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The northeastern U.S. has experienced a rapid rise in extreme precipitation events and total precipitation due to climate change. Despite higher overall precipitation, long-term near-surface soil moisture at the Harvard Forest in Petersham, MA has decreased since 2010, a pattern also observed in other global temperate forest regions. In this study, we used more than thirty years of ecosystem-atmosphere water and carbon exchange at the Harvard Forest to understand the impact of precipitation extremes during the past decade on ecosystem water and carbon fluxes and the strength of land-atmosphere coupling. We found that in this mesic temperate forest, well-drained post-glacial soils rapidly drain surplus moisture from large rain events, while the remaining moisture necessary to preserve local humidity is quickly lost to evapotranspiration unless frequently replenished by rainfall. This region has also experienced two hot summer droughts during the past decade, causing further hydrological stress with carbon cycle implications. Furthermore, meteorological conditions in the nongrowing season have particularly shifted to warmer, drier conditions that set the stage for more frequent summer soil moisture deficits. In response to this past decade of hydrological extremes, we have observed a dampening of canopy light response curves, indicating lower rates of carbon uptake during the growing season and a parallel decline in ecosystem respiration as soils dry. More frequent dry conditions during key phenological windows, the intense delivery of rainfall during a shorter temporal window in the growing season, and rising summer temperatures and lower humidity have combined to decrease the ecosystem carbon uptake by photosynthesis and created large interannual variation in the strength of the net carbon sink at Harvard Forest during the past decade compared to the prior two decades of this study.
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This content will become publicly available on November 17, 2026
Hydraulic Redistribution Decreases with Precipitation Magnitude and Frequency in a Dryland Ecosystem: A Data-Model Fusion Approach
Abstract. Hydraulic redistribution (HR), the movement of water via plant root systems that connect soil compartments with different water potential, should influences soil moisture dynamics particularly in water-limited ecosystems. Realistic representation of HR in ecosystem models is essential to improve the ability of these models to predict ecosystem function in dryland regions. In this study, we integrated HR into the Terrestrial ECOsystem model and employed a Bayesian Markov Chain Monte Carlo technique to optimize soil hydraulic parameters and root conductance using four years of soil moisture observations from a piñon-juniper woodland. We found that (i) integrating HR generally improved model prediction of soil moisture during dry periods, particularly in the top 30 cm of the soil profile, where more than 50 % of root biomass exists, mostly during dry periods; (ii) HR increased surface soil moisture by up to 60 % during dry periods; (iii) HR decreased with increasing precipitation magnitude and frequency, however, the length of dry spells between rainfall events also influenced HR rates; and (iv) upward HR in the top 60 cm soil profile became more pronounced as dry conditions progressed, with rates ranging from 0.10 to 0.50 mm d⁻¹. These findings highlight that HR plays a likely role in sustaining soil moisture during extended dry periods and has a limited effect during precipitation events. Future research should investigate the effect of HR on other ecosystem processes, such as net ecosystem exchange of carbon and evapotranspiration under varying climatic conditions.
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- Award ID(s):
- 2425290
- PAR ID:
- 10654350
- Publisher / Repository:
- Copernicus Publications
- Date Published:
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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