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The increasing intensity of the strongest tropical cyclones
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Atlantic tropical cyclones are getting stronger on average, with a 30-year trend that has been related to an increase in ocean temperatures over the Atlantic Ocean and elsewhere1–4. Over the rest of the tropics, however, possible trends in tropical cyclone intensity are less obvious, owing to the unreliability and incompleteness of the observational record and to a restricted focus, in previous trend analyses, on changes in average intensity. To quantify and determine the significance of these trends, we use quantile regression. Quantile regression as employed here is a method to estimate the change (trend) in lifetime-maximum wind speed quantile as a function of year. A quantile is a point taken from ntensities that cyclones achieve during their lifetimes), estimated from homogeneous data derived from an archive of satellite records. We find significant upward trends for wind speed quantiles above the 70th percentile, with trends as high as 0.36 0.09 m s21 yr21 (s.e.) for the strongest cyclones. We note separate upward trends in the estimated lifetime-maximum wind speeds of the very strongest tropical cyclones (99th percentile) over each ocean basin, with the largest increase at this quantile occurring over the North Atlantic, although not all basins show statistically significant increases. Our results are qualitatively consistent with the hypothesis that as the seas warm, the ocean has more energy to convert to tropical cyclone wind.
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Atlantic hurricanes and climate over the past 1,500 years
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Atlantic tropical cyclone activity, as measured by annual storm counts, reached anomalous levels over the past decade1. The short nature of the historical record and potential issues with its reliability in earlier decades, however, has prompted an ongoing debate regarding the reality and significance of the recent rise2–5. Here we place recent activity in a longer-term context by comparing two independent estimates of tropical cyclone activity over the past 1,500 years. The first estimate is based on a composite of regional sedimentary evidence of landfalling hurricanes, while the second estimate uses a previously published statistical model of Atlantic tropical cyclone activity driven by proxy reconstructions of past climate changes. Both approaches yield consistent evidence of a peak in Atlantic tropical cyclone activity during medieval times (around AD 1000) followed by a subsequent lull in activity. The statistical model indicates that the medieval peak, which rivals or even exceeds (within uncertainties) recent levels of activity, results from the reinforcing effects of La-Nina-like climate conditions and relative tropical Atlantic warmth.
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Coupling snowpack and groundwater dynamics to interpret historical streamflow trends in the western United States
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A key challenge for resource and land managers is predicting the consequences of climate warming on streamflow and water resources. During the last century in the western United States, significant reductions in snowpack and earlier snowmelt have led to an increase in the fraction of annual streamflow during winter and a decline in the summer. Previous work has identified elevation as it relates to snowpack dynamics as the primary control on streamflow sensitivity to warming. But along with changes in the timing of snowpack accumulation and melt, summer streamflows are also sensitive to intrinsic, geologically mediated differences in the efficiency of landscapes in transforming recharge (either as rain or snow) into discharge; we term this latter factor drainage efficiency. Here we explore the conjunction of drainage efficiency and snowpack dynamics in interpreting retrospective trends in summer streamflow during 1950–2010 using daily streamflow from 81 watersheds across the western United States. The recession constant (k) and fraction of precipitation falling as snow (Sf) were used as metrics of deep groundwater and overall precipitation regime (rain and/or snow), respectively. This conjunctive analysis indicates that summer streamflows in watersheds that drain slowly from deep groundwater and receive precipitation as snow are most sensitive to climate warming. During the spring, however, watersheds that drain rapidly and receive precipitation as snow are most sensitive to climate warming. Our results indicate that not all trends in western United States are associated with changes in snowpack dynamics; we observe declining streamflow in late fall and winter in rain-dominated watersheds as well. These empirical findings support both theory and hydrologic modelling and have implications for how streamflow sensitivity to warming is interpreted across broad regions.
KEY WORDS streamflow trend; hydrologic processes; groundwater processes; climate; warming
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Land cover effects on runoff patterns in eastern Piedmont (USA) watersheds
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Physiography and land cover determine the hydrologic response of watersheds to climatic events. However, vast differences in climate regimes and variation of landscape attributes among watersheds (including size) have prevented the establishment of general relationships between land cover and runoff patterns across broad scales. This paper addresses these difficulties by using power spectral analysis to characterize area-normalized runoff patterns and then compare these patterns with landscape features among watersheds within the same physiographic region. We assembled long-term precipitation and runoff data for 87 watersheds (first to seventh order) within the eastern Piedmont (USA) that contained a wide variety of land cover types, collected environmental data for each watershed, and compared the datasets using a variety of statistical measures. The effect of land cover on runoff patterns was confirmed. Urban-dominated watersheds were flashier and had less hydrologic memory compared with forest-dominated watersheds, whereas watersheds with high wetland coverage had greater hydrologic memory. We also detected a 10–15% urban threshold above which urban coverage became the dominant control on runoff patterns. When spectral properties of runoff were compared across stream orders, a threshold after the third order was detected at which watershed processes became dominant over precipitation regime in determining runoff patterns. Finally, we present a matrix that characterizes the hydrologic signatures of rivers based on precipitation versus landscape effects and low-frequency versus high-frequency events. The concepts and methods presented can be generally applied to all river systems to characterize multiscale patterns of watershed runoff.
KEY WORDS watershed hydrology; power spectral analysis; hydrologic signatures; fluvial landscape ecology; hydrologic memory
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How and Why Do Insects Migrate?
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Countless numbers of insects migrate within and between continents every year, and yet we know very little about the ultimate reasons and proximate mechanisms that would explain these mass movements. Here we suggest that perhaps the most important reason for insects to migrate is to hedge their reproductive bets. By spreading their breeding efforts in space and time, insects distribute their offspring over a range of environmental conditions. We show how the study of individual long-distance movements of insects may contribute to a better understanding of migration. In the future, advances in tracking methods may enable the global surveillance of large insects such as desert locusts.
