Hydrologic Change & Riparian Forests
Jason Ward
Winter Ecology – Spring 2008
Mountain Research Station – University of Colorado, Boulder

-How is climate change affecting Hydrology in the
Rockies?

-How is climate change affecting Hydrology in the
Rockies?
-How will this effect willows and
Cottonwoods in Riparian forests?

-Changes will vary Spatially
-Large Scale - Hemisphere
-Small Scale - C1 station to D1 station
-Not only the overall annual discharge is ecologically important, but also seasonal pattern of stream flow

Locations of hydrometric gauges
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Slightly increased winter flows

Earlier spring melt and run-off

Earlier spring peak discharge

Considerably decreased summer flows, especially in late summer and early autumn.

Annual hydrographs for the Bow River at Banff

1) Slightly increased winter flows
2) Earlier spring melt and run-off
3) earlier spring peak discharge
4) considerably decreased summer flows, especially in late summer and early autumn.

How will this impact Riparian cottonwoods and willows?

• Slight influence.
• Cottonwoods, willows and other deciduous riparian plants are leafless and physiologically relatively inactive and insensitive in winter.
• Changing winter flow regime will impact ice formation and break-up that provides a fluvial geomorphic force that produces colonization sites for seedlings and scarifies cottonwoods and willows

Earlier spring run-off and peak flows
• Slight to considerable stress.
• Plant life cycle and timing is coordinated with patterns of the natural flow regime, including floodplain inundation, bank scour and deposition, and water stage patterns that influence surface moisture and groundwater.
• The partial uncoupling of the phenology of cottonwoods and willows with the river flow regime would reduce seedling recruitment and may limit colonization to lower bank elevations, resulting in narrower bands of new cottonwoods, and narrower floodplain forests

• Major stress.
• Especially in arid and semi-arid regions, riparian groundwater is recharged with water from the stream during the summer.
• Decreasing stream flow would reduce this recharge, resulting in drought stress
• Seedlings and saplings would be particularly vulnerable and this would further diminish reproduction that is essential for long-term forest survival

• due to the changes in river flow seasonality there will be fewer years with cottonwood seedling recruitment, and narrower bands of recruits during those favorable years.
• Reduced summer flows will likely become the most difficult hydrologic stress to overcome.
• AS riparian ecoregions reced and surrounding systems infiltrate, the system will become more susceptible to other challenges such as from livestock grazing, the encroachment of upland vegetation and from invasive weeds

• Declining summer flows of Rocky Mountain rivers: Changing seasonal hydrology and probable impacts on floodplain forestsStewart B. Rood , a , , Jason
Pan a , Karen M. Gill a , Carmen G. Franks a , Glenda M. Samuelson a and Anita
Shepherd a a Environmental Science Program, University of Lethbridge, Lethbridge,
Alberta, Canada T1K 3M4 Received 17 November 2006; ﾊ revised 24 August 2007; ﾊ accepted 13 November 2007.
ﾊ Available online 22 November 2007.
• LEE E. BROWN, DAVID M. HANNAH, ALEXANDER M. MILNER (2007) Vulnerability of alpine stream biodiversity to shrinking glaciers and snowpacks Global
Change Biology 13 (5) , 958 ﾐ 966 doi:10.1111/j.1365-2486.2007.01341.x
• Division of Atmospheric Sciences, Department of Physical Sciences,
University of Helsinki, P.O. Box 64, Gustaf H 獲 lstr 嗄 in katu 2, 00014 ﾊ
Helsinki, Finland