New Research from Harvard Forest Reveals How Intense Rainfall Contributes to Future Droughts

A new study published in Water Resources Research sheds light on how New England’s soils interact with extreme precipitation, revealing a feedback loop that may contribute to future drought conditions. This research began in 2023 at Harvard Forest as part of the National Science Foundation (NSF) Research Experience for Undergraduates (REU) program and was led by Sam Jurado, then an undergraduate at Cornell University who was mentored by Dr. Jackie Matthes, a Harvard Forest Senior Scientist. The study continued through the summer of 2024 with support from the NSF Long-Term Ecological Research (LTER) program and in collaboration with Dr. Matthes leveraging long-term data from Harvard Forest and the National Ecological Observatory Network

Key Findings

The research, Increasing Large Precipitation Events and Low Available Water Holding Capacity Create the Conditions for Dry Land‐Atmosphere Feedbacks in the Northeastern United States, identifies a crucial relationship between precipitation patterns and soil types in New England. Despite the region experiencing intense rainfall events, the study found that these short bursts of rain onto rocky soils leads to rapid drainage through the soil without enough time for water to be retained in upper soil layers effectively. This leads to drier near-surface soils, despite higher overall rainfall, that leads to less evaporation and lower moisture in the atmosphere that could contribute to future rainfall. In contrast, sustained and small to moderate rainfall events allow for more effective water retention in the soil, preserving soil moisture and supporting future rainfall. "It seems counterintuitive, that it can be raining more while the soil is becoming drier, but we found that our rocky, post-glacial soils at Harvard Forest play a critical role in regulating this feedback between the forest and future rainfall," said Matthes.

Additionally, the study found that seasonal moisture levels are interconnected—dry conditions in the spring, for example, reduce soil moisture availability in the summer, which in turn decreases the likelihood of stable precipitation patterns during the growing season. "While dry soils are commonly assumed to be a reliable indicator of a lack of recent rainfall, they may also prevent future rain by not releasing enough moisture back into the atmosphere," explains Jurado. "Dry soils make for dry skies, meaning that when ecosystems experience a water deficit, they become increasingly dependent on water transported by the winds for the rest of the season."

Why It Matters

This research has critical implications for weather forecasting, water resource management, and agriculture. Understanding how soil moisture influences precipitation feedback loops can improve storm and drought predictions, helping decision-makers anticipate and prepare for water shortages more effectively.

• Public Water Supplies: Many communities rely on surface water reservoirs that are highly sensitive to drought conditions. A better grasp of precipitation patterns can help water managers make informed decisions earlier, mitigating the impact of water shortages.
• Agriculture & Gardening: Farmers and gardeners can use this information to anticipate drought conditions, selecting crops that are better suited to drier growing seasons.
• Forest Resilience: Trees have adapted to drought conditions over millennia, with species that grow deeper roots proving more resilient. This research underscores the importance of studying natural ecosystems to inform climate adaptation strategies.

 Looking Ahead

As climate change continues to alter weather patterns, this study emphasizes the interconnectedness of ecosystems across time. Just as winter snowmelt helps stabilize summer atmospheric moisture, our decisions today—whether in conservation, agriculture, or urban planning—can help shape a more sustainable climate future.