Preliminary research shows that vineyards and alfalfa show no significant yield penalties after controlled flooding from the end of winter to early spring when the fields overlay highly permeable soils . Thus, land parcels planted with vineyards, pasture , idle lands , grain and hay crops , and field crops, which likely are fallowed in the wet season, were deemed suitable for Ag-MAR.Geospatial data of existing surface water conveyance infrastructure were provided by nine water management agencies . For the remaining surface water districts, conveyance infrastructure was digitized from publicly available maps and aerial images. In areas where surface water conveyance infrastructure was visible in air photographs, features were digitized at a scale of 1:10,000. GIS data of larger conveyance infrastructure were obtained from the California Open Data Portal . Groundwater well capture zones are defined as the areal extent and volumetric portion of a groundwater system that contribute discharge to a particular well . Captures zones were derived for all domestic wells in rural communities using the California Department of Water Resources’ Online System for Well Completion Reports and the California Central Valley Groundwater-Surface Water Simulation Model .C2VSim was used to extract a generalized groundwater flow field for the study area. C2VSim is an integrated surface water-groundwater model based on the finite element code of the Integrated Water Flow Model capable of accounting for reservoir deliveries, stream flow, stream diversions, canal distribution systems, irrigation, runoff, crop water uses, vadose zone processes, and groundwater-surface water-irrigated landscape interactions typical of irrigated agricultural basins . The model domain covers the entire CV alluvial aquifer. More information on the model development, calibration and validation, and application for Ag-MAR can be found in Brush et al. , Brush and Dogrul , and Kourakos et al. .

The fine grid model version was used to extract a quasisteady-state representation of the regional groundwater flow field ,hydroponic nft channel taken as the mean of the monthly flow fields from October 2005 to September 2015, to best inform recharge efforts.In the State of California, construction of a new well must be reported to OSWCR. Well locations in OSWCR are reported at a 2.6 km2 resolution by stating the centroid coordinates of the 2.6 km2 Public Land Survey System section a well is located within . For this study, well logs of 27,482 domestic wells located within the study area were downloaded from OSWCR. Wells located within a 1.61 km radius of any of the 288 rural communities were extracted, reducing the number of domestic wells to 7,673 . Well logs were screened for completeness of the following well construction information: well depth, depth to the top of the well screen, and depth to the bottom of the well screen . For wells with incomplete records, well status modeling was used to impute missing information, specifically the depth to the top of the well screen and the submergence depth of the well pump .Investigation and mapping of factors that increase vulnerability to or probability of natural and socio-economic hazards can provide a useful way to prioritize where efforts should be focused . To determine community vulnerability to change in groundwater supply, data describing domestic well failures, domestic well reliance, pesticide applications, land subsidence, and socio-economic factors were used.A thematic layer describing “domestic well failures” was generated using domestic well construction logs, groundwater table information, and self-reported drinking water supply shortages . The California Household Water Supply Shortage Reporting System contains information on self-reported household drinking water supply shortages due to well failure, well under performance, or loss of surface water supply. During the 2012–2016 drought, 867 wells were reported dry within our 288 rural communities. However, this is assumed to be an underestimation of the actual water supply shortages experienced during the 2012–2016 drought, since reporting is optional and many rural communities likely lack access to these tools.

Submergence of the well screen and pump intake are desired to ensure proper well function . The initial installation of the pump intake is usually above zt to minimize costs of screen installation and to maximize the capacity for useable water production . It was assumed that the cost of rehabilitating wells to alleviate well production losses caused by falling groundwater levels would be prohibitive for rural communities. Thus, the analysis assumed that pump intakes would remain at some depth above zt and wells would become inactive if the groundwater level dropped below the pump intake . Since the OSWCR contains no information on the pump intake depth, a submergence value, hs, was calibrated using the reported well failures as a validation data set. Submergence in this study is defined as the depth of the top of the well screen below the groundwater table. Depth to the groundwater table and estimated zt values were used to quantify changes in well status between Spring of 2011 and Fall of 2015 . Groundwater depths at each well location were extracted from interpolated seasonal groundwater levels spanning the entire shallow to semi-confined CV aquifer system . To calibrate the required submergence value, hs, zt values were compared to predrought and post drought groundwater levels to identify wells that became inactive as a result of groundwater level declines. Using the reported well failures in rural communities as validation data, the required pump submergence value was calibrated to be hs = 10 m for which the model estimated 923 well failures during the drought period, most of which were concentrated in the northeastern region .Many rural communities in the southern CV are not connected to municipal water supply systems and generally rely on a single water source, typically a groundwater well, which puts them at risk of water supply failures . Water supply connection density is a metric that describes the pressure exerted on community drinking water supply sources, given as the ratio of active public water supply sources to water supply connections in each community .

