Evaluation of Surface-Water/Ground-Water Interactions in the Santa Clara River Valley, Ventura County, California

U.S. Geological Survey (USGS) | May 28th, 1999

The interactions of surface water and ground water along the Santa Clara River in Ventura County, California, were evaluated by analyzing river-discharge and water-qua

The interactions of surface water and ground water along the Santa Clara River in Ventura County, California, were evaluated by analyzing river-discharge and water-quality data and geohydrologic information collected by the U.S. Geological Survey between 1993 and 1995 for the Piru, Fillmore, and Santa Paula subbasins. Measurements of discharge and water quality were made at multiple locations along the Santa Clara River and its tributaries at eight different time periods during different releases from Lake Piru. Geologic, hydraulic, and water-quality data were collected from three new multiple-completion ground-water monitoring wells. These data, together with data collected as part of the U.S. Geological Survey Southern California Regional Aquifer-System Analysis (RASA) study, were analyzed in order to quantify rates and locations of ground-water recharge and discharge within the river, characterize the correlation of recharge and discharge rates with ground-water conditions and reservoir releases, and better characterize the three-dimensional ground-water flow system. Analysis of the data indicates that the largest amount of ground-water recharge from the river consistently occurs in the Piru subbasin. Some ground-water recharge from the river may occur in the upper part of the Fillmore subbasin. Increases in sulfate concentrations indicate that increases in flow at the lower ends of the Piru and Fillmore subbasins result from high-sulfate ground-water discharge. Increases in flow in the lower part of the Santa Paula subbasin are not accompanied by significant sulfate increases. Several sets of regressions indicate possible correlation between net flow changes in the river and depths to ground water and release rates from Lake Piru. These statistical relations may be of use for evaluating alternative Lake Piru release strategies. Data on the stable isotopes of hydrogen and oxygen from the ground-water monitoring wells that were installed as part of this investigation were used to distinguish between zones affected by recharge from the Santa Clara River and zones affected by recharge from local precipitation. Tritium data from a new multiple-completion monitoring site indicate that near the river in the upper Santa Paula subbasin, recent (post-1950) recharge water is not present at depths greater than about 350 feet below land surface. Water-level and lithologic data from the monitoring site indicate that the river and the Shallow aquifer have only limited hydraulic connection to the underlying aquifers at this location. Water-level data from the Shallow aquifer and from an in-stream drive point were used in an analytic model to estimate hydraulic properties governing stream-aquifer interactions in the upper Santa Paula subbasin. Hydraulic conductivities in all the USGS monitoring wells were estimated on the basis of slug tests.  

Evaluation of the Hydrologic System and Selected Water-Management Alternatives in the Owens Valley, California

U.S. Geological Survey (USGS) | May 9th, 2000

The Owens Valley, a long, narrow valley along the east side of the Sierra Nevada in east-central California, is the main source of water for the city of Los Angeles. The

