Areas showing “no benefit” or that were not included in statewide calculations were not included in mapping analyses. These areas of no benefit are likely due to a combination of factors, including soil properties such as high clay or sand soils, and organic-rich soils. To help evaluate a more accurate representation of agricultural lands in San Diego unincorporated county, this study combines two agricultural data sources. These sources include the Farmland Mapping and Monitoring Program and agriculture listed in SANDAG’s current land use. FMMP aims to show the relationship between the quality of soils for agricultural production and the land’s use for agricultural, urban, and other purposes . Agricultural land is ranked as “unique”, “prime”, “grazing lands”, and “important” locally and/or statewide based on soil quality as a metric for quality and irrigation status as a metric for status of use . While FMMP helps identify the quality and location of the region’s designated farmland, it is important to consider that FMMP may under represent the total agricultural land that exists in San Diego. Furthermore, the lands that are not represented and/or classified with FMMP are important features of the region, and are thus important to include in analysis. Current land use maps from the county’s data portal utilize “extensive” and “intensive” to illustrate current agricultural land . Extensive and intensive lands are combined with FMMP lands to provide a more accurate and complete context of existing agriculture. Combined,good drainage pots these lands represent the agricultural lands study area used throughout this report. Several conservation programs exist in efforts to preserve San Diego’s agricultural lands.
Easements and formal protection of land listed on the California Conservation Easement Database and California Protected Areas Database are included in analyses to understand the areas of agricultural land study area that are currently protected . Planned land use layers from SANDAG Regional GIS Data Warehouse are created for the Regional Growth Forecast, outlining projected growth for the San Diego region to suitable areas.Non-agricultural land use types are separated as “urban”, including commercial, industrial, and/or urban designation, or non-urban, including water and open space/parks. Land use data planned for urban use by 2050 are overlaid with existing agricultural lands to identify agricultural lands threatened by future urban development . The county-averaged difference from the baseline scenario is -0.25 inches per year for CWD and 0.25 in/yr for AET. This represents that soil management of 3% added SOM can yield a -0.25 change in CWD from the baseline average of 15 and a 0.25 change in AET from the baseline average of 10 in/yr. Additionally, soil moisture has an average change of 1.69 from the baseline average of 9.1 . The entire San Diego region shows a total hydrologic benefit area of 590,582 acres, with 14% of benefit area within the incorporated county and 86% of benefit area within the unincorporated county. These results indicate that many areas in San Diego have the potential to experience increase in forage production , reduced landscape stress and irrigation demand , and increased hydrologic resilience to climate change . Analyses show that CWD and AET have the most significant changes under a +3% SOM management scenario, and thus, the hydrologic benefit index is heavily reflective of these two variables. Of the total agricultural land study area, a total area of 238,457 acres agricultural lands fall within an area of hydrologic benefit.
A total of 223,383 acres of FMMP lands coincide with areas hydrologic benefit from increased SOM , representing 66% of total FMMP lands. Notably, FMMP “Farmland of Statewide” and “of Local Importance” land classes show a total benefit area of 102,549 acres. Planned city land use projections show further increases in urban extents by 2050, with 45% of non-agricultural lands planned for commercial, industrial, or commercial land uses. As these urban areas expand, agricultural lands are increasingly at risk of conversion. Figure 17 illustrates the total area of current agricultural land that could be lost by 2050 based on planned urban development. These losses can be quantified in terms of the potential hydrologic benefit estimated for soil management on these agricultural lands that will be lost if converted to urban use. The lost potential hydrologic benefit associated with soil management on current agricultural lands spans a total area of 144,804 acres, representing a 65% loss of the total potential hydrologic benefit on current agricultural lands. Within the total area of lands at-risk of urban development, 13% are listed as protected under CCED and/or CPAD. San Diego’s agricultural community is especially sensitive to the impacts of a changing hydroclimate, making water resources a main area of focus for climate resiliency in the region. The region’s agricultural lands, and the multifaceted benefits they provide, are utilized across society. Thus, as the county continues to expand its efforts in climate mitigation, partnering with agricultural partners presents a key opportunity to ensure a resilient region . With model agreement over increased precipitation variability, and resulting changes in water availability, quality, and quantity over time, it is critical that a spectrum of strategies be implemented that can especially buffer the region’s changing water resources. As a state faced with distinct water-resource challenges, there is an increased need for planning and management decisions based at the local and regional level.
