San Diego’s landscape has historical and cultural importance, with more than 18 federally recognized tribes which is more Indian reservations than any other county in the United States . The combination of these natural open and agricultural lands, pristine coastal areas, diverse urban neighborhoods, and rich cultural history makes San Diego a vibrant and unique region that supports a variety of human communities and industries.Agricultural rangelands and croplands are an important feature within San Diego’s landscape, constituting 5.11% of the county’s total land with more than 250,000 acres and 5,000 farmers . These working lands are deeply rooted in the county’s landscape, holding historic, economic, environmental, and social significance while providing a multitude of local benefits. Not only are these working lands important to the county for providing the public with local products and counteracting urban growth, they have significant economic value. Ranked 12th largest in the nation, San Diego agriculture has an estimated $2.88 billion annual value to the economy . The region’s agriculture encompasses rangeland, pastureland, and cropland, used for growing annual, perennial, nursery, and field crops . Top crops include nursery products and crops, avocados, citrus, and miscellaneous vegetables . While the relatively moderate Mediterranean climate, in addition to a range of micro-climates, makes San Diego an ideal place to grow agricultural crops and livestock products , there are many challenges associated with farming in the region. San Diego’s current farmers face constraints on water-use efficiency and water availability that limits crop selection and efforts efforts to maximize production while also making a profit. From high irrigation demand,blueberry plant container increasing water costs and land prices, to pervasive pest and plant diseases, San Diego farmers have no choice but to utilize innovative farming techniques and choose smart crop choices .

Due to historic development patterns in San Diego, agriculture is often embedded within urban areas, with more small farms than any other county in the nation. Because of the average size of farms, the agricultural sector is spatially scattered throughout the unincorporated county, which can be difficult for identifying and monitoring existing agricultural land and practices. Nonetheless, San Diego’s agricultural production remains more valuable than many other urbanized areas of California, including San Francisco, Orange County, and Los Angeles combined . San Diego’s agricultural landscape is composed of diverse lands, with varying terrain, vegetation, and agricultural use. These lands provide valuable and beneficial services for the region’s food supply and ecosystems, including creation of wildlife, habitat, food for people and pollinators, and water filtration .At a latitude of approximately 32 degrees North, San Diego is situated in the heart of the subtropical climate zone. The region encompasses a unique landscape, positioned between the coastal zone of the Pacific Ocean to the west and the foothills, interior mountains, valleys, and deserts to the east. Like most areas in California, the region is known for its Mediterranean climate in which it experiences hot, dry summers, and mild winters . San Diego’s climate is characterized seasonally by latitudinal climate influences that cause this subtropical dryness in the summer and midlatitude storm-tracks in a concentrated wet season from October through April . Additionally, coastal low clouds and fog are a defining characteristic of San Diego’s climate. CLCF typically persist throughout early summer months, helping moderate heating, buffer dryness and solar insolation, while also providing cooling and water for the region’s coastal ecosystems . The combination of complex topography, coastal effects, and wide altitudinal ranges coupled with subtropical and midlatitude influences results in a range of diverse micro-climates throughout the region . In addition to impacting temperatures and humidity on the coast and further inland, the combination of these factors produce variability in monthly precipitation during the winter months . With annual precipitation totals varying from as little as 50% to greater than 200% of long-term averages, California experiences the largest yearly variations in precipitation compared to any other region in the U.S .

In particular, the year-to-year variability in southern California is higher than anywhere else in the U.S . The average annual precipitation for San Diego is 10.34 inches , however, historical averages reaching as low as 3.3 inches in 2002 and as high as 22.60 inches in 2005 highlight the region’s large inter-annual variability. Variability in precipitation is primarily tied to the number of extreme precipitation events, known as Atmospheric Rivers . ARs contribute to 68% of extreme-rainfall accumulations in southern California . Figure 4 illustrates the correlation between the number of these top 5% of rainy days and precipitation variability. Given that the occurrence of a few AR events each year dictate floods, droughts , and water availability , understanding these extreme events are important for regional weather forecasting, infrastructure planning, and resource management. The San Diego County Water Authority has served as the wholesale supplier for San Diego since its creation in 1944, working to secure reliable water supply for the region. SDCWA’s water supply sources have changed throughout San Diego’s unique historical periods. Despite these changes, SDCWA has consistently relied on imported water in some capacity . Currently, San Diego County imports around 80% of its water supply, using both local and imported sources . In the past, San Diego relied heavily on a single supplier of water, the Metropolitan Water District of Southern California , which includes water from Northern California and the Colorado Basin. Since the enactment of the Colorado River Compact in 1922, allowing for the diversion of water from the river to surrounding states, Colorado has been a major supplier for San Diego . In 1991, the MWD constituted 95% of San Diego’s water supply . In the last two decades, after an extensive drought that caused MWD to reduce water delivery to San Diego, SDCWA has developed several strategies and long-term plans to diversify the region’s water supply portfolio. These strategies aim to improve the region’s water infrastructure, promote water-use efficiency, and ultimately secure reliability of supply . In 2017, supply from MWD had significantly declined to 40%, allowing for inclusion of other sources. Agreements made with the Imperial Irrigation District, and the Coachella and All-American canals, which source water from the Colorado Basin, contributes another 40% of imported water to San Diego’s current supply portfolio. Local sources contribute the remainder of supply, including groundwater, recycled water, and desalination . Agriculture is one of the many sectors that is greatly dependent on these water resources. With water pricing escalating since the early 1990’s, water costs have been the primary water concern for San Diego farmers .

