David Purkey

WEAP21 - A Demand-, Priority-, and Preference-Driven Water Planning Model Part 1: Model Characteristics

Abstract The Water Evaluation and Planning Version 21 (WEAP21) Integrated Water Resource Management (IWRM) model seamlessly integrates water supplies generated through watershed-scale hydrologic processes with a water management model driven by water demands and environmental requirements and is governed by the natural watershed and physical network of reservoirs, canals, and diversions. This version (WEAP21) extends the previous WEAP model by introducing the concept of demand priorities and supply preferences, which are used in a linear programming heuristic to solve the water allocation problem as an alternative to multi-criteria weighting or rule-based logic approaches. WEAP21 introduces a transparent set of model objects and procedures that can be used to analyze a full range of issues faced by water planners through a scenario-based approach. These issues include climate variability and change, watershed condition, anticipated demands, ecosystem needs, the regulatory environment, operational objectives, and available infrastructure.

WEAP21 -a demand-, priority-, and preference-driven water planning model Part 2 : Aiding freshwater ecosystem service evaluation

Abstract Potential conflicts arising from competing demands of complex water resource systems require a holistic approach to address the tradeoff landscape inherent in freshwater ecosystem service evaluation. The Water Evaluation and Planning model version 21 (WEAP21) is a comprehensive integrated water resource management (IWRM) model that can aid in the evaluation of ecosystem services by integrating natural watershed processes with socio-economic elements that include the infrastructure and institutions that govern the allocation of available freshwater supplies. The bio-physical and socioeconomic components of Battle Creek and Cow Creek, two tributaries of the Sacramento River of Northern California, USA, were used to illustrate how a new hydrologic sub-module in WEAP21 can be used in conjunction with an imbedded water allocation algorithm to simulate the hydrologic response of the watersheds and aid in evaluating freshwater ecosystem service tradeoffs under alternative scenarios.

Fish, Floods, and Ecosystem Engineers: Aquatic Conservation in the Okavango Delta, Botswana

The Okavango Delta, Botswana, is a major wetland surrounded by the Kalahari Desert. The delta supports a diverse fish fauna that depends on highly seasonal flooding from inflowing rivers, and on the actions of ecosystem engineers (hippopotamuses, elephants, and termites), for creation and maintenance of their habitats. Conflicts in resource use, especially water, are likely to affect fish populations and the Okavango ecosystem in the near future. We present conceptual models of this remarkable aquatic ecosystem in relation to fish and fisheries as the basis for future research and conservation efforts. Developing understanding of the environmental flow requirements of the delta is key to the management of the Okavango Delta as an ecosystem supporting diverse and abundant fish and wildlife. Once developed, this understanding can be used to allocate water within the Okavango watershed.

Water Management Adaptations to Prevent Loss of Spring-Run Chinook Salmon in California under Climate Change

AbstractSpring-run Chinook salmon (Oncorhynchus tshawytscha) are particularly vulnerable to climate change because adults over-summer in freshwater streams before spawning in autumn. We examined streamflow and water temperature regimes that could lead to long-term reductions in spring-run Chinook salmon (SRCS) in a California stream and evaluated management adaptations to ameliorate these impacts. Bias-corrected and spatially downscaled climate data from six general circulation models and two emission scenarios for the period 2010–2099 were used as input to two linked models: a water evaluation and planning (WEAP) model to simulate weekly mean streamflow and water temperature in Butte Creek, California that were used as input to SALMOD, a spatially explicit and size/stage structured model of salmon population dynamics in freshwater systems. For all climate scenarios and model combinations, WEAP yielded lower summer base flows and higher water temperatures relative to historical conditions, while SALMOD yi...

An integrated assessment of water-energy and climate change in sacramento, california: how strong is the nexus?

This paper is among the first to report on the full integration of basin-scale models that include projections of the demand and supply of water and energy for residential, commercial, industrial, and agricultural sector users. We link two widely used regional planning models that allow one to study the impact of rising climate variability on water and electricity use in Sacramento, California. Historic data combined with the current energy and water system configuration was used to assess the implications of changes in temperature and precipitation. Climate simulations suggest that electricity imports to the region would increase during hot dry spells, when regional power production is most constrained. In particular, regional imports of electricity would increase over 35xa0% in hot dry years, assuming a 4xa0°C increase in average temperature and a 25xa0% decrease in average precipitation.

Potential Impacts of Climate Warming on Water Supply Reliability in the Tuolumne and Merced River Basins, California

We present an integrated hydrology/water operations simulation model of the Tuolumne and Merced River Basins, California, using the Water Evaluation and Planning (WEAP) platform. The model represents hydrology as well as water operations, which together influence water supplied for agricultural, urban, and environmental uses. The model is developed for impacts assessment using scenarios for climate change and other drivers of water system behavior. In this paper, we describe the model structure, its representation of historical streamflow, agricultural and urban water demands, and water operations. We describe projected impacts of climate change on hydrology and water supply to the major irrigation districts in the area, using uniform 2°C, 4°C, and 6°C increases applied to climate inputs from the calibration period. Consistent with other studies, we find that the timing of hydrology shifts earlier in the water year in response to temperature warming (5–21 days). The integrated agricultural model responds with increased water demands 2°C (1.4–2.0%), 4°C (2.8–3.9%), and 6°C (4.2–5.8%). In this sensitivity analysis, the combination of altered hydrology and increased demands results in decreased reliability of surface water supplied for agricultural purposes, with modeled quantity-based reliability metrics decreasing from a range of 0.84–0.90 under historical conditions to 0.75–0.79 under 6°C warming scenario.

Exploring scientific information for policy making under deep uncertainty

Each actor evaluating potential management strategies brings her/his own distinct set of objectives to a complex decision space of system uncertainties. The diversity of these objectives and uncertainties requires detailed and rigorous analyses that respond to multifaceted challenges. The utility of this information depends on the accessibility of scientific information to decision makers. This paper demonstrates data visualization tools for presenting scientific results to decision makers in two case studies, La Paz/El Alto, Bolivia, and Yuba County, California. Visualization output from the case studies combines spatiotemporal, multivariate and multirun/multiscenario information to produce information corresponding to the objectives and uncertainties described by key actors. These tools can manage complex data and distill scientific information into accessible formats. Using the visualizations, scientists and decision makers can navigate the decision space and potential objective trade-offs to facilitate discussion and consensus building. These efforts can help identify stable negotiated agreements between different stakeholders. We present a Decision Space Visualization (DSV) that condenses model results to tackle complex water management challenges.DSV enables comparisons between potential management options against many uncertainties.It allows exploring results in meaningful formats for decision makers that answers their most pressing questions.The case studies presented suggests that DSV stimulates active engagement from stakeholders.