Climate Science PDFs
Climate Science PDFs Collection
- Climate change and the ecologist
- The evidence for rapid climate change now seems overwhelming. Global temperatures are predicted to rise by up to 4 °C by 2100, with associated alterations in precipitation patterns. Assessing the consequences for biodiversity, and how they might be mitigated, is a Grand Challenge in ecology.
- SPECIAL REPORT:CLIMATE OF OPPORTUNITY
- Awareness about climate change is at an all-time high. Will this surge of attention translate into more jobs for climate scientists?
- Aerosols heat up
- Solid particles suspended in the atmosphere have long played second fiddle to greenhouse gases as agents of climate change. A study of atmospheric heating over the Indian Ocean could provoke a rethink.
- Scientific reticence and sea level rise
- I suggest that ‘scientific reticence’, in some cases, hinders communication with the public about dangers of global warming. If I am right, it is important that policy-makers recognize the potential influence of this phenomenon. Scientific reticence may be a consequence of the scientific method. Success in science depends on objective skepticism. Caution, if not reticence, has its merits. However, in a case such as ice sheet instability and sea level rise, there is a danger in excessive caution. We may rue reticence, if it serves to lock in future disasters.Barber (1961) describes a ‘resistance by scientists to scientific discovery’, with a scholarly discussion of several sources of cultural resistance.There are aspects of the phenomenon that Barber discusses in the ‘scientific reticence’ that I describe, but additional factors come into play in the case of global climate change and sea level rise.
- Projections of Future Drought in the Continental United States and Mexico
- Using the Palmer drought severity index, the ability of 19 state-of-the-art climate models to reproduce ob- served statistics of drought over North America is examined. It is found that correction of substantial biases in the models’ surface air temperature and precipitation fields is necessary. However, even after a bias correction, there are significant differences in the models’ ability to reproduce observations. Using metrics based on the ability to reproduce observed temporal and spatial patterns of drought, the relationship between model per- formance in simulating present-day drought characteristics and their differences in projections of future drought changes is investigated. It is found that all models project increases in future drought frequency and severity. However, using the metrics presented here to increase confidence in the multimodel projection is complicated by a correlation between models’ drought metric skill and climate sensitivity. The effect of this sampling error can be removed by changing how the projection is presented, from a projection based on a specific time interval to a projection based on a specified temperature change. This modified class of projections has reduced intermodel uncertainty and could be suitable for a wide range of climate change impacts projections.
- THE SPATIAL AND TEMPORAL VARIABILITY OF RAIN-ON-SNOW
- Snow melt during rainfall causes large-scale flooding and avalanching. These rain-on- snow events are most well-documented in the coastal mountain ranges of western North America. To determine what role they play in interior mountains, we analyzed flood frequencies in the Columbia River basin and modeled rain-on-snow potential from daily temperature and precipitation data. Applying the model with geographically distributed weather data allowed maps of rain-on-snow potential at 2km spatial resolution to be generated for characteristic climate years of 1982 (cold and wet), 1988 (warm and dry), and 1989 (average). It was found that rain-on-snow events are more likely during cool, wet years (such as 1982). A greater number of events and more widespread distribution of events occur during this type of climate. The cool temperatures allow low-elevation snow to accumulate and frequent storms bring the possibility of mid-winter rain. Warm, dry years (1988) are less likely to experience rain-on-snow events. There is little low-elevation snow at these times and only occasional precipitation. During all years, areas most susceptible to rain-on-snow are those where topography allows incursion of relatively warm, moist marine air that flows from the Pacific Ocean into the Columbia Plateau and up the Snake River Valley. These areas include the Cascade mountains; northern Idaho, northeastern Washington, and northwestern Montana where valleys open into the Columbia plateau; the Blue Mountains of northeastern Oregon; and western Wyoming and central Idaho adjacent to the Snake River. KEYWORDS: snow, avalanches, rain-on-snow, floods
- RAIN-ON-SNOW EVENTS IN THE WESTERN UNITED STATES
- Severity of rain on snow depends on a number of factors, and an overall decrease in these events appears to be driven, in part, by changes in El Niño–Southern Oscillation.
