Investigating Climate Related Changes to Chill Hours in North Carolina Utilizing Mesonet Observations

The production of berries in North Carolina is a significant industry with blueberry production ranking 7^th in the nation in 2021. In addition to the standard agricultural climate concerns of growing season temperatures and precipitation, blackberry and blueberry shrubs also require a certain number of chilling hours during their winter dormancy period. These chilling hours are typically defined as the number of hours between 0-7°C, but more intricate models exist depending on the berry cultivar. Thus, a warming climate poses a risk to berry farmers throughout the state as warmer winter temperatures reduce the number of chill hours these shrubs receive, and ultimately, constrains the viable berry cultivars that farmers can grow. In this study, we address two key objectives to support the climate readiness of North Carolina’s berry producers. First, we leverage both Mesonet observations and gridded Parameter-elevation Relationships on Independent Slopes Model (PRISM) estimates to determine how chill hours vary spatially and temporally across the state’s eight climate divisions under current climate conditions (i.e., 2008-2023). Second, we utilize statistically downscaled climate projections from the Multivariate Adaptive Constructed Analogs (MACA) dataset to determine how chill hours throughout the state will change by the middle and end of the 21^st century. Preliminary findings in the current climate indicate that years with negative Arctic and North Atlantic Oscillation Indices during the chill season tend to have higher chill values due to cooler conditions, except in the mountains where the cooler climate can lead to subfreezing conditions. Across most of the state, chill hours will decrease on the order of tens of hours each chill season by the end of the 21^st century following the Representative Concentration Pathway (RCP) 4.5 scenario and on the order of hundreds of hours following the RCP 8.5 scenario. These reductions in chill hours are especially large in North Carolina’s southern coastal plain, where the majority of the state’s commercial blueberry production is located. As a result, berry growers in the state will need to act over the coming decades to transition their crops to berry cultivars with lower chill requirements.