Increasing large precipitation events and low available water holding
capacity create the conditions for dry land-atmosphere feedbacks in the
Northeastern United States
Abstract
As a warmer climate enables an increase in atmospheric humidity, extreme
precipitation events have become more frequent in the northeastern
United States. Understanding the impact of evolving precipitation
patterns is critical to understanding water cycling in temperate forests
and moisture coupling between the atmosphere and land surface. Although
the role of soil moisture in evapotranspiration has been extensively
studied, few have analyzed the role of soil texture in determining
ecosystem-atmosphere feedbacks. In this study, we utilized long term
data associated with ecosystem water fluxes to deduce the strength of
land-atmosphere coupling at Harvard Forest, Petersham, MA, USA. We found
a 1.5% increase in heavy precipitation contribution per decade where
high-intensity events compose upwards of 50% of total yearly
precipitation in 2023. Intensifying precipitation trends were found in
conjunction with a long-term soil drying at the Harvard despite no
significant increase in evapotranspiration over 32 years. This suggests
that soil water holding capacity is a key mediating variable controlling
the supply of water to ecosystems and the atmosphere. We found that
these land surface changes directly impacted the lifted condensation
level (LCL) height over Harvard Forest which was found to be decreasing
at a rate of 6.62 meters per year while atmospheric boundary layer (ABL)
heights have fallen at a modest rate of 1.76 meters per year. This has
amplified dry feedbacks between the land surface and the atmosphere such
that 80% of observed summers ending in a water deficit also had an
anomalously low soil water content in the spring.