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Goal: Apply Knowledge Globally Longer growing seasons result in greater water use in hardwood forests

Stream gauge (weir) at Coweeta

Changing streamflow patterns in southern Appalachian forested watersheds are a result of changing forest condition, climate change and variability, and their interactions. Some of these changes have been quantified using gaged watersheds (above); however, new techniques such as remote sensing and modeling are required to predict responses in ungauged watersheds and at larger spatial scales. (Forest Service photo by James M. Vose)

Introduction

Most studies of hydrologic responses to climate variability do not account for changes in vegetation that may co-occur with changing climate. Warming has lengthened the growing season. Longer growing seasons result in greater forest water use, and hence less streamflow. Accounting for this variation in a process-based model improved predictions of streamflow and will help watershed managers anticipate and plan for changes in future water supply.

Summary

Forested watersheds provide important ecosystem services such as high quality freshwater, flood mitigation, and maintenance of base flows. Climate variability could dramatically alter such ecosystem services; however, most modeling studies do not account for co-occurring changes in forest vegetation structure and dynamics that influence water use and impact streamflow. SRS researchers used a combination of remote sensing, gauged watersheds, climate measurements, and modeling to understand changes in climate, vegetation, and streamflow.

Long-term climate and streamflow data indicate that forest vegetation has begun using significantly more water over the last three decades. Increased water use was significantly correlated with changes in growing season length and vegetation growth. The longer growing seasons and faster growth are primarily attributed to increases in minimum temperatures – the coldest days of the year are not as cold as they once were. Minimum temperatures are increasing faster and more consistently than changes in maximum temperatures. Incorporating changes in temperature-driven phenology and vegetation growth responses into a process-based model improved streamflow predictions.

Principal Investigator
James M. Vose, Project Leader
RWU
4855 - Center for Integrated Forest Science
Strategic Program Area
Water, Air, and Soil
Publication
Nonstationary hydrologic behavior in forested watersheds is mediated by climate-induced changes in growing season length and subsequent vegetation growth
External Partners
Katherine L. Martin, North Carolina State University
Tae Hee Hwang, University of Indiana
Yuri Kim, University of Indiana
Larry Band, University of Virginia
Brian Miles, University of North Carolina