📄 earth_science

Blue Water Footprint of Hydropower Generation under Arid and Semi-Arid Climatic Conditions

This study quantifies the blue water footprint of 25 Iranian hydropower plants from 2004 to 2021, revealing that evaporation losses in arid and semi-arid regions are significantly high and highly variable, thereby underscoring the urgent need for improved reservoir management and climate-integrated strategies to ensure sustainable energy-water interactions.

Original authors: Seyed Mohsen Mousavi, Forouzan Farrokhian

Published 2026-07-08

📖 4 min read☕ Coffee break read

CC BY 4.0

Original authors: Seyed Mohsen Mousavi, Forouzan Farrokhian

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine you have a giant swimming pool in your backyard. You want to use the water in that pool to power a small water wheel that generates electricity for your house. This is basically how a hydropower plant works: a dam holds back a river to create a reservoir (the pool), and the water flows through turbines to make power.

But here's the catch: your backyard is in a very hot, dry desert. Every day, the sun beats down on that pool, and a lot of the water simply turns into vapor and floats away into the sky. This is called evaporation.

This research paper is like a detailed audit of 25 different "backyard pools" (hydropower plants) across Iran, a country known for its hot and dry climate. The authors, Seyed Mohsen Mousavi and Forouzan Farrokhian, wanted to answer a simple question: How much water does it actually "cost" to make one unit of electricity when you have to account for all that water disappearing into the air?

The "Blue Water Footprint"

Think of the "Blue Water Footprint" as a water receipt. It tells you exactly how much water was "spent" to get a specific amount of energy. In this study, they calculated how many cubic meters of water evaporated for every Terajoule (a huge unit of energy) of electricity produced.

What They Found

The researchers looked at data from 2004 to 2021 and found some surprising things:

Size Doesn't Always Mean Efficiency: You might think a giant dam is the most efficient way to make power. While big dams produce more total power, the study found that smaller dams often have a much higher "water cost" per unit of electricity.
- The Analogy: Imagine a tiny, shallow puddle in the sun versus a deep, massive lake. The puddle loses a huge percentage of its water to evaporation every day compared to how much water it holds. Similarly, small reservoirs in hot areas lose a disproportionate amount of water relative to the tiny amount of electricity they generate.
- The Result: The Golab plant (a small one) had the highest water cost, losing a massive amount of water for every bit of power it made. The Shah Qasim plant had the lowest cost.
The Heat Factor: The location matters more than you might think. Plants in the hottest, driest parts of Iran lost way more water than those in slightly cooler or wetter areas. It's like leaving a glass of water on a scorching sidewalk versus in a cool basement; the sidewalk glass disappears much faster.
The "Drought Year" Spike: The study noticed that in 2021, the water cost skyrocketed. Why? Because 2021 was one of the driest years in Iran's recent history. The air was hotter, and there was less rain. This caused the reservoirs to evaporate even faster, making the "water receipt" for electricity much more expensive that year.

The "Shared Pool" Problem

Many of these dams aren't just for electricity. They are also used for farming (irrigation), drinking water, and flood control.

The Analogy: Imagine five friends sharing a pizza. If you say the whole pizza was eaten just to satisfy one friend's hunger, that's unfair.
The Study's Fix: The authors used a special math method to split the "evaporation bill" fairly. If a dam has 5 purposes and electricity is the 3rd most important one, they only counted 1/5th (or a specific share) of the evaporated water as the cost for electricity. This ensures they aren't blaming the power plant for water lost to farming or drinking needs.

The Big Takeaway

The paper concludes that in hot, dry places like Iran, building massive reservoirs for hydropower is a tricky trade-off. While it produces clean energy, it also "consumes" a lot of precious water just by letting it evaporate into the sky.

The authors suggest that in these dry regions, we need to be smarter about how we manage these "pools." They recommend:

Building different types of power systems that don't rely on huge, open pools of water (like run-of-river systems).
Using technology to cover the water surface (like floating solar panels) to stop evaporation.
Planning for the future by considering that the climate is getting hotter and drier, which will make evaporation even worse.

In short: Hydropower is great, but in a desert, it comes with a hidden "water tax" that we need to pay attention to.

Technical Summary: Blue Water Footprint of Hydropower Generation under Arid and Semi-Arid Climatic Conditions

Problem Statement
Freshwater resources are increasingly constrained by population growth, economic expansion, and climate change, a situation particularly acute in arid and semi-arid regions like Iran. While hydropower is a critical renewable energy source, its reliance on large reservoirs creates a significant "hidden water cost" through surface evaporation. In warm, dry climates, these evaporative losses can drastically reduce water availability for other sectors and undermine the sustainability of hydropower. Despite the importance of the water-energy nexus, there is a scarcity of comprehensive, quantitative assessments of the blue water footprint (BWF)—specifically the volume of surface and groundwater consumed and not returned to the catchment—associated with hydropower generation in Iran. Existing studies often lack detailed regional data or fail to adequately account for the multi-purpose nature of reservoirs and the influence of climatic variability on evaporation rates.

