California is a global leader in the agricultural sector and produces more than 400 types of commodities. The state produces over a third of the country’s vegetables and two-thirds of its fruits and nuts. Despite being highly productive, current and future climate change poses many challenges to the agricultural sector. This paper provides a summary of the current state of knowledge on historical and future trends in climate and their impacts on California agriculture. We present a synthesis of climate change impacts on California agriculture in the context of: (1) historic trends and projected changes in temperature, precipitation, snowpack, heat waves, drought, and flood events; and (2) consequent impacts on crop yields, chill hours, pests and diseases, and agricultural vulnerability to climate risks. Finally, we highlight important findings and directions for future research and implementation. The detailed review presented in this paper provides sufficient evidence that the climate in California has changed significantly and is expected to continue changing in the future, and justifies the urgency and importance of enhancing the adaptive capacity of agriculture and reducing vulnerability to climate change. Since agriculture in California is very diverse and each crop responds to climate differently, climate adaptation research should be locally focused along with effective stakeholder engagement and systematic outreach efforts for effective adoption and implementation. The expected readership of this paper includes local stakeholders, researchers, state and national agencies, and international communities interested in learning about climate change and California’s agriculture.

Many agricultural production areas worldwide are characterized by high variability of water supply conditions, or simply lack of water, creating a dependence on irrigation since Neolithic times. The aim of this paper is to provide an overview of the evolution of irrigation of agricultural lands worldwide, based on bibliographical research focusing on ancient water management techniques and ingenious irrigation practices and their associated land management practices. In ancient Egypt, regular flooding by the Nile River meant that early agriculture probably consisted of planting seeds in soils that had been recently covered and fertilized with floodwater and silt deposits. On the other hand, in arid and semi-arid regions farmers made use of perennial springs and seasonal runoff under circumstances altogether different from the river civilizations of Mesopotamia, Egypt, India, and early dynasties in China. We review irrigation practices in all major irrigation regions through the centuries. Emphasis is given to the Bronze Age civilizations (Minoans, Egyptians, and Indus valley), pre-Columbian, civilizations from the historic times (e.g., Chinese, Hellenic, and Roman), late-Columbians (e.g., Aztecs and Incas) and Byzantines, as well as to Ottomans and Arabs. The implications and impacts of irrigation techniques on modern management of water resources, as well as on irrigated agriculture, are also considered and discussed. Finally, some current major agricultural water management challenges are outlined, concluding that ancient practices could be adapted to cope with present challenges in irrigated agriculture for increasing productivity and sustainability.

In California, alfalfa is grown on a large area ranging between 325,000 and 410,000 hectares and ranks among the thirstiest crops. While the hay production industry is often scrutinized for the large usage of the state’s agricultural water, alfalfa is a crucial feed-supplier for the livestock and dairy sectors, which rank among the most profitable commodity groups in the state. Sub-surface drip irrigation (SDI), although only practiced on approximately 2% of the alfalfa production area in California, is claimed to have the potential to significantly increase hay yield (HY) and water productivity (WP) compared with surface irrigation (SI). In 2014–2016 we interviewed a number of growers pioneering SDI for alfalfa production in Central and Southern California who reported that yield improvements in the order of 10–30% and water saving of about 20–30% are achievable in SDI-irrigated fields compared with SI, according to their records and perceptions collected over few years of experience. Results from our research on SDI at the University of California, Davis, revealed significantly smaller yield gain (~5%) and a slight increase of water use (~2–3%) that are similar to findings from earlier research studies. We found that most of the interviewed alfalfa producers are generally satisfied with their SDI systems, yet face some challenges that call for additional research and educational efforts. Key limitations of SDI include high investment costs, use of energy to pressurize water, the need for more advanced irrigation management skills, and better understanding of soil-water dynamics by farm personnel. SDI-irrigated fields also need accurate water monitoring and control, attentive prevention and repair of rodent damages, and careful salinity management in the root zone. In this paper we attempt to evaluate the viability of the SDI technology for alfalfa production on the basis of preliminary results of our research and extension activities, with focus on its water and energy footprints within the context of resource efficiency.

Proximal sensing is being integrated into vineyard management as it provides rapid assessments of spatial variability of soils’ and plants’ features. The electromagnetic induction (EMI) technology is used to measure soil apparent electrical conductivity (EC_a) with proximal sensing and enables to appraise soil characteristics and their possible effects on plant physiological responses. This study was conducted in a micro irrigated Cabernet Sauvignon (Vitis viniferaL.) vineyard to investigate the technical feasibility of appraising plant water status and its spatial variability using soil EC_aand must carbon isotope ratio analysis (δ¹³C). Soil temperature and soil water content were monitoredin-situusing time domain reflectometry (TDR) sensors. Soil EC_awas measured with EMI at two depths [0–1.5 m (deep EC_a) and 0–0.75 m (shallow EC_a)] over the course of the crop season to capture the temporal dynamics and changes. At the study site, the main physical and chemical soil characteristics, i.e. soil texture, gravel, pore water electrical conductivity (EC_e), organic carbon, and soil water content at field capacity, were determined from samples collected auguring the soil at equidistant points that were identified using a regular grid. Midday stem water potential (Ψ_stem) and leaf gas exchange, including stomatal conductance (g_s), net carbon assimilation (A_n), and intrinsic water use efficiency (WUE_i) were measured periodically in the vineyard. The δ¹³C of produced musts was measured at harvest. The results indicated that soil water content (relative importance = 24%) and texture (silt: relative importance = 22.4% and clay: relative importance = 18.2%) were contributing the most towards soil EC_a. Deep soil EC_awas directly related to Ψ_stem(r² = 0.7214) andg_s(r² = 0.5007). Likewise, δ¹³C of must was directly related to Ψ_stem(r² = 0.9127),g_s(r² = 0.6985), andA_n(r² = 0.5693). Results from this work provided relevant information on the possibility of using spatial soil EC_asensing and δ¹³C analysis to infer plant water status and leaf gas exchange in micro irrigated vineyards.