Annette Semadeni-Davies

Urban water management vs. climate change: impacts on cold region waste water inflows.

Failure to account for non-climatic changes to water systems, such as design and operation, within climate change impact assessments leads to misconceptions because these activities buffer the human built enviroment from bio-physical impacts. Urban drainage in cold regions, which is dominated by snowmelt, is especially vulnerable to climate change and is investigated in this paper within the context of future rehabilitation of the sewer network. The objectives are to illustrate the relative response of urban drainage to changes in both the pipe network and climate and demonstrate the use of response surfaces for climate change studies. An incremental climate scenario approach is used to generate two sensitivity analyses for waste water inflows to the Lycksele waste water treatment plant in north-central Sweden. Air temperature and precipitation data (1984–1993) are altered incrementally between –5 and +15 °C and –10 and +40% respectively. These data are then used to drive a hydrological transformation model to obtain estimates of sewer infiltration from groundwater. The results are presented as winter and spring response surfaces – these are graphical representations of a response matrix where each point relates to a single model run. Climate scenario envelopes which summarise a series of GCM runs (ACACIA; Carter, 2002, pers. comm.) are overlaid to indicate the range of plausible waste water inflows. Estimates of natural multi-decadal variability are also included. The first sensitivity analysis assumes no change to the drainage system while the second simulates sewer renovation in which the system is fully separated and sewer infiltration is reduced. The main conclusions are that innovations in drainage network technology have a greater potential to alter waste water inflows than climate change and that, while the direction of climate change is fairly certain, there is great uncertainty surrounding magnitude of those changes and their impacts.

Monthly snowmelt modelling for large-scale climate change studies using the degree day approach

Abstract The degree day or temperature index snowmelt modelling approach has been adapted to provide a simple conceptual, semi-distributed snowmelt-runoff model suitable for large-scale climate impact investigations. The model is forced by pseudo-daily data derived from standard monthly meteorological data. Generic rather than site-specific parameters are used where possible to allow spatial and temporal transferability. Spatial distribution is achieved by elevation and broad vegetation cover. Snow accumulation and melt are determined from air temperature. Catchment runoff is simulated with a one-dimensional water balance sub-model consisting of two soil layers. Available water capacity, percolation and drainage rates are defined by soil texture. The model was tested in three catchments: Valuoja in Estonia and Gimdalsbyn and Kultsjon in Sweden. The catchment areas ranged from approximately 4–2200 km 2 , simulation lengths were 10, 21 and 26 years. The snow season timing matched that observed in all three catchments. Comparisons of measured and estimated snow water equivalence in Kultsjon demonstrated that the model can adequately predict snow cover below the tree line. Simulated monthly runoff at Valuoja gave good agreement with observations ( r = 0.87) and a paired t -test showed no significant differences. The seasonal discharge pattern at Kultsjon also fitted well ( r = 0.85) although the hydrograph generated was too low, probably due to precipitation undercatch. The discharge pattern at Gimdalsbyn was less well modelled ( r = 0.55), but the annual runoff totals were similar suggesting a lagged runoff response. Sensitivity analysis showed that the model is insensitive to the generic parameters but is sensitive to local soil texture. The model is able to capture, from standard meteorological data, patterns of snow accumulation, melt and runoff with a reasonable degree of accuracy without the need to optimise parameters. These features make the model a potentially useful tool for evaluating the impacts of climate change on regional and continental water balances.

Snowmelt sensitivity to radiation in the urban environment

Abstract Despite having the same snowmelt processes, snowpacks in urban environments experience a range of conditions different from those of rural areas. Melt is intensified at some sites due to greater radiative energy. Shading, however, can reduce radiation and melt at other sites. Changes to the radiation balance and snowpack processes have been investigated. A physical snowpack model was developed and tested against data from an impervious study plot in Sweden. Estimated surface runoff compared favourably with that measured. An urban radiation scheme captured the observed net allwave radiation well. Series of sensitivity analyses were made by perturbing the scheme to represent three urban locations: open ground and the southern (sunny) and north (shaded) sides of a hypothetical building. Cloudiness, albedo, wall temperature and sky view were altered to reproduce common urban conditions. Even without perturbation, the shaded and sunny sides of the building had different radiation fluxes—the south side...

The water balance of a sub-Arctic town

Urban water balances differ from their rural counterparts due to extreme spatial heterogeneity, water imported from outside catchment boundaries and changed flow paths (e.g., drainage pipes and impervious surfaces). Urban catchments are characterized by increased peak discharges and fast response times, each contributing to specific environmental problems. The water balances of towns in the northern high latitudes are further complicated by snow which represents an energy dependent seasonal water store. This paper investigates the monthly water balance of Lulea (June 1992 to June 1996), a Swedish town of 71 000 inhabitants 100 km south of the Arctic Circle. The town has snow cover for five to six months of the year and thaw is usually in late April. Data available included daily precipitation, temperature and inflow to the Uddebo waste water treatment plant; and monthly potential evapotranspiration, groundwater levels and water supply statistics. Of interest were the seasonal differences in runoff volumes and flow pathways to the waste water treatment plant and receiving waters. It was found that increased volumes of runoff, reduced concentration times and long duration led to flooding and high waste water loads at the treatment plant. The surface water component of sewage originates from direct flow into pipe inlets and infiltration into sewer pipes. Autumn and spring were found to be the periods of groundwater recharge, although frozen soil can limit water percolation. Copyright (C) 1999 John Wiley & Sons, Ltd. (Less)

Radiation balance of urban snow: a water management perspective

The radiation balance of urbanised catchments differs from their rural counterparts, with snowpacks experiencing either enhanced or decreased irradiance depending on snowpack location and condition. As snowmelt is largely driven by radiation inputs, changes to localised irradiance (and melt rates) have implications for urban runoff generation. Storm- and wastewater drainage systems in cold regions are currently dimensioned for rain according to practices developed for temperate climates. They are not designed to cope with wintry conditions, which can lead to surface flooding, hydraulic overloads and poor water quality at receiving waters. Net allwave radiation measurements over snow made at the Swedish city of Lulea during April 1997 and 1998 are presented. The 1997 measurements were made in the vicinity of a matt-black-painted metal building at Lulea University of Technology, whereas the 1998 measurements are from a specially constructed 3×6-m black plastic-clad wall built on an open field just outside the town. Black minimises multiple reflections between the snow and walls, while maximising absorption of shortwave radiation by walls. The data were compared to the outputs of an urban radiation model. The results show that urban structures significantly alter radiation over snow. The temperature of the south-facing walls translates to longwave enhancements in the order of 150 W m−2 for several metres from the walls on sunny days. Shaded snow near the north-facing wall showed a net allwave radiation loss of the same order of magnitude. Radiation inputs to snow are similar both to the north and south of walls when the sky is overcast. The need to include snowmelt energetics within design and management techniques is discussed in light of the results.