down relative to the baked landscape nearby.
This effect is most pronounced in the hottest and driest months, like July, when average high temperatures reach 36°C (96°F). The extensive urban greenery is a powerful heat mitigation tool. Studies quantifying the effect found that the largest green spaces in Tashkent have a heat mitigation index of up to 0.83, where a value of 1 would mean the UHI effect is completely eliminated. While the nighttime heat island presents challenges, the daytime cool island shows how massive-scale green infrastructure, a part of the city's history, can fundamentally alter a local climate.
💡Fun Facts
Tashkent's complex canal system, which enables the cooling effect, has ancient roots. The Kalkaus Canal, for instance, may be over 2,000 years old.
Satellites like NASA's Terra and Aqua, equipped with the MODIS instrument, are tools for studying these temperature anomalies by measuring land surface temperature from orbit.
Much of Tashkent's modern green layout was established during its rebuilding as a model Soviet city after a devastating earthquake in 1966.
The city's shape, a compact area roughly 24 by 26 kilometers, also influences its microclimate by altering wind patterns.
The phenomenon is observable 24/7. The "cool island" effect is most noticeable on hot, clear summer afternoons (June-August), while the "heat island" is strongest on clear nights.
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The effect can be experienced throughout the city. Public parks, like the Tashkent Botanical Garden, are ideal places to observe the localized cooling from evapotranspiration.