Historical and Future Stream Temperature Change Predicted by a Lidar‐Based Assessment of Riparian Condition and Channel Width

Abstract

Riparian forests attenuate solar radiation, thereby mediating an important component of the thermal budget of streams. Here, we investigate the relationship between riparian degradation, stream temperature, and channel width in the Chehalis River Basin, Washington State. We used lidar data to measure canopy opening angle, the angle formed between the channel center and trees on both banks; we assumed historical tree heights and calculated the change in canopy angle relative to historical conditions. We then developed an empirical relationship between canopy angle and water temperature using existing data, and simulated temperatures between 2002 and 2080 by combining a tree growth model with climate change scenarios from the NorWeST regional prediction. The greatest change between historical and current conditions (~7°C) occurred in developed portions of the river network, with the highest values of change predicted at channel widths less than ~40 m. Tree growth lessened climate change increases in maximum temperature and the length of river exceeding biologically critical thresholds by ~50%–60%. Moreover, the maximum temperature of channels with bankfull widths less than ~50 m remained similar to current conditions, despite climate change increases. Our findings are consistent with a possible role for the riparian landscape in explaining the low sensitivity of stream temperatures to air temperatures observed in some small mountain streams.

Using a Mechanistic Model to Develop Management Strategies to Cool Apache Trout Streams under the Threat of Climate Change

“…; Cristea and Burges ; Seixas et al. ). Furthermore, planting of vegetation provides additional benefits, such as buffering sediment and pollutant input, stabilizing banks, and providing food and nutrients to aquatic organisms.…”

“…; Seixas et al. ; Wondzell et al. ) that increasing shade provided by riparian vegetation is one of the most effective, feasible means to keep streams from heating.…”

“…Modeling approaches have examined how shading (Cristea and Burges ; Johnson and Wilby ; Seixas et al. ), environmental water transfers (Elmore et al. ; Null et al.…”

Evaluation of Riparian Tree Cover and Shading in the Chauga River Watershed Using LiDAR and Deep Learning Land Cover Classification

“…The high resolution of LiDAR data enables an accurate examination of the tree canopy shading of rivers, and therefore the solar radiation reaching the rivers, without the need for field sampling [1,17]. Seixas et al (2018) [18] used LiDAR data to calculate canopy opening as an influence on water temperature and found that trees reduced maximum river temperatures in small channel widths. A meta-analysis of solar radiation calculations found that using 3D data ensures more accurate solar radiation calculations because it can incorporate the impact of vegetation structure on light filtration through the canopy [19].…”

An evaluation of different forest cover geospatial data for riparian shading and river temperature modelling

“…There is increasing concern that climate change could alter the suitability of rivers for socio‐economically important fish species, in particular salmonids which are adapted to cold water environments (Ficke, Myrick, & Hansen, ; Isaak, Wollrab, Horan, & Chandler, ; Jonsson & Jonsson, ). It is increasingly accepted that riparian woodland reduces the sensitivity of rivers to climate forcing and is a potentially valuable climate mitigation measure (Battin et al, ; Bowler, Mant, Orr, Hannah, & Pullin, ; Hannah, Malcolm, Soulsby, & Youngson, ; Seixas, Beechie, Fogel, & Kiffney, ). However, the circumstances and geographical context under which riparian woodland has the greatest impact on stream temperature are less well understood.…”