Simulating future trends in urban stormwater quality for changing climate, urban land use and environmental controls

Borris, M., M. Viklander, A.-M. Gustafsson, and J. Marsalek, 2013: “Simulating future trends in urban stormwater quality for changing climate, urban land use and environmental controls.” Water Science and Technology, v. 68, pp. 2082–2089, doi: 10.2166/wst.2013.465.

The effects of climatic changes, progressing urbanization and improved environmental controls on the simulated urban stormwater quality in a northern Sweden community were studied. Future scenarios accounting for those changes were developed and their effects simulated with the Storm Water Management Model (SWMM). It was observed that the simulated stormwater quality was highly sensitive to the scenarios, mimicking progressing urbanization with varying catchment imperviousness and area. Thus, land use change was identified as one of the most influential factors and in some scenarios, urban growth caused changes in runoff quantity and quality exceeding those caused by a changing climate. Adaptation measures, including the reduction of directly connected impervious surfaces (DCIS) through the integration of more green spaces into the urban landscape, or disconnection of DCIS were effective in reducing runoff volume and pollutant loads. Furthermore, pollutant source control measures, including material substitution, were effective in reducing pollutant loads and significantly improving stormwater quality.

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Consequences of climate change for biotic disturbances in North American forests

Weed, A.S., M.P. Ayres, and J.A. Hicke, 2013: “Consequences of climate change for biotic disturbances in North American forests.” Ecological Monographs, v. 83, pp. 441–470, doi: 10.1890/13-0160.1.

About one-third of North America is forested. These forests are of incalculable value to human society in terms of harvested resources and ecosystem services and are sensitive to disturbance regimes. Epidemics of forest insects and diseases are the dominant sources of disturbance to North American forests. Here we review current understanding of climatic effects on the abundance of forest insects and diseases in North America, and of the ecological and socioeconomic impacts of biotic disturbances. We identified 27 insects (6 nonindigenous) and 22 diseases (9 nonindigenous) that are notable agents of disturbance in North American forests. The distribution and abundance of forest insects and pathogens respond rapidly to climatic variation due to their physiological sensitivity to temperature, high mobility, short generation times, and high reproductive potential. Additionally, climate affects tree defenses, tree tolerance, and community interactions involving enemies, competitors, and mutualists of insects and diseases. Recent research affirms the importance of milder winters, warmer growing seasons, and changes in moisture availability to the occurrence of biotic disturbances. Predictions from the first U.S. National Climate Assessment of expansions in forest disturbances from climate change have been upheld, in some cases more rapidly and dramatically than expected. Clear examples are offered by recent epidemics of spruce beetles in Alaska, mountain pine beetle in high-elevation five-needle pine forests of the Rocky Mountains, and southern pine beetle in the New Jersey Pinelands. Pathogens are less studied with respect to climate, but some are facilitated by warmer and wetter summer conditions.

Changes in biotic disturbances have broad consequences for forest ecosystems and the services they provide to society. Climatic effects on forest insect and disease outbreaks may foster further changes in climate by influencing the exchange of carbon, water, and energy between forests and the atmosphere. Climate-induced changes in forest productivity and disturbance create opportunities as well as vulnerabilities (e.g., increases in productivity in many areas, and probably decreases in disturbance risks in some areas). There is a critical need to better understand and predict the interactions among climate, forest productivity, forest disturbance, and the socioeconomic relations between forests and people.

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Effects of thinning on drought vulnerability and climate response in north temperate forest ecosystems

D’Amato, A.W., J.B. Bradford, S. Fraver, and B.J. Palik, 2013: “Effects of thinning on drought vulnerability and climate response in north temperate forest ecosystems.” Ecological Applications, v. 23, pp. 1735–1742, doi: 10.1890/13-0677.1.

Reducing tree densities through silvicultural thinning has been widely advocated as a strategy for enhancing resistance and resilience to drought, yet few empirical evaluations of this approach exist. We examined detailed dendrochronological data from a long-term (>50 years) replicated thinning experiment to determine if density reductions conferred greater resistance and/or resilience to droughts, assessed by the magnitude of stand-level growth reductions. Our results suggest that thinning generally enhanced drought resistance and resilience; however, this relationship showed a pronounced reversal over time in stands maintained at lower tree densities. Specifically, lower-density stands exhibited greater resistance and resilience at younger ages (49 years), yet exhibited lower resistance and resilience at older ages (76 years), relative to higher-density stands. We attribute this reversal to significantly greater tree sizes attained within the lower-density stands through stand development, which in turn increased tree-level water demand during the later droughts. Results from response–function analyses indicate that thinning altered growth–climate relationships, such that higher-density stands were more sensitive to growing-season precipitation relative to lower-density stands. These results confirm the potential of density management to moderate drought impacts on growth, and they highlight the importance of accounting for stand structure when predicting climate-change impacts to forests.