The Owens Valley, a long, narrow valley along the east side of the Sierra Nevada in east-central California, is the main source of water for the city of Los Angeles. The city diverts most of the surface water in the valley into the Owens River–Los Angeles Aqueduct system, which transports the water more than 200 miles south to areas of distribution and use. Additionally, ground water is pumped or flows from wells to supplement the surface-water diversions to the river–aqueduct system. Pumpage from wells needed to supplement water export has increased since 1970, when a second aqueduct was put into service, and local residents have expressed concerns that the increased pumping may have a detrimental effect on the environment and the native vegetation (indigenous alkaline scrub and meadow plant communities) in the valley. Native vegetation on the valley floor depends on soil moisture derived from precipitation and from the unconfined part of a multilayered ground-water system. This report, which describes the evaluation of the hydrologic system and selected water-management alternatives, is one in a series designed to identify the effects that ground-water pumping has on native vegetation and evaluate alternative strategies to mitigate any adverse effects caused by pumping. The hydrologic system of the Owens Valley can be conceptualized as having three parts: (1) an unsaturated zone affected by precipitation andevapotranspiration; (2) a surface-water system composed of the Owens River, the Los Angeles Aqueduct, tributary streams, canals, ditches, and ponds; and (3) a saturated ground-water system contained in the valley fill. Analysis of the hydrologic system was aided by development of a ground-water flow model of the “aquifer system,” which is defined as the most active part of the ground-water system and which includes nearly all of the Owens Valley except for the area surrounding the Owens Lake. The model was calibrated and verified for water years 1963–88 and used to evaluate general concepts of the hydrologic system and the effects of past water-management practices. The model also was used to evaluate the likely effects of selected water-management alternatives designed to lessen the adverse effects of ground-water pumping on native vegetation. Results of the model simulations confirm that a major change in the hydrologic system was caused by the additional export of water from the valley beginning in 1970. Average ground-water pumpage increased by a factor of five, discharge from springs decreased almost to zero, reaches of the Owens River that previously had gained water from the aquifer system began losing water, and total evapotranspiration by native plants decreased by about 35 percent. Water-management practices as of 1988 were defined and evaluated using the model. Simulation results indicate that increased ground-water pumpage since 1985 for enhancement and mitigation projects within the Owens Valley has further stressed the aquifer system and resulted in declines of the water table and reduced evapotranspiration. Most of the water-table declines are beneath the western alluvial fans and in the immediate vicinity of production wells. The water-table altitude beneath the valley floor has remained relatively constant over time because of hydrologic buffers, such as evapotranspiration, springs, and permanent surface-water features. These buffers adjust the quantity of water exchanged with the aquifer system and effectively minimize variations in water-table altitude. The widespread presence of hydrologic buffers is the primary reason the water-table altitude beneath the valley floor has remained relatively constant since 1970 despite major changes in the type and location of ground-water discharge. Evaluation of selected water-management alternatives indicates that long-term variations in average runoff to the Owens Valley of as much as 10 percent will not have a significant effect on the water-table altitude. However, reductions in pumpage to an average annual value of about 75,000 acre-ft/yr are needed to maintain the water table at the same altitude as observed during water year 1984. A 9-year transient simulation of dry, average, and wet conditions indicates that the aquifer system takes several years to recover from increased pumping during a drought, even when followed by average and above-average runoff and recharge. Increasing recharge from selected tributary streams by additional diversion of high flows onto the alluvial fans, increasing artificial recharge near well fields, and allocating more pumpage to the Bishop area may be useful in mitigating the adverse effects on native vegetation caused by drought and short-term increases in pumpage. Analysis of the optimal use of the existing well fields to minimize drawdown of the water table indicates no significant lessening of adverse effects on native vegetation at any of the well fields at the end of a 1-year simulation. Some improvement might result from pumping from a few high-capacity wells in a small area, such as the Thibaut–Sawmill well field; pumping from the upper elevations of alluvial fans, such as the Bishop well field; or pumping in an area surrounded by irrigated lands, such as the Big Pine well field. Use of these water-management techniques would provide some flexibility in management from one year to another, but would not solve the basic problem that increased ground-water pumpage causes decreases in evapotranspiration and in the biomass of native vegetation. Furthermore, the highly transmissive and narrow aquifer system will transmit the effects of pumping to other more sensitive areas of the valley within a couple of years. Other possible changes in water management that might be useful in minimizing the short-term effects of pumping on native vegetation include sealing well perforations in the unconfined part of the aquifer system; rotating pumpage among well fields; continuing or renewing use of unlined surface-water features such as canals and ditches; developing recharge and extraction facilities in deeper volcanic deposits near Big Pine or in alluvial fan deposits along the east side of the valley; installing additional wells along the west side of the Owens Lake; and conjunctively using other ground-water basins between the Owens Valley and Los Angeles to store exported water for subsequent extraction and use during droughts.

Evapotranspiration frequently increases during droughts

Nature Portfolio (Springer Nature) | October 27th, 2022

Changes in evapotranspiration (ET) affect water availability and ecosystem health. Higher evaporative demand during drought acts to increase ET, but droughts also reduce

Changes in evapotranspiration (ET) affect water availability and ecosystem health. Higher evaporative demand during drought acts to increase ET, but droughts also reduce the moisture supply necessary for ET, limiting predictions of even the sign of ET anomalies. Drought-driven increases in ET (ET+drought) are of particular concern because they quickly deplete water resources, causing flash droughts and acute stress on ecosystems. Here, using a water balance approach, we show that ET+drought is globally widespread, occurring in 44.4% of drought months. The sign of ET’s drought response depends most on the magnitude of precipitation and total water storage anomalies, rather than its location. The Coupled Model Intercomparison Project Phase 6 Earth system models underestimate the ET+drought probability by nearly one-half, and more so in drier regions, primarily due to missing representations of soil structure effects on soil evaporation, as well as incorrectly parameterized plant and soil traits. These processes should be prioritized to reduce model uncertainties in the water–energy–food nexus.

Evapotranspiration of urban landscapes in Los Angeles, California at the municipal scale

American Geophysical Union (AGU) | May 24th, 2017

Evapotranspiration (ET), an essential process in biosphere-atmosphere interactions, is highly uncertain in cities that maintain cultivated and irrigated landscapes. We e