As drought conditions increasingly threaten the region’s imported water sources, farmers have shifted their focus towards water availability as well . While SDCWA has worked to ensure reliable and diversified water sources over the last few decades, new water sources have proven to be expensive . In the last 12 years, the price of water has tripled, while the revenue from farm products are generally consistent, creating challenges for farmers across the region. Water alone constitutes the largest monthly expense for many farmers . Thus, farmers are eager to adopt strategies that maximize water-use efficiency, minimize use and overall costs, and increase financial returns. For farmers who choose to participate in SDCWA’s special agricultural water pricing, water charges are priced at discounted rates. Nonetheless, costs per acre foot remain high, and much of the sector, specifically nursery, flower, fruit, and livestock farmers, do not participate . Not all of San Diego receives the imported water supplied by MWD and geographically,30 plant pot the majority of the unincorporated area is reliant on groundwater-dependent districts or private wells that are managed separately from SDCWA . Thus, these areas are completely reliant on groundwater resources and are impacted by its availability. The agricultural sector also relies on groundwater resources, and is considered one of the “large quantity” groundwater users . These groundwater resources are often limited due to unfavorable geology, resulting in aquifers with limited groundwater in storage volume and/or groundwater recharge. Several areas throughout the county that are groundwater-dependent, specifically the unincorporated county, face groundwater hydrology issues. Given that agricultural users are not regulated or metered for water quantity, these large quantity users can create localized groundwater problems throughout the groundwater dependent areas . It is clear that water resources, availability, and supply are major focuses for the county, especially the agricultural sector. With the need to limit water use to allow for profits, water concerns continue to be a driving force for the conservation efforts of San Diego’s farming community. It is projected that over the next several decades, California will continue to experience several changes associated with climate change, including sea level rise, precipitation patterns, and temperatures. Amid historic coastline and mountains, San Diego region encompasses many diverse climate zones. In turn, the region will likely experience a myriad of changes with dynamic, complex, and compounded effects. As a result, the county will face several challenges that could ultimately threaten the natural and human landscapes that it supports. While the region’s diverse ecological systems, industries and communities have adapted to San Diego’s variable and seasonal climate, climate change could exacerbate these conditions and ultimately threaten the survival of these valuable systems . As one of the most “climate-challenged” regions in North America, it is critical that the county understand these regional variations in climate impacts and vulnerability .

In the region, climate change will significantly increase yearly average temperature over the next several decades, with projections ranging from 5-10° Fahrenheit depending on the Representative Concentration Pathway greenhouse gas concentration and region . San Diego and neighboring areas will face varying changes in the average hottest day per year, daily maximum temperature and daily minimum temperature because of the region’s diverse topography and distinct micro-climates. Under RCP 8.5, representing a high concentration scenario, the average hottest day per year will increase from the historic range of 90-100° F to 100-110° F in coastal zones, and from 105-115° F to 110-125° F in desert regions . Temperature extremes are projected to increase, with climate warming increasing duration, frequency, and intensity of heat waves compared to historic climate . The probability of heat waves varies regionally, with some locations expected to have a greater probability of increase in the number of extremes, and in either daytime or nighttime heat waves. Extreme temperature events and increasing Tmax will further intensify the impacts of drought . Although it is projected that there will be fewer total wet days and a decrease in the number of ARs globally, these wet events will likely increase in width and length by 25%, in addition to intensity . With a Mediterranean climate that is uniquely balanced between both mid-latitude storms and expanding subtropical zones, projections for California’s precipitation regime show more uncertainty and variability compared to most other Mediterranean climates around the world. While models consistently project future drying over Mediteranean climates globally, projections for California diverge from these trends, becoming wetter in winter aggregate and experiencing increases in mean precipitation . As a result, the region will likely experience wetter winters yet longer, dryer warm seasons, contributing to increased year-to-year variability. With intensified extreme precipitation events, climate models indicate that the variable character of Southern California’s precipitation will continue to increase .It is projected that precipitation will increase during the region’s concentrated wet winter season, while decreasing in both autumn and spring . Warmer temperatures are causing winter precipitation to fall in the form of rain rather than snow, meaning that the snow pack that acts as a natural reservoir for the state’s water supply will be diminished . As less precipitation is stored in these snow pack reservoirs, compounded with warming temperatures, the state is experiencing earlier springtime snow melt . These projected changes in snow pack, precipitation and springtime snow melt will continue to challenge many regions of California, defining the state’s current and future water resources . Although local snow pack is not significant, loss of snow pack in the state overall will negatively impact the imported water supplies that San Diego relies upon.Coastal low clouds and fog that migrate along the West Coast fluctuate on annual and decadal scales, as a response to a combination of naturally occurring climate and weather patterns .