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Spatio-temporal relations between temperature and precipitation regimes: Implications for temperature-induced changes in the hydrological cycle

Zhang, Q., J. Li, V.P. Singh, and M. Xiao, 2013: “Spatio-temporal relations between temperature and precipitation regimes: Implications for temperature-induced changes in the hydrological cycle.” Global and Planetary Change, v. 111, pp. 57-76, doi: 10.1016/j.gloplacha.2013.08.012.

Changes in the precipitation regime as a result of temperature changes are important for water resources management and management of water-related natural hazards. In this study, daily temperature and precipitation datasets from 590 stations from across China are analyzed to investigate possible relations between precipitation and temperature regimes in both space and time. The K-means method is applied to group 590 stations into 4 homogenous sub-regions and then trends are detected by the modified Mann–Kendall test. The field significance test and false discovery rate approaches are used to determine spatial correlations. Results show that: (1) significant increases in temperature extremes are detected across China. However, the magnitude of increase in the minimum temperature is larger than that in the maximum temperature. The warming in China is reflected mainly by the remarkable increase in the minimum temperature; (2) precipitation changes are extremely uneven in both space and time. Generally, a wetting tendency is detected in western China, and a drying tendency in northeastern China annually and in summer. In winter, however, a wetting tendency is observed; and (3) different regional responses of precipitation extremes to increasing temperature can be identified across China. Under the influence of increasing temperature, precipitation is intensifying in southeastern China and winter is having a wetting tendency. The responses of changes in weak precipitation extremes to climate warming are comparatively complicated and diverse. Even then it can be confirmed that increasing temperature tends to trigger the intensification of precipitation. Temporal and spatial changes of water vapor divergence can well aid in the interpretation of seasonal and spatial alterations of precipitation regimes. Temperature changes can influence precipitation changes by altering thermo-dynamic properties of air mass and hence the moisture transportation.

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Climate change and deforestation: The evolution of an intersecting policy domain

Buizer, M., D. Humphreys, and W. de Jong, 2014: “Climate change and deforestation: The evolution of an intersecting policy domain.” Environmental Science and Policy, v. 35, pp. 1-11, doi: 10.1016/j.envsci.2013.06.001.

Forests and climate change are increasingly dealt with as interconnected policy issues. Both the potential synergies and policy conflicts between forest conservation and restoration and climate change mitigation now receive sustained and high level attention from academic, policy analysis and practitioner communities across the globe. Arguably the most pronounced contemporary policy manifestation of this is the debate on Reducing Emissions from Deforestation and Forest Degradation in Developing Countries (or REDD+) by which governments and private investors from developed countries may compensate actors in tropical forest countries for reducing forest loss beneath an agreed baseline. Problems of climate–forest policies implementation and governance, however, can also be found in countries such as Canada, the USA, the UK and Australia. The future of instruments like REDD+ is uncertain with growing critiques on payment and performance-based mechanisms and unresolved issues of governance, government and accountability. This paper, and the special issue it introduces, illustrates that in the REDD+ debate many contentious issues have resurfaced from past debates. These issues include the participation and rights of local communities in forest policy and management; the relationship between internationally agreed payment and performance-based programmes and formal democratic decision-making processes and structures; the complexities of rights to carbon versus tenure rights; and the ways in which – in spite of the high expectations of both developing and developed countries to combat carbon emissions from deforestation and forest degradation through the REDD+ mechanism – effective climate-focused forestry policies are seldom found in most tropical forest-rich countries. REDD+ is now very much the dominant discourse at the forest–climate interface, and one with a primary focus on measurability to communicate carbon mitigation results across various levels. However, this serves to disperse and displace, rather than resolve, policy-making on non-carbon values.

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Constraints and potentials of future irrigation water availability on agricultural production under climate change

Elliott, J., D. Deryng, C. Müller, K. Frieler, M. Konzmann, D. Gerten, M. Glotter, M. Flörke, Y. Wada, N. Best, S. Eisner, B.M. Fekete, C. Folberth, I. Foster, S.N. Gosling, I. Haddeland, N. Khabarov, F. Ludwig, Y. Masaki, S. Olin, C. Rosenzweig, A.C. Ruane, Y. Satoh, E. Schmid, T. Stacke, Q. Tang, and D. Wisser, 2013: “Constraints and potentials of future irrigation water availability on agricultural production under climate change.” Proceedings of the National Academy of Sciences, doi: 10.1073/pnas.1222474110.

