Material Insights · Understanding the Material World

Hydropower dams and Water

A dam's output is set by how much water reaches its reservoir, so a weak monsoon or a drought cuts generation and forces coal or gas to fill the gap. Reservoirs also lose water to evaporation and share it with irrigation and cities, which ties hydropower to water policy.

Hydropower dams (energy) and Water (commodity): 5 relationships.

How they are linked

1. Water is the fuel

Physical flow · Strong · River inflow to dam generation

A hydro plant turns the energy of falling water into electricity, so its output each season depends on rainfall and snowmelt filling the reservoir.

  • 16.3% fall in India's hydro generation, FY2023/24, the steepest in 38 years
  • 8.3% hydro share of India's power output in FY2023/24, a record low

Inadequate rainfall in 2023 cut India's hydro output and pushed the power system further onto coal, with fossil fuels reaching 77.2% of generation in 2023/24. Reservoirs smooth flows within a year but cannot cover a full failed season. Hydro output is therefore a weather-driven variable for grid operators and coal planners.

Sources: Power Technology

2. Drought risk

Shared risk · Strong · Low reservoirs cut supply in hydro-heavy grids

Countries that rely on one large reservoir for most of their power have no quick substitute when inflows fail, so a drought becomes a power shortage.

  • 215 of 1,080 MW Zambia's output at Kariba against capacity, 2024
  • 8.7% usable live storage at Kariba, 26 August 2024
  • 84.2% hydro share of Zambia's power generation, 2024

In 2024 Zambia's blackouts reached 17 to 21 hours a day and it planned its first ever halt of generation at Kariba. The episode shows that the water risk is concentrated: grids with diverse sources absorb a dry year, while hydro-dependent ones ration power and hit mining and industry.

Sources: bne IntelliNews

3. Climate shifts the water supply

Transition · Rising · Warming changes flows and evaporation

Higher temperatures make river flows more erratic, shift their timing and raise evaporation from reservoirs, which lowers and destabilises hydro output.

  • about 5.1 to 6.8% projected fall in hydro capacity factor on the Indian subcontinent by 2100, by warming scenario
  • 14.5% hydro share of electricity generation in South and Southeast Asia (IEA, 2021)

The IEA projects the decline to the end of the century relative to a 1970 to 2000 baseline, with the larger fall in a scenario above 4°C of warming. Heavier extreme rainfall also brings floods and landslides that damage plants. A falling and more variable capacity factor raises the cost of hydro per unit and the value of storage and backup.

Sources: IEA

4. Shared reservoirs, competing uses

Policy · Medium · Dams allocate water between power, farms and cities

Many reservoirs serve irrigation, drinking water and flood control as well as power, and evaporation from the reservoir surface is a real water loss charged to all of them.

  • 68 m3 per GJ average evaporative water footprint of 35 hydro plants studied
  • 10% estimated blue water footprint of all hydropower relative to that of global crop production, 2000
  • 166 reservoirs monitored weekly by India's Central Water Commission

68 m3 per GJ is roughly 245 m3 per MWh, but the range across plants is very wide, from 0.3 to 846 m3 per GJ, because shallow tropical reservoirs evaporate far more. Release schedules set by water authorities can favour irrigation over power in dry years. In India, weekly storage reports give an early signal of hydro output ahead of the dry season.

Sources: Central Water Commission, India; Hydrology and Earth System Sciences

5. Price link: resource

Cost and price · Weak · Both ways

Dam output depends on river flow, but the US water price index is a California market price that reflects local scarcity, not dam costs.

  • 0.09 monthly change correlation
  • -0.28 12-month change correlation
  • -0.02 fitted elasticity

Hydro has almost no fuel cost, so the water link shows up in volumes generated and in the price of the power that replaces it, not in a water price. Reservoir storage levels are the indicator that carries the relationship.

Sources: Material Insights (World Bank, FRED, IMF data)

For investors

Key learnings

  1. Hydro output is a weather variable: a weak monsoon in 2023 cut India's hydro generation by 16.3% and raised coal burn.
  2. Grids that depend on one large reservoir, such as Zambia's, turn droughts into power rationing that hits mining and industry.
  3. Warming is projected to cut hydro capacity factors on the Indian subcontinent by about 5 to 7% by the end of the century, which raises the value of storage and flexible backup.

What to track

  • Live storage in hydro reservoirs against normal: Below-normal storage before the dry season points to lower hydro and higher coal or gas generation (Weekly · Central Water Commission)
  • Monsoon rainfall against long-period average: A deficit signals lower inflows and hydro output in the following months (Weekly in season · India Meteorological Department)
  • Hydro generation and share: Shows how much thermal capacity is filling the gap (Monthly · Central Electricity Authority; Grid-India)

For policymakers

Key learnings

  1. Hydro reliability depends on rainfall, so capacity plans should assume dry years and hold thermal or storage backup.
  2. Reservoir release rules decide how water is shared between power and irrigation, which becomes contested in drought years.
  3. Evaporation from reservoirs is a real water cost that should count in comparing hydro with other low-carbon options.

What to track

  • Reservoir storage against 10-year average: Early warning for power and irrigation shortfalls (Weekly · Central Water Commission)
  • Hydro capacity factor trends: A falling trend signals climate effects on planned output (Annual · Central Electricity Authority; IEA)

India

India's hydro output fell 16.3% in FY2023/24 after poor rains, taking its share of power to a record low of 8.3%, and the Central Water Commission's weekly storage bulletin gives the best early signal of hydro supply.

Sources

  1. Hydropower generation in India has fallen at its fastest rate in 38 years, Power Technology (2024)
  2. Climate impacts on South and Southeast Asian hydropower: executive summary, IEA (2021)
  3. Historic drought compels Zambia to take unprecedented step of shuttering its largest hydropower plant, bne IntelliNews (2024)
  4. Live storage status of 166 reservoirs, bulletin of 19 February 2026, Central Water Commission, India (2026)
  5. The blue water footprint of electricity from hydropower (Mekonnen and Hoekstra, HESS 16, 179 to 187), Hydrology and Earth System Sciences (2012)
  6. Price correlation, Material Insights, Material Insights (World Bank, FRED, IMF data) (2026)