Climate Change and...
Effects of Climate Change
- Climate Variability
- Climate Models
Effects of Climate Change
ABSTRACT: Riparian corridors possess an unusually diverse array of species and environmental processes. This 'ecological' diversity is related to variable flood regimes, geomorphic channel processes, altitudinal climate shifts, and upland influences on the fluvial corridor. This dynamic environment results in a variety of life history strategies, and a diversity of biogeochemical cycles and rates, as organisms adapt to disturbance regimes over broad spatio-temporal scales. These facts suggest that effective riparian management could ameliorate many ecological issues related to land use and environmental quality. We contend that riparian corridors should play an essential role in water and landscape planning, in the restoration of aquatic systems, and in catalyzing institutional and societal cooperation for these efforts.
Greenwald, D.N., L. B. Brubaker (2001). A 5000-year record of disturbance and vegetation change in riparian forests of the Queets River, Washington, U.S.A.. Canadian Journal of Forest Research 31 (8): 1375-1385
ABSTRACT: We used fossil pollen, charcoal, and sediment stratigraphy in three small hollows to investigate disturbance events and changes in the composition of riparian forests on a small section of the Queets River floodplain, Olympic Peninsula, Washington. The records ranged in age from approximately 500 years at two sites 300 and 550 m from the river, to 5000 years at a site 800 m from the river. Approximately 400–600 years BP, the two sites nearest the river were either inundated by a very large flood or covered by the active channel, which would have occupied a substantially different position than its present course. Following inundation or channel movement, the pollen record suggests thatAlnus rubra Bong., the primary mesic forest colonizer in the Pacific Northwest, increased and was then replaced byPicea sitchensis (Bong.) Carrière andTsuga heterophylla (Raf.) Sarg. At the site farthest from the river, two fires occurred within the last ca. 4500 years. One of the fires was followed by a period of shrub dominance and succession toTsuga heterophylla . The other fire did not cause a change in the pollen record. A recent unprecedented rise inTsuga heterophylla pollen, which began ca. 1000 years BP, might be in response to cooling during the Little Ice Age. Overall, the small hollow records highlight the complex effect of floods, fire, and possibly climate change on riparian forests of the Queets River.
ABSTRACT: I investigated the dates of origin of riparian forests dominated byPopulus angustifolia James, and recent interannual fluctuation inP. angustifolia seedling abundance on a relatively undisturbed 6-mile reach of the Animas River in southwestern Colorado. The goal was to develop plausible hypotheses about the roles of floods and interannual climatic fluctuation in structuring these forests. I determined the year of origin 242 recently-established seedlings and fifty-seven forest stands, and then developed empirical models relating seedling abundance and stand-origin events to climatic and hydrologic fluctuations. Seedlings were most abundant in years with cool winters, wet springs, and cool, wet falls (R2adj =0.98). Both good seedling years and stand-origin years were associated with winter blocking in the North Pacific and a persistent late-summer Arizona Monsoon. Extant stand originated in ten to thirteen discrete periods between 1848 and 1976, in years with both high spring and fall peak discharges. Expected seedling abundance and stand-origin dates since 1914 were reconstructed using climate data, and were extended to 1556 using tree-ring chronologies. Model results suggest good seedling years occurred more frequently (about ever 3.4 years) than stand-origin years (about every 10-15 years). Good seedling years were 2-3 times, and stand-origin years were 5 times more common from 1848 to 1985 than from 1556 to 1848. Recent expansion ofP. angustifolia may have been favoured by more frequent cool, wet years since 1848.
D. J. Cooper, J. Dickens, N. T. Hobbs, L. Christensen, L. Landrum (2006). Hydrologic, geomorphic and climatic processes controlling willow establishment in a montane ecosystem. Hydrological Processes 20 (8): 1845-1864
ABSTRACT: Willow communities dominate mid-elevation riparian areas throughout the Rocky Mountains of North America. However, many willow stands are rapidly declining in aerial cover and individual plants in stature. A poor understanding of the processes that control willow establishment hinders identifying the causes of this decline. We analysed the processes that have facilitated or limited willow establishment over the last half of the 20th century on two large floodplains in Rocky Mountain National Park in Colorado by addressing two questions: (1) How does hydrologic regime control willow establishment on different fluvial landforms? (2) How might climate-driven variations in hydrologic regime affect future willow establishment? We precisely aged willows on the three most common fluvial landforms, stream point bars, drained beaver ponds, and abandoned channels, and statistically related establishment dates to patterns of annual stream peak flow. The role of peak flow on willow establishment varied significantly by landform. Willow recruitment had occurred nearly every year on point bars. In former beaver complexes, most willows had established following dam breaches, whereas willows had established on abandoned channels for several years following channel avulsion. Establishment on point bars and abandoned channels was driven by peak flows of 2- to 5-year return intervals, whereas in abandoned beaver ponds most establishment was associated with flow events of >5-year return interval. Models of climate change suggest that temperatures will increase and precipitation seasonality will shift over the coming decades in the Rocky Mountains, leading to earlier spring runoff, lower summer and fall flows, decreased snowpack and decreased soil moisture. Such changes are likely to diminish opportunities for willow establishment.