While coarse spatial resolution model projections of temperature and precipitation trends provide much of the available information for land and resource managers and climate assessments, recent modeling developments, such as the BCM, greatly enhance available data . Data on the response of these hydrologic variables presents highly valuable information on quantification of recharge, runoff, irrigation need, landscape stress, and the spatial distribution of hydrologic processes throughout a watershed . These modeling capabilities can now model the spatial distribution of hydrologic processes throughout a watershed at fine-scales, producing much needed high-resolution data and confident estimates that previous modeling lacked. There is a much needed opportunity to use these highly detailed and spatially explicit model projections for local resource management decisions and policy development .While the BCM’s advanced modeling capabilities improves the state’s understanding of hydrologic processes, soil management, and sequestration potential across the state’s terrestrial landscapes , it can also be used for informing local, regional, and water-shed specific assessments. The grid based regional water balance model can provide valuable insight on the role of precipitation in San Diego’s terrestrial ecosystems . Modeling the dynamic relationship between the pathways of precipitated water with landscape features can allow for more precise projections of both historical and future climate-hydrology assessments . Application of the BCM for San Diego provides a quantification of the benefit of carbon farming practices in both 1981-2011 assessments and future projections. This analysis exhibits that San Diego’s agricultural lands have the potential to improve hydrologic conditions with strategic management. Increases in WHC can allow for more water to stay in the watershed, maintaining base flow in low-flow periods, groundwater infiltration and recharge, while also minimizing the impacts of peak runoff during extreme precipitation events . For the unincorporated county, which shows a significant portion of the potential hydrologic benefit, soil management practices could significantly reduce water related challenges. Given that 65% of the unincorporated area is considered a groundwater-dependent area and subject to localized groundwater availability problems, practices that enhance hydrologic processes and contribute to overall water-use efficiency could greatly benefit this region. Most notably, San Diego could experience significant decreases in CWD in addition to increases of AET. As a result,best pots for blueberries the farming community could see improvements in soil moisture, irrigation costs, landscape stress, net primary productivity . Thus, these potential improvements ultimately enhance resilience to droughts and extreme events . Results further illustrate that, even in scenarios with projected climate change impacts, there are many areas throughout San Diego with potential increases in AET and decreases in CWD, if soil management practices are implemented. Projections highlight the ability of these practices to buffer the impacts of future drought conditions. Combining hydrologic benefit estimates with knowledge of existing regional agricultural lands can inform strategic, on-the-ground implementation efforts and direct carbon farming farming projects.
Existing agricultural lands constitute a large portion of the total area of estimated hydrologic benefit with increased SOM. Results can provide informed prioritization of feasible lands and management practices in addition to natural resource allocation across the region. Areas that intersect both hydrologic benefit and existing agricultural land can be used to identify areas where carbon farming efforts could be most attainable and readily employed. Translating potential hydrologic changes to their associated economic and productivity benefit provides a critical link between scientific research and practical on-farm application. Carbon farming practices aim to not only build SOC levels, but to ensure that these pools remain in the soil for many years. Thus, it is important to consider the agricultural areas vulnerable to land conversion for implementation of carbon farming projects, as these lands may not be able to sequester carbon for the long-term if converted. Areas at the intersection of current agricultural land and future urban development can be used to identify areas where demonstration sites and farming programs may be short-lived. Analyses identify the areas in which implementation of carbon farming sites and programs may not be able to yield benefits overtime, if not designated for production in years to come. With conversion of farmland in recent years and continued plans for urban development, there is a need to invest in programs that sustain the existing value of these lands while also supporting additional growth. Analyses indicate that only 13% of the total threatened agricultural lands are protected under CCED and/or CPAD conservation plans. Threatened areas showing the highest benefit values can advise future preservation strategies to target these priority lands. As the county faces demand for development, how we reconcile these pressures with the importance of agricultural lands is a critical piece to San Diego’s ultimate climate resilience. In light of these trade-offs, results such as these can help tell the story of these agricultural lands and the case for their preservation. Identifying these opportunities through scientifically based analyses helps portray the potential of carbon farming in the region, and articulate the value agricultural lands hold for their sequestration potential and co-benefits. On many fronts, California has adopted the role of a global leader in climate action, implementing an array of proactive technical instruments and political strategies ranging from the local to federal level. As agriculture is a critical backbone of the state’s booming economy, it is necessary that California put agriculture at the forefront of climate planning . Recognizing the benefits that well-managed soils provide, carbon farming has recently gained attention throughout the state as a promising form of climate adaptation and mitigation. However, for carbon sequestering practices to be effective, feasible, and widespread, it requires collaboration among interdisciplinary stakeholders. It is necessary that policy makers, environmental advocates, scientists, farmers, and economists join forces to spearhead these opportunities. Given the great diversity within the state’s 58 counties, appropriate soil management practices look different for each region. Additionally, regional climate impacts and specific areas of vulnerability differ between regions, and this may translate to unique goals. Thus, the tools and practices needed to address specific regional context, will vary. Home to the greatest number of small farms and certified organic farms of any county in the U.S. , San Diego’s agricultural setting presents unique opportunities and strengths for addressing climate challenges through widespread implementation of sustainable agriculture . Regional application of scientific tools, such as the BCM, can be used as a basis for advising interdisciplinary efforts to address specific county needs, such as water resources. While economic programs and supportive partnerships are essential for promoting the adoption of carbon farming practices, the BCM is a critical component to maximizing opportunities. With advanced science and modeling capabilities, a supportive and proactive network of entities, and the political will and economic incentives in place, opportunities for increasing carbon sequestration in California are more pertinent now than ever. The alignment of these factors makes this the opportune time for San Diego to embrace and advance powerful farming strategies.