Modeling of climate change effects on stream temperatures and fish habitats below dams and near groundwater inputs

A deterministic heat transport model was developed to calculate stream water temperatures downstream of reservoir outlets (tailwaters) and groundwater sources. The model calculates heat exchange between the atmosphere, the water and the sediments and is driven by climate and stream hydrologic parameters. Past and projected climate conditions were used as input to the stream water temperature model. To produce a projected future weather scenario, output from the Columbia University Goddard Institute for Space Studies (GISS) global circulation model (GCM) for a doubling of atmospheric CO₂ were used to adjust past (1955–1979) weather parameters. Stream reach lengths, within which water temperatures are suitable for survival or good growth of 28 fish species, were determined for four selected streams. Several alternative upstream inflow conditions were chosen: Discharges from surface (epilimnion) and bottom (hypolimnion) outlets of reservoirs, and two groundwater inflow scenarios. By applying water temperature criteria for fish survival and good growth (Stefanet al., 1993) to simulated stream temperatures, it was possible to estimate stream lengths with suitable habitat. When simulated suitable habitat was compared to actual fish observations, good agreement was found. For projected climate change, the simulations showed how much of the available stream habitat would be lost. In the examples presented the effect of cold hypolimnetic water release from a reservoir or groundwater discharges is felt as far as 48 km (30 miles) downstream from its source, especially in smaller shaded streams. The impact of climate change on stream temperatures below dams is more pronounced when the water release is from the epilimnion (reservoir surface) rather than the hypolimnion (deep water). Examples used for this study show elimination of coldwater habitat for rainbow trout when the upstream release is from the surface of a reservoir, but only reductions of coldwater habitat when the upstream release is from a reservoir hypolimnion.     

Effect of climate change on watershed system: a regional analysis

Climate-induced increase in surface temperatures can impact hydrologic processes of a watershed system. This study uses a continuous simulation model to evaluate potential implications of increasing temperature on water quantity and quality at a regional scale in the Connecticut River Watershed of New England. The increase in temperature was modeled using Intergovernmental Panel on Climate Change (IPCC) high and low warming scenarios to incorporate the range of possible temperature change. It was predicted that climate change can have a significant affects on streamflow, sediment loading, and nutrient (nitrogen and phosphorus) loading in a watershed. Climate change also influences the timing and magnitude of runoff and sediment yield. Changes in variability of flows and pollutant loading that are induced by climate change have important implications on water supplies, water quality, and aquatic ecosystems of a watershed. Potential impacts of these changes include deficit supplies during peak seasons of water demand, increased eutrophication potential, and impacts on fish migration.     

The effects of increased stream temperatures on juvenile steelhead growth in the Yakima River Basin based on projected climate change scenarios

Stakeholders within the Yakima River Basin expressed concern over impacts of climate change on mid-Columbia River steelhead (Oncorhynchus mykiss), listed under the Endangered Species Act. We used a bioenergetics model to assess the impacts of changing stream temperatures—resulting from different climate change scenarios—on growth of juvenile steelhead in the Yakima River Basin. We used diet and fish size data from fieldwork in a bioenergetics model and integrated baseline and projected stream temperatures from down-scaled air temperature climate modeling into our analysis. The stream temperature models predicted that daily mean temperatures of salmonid-rearing streams in the basin could increase by 1–2 °C and our bioenergetics simulations indicated that such increases could enhance the growth of steelhead in the spring, but reduce it during the summer. However, differences in growth rates of fish living under different climate change scenarios were minor, ranging from about 1–5 %. Because our analysis focused mostly on the growth responses of steelhead to changes in stream temperatures, further work is needed to fully understand the potential impacts of climate change. Studies should include evaluating changing stream flows on fish activity and energy budgets, responses of aquatic insects to climate change, and integration of bioenergetics, population dynamics, and habitat responses to climate change.     

