Impact of rainfall data resolution in time and space on the urban flooding evaluation

Notaro, V., C.M. Fontanazza, G. Freni, and V. Puleo, 2013: “Impact of rainfall data resolution in time and space on the urban flooding evaluation.” Water Science and Technology, v. 68, pp. 1984-1993, doi: 10.2166/wst.2013.435.

Climate change and modification of the urban environment increase the frequency and the negative effects of flooding, increasing the interest of researchers and practitioners in this topic. Usually, flood frequency analysis in urban areas is indirectly carried out by adopting advanced hydraulic models to simulate long historical rainfall series or design storms. However, their results are affected by a level of uncertainty which has been extensively investigated in recent years. A major source of uncertainty inherent to hydraulic model results is linked to the imperfect knowledge of the rainfall input data both in time and space. Several studies show that hydrological modelling in urban areas requires rainfall data with fine resolution in time and space. The present paper analyses the effect of rainfall knowledge on urban flood modelling results. A mathematical model of urban flooding propagation was applied to a real case study and the maximum efficiency conditions for the model and the uncertainty affecting the results were evaluated by means of generalised likelihood uncertainty estimation (GLUE) analysis. The added value provided by the adoption of finer temporal and spatial resolution of the rainfall was assessed.

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Morphological characteristics of urban water bodies: Mechanisms of change and implications for ecosystem function

Steele, M.K., and J.B. Heffernan, 2013: “Morphological characteristics of urban water bodies: Mechanisms of change and implications for ecosystem function.” Ecological Applications, doi: 10.1890/13-0983.1.

The size, shape, and connectivity of water bodies (lakes, ponds, and wetlands) can have important effects on ecological communities and ecosystem processes, but how these characteristics are influenced by land use and land cover change over broad spatial scales is not known. Intensive alteration of water bodies during urban development, including construction, burial, drainage, and reshaping, may select for certain morphometric characteristics and influence the types of water bodies present in cities. We used a database of over 1 million water bodies in 100 cities across the conterminous United States to compare the size distributions, connectivity (as intersection with surface flow lines), and shape (as measured by shoreline development factor) of water bodies in different land cover classes. Water bodies in all urban land covers were dominated by lakes and ponds, while reservoirs and wetlands comprised only a small fraction of the sample. In urban land covers, as compared to surrounding undeveloped land, water body size distributions converged on moderate sizes, shapes toward less tortuous shorelines, and the number and area of water bodies that intersected surface flow lines (i.e. streams and rivers). Potential mechanisms responsible for changing the characteristics of urban water bodies include: preferential removal, physical reshaping or addition of water bodies, and selection of locations for development. The relative contributions of each mechanism likely changes as cities grow. The larger size and reduced surface connectivity of urban water bodies may affect the role of internal dynamics and sensitivity to catchment processes. More broadly, these results illustrate the complex nature of urban watersheds and highlight the need to develop a conceptual framework for urban water bodies.

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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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Surface water quality is improving due to declining atmospheric N deposition

Eshleman, K.N., R.D. Sabo, and K.M. Kline, 2013: “Surface water quality is improving due to declining atmospheric N deposition.” Environmental Science and Technology, v. 47, pp. 12,193-12,200, doi: 10.1021/es4028748.

We evaluated long-term surface water nitrate and atmospheric nitrogen (N) deposition trends for a group of nine predominantly forested Appalachian Mountain watersheds during a recent multidecadal period (1986–2009) in which regional NOx emissions have been progressively reduced. Statistical analysis showed unexpected linear declines in both annual surface water nitrate-N concentrations (mean =46.4%) and yields (mean =47.7%) among the watersheds corresponding to comparable declines in annual wet N deposition (mean =34.4%) resulting from U.S. NOx emission control programs during the same time period. Nitrate-N concentration trends were robust across a large geographical region and appeared insensitive to watershed size across several orders of magnitude—suggesting that the improvements in water quality are probably propagated to surface and estuarine waters downstream. Surface waters are thus responding to declining atmospheric N deposition in much the same way they responded to declining sulfur deposition—although only one watershed showed a 1:1 relationship. Application of a kinetic N saturation model indicated that all nine forested watersheds are exhibiting signs of N saturation as evidenced by a limited, but variable, efficiency of demand for N. Further reductions in N deposition would be expected to produce additional reductions in streamwater N loads.

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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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Estimating effects of improved drinking water and sanitation on cholera

Leidner, A.J., and N.C. Adusumilli, 2013: “Estimating effects of improved drinking water and sanitation on cholera.” Journal of Water and Health, v. 11, pp. 671–683, doi: 10.2166/wh.2013.238.

Demand for adequate provision of drinking-water and sanitation facilities to promote public health and economic growth is increasing in the rapidly urbanizing countries of the developing world. With a panel of data on Asia and Africa from 1990 to 2008, associations are estimated between the occurrence of cholera outbreaks, the case rates in given outbreaks, the mortality rates associated with cholera and two disease control mechanisms, drinking-water and sanitation services. A statistically significant and negative effect is found between drinking-water services and both cholera case rates as well as cholera-related mortality rates. A relatively weak statistical relationship is found between the occurrence of cholera outbreaks and sanitation services.

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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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Threats and opportunities for freshwater conservation under future land use change scenarios in the United States

Martinuzzi, S., S.R. Januchowski-Hartley, B.M. Pracheil, P.B. McIntyre, A.J. Plantinga, D.J. Lewis, and V.C. Radeloff, 2014: “Threats and opportunities for freshwater conservation under future land use change scenarios in the United States.” Global Change Biology, v. 20, pp. 113–124, doi: 10.1111/gcb.12383.

Freshwater ecosystems provide vital resources for humans and support high levels of biodiversity, yet are severely threatened throughout the world. The expansion of human land uses, such as urban and crop cover, typically degrades water quality and reduces freshwater biodiversity, thereby jeopardizing both biodiversity and ecosystem services. Identifying and mitigating future threats to freshwater ecosystems requires forecasting where land use changes are most likely. Our goal was to evaluate the potential consequences of future land use on freshwater ecosystems in the coterminous United States by comparing alternative scenarios of land use change (2001–2051) with current patterns of freshwater biodiversity and water quality risk. Using an econometric model, each of our land use scenarios projected greater changes in watersheds of the eastern half of the country, where freshwater ecosystems already experience higher stress from human activities. Future urban expansion emerged as a major threat in regions with high freshwater biodiversity (e.g., the Southeast) or severe water quality problems (e.g., the Midwest). Our scenarios reflecting environmentally oriented policies had some positive effects. Subsidizing afforestation for carbon sequestration reduced crop cover and increased natural vegetation in areas that are currently stressed by low water quality, while discouraging urban sprawl diminished urban expansion in areas of high biodiversity. On the other hand, we found that increases in crop commodity prices could lead to increased agricultural threats in areas of high freshwater biodiversity. Our analyses illustrate the potential for policy changes and market factors to influence future land use trends in certain regions of the country, with important consequences for freshwater ecosystems. Successful conservation of aquatic biodiversity and ecosystem services in the United States into the future will require attending to the potential threats and opportunities arising from policies and market changes affecting land use.

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