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Disappearing Arctic sea ice reduces available water in the American west

American Geophysical Union (AGU) | March 24th, 2004

Summary

Recent decreases in Arctic sea ice cover and the probability of continued decreases have raised the question of how reduced Arctic sea ice cover will influence extrapo

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Divergent effects of climate change on future groundwater availability in key mid-latitude aquifers

Nature Portfolio (Springer Nature) | July 24th, 2020

Summary

Groundwater provides critical freshwater supply, particularly in dry regions where surface water availability is limited. Climate change impacts on GWS (groundwater stora

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Documentation of a Groundwater Flow Model (SJRRPGW) for the San Joaquin River Restoration Program Study Area, California

U.S. Geological Survey (USGS) | September 23rd, 2014

Summary

To better understand the potential effects of restoration flows on existing drainage problems, anticipated as a result of the San Joaquin River Restoration Program (SJRRP

To better understand the potential effects of restoration flows on existing drainage problems, anticipated as a result of the San Joaquin River Restoration Program (SJRRP), the U.S. Geological Survey (USGS), in cooperation with the U.S. Bureau of Reclamation (Reclamation), developed a groundwater flow model (SJRRPGW) of the SJRRP study area that is within 5 miles of the San Joaquin River and adjacent bypass system from Friant Dam to the Merced River. The primary goal of the SJRRP is to reestablish the natural ecology of the river to a degree that restores salmon and other fish populations. Increased flows in the river, particularly during the spring salmon run, are a key component of the restoration effort. A potential consequence of these increased river flows is the exacerbation of existing irrigation drainage problems along a section of the river between Mendota and the confluence with the Merced River. Historically, this reach typically was underlain by a water table within 10 feet of the land surface, thus requiring careful irrigation management and (or) artificial drainage to maintain crop health. The SJRRPGW is designed to meet the short-term needs of the SJRRP; future versions of the model may incorporate potential enhancements, several of which are identified in this report. The SJRRPGW was constructed using the USGS groundwater flow model MODFLOW and was built on the framework of the USGS Central Valley Hydrologic Model (CVHM) within which the SJRRPGW model domain is embedded. The Farm Process (FMP2) was used to simulate the supply and demand components of irrigated agriculture. The Streamflow-Routing Package (SFR2) was used to simulate the streams and bypasses and their interaction with the aquifer system. The 1,300-square mile study area was subdivided into 0.25-mile by 0.25-mile cells. The sediment texture of the aquifer system, which was used to distribute hydraulic properties by model cell, was refined from that used in the CVHM to better represent the natural heterogeneity of aquifer-system materials within the model domain. In addition, the stream properties were updated from the CVHM to better simulate stream-aquifer interactions, and water-budget subregions were refined to better simulate agricultural water supply and demand. External boundary conditions were derived from the CVHM. The SJRRPGW was calibrated for April 1961 to September 2003 by using groundwater-level observations from 133 wells and streamflow observations from 19 streamgages. The model was calibrated using public-domain parameter estimation software (PEST) in a semi-automated manner. The simulated groundwater-level elevations and trends (including seasonal fluctuations) and surface-water flow magnitudes and trends reasonably matched observed data. The calibrated model is planned to be used to assess the potential effects of restoration flows on agricultural lands and the relative capabilities of proposed SJRRP actions to reduce these effects.

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Documentation of Model Input and Output Values for the Geohydrology and Mathematical Simulation of the Pajaro Valley Aquifer System, Santa Cruz and Monterey Counties, California

U.S. Geological Survey (USGS) | July 14th, 1990

Summary

As part of a study of the geology and hydrology of the Pajaro Valley aquifer system, Santa Cruz and Monterey Counties, California, a three-layer mathematical mode

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Domestic well vulnerability to drought duration and unsustainable groundwater management in California's Central Valley

Environmental Research Letters (IOP) | March 18th, 2020

Summary

Millions of Californians access drinking water via domestic wells, which are vulnerable to drought and unsustainable groundwater management. Groundwater overdraft and th

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Downscaling global ocean climate models improves estimates of exposure regimes in coastal environments

Nature Portfolio (Springer Nature) | August 26th, 2020

Summary

Climate change is expected to warm, deoxygenate, and acidify ocean waters. Global climate models (GCMs) predict future conditions at large spatial scales, and these pred

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Dramatic declines in snowpack in the western US

Nature Portfolio (Springer Nature) | March 2nd, 2018

Summary

Mountain snowpack stores a significant quantity of water in the western US, accumulating during the wet season and melting during the dry summers and supplying

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DRERIP Ecosystem Conceptual Model: Chemical stressors

California Department of Fish and Wildlife (CDFW) | February 5th, 2008

Summary

The Sacramento-San Joaquin Delta ecosystem comprises many different habitat types, and is home to a large number of species. Thousands of chemical contaminants have been

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DRERIP Ecosystem Conceptual Model: Chinook Salmon & Steelhead

California Department of Fish and Wildlife (CDFW) | September 4th, 2012

Summary

This report constitutes the conceptual model for Chinook and steelhead for the Delta Regional Ecosystem Restoration Implementation Plan (DRERIP). The report describes