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THE INSURANCE VALUE OF BIODIVERSITY IN THE PROVISION OF ECOSYSTEM SERVICES
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From the text: In the face of uncertainty, diversity provides insurance for risk-averse economic agents. For example, investors in financial markets diversify their asset portfolio in order to hedge their risk; firms diversify their activities, products or services when facing an uncertain market environment; farmers traditionally grow a variety of crops in order to decrease the adverse impact of uncertain environmental and market conditions. In this paper, I argue that biological diversity plays a similar role: it can be interpreted as an insurance against the uncertain provision of ecosystem services, such as biomass production, control of water run-off, pollination, control of pests and diseases, nitrogen fixation, soil regeneration, etc. Such ecosystem services are generated by ecosystems and are used by utility- maximizing and risk-averse economic agents (Daily [1997], Millennium Ecosystem Assessment [2005]).
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TRUST, CULTURE, AND COOPERATION: A Social Dilemma Analysis of Pro-Environmental Behaviors
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Social dilemmas require a choice between cooperation, or sacrificing for the greater good, and self-interest. One commonly studied social dilemma is environmental conservation. Previous work suggests that trust predicts cooperation in the form of environmental protection. We contend that this view ignores cultural factors. Building on prior cross-cultural research, we predict an interaction between strength of social ties and trust on cooperation. Findings from General Social Survey data indicate that low trust levels found in the U.S. South (a collectivist culture) renders trust ineffective at promoting environmental protection. However, trust predicts cooperation in nonsouthern regions (which are more individualist), where trust levels are higher.
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Emergence of a mid-season period of low floral resources in a montane meadow ecosystem associated with climate change
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Summary. 1. Shifts in the spatial and temporal patterns of flowering could affect the resources available to pollinators, and such shifts might become more common as climate change progresses. 2. As mid-summer temperatures have warmed,we found that a montane meadow ecosystem in the southern Rocky Mountains of the United States exhibits a trend toward a bimodal distribution of flower abundance, characterized by a mid-season reduction in total flower number, instead of a broad, unimodal flowering peak lasting most of the summer season. 3. We examined the shapes of community-level flowering curves in this system and found that the typical unimodal peak results from a pattern of complementary peaks in flowering among three distinct meadow types (dry, mesic and wet) within the larger ecosystem. However, high mid-summer temperatures were associated with divergent shifts in the flowering curves of these individual meadow types. Specifically, warmer summers appeared to cause increasing bimodality in mesic habitats, and a longer interval between early and late flowering peaks in wet and dry habitats. 4. Together, these habitat-specific shifts produced a longer mid-season valley in floral abundance across the larger ecosystem in warmer years. Because of these warming-induced changes in flowering patterns, and the significant increase in summer temperatures in our study area, there has been a trend toward non-normality of flowering curves over the period 1974–2009. This trend reflects increasing bimodality in total community-wide flowering. 5. The resulting longer periods of low flowering abundance in the middle of the summer season could negatively affect pollinators that are active throughout the season, and shifts in flowering peaks within habitats might create mismatches between floral resources and demand by pollinators with limited foraging ranges. 6. Synthesis. Early-season climate conditions are getting warmer and drier in the high altitudes of the southern Rocky Mountains. We present evidence that this climate change is disrupting flowering phenology within and among different moisture habitats in a sub-alpine meadow ecosystem, causing a mid-season decline in floral resources that might negatively affect mutualists, especially pollinators. Our findings suggest that climate change can have complex effects on phenology at small spatial scales, depending on patch-level habitat differences.
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Thermal legacies: transgenerational effects of temperature on growth in a vertebrate
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Transgenerational plasticity (TGP), a generalisation of more widely studied maternal effects, occurs whenever environmental cues experienced by either parent prior to fertilisation results in a modification of offspring reaction norms. Such effects have been observed in many traits across many species. Despite enormous potential importance—particularly in an era of rapid climate change—TGP in thermal growth physiology has never been demonstrated for vertebrates. We provide the first evidence for thermal TGP in a vertebrate: given sufficient time, sheepshead minnows adaptively program their offspring for maximal growth at the present temperature. The change in growth over a single generation (c. 30%) exceeds the single-generation rate of adaptive evolution by an order of magnitude. If widespread, transgenerational effects on thermal performance may have important implications on physiology, ecology and contemporary evolution, and may significantly alter the extinction risk posed by changing climate.
Keywords
Cyprinodon variegatus, ecological epigenetics, maternal effects, sheepshead minnow.
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Can forest management be used to sustain water-based ecosystem services in the face of climate change?
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Forested watersheds, an important provider of ecosystems services related to water supply, can have their structure, function, and resulting streamflow substantially altered by land use and land cover. Using a retrospective analysis and synthesis of long-term climate and streamflow data (75 years) from six watersheds differing in management histories we explored whether streamflow responded differently to variation in annual temperature and extreme precipitation than unmanaged watersheds. We show significant increases in temperature and the frequency of extreme wet and dry years since the 1980s. Response models explained almost all streamflow variability (adjusted R2 . 0.99). In all cases, changing land use altered streamflow. Observed watershed responses differed significantly in wet and dry extreme years in all but a stand managed as a coppice forest. Converting deciduous stands to pine altered the streamflow response to extreme annual precipitation the most; the apparent frequency of observed extreme wet years decreased on average by sevenfold. This increased soil water storage may reduce flood risk in wet years, but create conditions that could exacerbate drought. Forest management can potentially mitigate extreme annual precipitation associated with climate change; however, offsetting effects suggest the need for spatially explicit analyses of risk and vulnerability.
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