气候变化背景下北极利益博弈与风险评估——建模与仿真

鉴于北极风险评估中定量数据匮乏、定性知识难以定量化和权重要素确定中主观性强等困难,传统的风险评估方法无法有效解决。通过引入"云模型"实现了定性知识的量化表达;运用模糊层次分析法提高了权重的客观性;针对气候变化背景下北极区域响应及其地缘格局变化和利益博弈问题,运用上述改进方法和技术途径对北极地区利益博弈和安全风险进行了评估建模和实验仿真,提出了一些研究见解和决策咨询信息。     

Effect of climate change on regional precipitation in Lake Balaton watershed

Summary A methodology is developed and applied to the area of Lake Balaton and its drainage basin, a region of Western Hungary, to estimate the space-time distribution of daily precipitation under climate change. Lake Balaton is the largest lake in Central and Western Europe; it has a central location in the country and its drainage basin covers about the 20% of Hungary (together with the Sió Canal). The methodology is based on an analysis of the semi-Markovian properties of atmospheric macrocirculation pattern types (MCP), and a stochastic linkage between daily (here 700 hPa) MCP types and daily precipitation events. Historical data and General Circulation Model (GCM) output of daily MCP corresponding to 1 · CO₂ and 2 · CO₂ scenarios are considered in this study. Time series of both local and areal precipitation corresponding for both scenarios are simulated and their statistical properties are compared. For the temperate continental climate of Western Hungary a slightly variable spatial response to climate change is obtained. Under 2 · CO₂ conditions most of the local and the areal average precipitation suggests, a somewhat dryer precipitation regime in Western Hungary. The sensitivity of the results to the GCM utilized should be considered.With 10 Figures     

Climate change impacts on wildfires in a Mediterranean environment

We analyse the observed climate-driven changes in summer wildfires and their future evolution in a typical Mediterranean environment (NE Spain). By analysing observed climate and fire data from 1970 to 2007, we estimate the response of fire number (NF) and burned area (BA) to climate trends, disentangling the drivers responsible for long-term and interannual changes by means of a parsimonious Multi Linear Regression model (MLR). In the last forty years, the observed NF trend was negative. Here we show that, if improvements in fire management were not taken into account, the warming climate forcing alone would have led to a positive trend in NF. On the other hand, for BA, higher fuel flammability is counterbalanced by the indirect climate effects on fuel structure (i.e. less favourable conditions for fine-fuel availability and fuel connectivity), leading to a slightly negative trend. Driving the fire model with A1B climate change scenarios based on a set of Regional Climate Models from the ENSEMBLES project indicates that increasing temperatures promote a positive trend in NF if no further improvements in fire management are introduced.     

Scaling from stand to landscape scale of climate change mitigation by afforestation and forest management: a modeling approach

There is a gap between the increased scientific understanding of carbon pools and fluxes at individual trees/stand and that of forested landscape with complex structures (i.e. variety of species, age classes, site characteristic and management practices). The question about how results generated from a simulated physiologically distinct individual(s)/stands grown at a particular location (scale) can be extrapolated (scaling) across a diverse population in time and space with diverse environments, has been troubling scientists for many years. Scale and scaling present three problems in common: (a) spatial heterogeneity, (b) non-linearity in response and (c) disturbance regimes. Scale, in particular, presents other three problems: (d) threshold scale for processes, (e) dominant processes with scales and (f) emerging properties of the system. Scaling presents problems with (g) feedbacks between plants and environment and (h) plant interactions. The present study proposes a modeling framework linking a process-based model SECRETS – to overcome some of the scale and scaling problems (a, b, c, d and g) – to a C accounting model GORCAM – to integrate the effects of C stock in wood products and from fossil fuel substitution. The capabilities of the modeling framework are tested against three theoretical complex forested landscapes that combine some of the five following scenarios: existing multifunctional forest under (1) actual and (2) changing environmental conditions, and afforestation of an agricultural area with (3) a new multifunctional forest or with (4) a short rotation coppice (poplar) or with (5) an agricultural crop (miscanthus) for bioenergy production. Forest reserves calculations are included for completeness of the landscape C balance and as reference. Results, on the one hand, suggest that the framework is able to simulate C sequestration and stock in ecosystem pools, wood products and fossil fuel substitution of the scenarios under actual environmental conditions. However, comparison of results under changing environmental conditions, against specific plant literature suggest SECRETS formulation must be improved with recent development in photosynthesis, stomatal conductance and N balances. On the other hand, results also suggest that under actual environmental conditions, the optimum landscape scenario to sequester C and avoid fossil emissions to the atmosphere is composed by existing multifunctional forest, reserves and afforestation with short rotation coppice for bioenergy production.     

