PCC March 2019

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Climate Change and California Agriculture By: Tapan B. Pathak | Division of Agriculture and Natural Resources, University of California, Merced, CA, Mahesh L. Maskey, Jeffery A. Dahlberg, Khaled M. Bali, Daniele Zaccaria | University of California, Division of Agriculture and Natural Resources (UCANR), Faith Kearns | Division of Agriculture and Natural Resources California Institute for Water Resources, University of California, Oakland, CA Introduction California is the largest and most diverse agricultural state that produces over a third of the country's vegetables and two-thirds of fruits and nuts. Among 400 different commodities, California is a leading producer of many of those commodities [1]. At the same time, changing climate signals such as temperatures, precipitation patterns, extreme calamities and water availability poses many challenges to the state’s agricultural sector, which would not only translate into national food security issues but also economic impacts that could disrupt state and national commodities systems. Recent publication by Pathak et al. [2] outlined a detailed literature review to document the most current understanding on California´s climate trends in terms of temperature, precipitation, snowpack, and extreme events such as heat waves, drought, and flooding, and their relative impacts on the state’s highly productive and diverse agricultural sector. For instance, both average and extreme temperatures and precipitation patterns influence crop yields, pest, and the length of the growing season. Because of climate change, extreme events, such as heat waves, floods, and droughts, may lead to larger production losses, earlier spring arrival, and warmer winters due to temperature increases allow disease and pest pressure increase, shrinking snowpack leading to a greater risk for agriculture water availability. This paper summarizes key findings from that paper in the context of: (a) historic trends and projected changes in temperature, precipitation and heat waves; (b) current situation and future expectations of drought and flood; and (c) consequent impacts on agriculture. Climate change trends in California The climate of California varies from hot desert to subarctic environments lying in the proximity to the Pacific Coast with Mediterranean climate influenced by the cold ocean currents and offshore winds. This section reviews historical and projected trends of key climatic parameters: temperature, precipitation, and extreme events like heat waves, drought and floods. Temperature Climate change in California is often exemplified by increased temperature in both space and time. While temperature has globally increased by 1.4°F since Degrees (F) 2.0 0.0 -2.0 1880, the rate of increase in minimum temperature is greater than that of mean or maximum temperatures. Figure 1 shows that observed mean temperature in the state has been increasing from 1.3 to 2.3 °F in the past century [3]. The recent severe drought in the state has been exaggerated by increased temperature and insignificant precipitation. As seen in Table 1 (see page 27), summer after spring happens with the largest warming trends and least warming is experienced during winter and spring after implying inter-annual variability for the period from 1895 to 2018 [4]. However, least warming during fall and winter has been reported for the period 1895-2010. Spatial variation of temperature also reveals that Southern part of the state 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 Figure 1: California statewide mean temperature departure in (°F), October through September [3]. Black line denotes 11-year running mean. 26 Progressive Crop Consultant March/April 2019
experiences greater warming than compared to Northern California. Outcome of different climate models reveals that there will be more pronounced increment in summer temperature than in winter resulting into more warming in inland areas than in coastal regions. The increasing temperature trends will decrease the snow-to-precipitation ratio [5]. The state’s Sierra snowpack starts to melt earlier and faster than usual due to frequent heat spells [6]. For instance, future trends for far north and far south of the state are presented in Figure 2 (see page 28) which suggests how temperatures will continue to increase until 2100 under different emission scenarios from different climate models. Precipitation is a crucial parameter to state’s water supply for the agricultural purposes and such parameter exhibits significant inter-annual variability [3]. The variability of precipitation in California is a unique phenomenon implying that such unpredictability is more notable in California than Table 1: California temperature departures, 1895-2018, for mean, max and min linear trends in °C within the period shown [4]. Linear departures Annual Winter Spring Summer Fall A. Mean Temperature 1895-2018 +1.88 1949-2018 1975-2018 B. Max temperature 1895-2018 1949-2018 1975-2018 C. Min temperature 1895-2018 1949-2018 1975-2018 +2.03 +1.32 +1.58 +1.18 +0.79 +2.18 +2.87 +1.85 +1.55 +4.74 +2.12 +1.68 +4.74 +2.39 +1.42 +4.74 +1.85 +1.20 +0.46 +0.89 +0.80 +0.29 +2.39 +1.60 +1.21 +1.72 +3.07 +2.02 +1.59 +2.82 +0.86 +0.75 +3.31 +3.18 +2.43 +1.70 +0.89 +0.68 +1.02 +0.59 +0.04 +2.39 +2.36 +1.40 other parts of the country. Having Mediterranean climate, most of the rainfall happens during cool season (October to April). Despite having unnoticeable temporal pattern, study shows total annual precipitation has increased at an average rate of 5 millimeter (mm) per decade for the contiguous 48 states. In addition, there is increase in extreme single day precipitation events and increased temporal Continued on Page 28 BANKABLE BLOOMS A strong bloom leads to improved set and higher yields. The investments you make now make all the difference later. Proven in your area to provide improved: plant vigor, nutrient uptake, root growth, and resistance to environmental stress. Choose Acadian ® for consistently higher yield • Trials and technical experts local to your area • Consistent quality and supply • 100% Ascophyllum nodosum • 30 years of lab and field trials Contact your local Acadian ® representative. Daniel Cathey (Northern CA) 916-578-6207 Chris Coolidge (Central CA) 559-779-3579 Taylor Hoover (Coastal CA) 949-547-0880 Annalisa Williams (CA) 805-801-5238 Jeff Downs (SoCal/AZ) 559-285-8448 Acadian Plant Health is a division of Acadian Seaplants Limited, Acadian ® is a registered trademark of Acadian Seaplants Limited. March/April 2019 www.progressivecrop.com 27
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PCC March 2019

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