Evapotranspiration (ET), an essential process in biosphere-atmosphere interactions, is highly uncertain in cities that maintain cultivated and irrigated landscapes. We estimated ET of irrigated landscapes in Los Angeles by combining empirical models of turfgrass ET and tree transpiration derived from in situ measurements with previously developed remotely sensed estimates of vegetation cover and ground-based vegetation surveys. We modeled irrigated landscapes as a two-component system comprised of trees and turfgrass to assess annual and spatial patterns of ET. Annual ET from vegetated landscapes (ETveg) was 11106 53 mm/yr and ET from the whole city (vegetated and nonvegetated areas, ETland) was three times smaller, reflecting the fractional vegetation cover. With the exception of May and June, monthly ETland was significantly higher than predicted by the North American Land Data Assimilation System. ETveg  was close to potential ET, indicating abundant irrigation inputs. Monthly averaged ETveg varied from 1.560.1 mm/d (December) to 4.360.2 mm/d (June). Turfgrass was responsible for 70% of ETveg. For trees, angiosperm species (71% of all trees) contributed over 90% to total tree transpiration, while coniferous and palm species made very small contributions. ETland was linearly correlated with median household income across the city, confirming the importance of social factors in determining spatial distribution of urban vegetation. These estimates have important implications for constraining the municipal water budget of Los Angeles and improving regional-scale hydrologic models, as well as for developing water-saving practices. The methodology used in this study is also transferable to other semiarid regions for quantification of urban landscape ET.

Evolution of global snow drought characteristics from 1850 to 2100

Environmental Research Letters (IOP) | June 6th, 2023

Examining the Contribution of the Observed Global Warming Trend to the California Droughts of 2012/13 and 2013/14

American Meteorological Society (AMS) | September 30th, 2014

In this study, we examine the November–February California droughts of 2012/13 and 2013/14. During 2013/14, California had its warmest and third driest rainy se

In this study, we examine the November–February California droughts of 2012/13 and 2013/14. During 2013/14, California had its warmest and third driest rainy season on record (1895–2014), while the 2012/13 season registered as the 45th warmest and 38th driest (Vose et al. 2014). The 2013 January–December calendar year was the driest on record (Water CA 2014). These consecutive below-normal seasons conspired with warm temperatures to reduce California’s snowpack to the second lowest level since 1960, when recording began, with snowpack at 24% of normal (Water CA 2014). Between January 2013 and January 2014, satellite observations documented dramatic snowpack-related land cover change (NASA Earth Observatory 2014): in 2014, the Cascade, Sierra Nevada, and Coastal ranges were almost completely devoid of snow. In February and March of 2014, air temperatures were extremely warm (NOAA NCDC 2014; HPRC 2014), and U.S. Geological Survey (USGS) observations indicated extreme or moderate hydrologic drought (USGS 2014) and high levels of vegetation stress (VegDRI 2014). The state declared a drought emergency (NIDIS 2014). While it is too soon to assess the full impact of the 2012/13 and 2013/14 California droughts, they seem likely to substantially impact the state’s ability to generate hydrologic power, support agriculture, reduce the risk of forest and bush fires, and protect fragile ecosystems (Huffington Post 2014). *Chapter 4, Explaining Extreme Events of 2013 from a Climate Perspective, Bull. Amer. Meteor. Soc., 95 (9)

Exploring the Spatially Compounding Multi‐Sectoral Drought Vulnerabilities in Colorado's West Slope River Basins

American Geophysical Union (AGU) | November 9th, 2024

Exploring Water System Vulnerabilities in California's Central Valley Under the Late Renaissance Megadrought and Climate Change

American Geophysical Union (AGU) | April 24th, 2025

Extreme hydrological changes in the southwestern US drive reductions in water supply to Southern California by mid century

Environmental Research Letters (IOP) | September 21st, 2016

The Southwestern United States has a greater vulnerability to climate change impacts on water security due to a reliance on snowmelt driven imported water. The State of C

The Southwestern United States has a greater vulnerability to climate change impacts on water security due to a reliance on snowmelt driven imported water. The State of California, which is the most populous and agriculturally productive in the United States, depends on an extensive arti cial water storage and conveyance system primarily for irrigated agriculture, municipal and industrial supply and hydropower generation. Here we take an integrative high-resolution ensemble modeling approach to examine near term climate change impacts on all imported and local sources of water supply to Southern California. While annual precipitation is projected to remain the same or slightly increase, rising temperatures result in a shift towards more rainfall, reduced cold season snowpack and earlier snowmelt. Associated with these hydrological changes are substantial increases in the frequency and the intensity of both drier conditions and ooding events. The 50 year extreme daily maximum precipitation and runoff events are 1.5–6 times more likely to occur depending on the water supply basin. Simultaneously, a clear de cit in total annual runoff over mountainous snow generating regions like the Sierra Nevada is projected. On one hand, the greater probability of drought decreases imported water supply availability. On the other hand, earlier snowmelt and signicantly stronger winter precipitation events pose increased flood risk requiring water releases from control reservoirs, which may potentially decrease water availability outside of the wet season. Lack of timely local water resource expansion coupled with projected climate changes and population increases may leave the area in extended periods of shortages.

Extreme Precipitation-Temperature Scaling in California: The Role of Atmospheric Rivers

American Geophysical Union (AGU) | July 25th, 2023