- Influence of Timber Harvest on Rain-On-Snow Runoff: A Mechanism for Cumulative Watershed Effects
- Rain-on-snow dominates many geomorphological processes in the Pacific Northwest. Wind-aided transfers of heat to snow during rain-on-snow comprise the largest source of heat for snowmelt during rainfall.␣ Recent field research in western. Oregon and western Washington has shown that timber harvest and thinning can increase both snow accumulation and the wind-aided transfers of heat, resulting in higher rates of water delivery to soil during rain-on-snow conditions.␣ Increased rates of water delivery to soil can lead to higher streamflows and to landslides on marginally stable slopes. Because of the magnitude of increase in water delivery to soils during common rain-on-snow conditions and a hydrologic recovery period that may require 40 years, rain-on-snow runoff is an important mechanism␣ whereby forest management activities might cumulatively affect water resources.
- Rain on Snow: Little Understood Killer in the North
- n October 2003, a severe rain-on-snow (ROS) event killed approximately 20,000 musk-oxen (Figure 1) on Banks Island, which is the westernmost of the Canadian Arctic islands (approximately 380 kilome- ters by 290 kilometers in size). The event reduced the isolated herd by 25% and sig- nificantly affected the people dependent on the herd’s well-being. Because of the sparsity of weather stations in the Arctic and the lack of routinely deployed weather equipment that was capable of accurately sensing the ROS event, its detection largely was based on reports from hunters who were in the affected areas at the time.Such events can significantly alter a fro- zen ecosystem—with changes that often persist for the remainder of a winter—by creating ice layers at the surface of, within, or below the snowpack. The water and ice layers are known to facilitate the growth of toxic fungi, significantly warm the soil surface under thick snowpack, and deter large grazing mammals.
- Simulating snowmelt process during rain-on-snow over a semi-arid mountain basin
- In the Pacific Northwest of North America, significant flooding can occur during mid-winter rain-on-snow events. Warm, wet Pacific storms caused significant floods in the Pacific Northwest in February 1996, January 1997 and January 1998. Rapid melting of the mountain snow cover substantially augmented discharge during these flood events. An energy-balance snowmelt model is used to simulate snowmelt processes during the January 1997 event over a small headwater basin within the Reynolds Creek Experimental Watershed located in the Owyhee Mountains of southwestern Idaho, U.S.A. This sub-basin is 34% forested 12% fir, 22% aspen and 66% mixed sagebrush primarily mountain big sage- brush)). Data from paired open and forested experimental sites were used to drive the model. Model-forcing data were corrected for topographic and vegetation canopy effects. The event was preceded by cold, stormy conditions that developed a significant snow cover over the sub- basin. The snow cover at sites protected by forest cover was slightly reduced, while at open sites significant snowmelt occurred. The warm, moist, windy conditions during the flooding event produced substantially higher melt rates in exposed areas, where sensible- and latent- heat exchanges contributed 60^90% of the energy for snowmelt. Simulated snow-cover devel- opment and ablation during the model run closely matched measured conditions at the two experimental sites. This experiment shows the sensitivity of snowmelt processes to both climate and land cover, and illustrates how the forest canopy is coupled to the hydrologic cycle in mountainous areas.