Methodology
This study employs a descriptive-analytical approach to quantify the BWF of 25 operational hydroelectric power plants in Iran over the period 2004–2021. The research population consisted of 73 active plants, from which 25 were purposively selected based on consistent operational data availability.

Data Sources: Annual electricity production (Terajoules, TJ) and reservoir evaporation volumes (cubic meters, m³) were extracted from official national energy balance sheets, reports by the Iran Water Resources Management Company, and data from the Hydropower Plants Management Center.
Water Footprint Calculation: The total water footprint ( $WF_{e,Total}$ ) was calculated as the sum of the construction phase ( $WF_{e,c}$ ) and the operational phase ( $WF_{e,o}$ ). Due to a lack of specific construction data for each dam, a proxy value of 0.3 m³/TJ (based on Golabi et al., 2019) was applied for the construction phase. The operational phase footprint was derived by dividing the annual evaporated volume ( $E_o$ ) by annual electricity production ( $P$ ).
Allocation of Evaporation: Recognizing that many reservoirs serve multiple purposes (e.g., irrigation, flood control, domestic supply), the study avoided attributing 100% of evaporation to hydropower. Instead, it utilized the allocation approach proposed by Scherer and Pfister (2016). An allocation factor ( $f_A$ ) was determined based on the priority ranking of hydropower among the reservoir's objectives ( $n$ ). If hydropower was ranked $r$ , the factor was calculated to distribute the evaporative loss proportionally.
Sensitivity Analysis: To address uncertainty in allocation assumptions, a sensitivity analysis was conducted comparing three scenarios: the study's baseline ranking-based allocation, an equal allocation among all purposes ( $f_A = 1/n$ ), and a full allocation to hydropower ( $f_A = 1.0$ ).
Statistical Analysis: Data normality was assessed using the Kolmogorov–Smirnov test, with analyses performed using SPSS version 23 and Excel.

Key Results
The study revealed significant heterogeneity in the blue water footprint across the 25 plants, heavily influenced by plant size, reservoir morphology, and local climate.

Variation by Plant Size: Contrary to the assumption that larger plants are always more efficient, the results showed that small-scale hydropower plants (<10 MW) exhibited the highest BWF per unit of energy produced.
- Highest BWF: The Golab plant (small scale) recorded the highest footprint at 283,852.15 m³/TJ.
- Lowest BWF: The Shah Qasim plant in Yasuj (small scale) had the lowest at 323.22 m³/TJ.
- Large Plants: Among large plants (>100 MW), Karkheh had the highest footprint (15,599.34 m³/TJ), while Karoon-3 had the lowest (412.84 m³/TJ).
Temporal Trends: The annual BWF fluctuated significantly between 2004 and 2021. The peak occurred in 2021 (11,136.44 m³/TJ), coinciding with one of the driest years in Iran's recent history, characterized by precipitation 40–50% below the long-term mean and higher temperatures. The lowest annual footprint was recorded in 2008 (3,690.31 m³/TJ).
Climatic Drivers: Plants in hot, arid regions demonstrated substantially higher water loss rates. The study confirmed that high temperatures, drought conditions, and low humidity directly intensified evaporation, thereby increasing the BWF.
Sensitivity Findings: While the absolute magnitude of the BWF varied significantly under different allocation assumptions (e.g., Golab's BWF ranged from ~283,000 m³/TJ in the baseline to ~1.77 million m³/TJ under full allocation), the relative ranking of the plants remained consistent. This suggests the study's principal conclusions regarding the high water intensity of specific plants are robust despite allocation uncertainties.

Significance and Claims
The paper claims to provide a novel framework for linking hydropower water use to climatic variability, offering a critical perspective on the sustainability of energy-water interactions in arid environments.

Re-evaluating Hydropower Sustainability: The findings challenge the conventional perception of hydropower as a universally sustainable energy source. In water-scarce regions like Iran, the high evaporation rates from large reservoirs can render such projects environmentally unjustified from a water-resource management perspective.
Methodological Contribution: The study demonstrates the necessity of integrating allocation factors and climate variability into water footprint assessments. It highlights that neglecting the multi-purpose nature of reservoirs or ignoring local climatic conditions leads to inaccurate sustainability evaluations.
Policy Implications: The authors argue that future hydropower planning in Iran must adopt a regionally differentiated approach. They suggest prioritizing run-of-river systems or smaller reservoirs with lower surface-area-to-volume ratios to minimize evaporation. Furthermore, the study advocates for the integration of water footprint analysis into national energy planning and the adoption of integrated water-energy management strategies to enhance resilience against climate change.
Global Context: The reported BWF values are generally higher than those in temperate regions but align with findings from other arid zones (e.g., southern Spain, South Africa), reinforcing the conclusion that local climate is the primary determinant of water footprint magnitude in hydropower systems.

The study concludes that while hydropower remains a key energy source, its sustainability in arid regions is contingent upon acknowledging and mitigating evaporative losses through improved reservoir management, climate-adaptive design, and diversification of the renewable energy portfolio.

The "Blue Water Footprint"

What They Found

The "Shared Pool" Problem

The Big Takeaway

Technical Summary: Blue Water Footprint of Hydropower Generation under Arid and Semi-Arid Climatic Conditions

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