California drought study shows forests and croplands maintain ET tracking via distinct water sources while grasslands decouple
The study demonstrates that comparable evapotranspiration responses during California drought conceal contrasting water-access mechanisms across land covers, with implications for resource management. Preprint analysis of 2008-2024 anomalies highlights groundwater-linked declines in demand tracking at over half of grid cells. Policy must integrate vegetation-specific hydrology and management adjustments rather than assuming uniform ET behavior.
The arXiv preprint by Yan Zhang quantifies demand-tracking ability via slopes relating ETa and ETo anomalies, separating vegetation types and distinguishing subsurface access in forests from managed irrigation plus fallowing in croplands. Active-field ET responses masked statewide crop-system adjustments, with higher fallow shares during drought than baseline. This challenges uniform drought-impact assumptions by showing similar ETa-ETo coupling can arise from hydrology versus policy-driven management. Groundwater depletion amplified regional declines in tracking ability, indicating thresholds where subsurface reserves no longer buffer demand. Water agencies relying solely on ET observations risk misallocating supplies if they overlook these mode differences. Joint hydrologic and land-use monitoring would better inform drought declarations and allocation rules under warming.
Zhang et al.: Statewide groundwater storage losses exceeding 15 km3 by 2028 will reduce positive ETa-ETo slopes below 0.4 in >65% of cropland grid cells.
Sources (3)
- [1]Primary Source(https://arxiv.org/abs/2610.09181)
- [2]Supporting Source(https://www.science.org/doi/10.1126/science.abq8331)
- [3]Supporting Source(https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2022WR033267)