L. Phil Graham

Simulation of high-latitude hydrological processes in the Torne-Kalix basin: PILPS Phase 2(e) 1: Experiment description and summary intercomparisons

Abstract Twenty-one land-surface schemes (LSSs) participated in the Project for Intercomparison of Land-surface Parameterizations (PILPS) Phase 2(e) experiment, which used data from the Torne–Kalix Rivers in northern Scandinavia. Atmospheric forcing data (precipitation, air temperature, specific humidity, wind speed, downward shortwave and longwave radiation) for a 20-year period (1979–1998) were provided to the 21 participating modeling groups for 218 1/4° grid cells that represented the study domain. The first decade (1979–1988) of the period was used for model spin-up. The quality of meteorologic forcing variables is of particular concern in high-latitude experiments and the quality of the gridded dataset was assessed to the extent possible. The lack of sub-daily precipitation, underestimation of true precipitation and the necessity to estimate incoming solar radiation were the primary data concerns for this study. The results from two of the three types of runs are analyzed in this, the first of a three-part paper: (1) calibration–validation runs—calibration of model parameters using observed streamflow was allowed for two small catchments (570 and 1300 km2), and parameters were then transferred to two other catchments of roughly similar size (2600 and 1500 km2) to assess the ability of models to represent ungauged areas elsewhere; and 2) reruns—using revised forcing data (to resolve problems with apparent underestimation of solar radiation of approximately 36%, and certain other problems with surface wind in the original forcing data). Model results for the period 1989–1998 are used to evaluate the performance of the participating land-surface schemes in a context that allows exploration of their ability to capture key processes spatially. In general, the experiment demonstrated that many of the LSSs are able to capture the limitations imposed on annual latent heat by the small net radiation available in this high-latitude environment. Simulated annual average net radiation varied between 16 and 40 W/m2 for the 21 models, and latent heat varied between 18 and 36 W/m2. Among-model differences in winter latent heat due to the treatment of aerodynamic resistance appear to be at least as important as those attributable to the treatment of canopy interception. In many models, the small annual net radiation forced negative sensible heat on average, which varied among the models between −11 and 9 W/m2. Even though the largest evaporation rates occur in the summer (June, July and August), model-predicted snow sublimation in winter has proportionately more influence on differences in annual runoff volume among the models. A calibration experiment for four small sub-catchments of the Torne–Kalix basin showed that model parameters that are typically adjusted during calibration, those that control storage of moisture in the soil column or on the land surface via ponding, influence the seasonal distribution of runoff, but have relatively little impact on annual runoff ratios. Similarly, there was no relationship between annual runoff ratios and the proportion of surface and subsurface discharge for the basin as a whole.

Hydrological change - Climate change impact simulations for Sweden

Climate change resulting from the enhanced greenhouse effect is expected to give rise to changes in hydrological systems. This hydrological change, as with the change in climate variables, will vary regionally around the globe. Impact studies at local and regional scales are needed to assess how different regions will be affected. This study focuses on assessment of hydrological impacts of climate change over a wide range of Swedish basins. Different methods of transferring the signal of climate change from climate models to hydrological models were used. Several hydrological model simulations using regional climate model scenarios from Swedish Regional Climate Modelling Programme (SWECLIM) are presented. A principal conclusion is that subregional impacts to river flow vary considerably according to whether a basin is in northern or southern Sweden. Furthermore, projected hydrological change is just as dependent on the choice of the global climate model used for regional climate model boundary conditions as the choice of anthropogenic emissions scenario.

On the scale problem in hydrological modelling

The problem of scales and particularly the modelling of macro or continental scale catchments in hydrology is addressed. It is concluded that the magnitude of the scale problem is related to the specific hydrologic problem to be solved and to the scientific approach and perspective of the modeller. A distributed modelling approach, based on variability parameters, is suggested for modelling of soil moisture dynamics and runoff generation. It is shown that the parameters of such an approach are relatively stable over a wide range of scales. An example of the application of a standard version of the Swedish HBV hydrological model to the continental scale catchment of the Baltic Sea is shown and its usefulness is discussed.

The Role of Climate Forecasts in Western U.S. Power Planning

The benefits of potential electric power transfers between the Pacific Northwest (PNW) and California (CA) are evaluated using a linked set of hydrologic, reservoir, and power demand simulation models for the Columbia River and the Sacramento–San Joaquin reservoir systems. The models provide a framework for evaluating climate-related variations and long-range predictability of regional electric power demand, hydropower production, and the benefits of potential electric power transfers between the PNW and CA. The period of analysis is 1917–2002. The study results show that hydropower production and regional electric power demands in the PNW and CA are out of phase seasonally but that hydropower productions in the PNW and CA have strongly covaried on an annual basis in recent decades. Winter electric power demand and spring and annual hydropower production in the PNW are related to both El Nino–Southern Oscillation (ENSO) and the Pacific decadal oscillation (PDO) through variations in winter climate. Summer power demand in CA is related primarily to variations in the PDO in spring. Hydropower production in CA, despite recent covariation with the PNW, is not strongly related to ENSO variability overall. Primarily because of strong variations in supply in the PNW, potential hydropower transfers between the PNW and CA in spring and summer are shown to be correlated to ENSO and PDO, and the conditional probability distributions of these transfers are therefore predictable with long lead times. Such electric power transfers are estimated to have potential average annual benefits of