Temperature extremes and wildfires in Siberia in the 21st century: the MGO regional climate model simulation

Possible changes in temperature extremes and wildfires in the 21st century in the regions of Russia are analyzed using a regional climate model (RCM) with high space-time resolution. The IPCC A2 scenario of greenhouse gas and aerosol concentration increase in the atmosphere is used. It is shown that changes in extreme wildfires appear to be in the 21st century most pronounced relative to changes in moderate and high wildfires. In some areas, along with decreased moderate and high wildfires, a significant increase in extreme wildfires is expected. Further studies should be associated both with RCM development, aimed at improving simulation of the wildfire atmospheric condition, and with enlarging the parameter set for wildfire analysis. Not only seasonal mean, but also monthly mean wildfire conditions should be studied, along with the use of statistical methods of model data interpretation to analyze intraseasonal and interannual variability of wildfire characteristics.     

Triggering transformative change: a development path approach to climate change response in communities

While climate change action plans are becoming more common, it is still unclear whether communities have the capacity, tools, and targets in place to trigger the transformative levels of change required to build fundamentally low-carbon, resilient, healthy communities. Evidence increasingly supports the finding that this transformation is not triggered by climate policy alone, but rather is shaped by a broad array of decisions and practices that are rooted in underlying patterns of development. Even so, these findings have rarely penetrated the domain of practice, which often remains squarely focused on a relatively narrow set of climate-specific policies. This article builds a conceptual framework for understanding the dynamics of community-level development path transformations that may both dramatically reduce GHG emissions and significantly enhance community resilience. This framework illuminates eight critical enablers of innovation on climate change, each of which is illustrated by compelling examples of community-level experimentation on climate change across the province of British Columbia, Canada. It is concluded that community-based climate (or sustainability) policy might be more likely to trigger development path shifts if it employs a longer time horizon, recognition of adaptability and feedbacks, integrated decision making, and systems thinking.     

Impacts of climate change on August stream discharge in the Central-Rocky Mountains

In the snowmelt dominated hydrology of arid western US landscapes, late summer low streamflow is the most vulnerable period for aquatic ecosystem habitats and trout populations. This study analyzes mean August discharge at 153 streams throughout the Central Rocky Mountains of North America (CRMs) for changes in discharge from 1950–2008. The purpose of this study was to determine if: (1) Mean August stream discharge values have decreased over the last half-century; (2) Low discharge values are occurring more frequently; (3) Climatic variables are influencing August discharge trends. Here we use a strict selection process to characterize gauging stations based on amount of anthropogenic impact in order to identify heavily impacted rivers and understand the relationship between climatic variables and discharge trends. Using historic United States Geologic Survey discharge data, we analyzed data for trends of 40–59 years. Combining of these records along with aerial photos and water rights records we selected gauging stations based on the length and continuity of discharge records and categorized each based on the amount of diversion. Variables that could potentially influence discharge such as change in vegetation and Pacific Decadal Oscillation (PDO) were examined, but we found that that both did not significantly influence August discharge patterns. Our analyses indicate that non-regulated watersheds are experiencing substantial declines in stream discharge and we have found that 89% of all non-regulated stations exhibit a declining slope. Additionally our results here indicate a significant (α?≤?0.10) decline in discharge from 1951–2008 for the CRMs. Correlations results at our pristine sites show a negative relationship between air temperatures and discharge and these results coupled with increasing air temperature trends pose serious concern for aquatic ecosystems in CRMs.     

Modeling the impacts of climate change on nitrogen retention in a 4th order stream