- Protecting Wildlife Migration Corridors and Crucial Wildlife Habitat in the West
- BACKGROUND 1. Large intact and functioning ecosystems, healthy fish and wildlife populations, and abundant public access to natural landscapes are a significant contributing factor to the West's economic and in-migration boom as well as quality of life. Critical wildlife migration corridors and crucial wildlife habitats are necessary to maintain flourishing wildlife populations. . 2. The Western States are particularly and uniquely affected by activity occurring in wildlife migration corridors and crucial wildlife habitats. Western States must also contend with an inter-connected mixture of private, state and federal lands. Migration corridors cross all political boundaries and States need to protect migration corridors on federal land through various state planning documents. 3. Natural resource development, urban development, and maintenance of the existing infrastructures of the West impact wildlife species, their habitats and migration corridors. Western States are increasingly expending limited state funds to participate in federal public land resource management planning as a result of the growing national focus on energy production and independence. States continue to expend scarce funds to protect or mitigate impacts to wildlife resources by energy development. 4. States possess broad trustee, police powers and primacy over fish and wildlife within their borders. With the exception of marine mammals, states retain concurrent jurisdiction even where Congress has directed specific federal authority of fish and wildlife speci
- Seasonal and diel patterns in the migrations of fishes between a river and a floodplain tributary
- The population behaviours associated with the migrations of fishes in lowland river ecosystems are amongst the most poorly-understood dispersal mechanisms of temperate freshwater organisms. This study evaluated the influence of four environmental variables (light levels, river discharge, water temperature and water velocity) on the timing, intensity and direction of fish movements between the River Avon (Hampshire, England) and a small floodplain tributary, Ibsley Brook, over a 12-month period. Using canonical correspondence analysis (CCA) to identify patterns of movement (by groups of species) and the relative strengths of explanatory variables in the data, the probability of fishes migrating between the river and tributary was determined using Bayesian modelling. The intensity and direction of fish movements between the river and tributary varied temporally, both on a diel and seasonal basis, and there were species- and age-specific patterns in behaviour. Diel movements appeared to be triggered by changes in light intensity and brook water velocity, whereas seasonal movements were mostly driven by changes in river discharge and water temperature, particularly those associated with floods. This study emphasises the importance of connectivity in river systems, as fishes migrated in all conditions, but especially during rapidly- rising discharge. ecosystem function; habitat connectivity; habitat fragmentation; habitat use; river discharge; water velocity
- Do small tributaries function as refuges from floods? A test in a salmonid-dominated mountainous river
- Excerpts from the text: On 8–10 August 2003, a powerful typhoon hit Hokkaido Island, Japan, accompanied with heavy rain, which allowed us to investigate the potential role of tributaries as refuges from flooding. We had just completed annual population census in four small tributaries of a river system 1–2 days before the typhoon.... Overall, our results did not support the hypothesis that many large fishes immigrate to small tributaries during floods. ... Despite the lack of evidence of mass movement, our result suggested a few immigrants from the main stem (i.e., juvenile white-spotted charr, sculpin and a few relatively large Dolly Varden). Because more than 100 small tributaries exist in the Shiisorapuchi River (Koizumi 2011), only a few individuals escaping to each tributary should accumulate to a great number enough to re-colonise main stem habitats even if fishes in the main stem were extirpated. Multiple refuges at different spatial scales should increase resistance and ⁄ or resilience of fish populations (Sedell et al. 1990; Pearsons et al. 1992). Thus, the roles of tributaries as refuges would deserve further attention
- Characteristics, distribution and geomorphic role of large woody debris in a mountain stream of the Chilean Andes
- The paper presents an analysis of amounts, characteristics and morphological impact of large woody debris (LWD) in the Tres Arroyos stream, draining an old-growth forested basin (9·1 km2) of the Chilean Southern Andes. Large woody debris has been surveyed along a 1·5 km long channel section with an average slope of 0·07 and a general step–pool/cascade morphology. Specific wood storage is very high (656 –710 m3 ha−1), comparable to that recorded in old-growth forested basins in the Pacific Northwest. Half of the LWD elements were located on the active floodplain, and around two-thirds of LWD elements were found in accumula- tions. Different types of log jam were observed, some heavily altering channel morphology (log-steps and valley jams), while others just line the channel edges (bankfull bench jams). Log-steps represent approximately 22% of all steps, whereas the elevation loss due to LWD (log-steps and valley jams) results in 27% loss of the total stream potential energy. About 1600 m3 of sediment is stored in the main channel behind LWD structures, corresponding to approximately 150% of the annual sediment yield. Keywords: large woody debris; channel morphology; valley jams; log-steps; Andes; stream sediment: sediment traps
