[1] We examined the effects of snow, event size, basin size, and forest harvest on floods using >1000 peak discharge events from 1953 to 2006 from three small (<1 km 2 ), paired-watershed forest-harvest experiments and six large (60-600 km 2 ) basins spanning the transient (400-800 m) and seasonal (>800 m) snow zones in the western Cascades of Oregon. Retrospectively classified rain-on-snow events delivered 75% more water to soils than rain events. Peak discharges of >10 year rain-on-snow events were almost twice as high as rain peaks in large basins but only slightly higher in small basins. Peak discharges of >1 year rain-on-snow events increased slightly (10%-20%) after logging in small basins, but small basin peaks do not account for the magnitudes of large basin rain-on-snow peak discharges during >1 year floods. In extreme floods, despite very high infiltration capacity, high soil porosity, and steep hillslope gradients, prolonged precipitation and synchronous snowmelt produce rapid, synchronized hydrograph responses to small variations in maximum precipitation intensity. At the large basin scale, forest harvest may increase the area of snowpack and simultaneous snowmelt, especially in elevation zones normally dominated by rain and transient snow, thereby increasing large basin peaks without producing very large percent increases in small basin peaks. Further work is needed to describe water flow paths in melting snowpack, snow cover and the area experiencing snowmelt, synoptic peak discharges, and routing of flood peaks through the stream network during extreme rain-on-snow floods. The evolving structure of the forest on the landscape is a potentially very important factor influencing extreme rain-on-snow floods.Citation: Jones, J. A., and R. M. Perkins (2010), Extreme flood sensitivity to snow and forest harvest, western Cascades,

Abstract:Large floods are often attributed to the melting of snow during a rain event. This study tested how climate variability, snowpack presence, and basin physiography were related to storm hydrograph shape in three small (<1 km 2 ) basins with old-growth forest in western Oregon. Relationships between hydrograph characteristics and precipitation were tested for approximately 800 storms over a nearly 30-year period. Analyses controlled for (1) snowpack presence/absence, (2) antecedent soil moisture, and (3) hillslope length and gradient. For small storms (<150 mm precipitation), controlling for precipitation, the presence of a snowpack on near-saturated soil increased the threshold of precipitation before hydrograph rise, extended the start lag, centroid lag, and duration of storm hydrographs, and increased the peak discharge. The presence of a snowpack on near-saturated soil sped up and steepened storm hydrographs in a basin with short steep slopes, but delayed storm hydrographs in basins with longer or more gentle slopes. Hydrographs of the largest events, which were extreme regional rain and rain-on-snow floods, were not sensitive to landform characteristics or snowpack presence/absence. Although the presence of a snowpack did not increase peak discharge in small, forested basins during large storms, it had contrasting effects on storm timing in small basins, potentially synchronizing small basin contributions to the larger basin hydrograph during large rain-on-snow events. By altering the relative timing of hydrographs, snowpack melting could produce extreme floods from precipitation events whose size is not extreme. Further work is needed to examine effects of canopy openings, snowpack, and climate warming on extreme rain-on-snow floods at the large basin scale.

ABSTRACT:In western Micronesia, sea levels are rising at three to four times the global average, saltwater intrusion is impacting freshwater supplies and food production, and local cultures are being forced to respond. Yap State, Federated States of Micronesia (9.5N, 138E), consists of a cluster of four main islands (MI) and 14 coral atolls and smaller outer islands (OI) spread over 400,000 km 2 of ocean. This paper examines three aspects of Yap State's adaptive capacity to climate change impacts: 1) differences in environmental conditions between the MI and OI; 2) relevant features of the MI's cultural heritage; and 3) relevant features of OI's cultural heritage, including values and practices surrounding the sawei system relationship. Cultural support networks in both the MI and OI will almost certainly be relied upon to lessen the severity of climate change impacts, perhaps especially as more OI residents relocate to the MI. More research is needed to document how features of intangible cultural heritage that create and maintain social resilience in Yap State will shape residents' adaptive capacity to climate change.

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This paper summarizes the potential contribution of organic farming to biodiversity conservation through an assessment of its impact on the World Wildlife Fund's conservation priorities: 238 global priority ecoregions and six global themes (living water, forests for life, toxics, species, endangered seas and climate change). Organic production (the production methods as well as the movement) has contributed to biodiversity conservation by: (1) identifying production systems with ambitious and comprehensive principles for sustainable agriculture; (2) demonstrating that alternative methods of production are commercially and economically viable; and (3) galvanizing an important and rapidly growing demand in the marketplace for more sustainably produced products. The lack of science-based indicators to measure environmental impacts of organic production, however, limits our ability to assess its impacts on biodiversity conservation. The safety of natural compounds should be investigated scientifically and not assumed. To identify truly sustainable production methods and move beyond statements of principles to measurable conservation results, robust, scientifically-based measures or indicators are needed to assess impacts and evaluate trade-offs between different kinds of production systems, including organic, on environmental criteria.