This report constitutes the conceptual model for Chinook and steelhead for the Delta Regional Ecosystem Restoration Implementation Plan (DRERIP). The report describes conceptual models, not numerical models, but several important considerations apply to both kinds, especially when they are used for management of living natural resources. First, the proper purpose of models is to help people think, not to think for them. Ignoring this can be disastrous, as exemplified by the current economic crisis. The world of credit default swaps was built on highly sophisticated models that persuaded many intelligent people that the associated risk was negligible, but they failed to recognize that a market based on houses that people could not pay for from their earnings is unsustainable. In short, the most important output of a good conceptual or numerical model is clear thinking. To help people think, the model must be focused on selected features of the world that are thought to be important for the purpose at hand: in this case, management of the Delta. A model that tries to include everything will be too complex to be useful for this purpose. Second, to be useful for management of natural living resources, numerical models must be unrealistic, because our knowledge of such resources is incomplete, and is based on data that includes measurement errors. According to Ludwig‘s paradox, "Effective management models cannot be realistic" (Ludwig 1994:516), because two kinds of uncertainty must be balanced (Figure I-1; see Ch. 14 in Williams (2006) for elaboration of this point). In our view, something similar applies to conceptual models of natural systems: to be useful, they must be simple. A schematic of the wiring in some electronic device is a conceptual model that may be useful as well as complex, but trying to develop a similar schematic of an ecosystem or part of an ecosystem is not useful, because our knowledge of such a system is much less complete than our knowledge of engineered devices, and we have only estimates of the relevant parameters. Finally, reality is too complex to capture with a single model. Eric Lander, a noted geneticist who co-chairs President Obama‘s Council of Advisors on Science and Technology, recently remarked that "You can never capture something like an economy, a genome or an ecosystem with one model or one taxonomy – it all depends on the questions you want to ask." (NY Times, 11/11/08). Models are tools that we use to try to think, and multi-purpose tools generally do nothing well. Therefore, although the complete life cycle of Chinook and steelhead is described here, the parts or aspects of the cycle that we think may be affected by management of the Delta are emphasized, and we try to keep it as simple as possible. More detail on most of the topics described here can be found in Quinn (2005), or in Williams (2006), from which this document draws very heavily.

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DRERIP Ecosystem Conceptual Model: Delta Aquatic Foodweb

California Department of Fish and Wildlife (CDFW) | October 3rd, 2008

Summary

This model is a stylization of the actual food web dynamics of the Sacramento-San Joaquin Delta, which are highly dynamic. The region itself comprises a variety of habita

This model is a stylization of the actual food web dynamics of the Sacramento-San Joaquin Delta, which are highly dynamic. The region itself comprises a variety of habitats, determined by salinity regimes, residence time, hydrology, benthos and physical structure. These physical parameters, or drivers, determine species composition and trophic relationships. The Delta is a tidal system which is subject to varying water inflow. Because inflow and outflow vary as the result of anthropogenic alterations and water management needs, habitats are not static. Rather they are subject to hourly, daily, seasonal and inter-annual variation, and different organisms respond in different ways to these time scales, depending upon their own life histories. Thus salinity and temperature regimes may create different outcomes from food web interactions, based upon how species distributional and recruitment patterns overlap. In general, food web linkages are not static or linear. Organisms switch feeding strategies opportunistically, and these patterns of variability in feeding strategy tend to increase with trophic level. Many organisms, particularly plankton, undergo many generations in the course of a year, and selective forces may allow for rapid evolution which can alter habitat preferences or other life history characteristics. The Delta food web is further dynamic in that new species are regularly introduced into the Estuary, competing with, replacing, or preying upon other organisms. For example, the overbite clam, Corbula amurensis, was introduced in 1986, precipitating a cascade of changes that are still not wholly understood. Zebra and quagga mussels are expected to invade the Delta within the next few years, and will bring further changes. The topology of a food web model will be necessarily complex given these factors. Even without such variability, the potential linkages create a spider web of relationships that is difficult if not impossible to disentangle. In order to create a working model of the Delta food web that is useful for education, for hypothesis?generation, and for management decision?making, it is necessary to create limits to what linkages will be examined. In order to do this, this Delta food web model focuses on organisms that supply food for fish. This is particularly important given the recent concern for pelagic organism decline, which is described mostly for fishes, some of which are listed as endangered or threatened. A key assumption is that fish are integrators of ecosystem function. Also included in the model are invasive organisms that have a large impact on food web dynamics (such as C. amurensis), as are organisms that are particularly abundant (such as the copepod Limnoithona tetraspina), whether or not they are used directly by fish.

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Page : 15

Disappearing Arctic sea ice reduces available water in the American west

Divergent effects of climate change on future groundwater availability in key mid-latitude aquifers

Documentation of a Groundwater Flow Model (SJRRPGW) for the San Joaquin River Restoration Program Study Area, California

Documentation of Model Input and Output Values for the Geohydrology and Mathematical Simulation of the Pajaro Valley Aquifer System, Santa Cruz and Monterey Counties, California

Domestic well vulnerability to drought duration and unsustainable groundwater management in California's Central Valley

Downscaling global ocean climate models improves estimates of exposure regimes in coastal environments

Dramatic declines in snowpack in the western US

DRERIP Ecosystem Conceptual Model: Chemical stressors

DRERIP Ecosystem Conceptual Model: Chinook Salmon & Steelhead

DRERIP Ecosystem Conceptual Model: Delta Aquatic Foodweb

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