Growing Season Water Balance Model Applied to Two Douglas Fir Stands

The forest water balance model presented requires only daily solar radiation, maximum and minimum air temperature, and rainfall as the input weather data. Site parameters are root zone depth, soil water retention and drainage characteristics, estimated canopy leaf area index, and the coefficients of the evapotranspiration and rainfall interception submodels. The evapotranspiration submodel calculates the forest evapotranspiration rate as the lesser of energy-limited and soil-limited rates. The former is calculated from the 24-hour net radiation and the latter from the fraction of extractable water in the root zone. Solar radiation and air temperature are used to calculate net radiation. Interception is calculated from the daily rainfall. The root zone is treated as a single layer with drainage calculated as a function of the root zone water content. Water deficits and the matric potential of the root zone are used to indicate tree Water stress. The model was tested on two Douglas fir stands of different stand density and leaf area index. The coefficients used in the evapotranspiration submodel were found to be the same for both stands. It was also found that over 20% of the growing season rainfall was lost through interception. An edited version of this paper was published by AGU. Copyright 1981a American Geophysical Union.Land and Food Systems, Faculty ofReviewedFacult

Suburban Energy Balance Estimates for Vancouver, B.C., Using the Bowen Ratio-Energy Balance Approach.

The energy balance of a suburban site in Vancouver, B.C. in late summer is presented. The balance is obtained from direct measurements of net radiation, parameterized heat storage and turbulent fluxes determined according to the Bowen ratio-energy balance method with reversing psychrometers. An error analysis shows the turbulent fluxes are good to within 10–20% by day. Features of the suburban energy balance are found to be intermediate between those previously reported for urban and rural surfaces. Average daytime Bowen ratios are usually in the range 0.5–1.0 with some days as high as 2.5. The daytime sensible heat flux is in-phase with the net radiation. At night this flux is sometimes positive. Evapotranspiration is always an important term in the balance. The role of urban irrigation and microscale heat advection in maintaining evapotranspiration rates is discussed. Copyright 1980 American Meteorological Society (AMS). Permission to use figures, tables, and brief excerpts from this work in scientific and educational works is hereby granted provided that the source is acknowledged. Any use of material in this work that is determined to be “fair use” under Section 107 of the U.S. Copyright Act or that satisfies the conditions specified in Section 108 of the U.S. Copyright Act (17 USC §108, as revised by P.L. 94-553) does not require the AMS’s permission. Republication, systematic reproduction, posting in electronic form, such as on a web site or in a searchable database, or other uses of this material, except as exempted by the above statement, requires written permission or a license from the AMS. Additional details are provided in the AMS Copyright Policy, available on the AMS Web site located at (http://www.ametsoc.org/) or from the AMS at 617-227-2425 or [email protected], Faculty ofGeography, Department ofReviewedFacult

Spatial and Temporal Variability of Potential Evaporation across North American Forests

Given the widespread ecological implications that would accompany any significant change in evaporative demand of the atmosphere, this study investigated spatial and temporal variation in several accepted expressions of potential evaporation (PE). The study focussed on forest regions of North America, with 1 km-resolution spatial coverage and a monthly time step, from 1951–2014. We considered Penman’s model (EPen), the Priestley–Taylor model (EPT), ‘reference’ rates based on the Penman–Monteith model for grasslands (ERG), and reference rates for forests that are moderately coupled (ERFu) and well coupled (ERFc) to the atmosphere. To give context to the models, we also considered a statistical fit (EPanFit) to measurements of pan evaporation (EPan). We documented how each model compared with EPan, differences in attribution of variance in PE to specific driving factors, mean spatial patterns, and time trends from 1951–2014. The models did not agree strongly on the sensitivity to underlying drivers, zonal variation of PE, or on the magnitude of trends from 1951–2014. Sensitivity to vapour pressure deficit (Da) differed among models, being absent from EPT and strongest in ERFc. Time trends in reference rates derived from the Penman–Monteith equation were highly sensitive to how aerodynamic conductance was set. To the extent that EPanFit accurately reflects the sensitivity of PE to Da over land surfaces, future trends in PE based on the Priestley–Taylor model may underestimate increasing evaporative demand, while reference rates for forests, that assume strong canopy-atmosphere coupling in the Penman–Monteith model, may overestimate increasing evaporative demand. The resulting historical database, covering the spectrum of different models of PE applied in modern studies, can serve to further investigate biosphere-hydroclimate relationships across North America.Forestry, Faculty ofNon UBCReviewedFacult

Applying Resilience Concepts in Forest Management: A Retrospective Simulation Approach

Increasing the resilience of ecological and sociological systems has been proposed as an option to adapt to changing future climatic conditions. However, few studies test the applicability of those strategies to forest management. This paper uses a real forest health incident to assess the ability of forest management strategies to affect ecological and economic resilience of the forest. Two landscape scale strategies are compared to business as usual management for their ability to increase resilience to a climate-change induced mountain pine beetle outbreak in the Kamloops Timber Supply Area, British Columbia, Canada for the period 1980 to 2060. Proactive management to reduce high risk species while maintaining or increasing diversity through reforestation was found to be more resilient in terms of the metrics: post-disturbance growing stock, improved volume and stability of timber flow, and net revenue. However, landscape-scale indicators of diversity were little affected by management. Our results were robust to uncertainty in tree growth rates and timber value and show that adapting to climate change through improving the resilience of forested landscapes is an economically viable option

Upper Penticton Creek data note

The Upper Penticton Creek Watershed Experiment is one of a handful of forestry-focused pairedcatchment experiments in the snow-dominated zone of western North America. The study involves an undisturbed control catchment and two treatment catchments. Streamflow has been monitored at weirs on all three streams since 1985. Following a pre-harvest monitoring period, the treatment catchments were subject to clearcut harvesting in multiple passes that cumulatively covered ~50% of the catchments. In addition to streamflow, available hydrometeorological data sets include weather observations, snowpack water equivalent, rainfall interception, soil water content, and water table levels in soil piezometers and bedrock wells. The data archive also includes digital elevation models, a Lidar-derived image of tree heights in 2016, and vector data associated with lakes and reservoirs, the stream network, clearcut boundaries, a soil map and the logging road network. Together, these data sets provide a basis for empirical analyses of hydrological response to forest dynamics and climatic variability, and for calibration and testing hydrological models using internal variables. They should also provide useful data sets for educational purposes.Arts, Faculty ofForestry, Faculty ofNon UBCForest Resources Management, Department ofGeography, Department ofReviewedFacultyPostdoctoralOthe