Mulholland, P. J., Roberts, B. J., Hill, W. R., Smith, J. G. (2009). Stream ecosystem responses to the 2007 spring freeze in the southeastern United States: unexpected effects of climate change. Global Change Biology 15 (7): 1767-1776
ABSTRACT: Some expected changes in climate resulting from human greenhouse gas emissions are clear and well documented, but others may be harder to predict because they involve extreme weather events or heretofore unusual combinations of weather patterns. One recent example of unusual weather that may become more frequent with climate change occurred in early spring 2007 when a large Arctic air mass moved into the eastern United States following a very warm late winter. In this paper, we document effects of this freeze event on Walker Branch, a well-studied stream ecosystem in eastern Tennessee. The 2007 spring freeze killed newly grown leaf tissues in the forest canopy, dramatically increasing the amount of light reaching the stream. Light levels at the stream surface were sustained at levels considerably above those normal for the late spring and summer months due to the incomplete recovery of canopy leaf area. Increased light levels caused a cascade of ecological effects in the stream beginning with considerably higher (two–three times) rates of gross primary production (GPP) during the late spring and summer months when normally low light levels severely limit stream GPP. Higher rates of stream GPP in turn resulted in higher rates of nitrate (NO3 − ) uptake by the autotrophic community and lower NO3 − concentrations in stream water. Higher rates of stream GPP in summer also resulted in higher growth rates of a dominant herbivore, the snailElimia clavaeformis . Typically, during summer months net NO3 − uptake and snail growth rates are zero to negative; however, in 2007 uptake and growth were maintained at moderate levels. These results show how changes in forest vegetation phenology can have dramatic effects on stream productivity at multiple trophic levels and on nutrient cycling as a result of tight coupling of forest and stream ecosystems. Thus, climate change-induced changes in canopy structure and phenology may lead to large effects on stream ecosystems in the future.
J. Steiger, E. Tabacchi, S. Dufour, D. Corenblit, J.-L. Peiry (2005). Hydrogeomorphic processes affecting riparian habitat within alluvial channel-floodplain river systems: a review for the temperate zone. River Research and Applications 21 (7): 719-737
ABSTRACT: Hydrogeomorphic processes within alluvial river systems create, maintain and degrade riparian habitat. The dynamic interactions between water, sediment, aquatic-terrestrial landforms and biotic elements control the functional processes and biodiversity patterns within the riparian zone and, thus, contribute directly to their ecological integrity and societal value. Numerous researchers from different disciplines publish work on the physical, biological, economic and societal functions of the riparian zone within various physiographic areas. The present paper aims to review the hydrogeomorphic processes of unconfined alluvial channel-floodplain rivers within the temperate zone. These processes and their interactions with the biotic environment provide the basis for understanding the physical as well as the ecological functioning of fluvial hydrosystems. The review focuses mainly on the European context, but major advances in riparian research from other continents are also considered. Rehabilitation and management strategies for the riparian zone are summarized and recommendations for further research conclude this review.
A. Serrat-Capdevila, J. B. Valdés, J. González Péreze, K. Baird, L. J. Mata, Maddock, T., III (2007). Modeling climate change impacts – and uncertainty – on the hydrology of a riparian system: The San Pedro Basin (Arizona/Sonora). Journal of Hydrology 347 (1-2): 48-66
ABSTRACT: An assessment of climate change impacts in the water resources of a semi-arid basin in southeastern Arizona and northern Sonora is presented using results from an ensemble of 17 global circulation models (GCMs) and four different climate change scenarios from the Intergovernmental Panel on Climate Change (IPCC). Annual GCM precipitation data for the region is spatially downscaled and used to derive spatially distributed recharge estimates in the San Pedro Basin. A three dimensional transient groundwater-surface water flow model is used to simulate the hydrology of the current century, from 2000 to 2100, under different climate scenarios and model estimates. Groundwater extraction in the basin was maintained constant and equal to current. The use of multiple climate model results provides a highest-likelihood mean estimate as well as a measure of its uncertainty and a range of less probable outcomes. Results suggest that recharge in the San Pedro basin will decrease, affecting the dynamics of the riparian area in the long term. It is shown that mean net stream gain, i.e. base flow, will decrease and the effects on the riparian area could be significant. The results of this work provide a basis for the inclusion of representative climate scenarios into the basin’s existing decision support system model.