A brown wave of riparian woodland mortality following groundwater declines during the 2012–2019 California drought

Abstract As droughts become more frequent and severe under anthropogenic climate change, water stress due to diminished subsurface supplies may threaten the health function of semi-arid riparian woodlands, which are assumed be largely groundwater dependent. To better support management woodlands changing climatic conditions, it is essential understand sensitivity depth (DTG) across space time. In this study, we examined six stands woodland along 28 km Santa Clara River in southern California. Combining remote sensing data fractional land cover, based on spectral mixture analysis, with historical data, assessed changes response DTG during unprecedented 2012–2019 California drought. We observed a coherent ‘brown wave’ tree mortality, characterized by decreases healthy vegetation cover increases dead/woody progressed downstream through corridor between 2012 2016. also found consistent, significant relationships separately indicating that deteriorated predictable fashion as table declined at different sites times. Based these findings, conclude brown wave dieback was likely caused local associated propagation precipitation deficits into depleted shallow alluvial aquifer. These factors suggest strongly dependent availability, turn sensitive forcing.