Exploring the climate change and variability effects on almond phenology in California

Abstract:

Climate change threatens almond production in California due to factors such as increasing temperatures, droughts, and atmospheric CO₂ concentration. Here, we use historical data including gridMet dataset of daily high-spatial resolution (~4 km, 1/24 th degree) surface meteorological data covering the contiguous U.S. from 1979 to 2018 and historical trends in annual county yields in the Central Valley. Knowledge of thermal and moisture regimes likely to drive future variability in yields is very important to anticipate the effects that the expected changes in climate conditions will have on future almond production in the region. The aim of this study is to first construct biologically-based climate indices; that is, climate requirements to set off different phenological events of the almond tree and secondly, to use these climate parameters to quantify critical phenological thresholds. We then use dynamic factor analysis (DFA), a multivariate time series analysis technique that allows estimates of common patterns over time in annual county yields and the effects of explanatory time- dependent variables. We describe a general pattern of climate impacts across the entire region of the Central Valley and heterogeneity of climate variability effects across geographic locales within the Central valley. This analysis furthers our understanding of how the effects of seasonal climates change and variability may affect the annual cycles of on almond trees phenology (dormancy, bloom, fruit development, harvest and post-harvest) and therefore overall yields in the Central Valley counties.