We compare ensembles of water supply and demand projections from 10 global hydrological models and six global gridded crop models. These are produced as part of the Inter-Sectoral Impacts Model Intercomparison Project, with coordination from the Agricultural Model Intercomparison and Improvement Project, and driven by outputs of general circulation models run under representative concentration pathway 8.5 as part of the Fifth Coupled Model Intercomparison Project. Models project that direct climate impacts to maize, soybean, wheat, and rice involve losses of 400–1,400 Pcal (8–24% of present-day total) when CO2 fertilization effects are accounted for or 1,400–2,600 Pcal (24–43%) otherwise. Freshwater limitations in some irrigated regions (western United States; China; and West, South, and Central Asia) could necessitate the reversion of 20–60 Mha of cropland from irrigated to rainfed management by end-of-century, and a further loss of 600–2,900 Pcal of food production. In other regions (northern/eastern United States, parts of South America, much of Europe, and South East Asia) surplus water supply could in principle support a net increase in irrigation, although substantial investments in irrigation infrastructure would be required.

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Traits of surface water pollution under climate and land use changes: A remote sensing and hydrological modeling approach

Jordan, Y.C., A. Ghulam, and S. Hartling, 2014: “Traits of surface water pollution under climate and land use changes: A remote sensing and hydrological modeling approach.” Earth-Science Reviews, v. 128, pp. 181-195, doi: 10.1016/j.earscirev.2013.11.005.

In this paper, spatial and temporal trajectories of land cover/land use change (LCLUC) derived from Landsat data record are combined with hydrological modeling to explore the implication of vegetation dynamics on soil erosion and total suspended sediment (TSS) loading to surface rivers. The inter-annual coefficient of variation (CoV) of normalized difference vegetation index (NDVI) is used to screen the LCLUC and climate change. The Soil and Water Assessment Tool (SWAT) is employed to identify the monthly TSS for two times interval (1991 to 2001 and 2001 to 2011) at subbasin levels. SWAT model is calibrated from 1991 to 2001 and validated from 2002 to 2011 at three USGS gauging sites located in the study area. The Spearman’s rank correlation of annual mean TSS is used to assess the temporal trends of TSS dynamics in the subbasins in the two study periods. The spatial correlation among NDVI, LCLUC, climate change and TSS loading rate changes is quantified by using linear regression model and negative/positive trend analysis. Our results showed that higher rainfall yields contribute to higher TSS loading into surface waters. A higher inter-annual accumulated vegetation index and lower inter-annual CoV distributed over the uplands resulted in a lower TSS loading rate, while a relatively low vegetation index with larger CoV observed over lowlands resulted in a higher TSS loading rate. The TSS loading rate at the basin outlet increased with the decrease of annual NDVI due to expanding urban areas in the watershed. The results also suggested nonlinearity between the trends of TSS loading with any of a specific land cover change because of the fact that the contribution of a factor can be influenced by the effects of other factors. However, dominant factors that shape the relationship between the trend of TSS loading and specific land cover changes were detected. The change of forest showed a negative relationship while agriculture and pasture demonstrated positive relationships with TSS loading change. Our results do not show any significant causal relationship between urbanization and the TSS loading change suggesting that further investigation needs to be carried out to understand the mechanism of the impact of urban sprawl on surface water quality.

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Multi-model assessment of water scarcity under climate change

Schewe, J., J. Heinke, D. Gerten, I. Haddeland, N.W. Arnell, D.B. Clarke, R. Dankers, S. Eisner, B.M. Fekete, F.J. Colón-González, S.M. Gosling, H. Kim, X. Liu, Y. Masaki, F.T. Portmann, Y. Satoh, T. Stacke, Q. Tang, Y. Wada, D. Wisser, T. Albrecht, K. Frieler, F. Piontek, L. Warszawski, and P. Kabat, 2013: “Multi-model assessment of water scarcity under climate change.” Proceedings of the National Academy of Sciences, doi: 10.1073/pnas.1222460110.

