Elliot M. Schneiderman

Examination of change factor methodologies for climate change impact assessment

[1] A variety of methods are available to estimate values of meteorological variables at future times and at spatial scales that are appropriate for local climate change impact assessment. One commonly used method is Change Factor Methodology (CFM), sometimes referred to as delta change factor methodology. Although more sophisticated methods exist, CFM is still widely applicable and used in impact analysis studies. While there are a number of different ways by which change factors (CFs) can be calculated and used to estimate future climate scenarios, there are no clear guidelines available in the literature to decide which methodologies are most suitable for different applications. In this study several categories of CFM (additive versus multiplicative and single versus multiple) for a number of climate variables are compared and contrasted. The study employs several theoretical case studies, as well as a real example from Cannonsville watershed, which supplies water to New York City, USA. Results show that in cases when the frequency distribution of Global Climate Model (GCM) baseline climate is close to the frequency distribution of observed climate, or when the frequency distribution of GCM future climate is close to the frequency distribution of GCM baseline climate, additive and multiplicative single CFMs provide comparable results. Two options to guide the choice of CFM are

Modeling watershed-scale effectiveness of agricultural best management practices to reduce phosphorus loading

Planners advocate best management practices (BMPs) to reduce loss of sediment and nutrients in agricultural areas. However, the scientific community lacks tools that use readily available data to investigate the relationships between BMPs and their spatial locations and water quality. In rural, humid regions where runoff is associated with saturation-excess processes from variable source areas (VSAs), BMPs are potentially most effective when they are located in areas that produce the majority of the runoff. Thus, two critical elements necessary to predict the water quality impact of BMPs include correct identification of VSAs and accurate predictions of nutrient reduction due to particular BMPs. The objective of this research was to determine the effectiveness of BMPs using the Variable Source Loading Function (VSLF) model, which captures the spatial and temporal evolutions of VSAs in the landscape. Data from a long-term monitoring campaign on a 164-ha farm in the New York City source watersheds in the Catskills Mountains of New York state were used to evaluate the effectiveness of a range of BMPs. The data spanned an 11-year period over which a suite of BMPs, including a nutrient management plan, riparian buffers, filter strips and fencing, was installed to reduce phosphorus (P) loading. Despite its simplicity, VSLF predicted the spatial distribution of runoff producing areas well. Dissolved P reductions were simulated well by using calibrated reduction factors for various BMPs in the VSLF model. Total P losses decreased only after cattle crossings were installed in the creek. The results demonstrated that BMPs, when sited with respect to VSAs, reduce P loss from agricultural watersheds, providing useful information for targeted water quality management.

Impacts of climate change on phosphorus loading from a grassland catchment: Implications for future management

Dynamic modelling was used to quantify the impact of projected climate change, and potential changes in population and land use, on phosphorus (P) export from a sub-catchment in SW Ireland using the Generalised Watershed Loading Functions (GWLF) model. Overall the results indicated that the increase in annual total phosphorus loads attributable to climate change was greater than that from either population or land use change, and therefore that future climate variability will pose an increasingly significant threat to the successful long-term implementation of catchment management initiatives. The seasonal pattern in projected P export mirrored changes in streamflow, with higher rates between January and April and lower rates in summer. The potential reduction in export in summer was, however, negated when increases in population were included in simulations. A change in the slurry spreading period from that stipulated in national regulations to the months between April and September could potentially mitigate against future increases in dissolved P export in spring. The results indicate that projected changes in climate should be included when undertaking modelling exercises in support of decision making for catchment management plans.

Effects of warmer world scenarios on hydrologic inputs to Lake Mälaren, Sweden and implications for nutrient loads

A simple, rapid, and flexible modelling approach was applied to explore the impacts of climate change on hydrologic inputs and consequent implications for nutrient loading to Lake Mälaren, Sweden using a loading function model (GWLF). The first step in the process was to adapt the model for use in a large and complex Swedish catchment. We focused on the Galten basin with four rivers draining into the western region of Mälaren. The catchment model was calibrated and tested using long-term historical data for river discharge and dissolved nutrients (N, P). Then multiple regional climate model simulation results were downscaled to the local catchment level, and used to simulate possible hydrological and nutrient loading responses to warmer world scenarios. Climate change projections for the rivers of Galten basin show profound changes in the timing of discharge and nutrient delivery due to increased winter precipitation and earlier snow melt. Impacts on total annual discharge and load are minimal, but the alteration in river flow regime and the timing of nutrient delivery for future climate scenarios is strikingly different from historical conditions.

A Saturation Excess Erosion Model

Abstract. Scaling-up sediment transport has been problematic because most sediment loss models (e.g., the Universal Soil Loss Equation) are developed using data from small plots where runoff is generated by infiltration excess. However, in most watersheds, runoff is produced by saturation excess processes. In this article, we improve an earlier saturation excess erosion model that was only tested on a limited basis, in which runoff and erosion originated from periodically saturated and severely degraded areas, and apply it to five watersheds over a wider geographical area. The erosion model is based on a semi-distributed hydrology model that calculates saturation excess runoff, interflow, and baseflow. In the development of the erosion model, a linear relationship between sediment concentration and velocity in surface runoff is assumed. Baseflow and interflow are sediment free. Initially during the rainy season in Ethiopia, when the fields are being plowed, the sediment concentration in the river is limited by the ability of the surface runoff to move sediment. Later in the season, the sediment concentration becomes limited by the availability of sediment. To show the general applicability of the Saturation Excess Erosion Model (SEEModel), the model was tested for watersheds located 10,000 km apart, in the U.S. and in Ethiopia. In the Ethiopian highlands, we simulated the 1.1 km 2 Anjeni watershed, the 4.8 km 2 Andit Tid watershed, the 4.0 km 2 Enkulal watershed, and the 174,000 km 2 Blue Nile basin. In the Catskill Mountains in New York State, the sediment concentrations were simulated in the 493 km 2 upper Esopus Creek watershed. Discharge and sediment concentration averaged over 1 to 10 days were well simulated over the range of scales with comparable parameter sets. The Nash-Sutcliffe efficiency (NSE) values for the validation runs for the stream discharge were between 0.77 and 0.92. Sediment concentrations had NSE values ranging from 0.56 to 0.86 using only four calibrated sediment parameters together with the subsurface and surface runoff discharges calculated by the hydrology model. The model results suggest that correctly predicting both surface runoff and subsurface flow is an important step in simulating sediment concentrations.