Projections of Future Anthropogenic Climate Change

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The role of aerodynamic roughness for runoff and snow evaporation in land-surface schemes—comparison of uncoupled and coupled simulations

79 million for CA and the PNW, respectively, at the year-2000 regional demand level. These benefits are on average 11%–27% larger during cold ENSO/PDO events and are 16%–30% lower during warm ENSO/PDO events. Power transfers from the PNW to CA and hydropower production in CA are comparable in magnitude, on average.

Modelling Climate Change Impacts on Water Resources in the Swedish Regional Climate Modelling Programme

This chapter focuses on summarising projections of future anthropogenic climate change for the Baltic Sea Basin. This includes the science of climate change and how future projections are made, taking into account anthropogenic influence on greenhouse gases (GHG). Looking forward to-ward future climates requires using state-of-the-art modelling tools to represent climate processes.

Design and test of a model-assisted participatory process for the formulation of a local climate adaptation plan

This paper describes the impact of changes in aerodynamic roughness length for snow-covered surfaces in a land-surface scheme (LSS) on simulated runoff and evapotranspiration. The study was undertaken as the LSS in question produced widely divergent results in runoff, depending on whether it was used in uncoupled one-dimensional simulations forced by observations from the PILPS2e project, or in three-dimensional simulations coupled to an atmospheric model. The LSS was applied in two versions (LSS1 and LSS2) for both uncoupled and coupled simulations, where the only difference between the two versions was in the roughness length of latent heat used over snow-covered surfaces. The results show that feedback mechanisms in temperature and humidity in the coupled simulations were able to compensate for deficiencies in parameterizations and therefore, LSS1 and LSS2 yielded similar runoff results in this case. Since such feedback mechanisms are absent in uncoupled simulations, the two LSS versions produced very different runoff results in the uncoupled case. However, the magnitude of these feedback mechanisms is small compared to normal variability in temperature and humidity and cannot, by themselves, reveal any deficiencies in a parameterization. The conclusion we obtained is that the magnitude of the aerodynamic resistance is important to correctly simulate fluxes and runoff, but feedback mechanisms in a coupled model can partly compensate for errors.

Abstract to “On the scale problem in hydrological modelling” [Journal of Hydrology 211 (1998) 253–265]☆

The Swedish Regional Climate Modelling Programme (SWECLIM) focuses on interpretation of climate scenarios for the Nordic Region. Water resources studies include hydrological model simulations both at the large scale to simulate trends for the entire Baltic Basin and at smaller basin scales to simulate local impacts in Sweden. Global climate model simulations (GCMs) provide lateral boundary conditions to drive the finer resolution Rossby Centre regional atmospheric climate model (RCA) in dynamical downscaling. Two different GCMs—HadCM2 and ECHAM4/OPYC3—have thus far been used. Analyses of future climates are created from differences in 10-year time slices between RCA control runs of the present climate and RCA scenario climate runs with transient greenhouse gas simulations. These differences drive the offline hydrological impacts assessment models. Both of the RCA climate scenarios show overall increases in temperature and precipitation for the Nordic Region, although spatial and temporal distribution varies between them. Hydrological model scenario simulations show a strong decrease in snowmelt peak river discharge. Modelled changes to average annual freshwater inflow to the Baltic Sea vary from +8% to 21% from present day conditions. The interface between atmospheric models and hydrological impact models is a weak link in the process, as is representation of evapotranspiration in the hydrological models for a future climate.

Assessing climate change impacts on hydrology from an ensemble of regional climate models, model scales and linking methods – a case study on the Lule River basin

This article presents the design and testing of a model-assisted participatory process for the formulation of a local adaptation plan to climate change. The pilot study focused on small-scale and commercial agriculture, water supply, housing, wildlife, livestock and biodiversity in the Thukela River basin, KwaZulu-Natal, South Africa. The methodology was based on stakeholders identifying and ranking the severity of climate-related challenges, and downscaled stakeholder-identified information provided by modellers, with the aim of addressing possible changes of exposure in the future. The methodology enables the integration of model-based information with experience and visions based on local realities. It includes stakeholders’ own assessments of their vulnerability to prevailing climate variability and the severity, if specified, of climate-related problems that may occur more often in the future. The methodology made it possible to identify the main issues to focus on in the adaptation plan, including barriers to adaptation. We make recommendations for how to design a model-assisted participatory process, emphasizing the need for transparency, to recognize the interests of the stakeholders, good advance planning, local relevance, involvement of local champions, and adaptation of Information material to each groups previous experience and understanding.