Water scarcity severely impairs food security and economic prosperity in many countries today. Expected future population changes will, in many countries as well as globally, increase the pressure on available water resources. On the supply side, renewable water resources will be affected by projected changes in precipitation patterns, temperature, and other climate variables. Here we use a large ensemble of global hydrological models (GHMs) forced by five global climate models and the latest greenhouse-gas concentration scenarios (Representative Concentration Pathways) to synthesize the current knowledge about climate change impacts on water resources. We show that climate change is likely to exacerbate regional and global water scarcity considerably. In particular, the ensemble average projects that a global warming of 2 °C above present (approximately 2.7 °C above preindustrial) will confront an additional approximate 15% of the global population with a severe decrease in water resources and will increase the number of people living under absolute water scarcity (3 per capita per year) by another 40% (according to some models, more than 100%) compared with the effect of population growth alone. For some indicators of moderate impacts, the steepest increase is seen between the present day and 2 °C, whereas indicators of very severe impacts increase unabated beyond 2 °C. At the same time, the study highlights large uncertainties associated with these estimates, with both global climate models and GHMs contributing to the spread. GHM uncertainty is particularly dominant in many regions affected by declining water resources, suggesting a high potential for improved water resource projections through hydrological model development.

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First look at changes in flood hazard in the Inter-Sectoral Impact Model Intercomparison Project ensemble

Dankers, R., N.W. Arnell, D.B. Clark, P.D. Falloon, B.M. Fekete, S.N. Gosling, J. Heinke, H. Kim, Y. Masaki, Y. Satoh, T. Stacke, Y. Wada, and D. Wisser, 2013: “First look at changes in flood hazard in the Inter-Sectoral Impact Model Intercomparison Project ensemble.” Proceedings of the National Academy of Sciences, doi: 10.1073/pnas.1302078110.

Climate change due to anthropogenic greenhouse gas emissions is expected to increase the frequency and intensity of precipitation events, which is likely to affect the probability of flooding into the future. In this paper we use river flow simulations from nine global hydrology and land surface models to explore uncertainties in the potential impacts of climate change on flood hazard at global scale. As an indicator of flood hazard we looked at changes in the 30-y return level of 5-d average peak flows under representative concentration pathway RCP8.5 at the end of this century. Not everywhere does climate change result in an increase in flood hazard: decreases in the magnitude and frequency of the 30-y return level of river flow occur at roughly one-third (20–45%) of the global land grid points, particularly in areas where the hydrograph is dominated by the snowmelt flood peak in spring. In most model experiments, however, an increase in flooding frequency was found in more than half of the grid points. The current 30-y flood peak is projected to occur in more than 1 in 5 y across 5–30% of land grid points. The large-scale patterns of change are remarkably consistent among impact models and even the driving climate models, but at local scale and in individual river basins there can be disagreement even on the sign of change, indicating large modeling uncertainty which needs to be taken into account in local adaptation studies.

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Impacts of climate and catastrophic forest changes on streamflow and water balance in a mountainous headwater stream in Southern Alberta

Mahat, V., and A. Anderson, 2013: “Impacts of climate and catastrophic forest changes on streamflow and water balance in a mountainous headwater stream in Southern Alberta.” Hydrology and Earth System Sciences, v. 17, pp. 4941-4956, doi: 10.5194/hess-17-4941-2013.

Rivers in Southern Alberta are vulnerable to climate change because much of the river water originates as snow in the eastern slopes of the Rocky Mountains. Changes in likelihood of forest disturbance (wildfire, insects, logging, etc.) may also have impacts that are compounded by climate change. This study evaluates the impacts of climate and forest changes on streamflow in the upper parts of the Oldman River in Southern Alberta using a conceptual hydrological model, HBV-EC (Hydrologiska Byråns attenbalansavdelning, Environment Canada), in combination with a stochastic weather generator (LARS-WG) driven by GCM (global climate model) output climate data. Three climate change scenarios (A1B, A2 and B1) are selected to cover the range of possible future climate conditions (2020s, 2050s, and 2080s). The GCM projected less than a 10% increase in precipitation in winter and a similar amount of precipitation decrease in summer. These changes in projected precipitation resulted in up to a 200% (9.3 mm) increase in winter streamflow in February and up to a 63% (31.2 mm) decrease in summer flow in June. Flow also decreased in July and August, when irrigation is important; these reduced river flows during this season could impact agriculture production. The amplification in the streamflow is mostly driven by the projected increase in temperature that is predicted to melt winter snow earlier, resulting in lower water availability during the summer. Uncertainty analysis was completed using a guided GLUE (generalized likelihood uncertainty estimation) approach to obtain the best 100 parameter sets and associated ranges of streamflows. The impacts of uncertainty in streamflows were higher in spring and summer than in winter and fall. Forest change compounded the climate change impact by increasing the winter flow; however, it did not reduce the summer flow.

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