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https://www.wired.com/story/why-tehran-is-running-out-of-water-iran-climate-change-drought-extreme-weather/
Why
Tehran Is Running Out of Water
Because of shifting storms and
sweltering summers, Iran’s capital faces a future “Day Zero” when the taps
run dry.
During the summer of 2025, Iran experienced an
exceptional heat wave, with daytime temperatures across several regions,
including Tehran, approaching 50 degrees Celsius (122 degrees Fahrenheit) and
forcing the temporary closure of public offices and banks.
During this period, major reservoirs supplying the Tehran region reached
record-low levels, and water supply systems came under
acute strain. By early November, the reservoir behind Amir Kabir
Dam, a main source of drinking water for Tehran, had dropped to about 8 percent of its capacity. The present crisis
reflects not only this summer’s extreme heat but also several consecutive
years of reduced precipitation and ongoing drought conditions across Iran. As
a result, the capital of Iran is now facing a potential “Day Zero” when taps
could run dry.
The drought quickly disrupted Tehran’s urban systems. With
dry soils and high evaporation, rivers and wetlands shrank. Falling reservoir
levels led to disruptions in hydropower generation,
and water shortages prompted strict saving measures across parts of the
capital. Amid these escalating pressures, officials warned that the capital
city may even have to be evacuated if
water supplies fail to recover. In November, President Masoud Pezeshkian said
the capital would have to be moved. These
cascading impacts exposed how vulnerable Tehran’s infrastructure, economy,
and communities have become under compounding heat and drought stress. These cascading impacts stem from a prolonged shortage of
precipitation in recent years (Figure 1a). Precipitation around Tehran
typically peaks between December and April, replenishing reservoirs behind
dams before the onset of the dry summer. Over the past five years,
precipitation during this wet period has remained consistently below the
long-term climatological baseline, with the 2024-25 season showing the most
pronounced and prolonged deficit across the entire rainy season. When such
prolonged dryness was followed by an exceptionally hot summer, it amplified
hydrological stress across the region. 
Seasonal
cycle of precipitation averaged over a 1°×1° region centered on Tehran, based
on GPM IMERG Final Run (V07B) dataset: monthly means for 2000/01–2019/20
(black), 2020/21–2024/25 (blue) and 2024/25 (red).
Illustration:
Yeonwoo Choi and Elfatih A.B. Eltahir/Bulletin of the Atomic Scientists This prolonged precipitation deficit was not confined to
Tehran but was part of a broader regional anomaly extending across much of
Iran (Figure 1b). Satellite-based estimates for November 2024 to April 2025
reveal a pronounced north–south precipitation dipole, with enhanced
precipitation north of latitude 40° N but markedly reduced precipitation
across central and southern Iran. The precipitation deficit was particularly
evident along a broad corridor extending from the eastern Mediterranean
through Iran, indicating reduced storm activity across the region. This
weakening of storm activity led to marked reductions in snowpack accumulation
and reservoir inflows, aggravating the ongoing water scarcity crisis. 
November-April
precipitation anomaly in 2024-25 relative to the 2000-01 to 2019-20 mean,
from GPM IMERG Final Run (V07B) dataset. Tehran is indicated by a black dot. Illustration: Yeonwoo Choi and Elfatih A.B.
Eltahir/Bulletin of the Atomic Scientists In maps of global projections of climate change impacts on
precipitation, the region over and around the Mediterranean basin stands out
because of the magnitude and significance of its precipitation decline. MIT
researchers Alexandre Tuel and Elfatih Eltahir have explained why this region stands out as a hot spot for
climate change. A more
recent follow-up study by our group projects future declines in winter
and spring precipitation extending to Mesopotamia and surrounding regions
under a high-emission scenario by the end of the century. The projected
change of the air circulation over the central and eastern Mediterranean,
where most storms originate during winter, inhibits the formation of storm
systems and consequently limits their eastward propagation, thereby reducing
precipitation over Mesopotamia and adjacent regions eastward, including the
area around Tehran. Another contributing factor is the poleward
displacement of storm tracks. During the spring season, the projected
changes in regional air circulation due to global climate change move
northward from the Mediterranean into southern Europe pushing the storm
tracks further north and creating a dipole pattern (more precipitation in the
north, less precipitation to the south) that reduces precipitation around
Tehran. Consistent with this theory, simulations by IPCC (Intergovernmental
Panel on Climate Change) models of future climate in this region project a
pattern of change that resembles the regional pattern observed this last
year, especially during the spring (Figure 1c). This similarity between
observed and projected patterns suggests that the dry conditions observed
this year may offer a glimpse of relatively dry conditions in the future,
especially in spring season. 
Projected
Spring (March–May) precipitation change derived from an ensemble mean of
three CMIP6 global climate models (MPI-ESM1-2-LR, HadGEM3-GC31-LL, and
NorESM2-LM), selected for their ability to capture the long-term mean climate
and its trends. Superimposed hatching denotes agreement (100 percent) by
three GCMs on the sign of the change. Illustration:
Yeonwoo Choi and Elfatih A.B. Eltahir/Bulletin of the Atomic Scientists The region around Tehran falls in a transitional zone
between the tropics and midlatitudes, with complex dynamics of storms
systems. The nature and origins of storms in this region are different
between winter and spring seasons. IPCC models do not fully agree on the
projections of winter precipitation around Tehran. Future research will be
needed to better understand natural climate variability as well as impacts of
future climate change on precipitation, especially during the winter season.
The extreme heat and drought affecting Tehran this year were
exceptional in both magnitude and duration. Events of this kind are projected
to become more frequent in the future around this region as the climate
warms. If this trajectory continues, Tehran is likely to face more frequent
droughts, reducing reservoir levels, limiting urban water supply, and
presenting significant hazards to the vital systems of public health, energy,
and food supply. Taken collectively, the findings from this recent event expose
an outstanding set of climate related risks and underscore the need for
immediate, dual-track action—rapid global emissions mitigation alongside
proactive local adaptation—to limit escalating risk.
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