Investigating the impact of climate change on New York City’s primary water supply

Future climate scenarios projected by three different General Circulation Models and a delta-change methodology are used as input to the Generalized Watershed Loading Functions – Variable Source Area (GWLF-VSA) watershed model to simulate future inflows to reservoirs that are part of the New York City water supply system (NYCWSS). These inflows are in turn used as part of the NYC OASIS model designed to simulate operations for the NYCWSS. In this study future demands and operation rules are assumed stationary and future climate variability is based on historical data to which change factors were applied in order to develop the future scenarios. Our results for the West of Hudson portion of the NYCWSS suggest that future climate change will impact regional hydrology on a seasonal basis. The combined effect of projected increases in winter air temperatures, increased winter rain, and earlier snowmelt results in more runoff occurring during winter and slightly less runoff in early spring, increased spring and summer evapotranspiration, and reduction in number of days the system is under drought conditions. At subsystem level reservoir storages, water releases and spills appear to be higher and less variable during the winter months and are slightly reduced during summer. Under the projected future climate and assumptions in this study the NYC reservoir system continues to show high resilience, high annual reliability and relatively low vulnerability.

A Strategy for Reservoir Model Forecasting Based on Historic Meteorological Conditions

ABSTRACT A strategy for the application of linked watershed and reservoir models in the analysis of water quality management proposals for a water supply reservoir is presented. This strategy is based on the use of a long-term historical record of meteorological data, so that die predicted changes in water quality may be evaluated by considering the variations in streamflow, material loading, reservoir heat transfer and mixing associated with natural variations in meteorological conditions. Model simulations for a baseline condition and for several management proposals involving point source nutrient control, nonpoint source nutrient reduction, and reservoir operations are presented. The predictions are presented as distributions of the frequency of occurrence of selected annual statistics of nutrient loading, reservoir stratification, and reservoir water quality. Simulations for Cannonsville Reservoir indicate that reductions in phosphorus loading from wastewater treatment plants in the watershed would h...

Modelling the Impacts of Climate Change on Dissolved Organic Carbon

Dissolved organic carbon (DOC) from peat soils has implications both for the ecology of receiving waters and for the quality and treatment costs of water used for human consumption. Fluxes of DOC from peat soils are also relevant in the context of the global carbon cycle. Chapter 12 in this volume has reviewed the evidence for the effects of different environmental factors on the decomposition of peat soils and the export of DOC, drawing on literature and long-term data acquired from a number of European sites. The conclusion from this and many other studies is that, although there may be other influences such as land management and recovery from acid deposition, climate factors are a major player in both the short-term variability and longer-term trends seen in measured DOC concentrations and fluxes. Given the importance of DOC and likely future changes in climate, it is timely and opportune to make use of our current understanding to project possible future DOC.

Modeling the Effects of Climate Change on the Supply of Phosphate-Phosphorus

The transfer of phosphorus from terrestrial to aquatic ecosystems is a key route through which climate can influence aquatic ecosystems. A number of climatic factors interact in complex ways to regulate the transfer of phosphorus and modulate its ecological effects on downstream lakes and reservoirs. Processes influencing both the amount and timing of phosphorus export from terrestrial watersheds must be quantified before we can assess the direct and indirect effects of the weather on the supply and recycling of phosphorus. Simulation of the export of phosphorus from the terrestrial environment is complicated by the fact that it is difficult to describe seasonal and inter-annual variations by existing process-based and empirical models. These variations are also strongly influenced by the history of the weather and by the frequency of extreme weather events. For example, the effects of storm runoff on the export of phosphorus can be very sensitive to levels of soil saturation and soil moisture, which are in turn influenced by the past history of precipitation and evapotranspiration. Inclusion of effects such as these is impossible using simple empirical models and difficult using process based models when model parameterization changes in response to antecedent conditions.

Modelling the Effects of Climate Change on the Supply of Inorganic Nitrogen

Human-induced changes in the nitrogen cycle due to the increased use of artificial fertilisers, the cultivation of nitrogen-fixing crops and atmospheric deposition have made nitrogen pollution to surface waters a long-standing cause for concern. In Europe, legislation has been introduced to minimise the risk of water quality degradation from excessive nitrogen inputs e.g., the European Union Nitrates Directive (EU, 1991), Drinking Water Directive (EU, 1998) and Water Framework Directive (EU, 2000). Coastal regions in particular have been an important focus, since coastal eutrophication has been attributed to increased fluxes of nitrogen from the landscape (Howarth et al., 1996; Boesch et al., 2006). While nitrogen is typically not the limiting nutrient in inland waters, increases in the nitrogen supply to rivers and lakes can impact the N:P ratio, influence the structure of aquatic food webs (Elser and Urabe, 1999; Arbuckle and Downing, 2001), regulate the seasonal development of phytoplankton (Van den Brink et al., 1993) and promote the growth of aquatic macrophytes (Kirchmann et al., 2004).