Lower values indicate a higher per capita reliance on active public water supply sources, indicating the community has lower water supply security. Communities that rely on a single public water supply source are especially vulnerable to shortages and contamination, as the failure of a single source compromises the community’s entire water supply. In the study area, 91 rural communities only have a single public water supply source of which more than 75% rely on groundwater. Communities solely reliant on unregulated domestic wells do not have any access to public water supply sources and as such, are the most vulnerable to shortages and contamination. The communities reliant on single or unregulated sources are concentrated in the northeastern and eastern regions of the southern CV.Prolonged and unsustainable groundwater pumping causes severe settling or sinking of the land surface due to subsurface compaction of earth materials, known as land subsidence . Land subsidence rates estimated with In SAR technology between May 2015 and September 2016 was used in this analysis. The data reveal two major subsidence bowls in the northwestern and eastern regions of the southern CV and the development of a new hot spot between them . Land subsidence is of particular concern because it directly affects major surface water conveyance systems and threatens the integrity of shallow, domestic wells.Socio-economic parameters of poverty status, linguistic isolation,nft growing system and educational attainment were selected as unique and complementary factors contributing to community vulnerability to change in groundwater supply . Socio-economic data were obtained by block group from the U.S. Census Bureau’s American Community Survey’s 5-year estimates for 2011–2015 and processed using the R library tidycensus .

For each of the three parameters described below, demographic percentages were calculated for all block groups in the region. If multiple block groups intersected a community, an area-weighted average was calculated and the value was applied to each respective community. Poverty status is defined as the percentage of the population for whom the ratio of income to national poverty level in the previous 12 months was below one . Poverty status is believed to contribute to community vulnerability as poorer households have less financial capacity to preemptively address or remediate water supply shortages . Linguistic isolation is defined as the percentage of households that are limited English-speaking households . Households that have limited English-speaking capacity are to a lesser extent able to engage with administrative authorities to voice concerns or resolve problems, and thus have increased community vulnerability . Educational attainment is defined as the percentage of population over 25 years of age, who have completed some education above the high school level . Educational attainment can influence risk perception, skills and knowledge, and access to information and resources, hence less educated populations may be less empowered to prepare and recover from resource shortages .A GIS-based MCDA was used to combine the biophysical, hydrological, and social-ecological data listed in Table 1 to delineate and prioritize locations for multi-benefit Ag-MAR. An equal weighting scheme for thematic layers and proposed rankings of categorical features was adopted in this study following recommendations of Visser and based on the variability present in existing recharge mapping studies . The well status model was used to impute missing well data and provide a more spatially complete estimate of the domestic well failures that occurred during the 2012–2016 drought. Of the 27,482 domestic wells in the study area, 2,907 wells were excluded from the model development because the top of the well screen was shallower than the predrought groundwater levels in spring of 2011. The remaining 24,575 wells were used to estimate the depth to the top of the well screen, zt, using Equation 1. Of the 7,673 domestic wells located within the rural communities, 291 wells were missing zb and the total completed well depth information, thus zt could not be estimated. However, zt was estimated for 279 of the 282 wells only missing zt data. For these 7,673 wells, well capture zones were estimated using groundwater modeling and particle tracking. Most of the capture zones delineated for the domestic wells within rural communities are concentrated in the northeastern and eastern regions of the study area, where the majority of the communities and domestic wells are located . Figures 5b and 5c focus in on the Orosi and Cutler communities east of Dinuba, CA, and the Okieville community, west of Tulare, CA. Both maps show a diverse pattern for the particle exit points of each well highlighting major differences in the groundwater flow velocity, well depths, and lengths of the well screen across the domestic wells in the study area. Well capture zones extend generally between 1 and 6 km upgradient of wells . Some neighboring wells show clear differences in groundwater flow direction and upgradient capture area, which are likely due to differences in well depth and well screen length .Community vulnerability index values were classified into five classes representing “Extreme Vulnerability,” “Very High Vulnerability,” “High Vulnerability,” “Moderate Vulnerability,” and “Low Vulnerability” . Communities classified as extremely vulnerable are concentrated in the eastern part of the study area while highly and very highly vulnerable communities are mainly seen in the northern and northeastern part of the southern CV . There are clear differences in the mean theme scores between the most and least vulnerable communities . For example, in the 30 communities classified as extremely vulnerable, on average, 44.6% of the population live below the poverty line, 30.7% of the households are limited English-speaking, and only 8.1% of the population above 25 years have completed some education above a high school degree. Extremely vulnerable communities are also characterized by higher well failure rates, greater land subsidence, and higher pesticide applications on fields surrounding these communities . In these communities, on average, over 99 households rely on a single water supply source .These communities had, on average, much lower well failure rates during the 2012–2016 drought, less land subsidence, and no reported applications of the seven active ingredients contained in pesticides known to pollute groundwater. These communities also have a much lower percentage of the population living below the poverty line , a lower percentage of households that are limited English-speaking , and a higher percentage of the population above 25 years that have completed some education above a high school degree .