Research Collection Doctoral Thesis Canopy structure controls on forest snow cover dynamics Author(s): Mazzotti, Giulia Publication Date: 2020 Permanent Link: https://doi.org/10.3929/ethz-b-000476668 Rights / License: In Copyright - Non-Commercial Use Permitted This page was generated automatically upon download from the ETH Zurich Research Collection. For more information please consult the Terms of use. ETH Library Canopy structure controls on forest snow cover dynamics Giulia Mazzotti Diss. ETH No. 27121 Diss. ETH No. 27121 CANOPY STRUCTURE CONTROLS ON FOREST SNOW COVER DYNAMICS A thesis submitted to attain the degree of DOCTOR OF SCIENCES of ETH Zurich (Dr. sc. ETH Zurich) presented by GIULIA MAZZOTTI MSc ETH Env Eng born on 15 April 1990 citizen of Italy and Zurich ZH accepted on the recommendation of Prof. Dr. Daniel Farinotti, examiner Dr. Tobias Jonas, co-examiner Prof. Dr. Jessica Lundquist, co-examiner Dr. Manfred Stähli, co-examiner 2020 Contents Summary ............................................................................................................................ vii Sommario............................................................................................................................ ix Introduction ..................................................................................................................... 1 1.1 Rationale ............................................................................................................................... 1 Relevance of forest snow .............................................................................................. 1 Motivation of the project .............................................................................................. 2 1.2 Background ........................................................................................................................... 2 Forest snow processes and dynamics ........................................................................... 2 Forest snow models ..................................................................................................... 4 Research challenges and opportunities ....................................................................... 5 1.3 Project overview .................................................................................................................. 6 Research goals and framework .................................................................................... 6 Thesis outline ................................................................................................................ 7 Distributed snow and canopy structure datasets from airborne LiDAR ..................... 11 2.1 Introduction ....................................................................................................................... 13 2.2 Study areas and data .......................................................................................................... 14 Eastern Swiss Alps ....................................................................................................... 14 Grand Mesa, Colorado ................................................................................................ 16 2.3 Methods .............................................................................................................................. 16 Snow depth data processing ....................................................................................... 16 Canopy structure metrics and distance to canopy edge (DCE) algorithm ............... 16 Validation of ALS-based snow maps .......................................................................... 19 Data aggregation to the grid-cell level .......................................................................20 2.4 Results ................................................................................................................................. 21 Validation of ALS-derived snow depth from the Swiss dataset ................................ 21 Relationships between snow depth distribution and canopy structure at the pixel level .............................................................................................................................. 23 Relationships between snow depth distribution and canopy structure at the grid cell level ....................................................................................................................... 25 2.5 Discussion ........................................................................................................................... 27 Evaluation of LiDAR-derived snow depth datasets within forest stands ................. 27 Canopy-structure to snow-distribution relationships in the context of experimental studies and forest snow modelling .............................................................................29 i Contents 2.6 Conclusion .......................................................................................................................... 32 2.7 Supplementary material of the main publication ............................................................. 33 Further specifications of the DCE algorithm and the classification based on directional DCE ........................................................................................................... 33 Validation of the 1-m snow depth maps and comparison to the 3-m product ......... 35 Snow depth distribution within DCE classes at the pixel level ................................ 36 Example of differential snow depth maps at Grand Mesa ........................................ 37 2.8 Summary of additional publication ................................................................................... 39 Study goals and methods ............................................................................................ 39 Main results and discussion ...................................................................................... 40 Hyper-resolution forest snow modelling validated using snow distribution data .... 43 3.1 Introduction ....................................................................................................................... 45 3.2 Methods ............................................................................................................................. 46 Study sites and snow depth data ............................................................................... 46 Canopy structure metrics .......................................................................................... 48 The Flexible Snow Model (FSM2) ............................................................................. 49 Meteorological driving data ...................................................................................... 49 Model application and evaluation strategy................................................................ 50 3.3 Results ................................................................................................................................. 52 Empirical relationships between snow distribution and canopy structure .............. 52 Simulations of spatiotemporal snow depth distribution dynamics with alternative canopy representations ............................................................................................... 54 Model performance metrics ....................................................................................... 61 3.4 Discussion ........................................................................................................................... 63 3.5 Conclusion ......................................................................................................................... 64 3.6 Appendix of the main article: Description of the FSM2 forest canopy module ............. 66 3.7 Summary of additional publication .................................................................................. 69 Rationale..................................................................................................................... 69 Model overview ...........................................................................................................70 Distributed observations of forest snow energy balance components from mobile multi-sensor platforms ...................................................................................................... 73 4.1 Introduction ....................................................................................................................... 75 4.2 Data and methods ..............................................................................................................76 Theoretical background ..............................................................................................76 Instrumentation ..........................................................................................................78 Field areas and campaigns ..........................................................................................79 Handheld radiometer surveys and data processing ................................................. 80 Canopy structure data from hemispherical photography and airborne LiDAR ...... 80 ii Contents 4.3 Results ................................................................................................................................. 81 Sky-view fraction estimates from repeated handheld radiometer measurements .. 81 Validation of sky-view fraction estimates