Climate induced changes of temperature, discharge and nitrogen concentration may change natural denitrification processes in river systems. Until now seasonal variation of N-retention by denitrification under different climate scenarios and the impact of river morphology on denitrification have not been thoroughly investigated. In this study climate scenarios (dry, medium and wet) have been used to characterize changing climatic and flow conditions for the period 2050–2054 in the 4th order stream Weiße Elster, Germany. Present and future periods of nitrogen turnover were simulated with the WASP5 river water quality model. Results revealed that, for a dry climate scenario, the mean denitrification rate was 71% higher in summer (low flow period between 2050 and 2054) and 51% higher in winter (high flow period) compared to the reference period. For the medium and wet climate scenarios, denitrification was slightly higher in summer (3% and 4%) and lower in winter (9% and 3% for medium and wet scenarios, respectively). Additionally, the variability of denitrification rates was higher in summer compared to winter conditions. For a natural river section, denitrification was a factor of 1.22 higher than for a canalized river reach. Besides, weirs along the river decrease the denitrification rate by 16% in July for dry scenario conditions. In the 42 km study reach, N-retention through denitrification amounted to 5.1% of the upper boundary N load during summer low flow conditions in the reference period. For the future dry climate scenario this value increased up to 10.2% and for the medium climate scenario up to 5.4%. In our case study the investigated climate scenarios showed that future discharge changes may have a larger impact on denitrification rates than future temperature changes. Overall results of the study revealed the significance of climate change in regulating the magnitude, seasonal pattern and variability of nitrogen retention. The results provide guidance for managing nitrogen related environmental problems for present and future climate conditions.     

Risk and return of project-based climate change mitigation: a portfolio approach

We present a framework for evaluating the risks of investments in climate change mitigation projects to generate emission credits. Risk factors that influence the quantity of emission credits are identified for six project types. Since not all project types are affected by the same factors, diversification is a viable risk reduction strategy. We propose a methodology for quantifying risk and return of such investments, discuss data requirements, and illustrate it using a sample of voluntary projects. In our sample, the returns of an optimally diversified low-risk portfolio are up to 10 times higher than those of single projects, holding risk exposure constant.     

Relative detectability of greenhouse-gas and aerosol climate change signals

 The use of pattern correlations to compare observed temperature changes with predicted anthropogenic effects has greatly increased our confidence in the reality of these effects. Here we use synthetic observed data to determine the expected behavior of the pattern correlation statistic, R(t), and hence clarify some results obtained in previous studies. We show that, for the specific case considered here (near-surface temperature changes), even with a perfectly-known signal, expected values of R(t) currently should be only of order 0.3–0.5, as observed; that R(t) may show markedly non-linear variations in time; that the CO₂-alone signal pattern should be difficult to detect today primarily because of data coverage deficiencies; and why the signal due to combined CO₂-aerosol forcing is easier to detect than either the CO₂-alone or aerosol-alone signals. Finally, we show that little is to be gained at present by searching for a time-dependent signal compared with a representative constant signal pattern. Received: 24 June 1996/Revised: 3 March 1998     

Simulating the hydrological response to predicted climate change on a watershed in southern Alberta, Canada

The current body of research in western North America indicates that water resources in southern Alberta are vulnerable to climate change impacts. The objective of this research was to parameterize and verify the ACRU agro-hydrological modeling system for a small watershed in southern Alberta and subsequently simulate the change in future hydrological responses over 30-year simulation periods. The ACRU model successfully simulated monthly streamflow volumes (r ²?=?0.78), based on daily simulations over 27 years. The delta downscaling technique was used to perturb the 1961?C1990 baseline climate record from a range of global climate model (GCM) projections to provide the input for future hydrological simulations. Five future hydrological regimes were compared to the 1961?C1990 baseline conditions to determine the average net effect of change scenarios on the hydrological regime of the Beaver Creek watershed over three 30-year time periods (starting in 2010, 2040 and 2070). The annual projections of a warmer and mostly wetter climate in this region resulted in a shift of the seasonal streamflow distribution with an increase in winter and spring streamflow volumes and a reduction of summer and fall streamflow volumes over all time periods, relative to the baseline conditions (1961?C1990), for four of the five scenarios. Simulations of actual evapotranspiration and mean annual runoff showed a slight increase, which was attributed to warmer winters, resulting in more winter runoff and snowmelt events.     