- Distribution and characterization of in‐channel large wood in relation to geomorphic patterns on a low‐gradient river
- A 177 river km georeferenced aerial survey of in‐channel large wood (LW) on the lower Roanoke River, NC was conducted to determine LW dynamics and distributions on an eastern USA low‐gradient large river. Results indicate a system with approximately 75% of the LW available for transport either as detached individual LW or as LW in log jams. There were approximately 55 individual LW per river km and another 59 pieces in log jams per river km. Individual LW is a product of bank erosion (73% is produced through erosion) and is isolated on the mid and upper banks at low flow. This LW does not appear to be important for either aquatic habitat or as a human risk. Log jams rest near or at water level making them a factor in bank complexity in an otherwise homogenous fine‐grained channel. A segmentation test was performed using LW frequency by river km to detect breaks in longitudinal distribution and to define homogeneous reaches of LW frequency. Homogeneous reaches were then analyzed to determine their relationship to bank height, channel width/depth, sinuosity, and gradient. Results show that log jams are a product of LW transport and occur more frequently in areas with high snag concentrations, low to intermediate bank heights, high sinuosity, high local LW recruitment rates, and narrow channel widths. The largest concentration of log jams (21.5 log jams/km) occurs in an actively eroding reach. Log jam concentrations downstream of this reach are lower due to a loss of river competency as the channel reaches sea level and the concurrent development of unvegetated mudflats separating the active channel from the floodplain forest. Substantial LW transport occurs on this low‐gradient, dam‐regulated large river; this study, paired with future research on transport mechanisms should provide resource managers and policymakers with options to better manage aquatic habitat while mitigating possible negative impacts to human interests
- The floodplain large-wood cycle hypothesis: A mechanism for the physical and biotic structuring of temperate forested alluvial valleys in the North Pacific coastal ecoregion
- A ‘floodplain large-wood cycle’ is hypothesized as a mechanism for generating landforms and influencing river dynamics in ways that structure and maintain riparian and aquatic ecosystems of forested alluvial river valleys of the Pacific coastal temperate rainforest of North America. In the cycle, pieces of wood large enough to resist fluvial transport and remain in river channels initiate and stabilize wood jams, which in turn create alluvial patches and protect them from erosion. These stable patches provide sites for trees to ma- ture over hundreds of years in river valleys where the average cycle of floodplain turnover is much briefer, thus providing a future source of large wood and reinforcing the cycle. Different tree species can function in the floodplain large-wood cycle in different ecological regions, in different river valleys within regions, and within individual river valleys in which forest composition changes through time. The cycle promotes a physically complex, biodiverse, and self-reinforcing state. Conversely, loss of large trees from the system drives landforms and ecosystems toward an alternate stable state of diminished biogeomorphic complexity. Reestablishing large trees is thus necessary to restore such rivers. Although interactions and mechanisms may differ between biomes and in larger or smaller rivers, available evidence suggests that large riparian trees may have similarly fundamental roles in the physical and biotic structuring of river valleys elsewhere in the temperate zone. Dead wood; woody debris; stream; river; habitat; fish
- The use of large wood in stream restoration: experiences from 50 projects in Germany and Austria
- 1. Wood is increasingly used in restoration projects to improve the hydromorphological and ecological status of streams and rivers. However, despite their growing importance, only a few of these projects are described in the open literature. To aid practitioners, we conducted a postal mail survey to summarize the experiences gained in central Europe and compile data on 50 projects. 2. Our results indicated the potential for improvement from an ecological point of view, as the number and total wood volume, and the median volume of single wood structures placed in the streams per project, were low compared with the potential natural state. Moreover, many wood structures were placed nearly parallel to the water flow, reducing their beneficial effect on stream hydraulics and morphology. 3. Restoration success has been monitored in only 58% of the projects. General con- clusions drawn include the following. (i) The potential effects of wood placement must be evaluated within a watershed and reach-scale context. (ii) Wood measures are most successful if they mimic natural wood. (iii) Effects of wood structures on stream morphology are strongly dependent on conditions such as stream size and hydrology. (iv) Wood placement has positive effects on several fish species. (v) Most projects revealed a rapid improvement of the hydromorphological status. 