Above‐stream microclimate and stream surface energy exchanges in a wildfire‐disturbed riparian zone

Abstract

Abstract:Stream temperature and riparian microclimate were characterized for a 1Ð5 km wildfire-disturbed reach of Fishtrap Creek, located north of Kamloops, British Columbia. A deterministic net radiation model was developed using hemispherical canopy images coupled with on-site microclimate measurements. Modelled net radiation agreed reasonably with measured net radiation. Air temperature and humidity measured at two locations above the stream, separated by 900 m, were generally similar, whereas wind speed was poorly correlated between the two sites. Modelled net radiation varied considerably along the reach, and measurements at a single location did not provide a reliable estimate of the modelled reach average. During summer, net radiation dominated the surface heat exchanges, particularly because the sensible and latent heat fluxes were normally of opposite sign and thus tended to cancel each other. All surface heat fluxes shifted to negative values in autumn and were of similar magnitude through winter. In March, net radiation became positive, but heat gains were cancelled by sensible and latent heat fluxes, which remained negative. A modelling exercise using three canopy cover scenarios (current, simulated prewildfire and simulated complete vegetation removal) showed that net radiation under the standing dead trees was double that modelled for the pre-fire canopy cover. However, post-disturbance standing dead trees reduce daytime net radiation reaching the stream surface by one-third compared with complete vegetation removal. The results of this study have highlighted the need to account for reach-scale spatial variability of energy exchange processes, especially net radiation, when modelling stream energy budgets.

Determining the effects of wildfire on sediment sources using 137Cs and unsupported 210Pb: the role of landscape disturbances and driving forces

“…The watersheds have a distinct snowmelt hydrological regime, with melting typically starting in late March and the main flood discharges (pre-wildfire) occurring from mid April to late May Eaton et al 2010a;WSC 2012), with annual discharge peaks of approximately 5 to 8 m 3 s −1 (Leach and Moore 2010;WSC 2012). River discharge data are available for Fishtrap Creek at the WSC gauging station (WSC (2012), station ID 08LB024, see Eaton et al 2010a) of source materials (n027) was collected from Fishtrap and Jamieson watersheds soon after the 2003 wildfire in spring/ summer 2004 (for details see Owens et al 2006).…”

“…In addition, samples were collected from actively eroding channel banks; typically, these ranged in height from ca. 0.3 to 1.0 m and had vertical faces, with a post-fire riparian vegetative cover of standing dead defoliated trees, forbaceous shrubs and fireweed (Leach and Moore 2010). Each source sample represented a composite of five to ten subsamples collected within a ca.…”

Climate change, forests, fire, water, and fish: Building resilient landscapes, streams, and managers

“…Warmer air masses will also increase the temperature of the forest canopy, again increasing downwelling longwave radiation. Direct warming from sensible heat transfer will likely be comparatively small (Leach and Moore 2010) and could easily be offset from increased evaporation from reduced relative humidity. Strong correlations between stream temperature and air temperature have made air temperature a proxy in estimating future stream temperature (Mohseni and others 2003;Rieman and others 2007;Wenger and others 2011b).…”

The influence of riparian vegetation shading on water temperature during low flow conditions in a medium sized river

“…Solar radiation reaching the stream is influenced by different topographic factors, including the prevailing riparian vegetation buffer, which can decrease incoming energy by up to 95% (Rutherford et al, 1997;Moore et al, 2005;DeWalle, 2010). During summer heatwave periods in particular, solar energy plays a key role in influencing stream energy heat budget, and consequently stream water temperature (Johnson, 2004;Leach and Moore, 2010;Groom et al, 2011). Hence shading through riparian vegetation, primarily in small to medium sized and slowly flowing lowland rivers, is often most relevant to avoid excessive heating in order to mitigate adverse effects on the ecosystem (Ghermandi et al, 2009;He et al, 2011;Holzapfel et al, 2013).…”