Exploratory analyses of local institutions for climate change adaptation in the Mongolian grasslands: An agent-based modeling approach

There has been a decrease in grazing mobility in the Mongolian grasslands over the past decades. Sedentary grazing with substantial external inputs has increased the cost of livestock production. As a result, the livelihoods of herders have become more vulnerable to climate variability and change. Sedentary grazing is the formal institutional arrangement in Inner Mongolia, China. However, this may not be an efficient institutional arrangement for climate change adaptation. Self-organized local institutions for climate change adaptation have emerged and are under development in the study area. In this study, we did exploratory analyses of multiple local institutions for climate change adaptation in the Mongolian grasslands, using an agent-based modeling approach. Empirical studies from literature and our field work show that sedentary grazing, pasture rental markets, and reciprocal pasture-use groups are three popular institutional arrangements in the study area. First, we modeled the social–ecological performance (i.e., livelihood benefits to herders and grassland quality) of these institutions and their combinations under different climate conditions. Second, we did exploratory analyses of multiple social mechanisms for facilitating and maintaining cooperative use of pastures among herders. The modeling results show that in certain value-ranges of some model parameters with assumed values, reciprocal pasture-use groups had better performance than pasture rental markets; and the comparative advantage of cooperative use of pastures over sedentary grazing without cooperation becomes more evident with the increase in drought probability. Agent diversity and social norms were effective for facilitating the development of reciprocal pasture-use groups. Kin selection and punishments on free-riders were useful for maintaining cooperation among herders.     

Potential effects of climate change on a semi-permanent prairie wetland

We assessed the potential effects of a greenhouse gas-induced global climate change on the hydrology and vegetation of a semi-permanent prairie wetland using a spatially-defined, rule-based simulation model. An 11-yr simulation was run using current versus enhanced greenhouse gas climates. Projections of climatic change were from the Goddard Institute for Space Studies (GISS) general circulation model. Simulations were also run using a range of temperature (+2 and +4 °C) and precipitation change values (–20, –10, 0, +10, +20%) to determine the responsiveness of wetland vegetation and hydrology to a variety of climate scenarios.Maximum water depths were significantly less under the enhanced greenhouse gas scenario than under the current climate. The wetland dried in most years with increased temperature and changes in precipitation. Simulations also revealed a significant change in the vegetation, from a nearly balanced emergent cover to open water ratio to a completely closed basin with no open water areas. Simulations over a range of climate change scenarios showed that precipitation changes (particularly increases) had a greater impact on water levels and cover ratios when the temperature increase was moderate (+2 °C).These potential changes in wetland hydrology and vegetation could result in a dramatic decline in the quality of habitat for breeding birds, particularly waterfowl. Continued research on climate and wetland modeling is needed.     

On the added value of regional climate modeling in climate change assessment

Regional climate models represent a promising tool to assess the regional dimension of future climate change and are widely used in climate impact research. While the added value of regional climate models has been highlighted with respect to a better representation of land-surface interactions and atmospheric processes, it is still unclear whether radiative heating implies predictability down to the typical scale of a regional climate model. As a quantitative assessment, we apply an optimal statistical filter to compare the coherence between observed and simulated patterns of Mediterranean climate change from a global and a regional climate model. It is found that the regional climate model has indeed an added value in the detection of regional climate change, contrary to former assumptions. The optimal filter may also serve as a weighting factor in multi-model averaging.     

Predicting thermal vulnerability of stream and river ecosystems to climate change

We use a predictive model of mean summer stream temperature to assess the vulnerability of USA streams to thermal alteration associated with climate change. The model uses air temperature and watershed features (e.g., watershed area and slope) from 569 US Geological Survey sites in the conterminous USA to predict stream temperatures. We assess the model for predicting climate-related variation in stream temperature by comparing observed and predicted historical stream temperature changes. Analysis of covariance confirms that observed and predicted changes in stream temperatures respond similarly to historical changes in air temperature. When applied to spatially-downscaled future air temperature projections (A2 emission scenario), the model predicts mean warming of 2.2 °C for the conterminous USA by 2100. Stream temperatures are most responsive to climate changes in the Cascade and Appalachian Mountains and least responsive in the southeastern USA. We then use random forests to conduct an empirical sensitivity analysis to identify those stream features most strongly associated with both observed historical and predicted future changes in summer stream temperatures. Larger changes in stream temperature are associated with warmer future air temperatures, greater air temperature changes, and larger watershed areas. Smaller changes in stream temperature are predicted for streams with high initial rates of heat loss associated with longwave radiation and evaporation, and greater base-flow index values. These models provide important insight into the potential extent of stream temperature warming at a near-continental scale and why some streams will likely be more vulnerable to climate change than others.