A new study from the PIE lab shows that California’s dramatic swing from extreme drought in 2022 to record-breaking rains in 2023 didn’t reset the water cycle the way we might expect. Despite the surge in precipitation, evapotranspiration (ET) — the water returning to the atmosphere from soils and plants — stayed remarkably stable. Why? Because humans are a major driver of it.
During the drought, irrigation and other managed water use made up about 30% of statewide ET, buffering ecosystems and food production against collapse but increasing reliance on groundwater. In the wet year that followed, human activity still accounted for nearly half of ET in managed landscapes, revealing that exceptional rainfall will not compensate for California’s agricultural water demand. In California, the water cycle is not just shaped by climate — it’s co-engineered by people.