4. Most of the wood structures have been fixed, called ‘hard engineering’. However, soft engineering methods (use of non-fixed wood structures) are known to result in more natural channel features for individual stream types, sizes and sites, and are significantly more cost-effective. 5. Synthesis and applications. Large wood has been used successfully in several projects in central Europe, predominantly to increase the general structural complexity using fixed wood structures. Our results recommend the use of less costly soft engineering techniques (non-fixed wood structures), higher amounts of wood, larger wood struc- tures and improved monitoring programmes for future restoration projects comparable with those in this study. We recommend the use of ‘passive restoration’ methods (restor- ing the process of wood recruitment on large scales) rather than ‘active restoration’ (placement of wood structures on a reach scale), as passive restoration avoids the risk of non-natural amounts or diversity of wood loading developing within streams. Local, active placement of wood structures must be considered as an interim measure until passive restoration methods have increased recruitment sufficiently. Key-words: alpine streams, lowland streams, monitoring, mountain streams, passive restoration, restoration success, soft-engineering, woody debris
- A LIDAR‐DERIVED EVALUATION OF WATERSHED‐SCALE LARGE WOODY DEBRIS SOURCES AND RECRUITMENT MECHANISMS: COASTAL MAINE, USA
- In‐channel large woody debris (LWD) promotes quality aquatic habitat through sediment sorting, pool scouring and in‐stream nutrient retention and transport. LWD recruitment occurs by numerous ecological and geomorphic mechanisms including channel migration, mass wasting and natural tree fall, yet LWD sourcing on the watershed scale remains poorly constrained. We developed a rapid and spatially extensive method for using light detection and ranging data to do the following: (i) estimate tree height and recruitable tree abundance throughout a watershed; (ii) determine the likelihood for the stream to recruit channel‐spanning trees at reach scales and assess whether mass wasting or channel migration is a dominant recruitment mechanism; and (iii) understand the contemporary and future distribution of LWD at a watershed scale. We utilized this method on the 78‐km‐long Narraguagus River in coastal Maine and found that potential channel‐spanning LWD composes approximately 6% of the valley area over the course of the river and is concentrated in spatially discrete reaches along the stream, with 5 km of the river valley accounting for 50% of the total potential LWD found in the system. We also determined that 83% of all potential LWD is located on valley sides, as opposed to 17% on floodplain and terrace surfaces. Approximately 3% of channel‐spanning vegetation along the river is located within one channel width of the stream. By examining topographic and morphologic variables (valley width, channel sinuosity, valley‐ side slope) over the length of the stream, we evaluated the dominant recruitment processes along the river and often found a spatial disconnect between the location of potential channel‐spanning LWD and recruitment mechanisms, which likely explains the low levels of LWD currently found in the system. This rapid method for identification of LWD sources is extendable to other basins and may prove valuable in locating future restoration projects aimed at increasing habitat quality through wood additions. key words: large woody debris; lidar; river restoration; habitat
- Effects of Flow Regulation on Shallow-Water Habitat Dynamics and Floodplain Connectivity
- Our study examined the effects of flow regulation on the spatiotemporal availability of shallow habitat patches with slow current velocity (SSCV patches) and floodplain inundation in the unregulated Yellowstone River and the regulated Missouri River in Montana and North Dakota. We mapped representative sites and used hydraulic models and hydrograph data to describe the frequency and extent of floodplain inundation and the availability of SSCV habitat over time during different water years. In the Yellowstone River the distribution, location, and size of SSCV patches varied but followed an annual pattern that was tied to the snowmelt runoff hydrograph. There was less variation in patch distribution in the Missouri River, and the pattern of habitat availability was influenced by flow regulation. Regulated flows and their effects on channel mor- phology and patterns of vegetation establishment resulted in 3.0–3.5 times less area of inundated woody vegetation during normal and dry years in the Missouri River compared with the Yellow- stone River. The differences we observed in SSCV patch dynamics between rivers may have implications for fish populations and community structure through affecting the survival of early life stages. At a larger scale, the smaller area of vegetation inundated in the Missouri River suggests that nutrient cycling and the ecological benefits associated with a moving littoral zone are reduced by the altered flow and sediment regime in that river. Accurate assessments of the effects of flow alteration and successful efforts to restore riverine ecosystems will require consideration of physical and biotic processes that operate at multiple spatial and temporal scales.
- Influence of different tree-harvesting intensities on forest soil carbon stocks in boreal and northern temperate forest ecosystems
