Amanda Donaldson

UC Santa Cruz

“Aspect differences in vegetation type drive spatial variability in evapotranspiration and subsurface water storage within a California oak savanna “

Understanding how much water leaves hillslopes as evapotranspiration (i.e. evaporation and plant water use) is important for predicting water storage and movement within hillslopes. Small differences in solar radiation between adjacent hillslopes that face opposite directions can produce contrasting plant water use and hillslope water storage patterns. However, it remains unclear how the combination of differences of solar radiation and plant type (i.e. grasses and trees) influence evapotranspiration and water storage. Here, we combined on-site measurements and remote-sensing data to show that in central coastal California, a hillslope with oak trees that received less sunlight had higher evapotranspiration than a hillslope with grasses that received more sunlight. Importantly, we suggest that the cooler hillslope with oak trees may be drier and have lower groundwater recharge than the warmer hillslope with grasses, which is opposite the findings of previous studies with trees on both hillslopes. Our findings highlight the critical need for forest managers and modelers to consider hillslope-scale vegetation types to more accurately predict groundwater recharge and vegetation health within oak savannas.


Climate plays an important role in vegetation distributions which can have important consequences for available subsurface water supplies. Here, we explore the interplay between climate and vegetation water use patterns which is critical to better predict where and when groundwater recharge will occur.

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