# Human contributions to evapotranspiration mitigate swings in dry-to-wet year transitions

## TL;DR

Human activities like irrigation significantly influence evapotranspiration in California, even during wet years, reducing expected climate-driven changes.

## Contribution

A framework to separate natural and human-driven evapotranspiration during extreme climate transitions in California.

## Key findings

- Human contributions made up 30% of statewide evapotranspiration in 2022 and 50% in managed lands in 2023.
- Evapotranspiration changes were less than 10% despite a shift from drought to a wet year.
- Human activity dampens expected increases in evapotranspiration during extreme climate transitions.

## Abstract

California’s food and economic security depends on water availability, particularly under increasingly extreme climate scenarios. A key component of the water balance is evapotranspiration, the combination of soil and surface evaporation and plant transpiration. Evapotranspiration is influenced by natural drivers (e.g., climate, vegetation cover) and human intervention (e.g., irrigation, land management). Here, we analyze the transition between one of California’s driest years (2022) to an exceptionally wet year (2023) to assess evapotranspiration responses to climate extremes. Despite increased precipitation, total statewide evapotranspiration changed less than 10%. In 2022, human contributions accounted for 30% of statewide evapotranspiration and 80% in managed lands. In 2023, natural evapotranspiration increased, and human contributions fell by 30%, yet still comprised nearly 50% of evapotranspiration in managed areas. Our findings underscore the enduring role of human activity on California’s hydrology, even during wet years, and demonstrate a framework to separate natural and anthropogenic controls on evapotranspiration.

Human activities dampen the expected increase in evapotranspiration during California’s transition from extreme drought to an exceptionally wet year during 2022–2023, as revealed through a framework that disentangles natural and anthropogenic contributions to evapotranspiration.