Evolution of Forest Precipitation Water Storage Monitoring Methodologies

Precipitation intercepted by forests plays a major role in the hydrologic cycle for more than one fourth of the global land area. Direct in situ measurement of intercepted precipitation is a challenging task. We discuss and compare measurement methods for forest precipitation interception beyond classical budgeting methods, with an emphasis on estimating the critical water storage component for rain and snow, then recommend future directions for the improvement of water storage estimation and monitoring.

Comparison of techniques estimating water storage shows that methods submerging tree components produce the largest storage capacity values. Indirect methods typically result in the lowest water storage estimates. Whole tree lysimeters have been used with great success, yet are unable to separate trunk vs. canopy storage components. Remote sensing technologies, particularly signal attenuation, may permit this separation. Mechanical displacement methods show great promise and, perhaps as a result, have the greatest variety of techniques. Relating wind sway to canopy water storage via accelerometers also shows great promise, yet is in the proof-of-concept stage at present.

Recommended future directions for forest water storage estimation are, to (1) apply these methods individually under different conditions to identify further strengths/weaknesses, (2) apply methods in tandem to identify complimentary strengths and limitations, (3) improve scaling techniques for element- and tree-specific techniques, (4) increase temporal monitoring resolution to capture intrastorm processes that may drive interception loss, and (5) foster synergies between communities developing methodologies for specific precipitation types as differing methods often rely on similar underlying measurement principles. Through addressing these research needs, we hope the scientific community can develop an “integrated” monitoring plan incorporating multiple measurement techniques to characterize forest-scale water storage dynamics while simultaneously being able to investigate underlying components driving those dynamics across the spectrum of precipitation and forest conditions.