**5. Conclusions**

Overall, our study suggests that though the temperature has been increasing significantly in the major wild blueberry production region of Maine, drought has not been increasing significantly over the last 71 years. However, accelerated warming and a projected decrease in soil water content [7] may result in an increase in drought impact on agricultural systems in the future [48]. The water conditions and drought severity quantified by the drought index SPEI had a stronger impact on the vegetation status of the non-irrigated field compared to the irrigated field. The short-term (one year) SPEI was positively related to the yield of the non-irrigated field, whereas no significant correlation was found for the irrigated field, suggesting the sensitivity of wild blueberry yield to water conditions and the effectiveness of irrigation. However, maintaining optimum soil moisture is a challenge due to the high spatial variability in soil water retention capacity in wild blueberry fields. Therefore, developing a precision irrigation system could be an efficient way to mitigate the effects of water deficits. Interestingly, we found that long-term water conditions determine the vegetation vigor and yield more than the short-term water conditions for wild blueberries. Thus, although the wild blueberry is regarded as a droughttolerant species, maintaining good water conditions in the field during the growing season is important for securing a high yield for wild blueberries.

**Supplementary Materials:** The following are available online at https://www.mdpi.com/article/1 0.3390/cli9120178/s1: Table S1. Pearson correlation analysis between average enhanced vegetation index (EVI) of the growing season (May–September) and different scales of the SPEI from May to September at three different wild blueberry study zones: Airport (irrigated field, Deblois, ME), Baxter (non-irrigated field, Deblois, ME), and Downeast, Maine (all wild blueberry fields). Table S2. Pearson correlation analysis between average yield per year and different scales of the SPEI from May to September at three different wild blueberry study zones: Airport (irrigated field, Deblois, ME), Baxter (non-irrigated field, Deblois, ME), and Maine (all wild blueberry fields).

**Author Contributions:** Conceptualization, Y.-J.Z. and K.B.; methodology, K.B., R.T. and P.R.-B.; software, K.B.; validation, Y.-J.Z., K.B. and R.T.; formal analysis, K.B.; investigation, K.B.; resources, Y.- J.Z. and B.H.; data curation, K.B.; writing—original draft preparation, R.T. and K.B.; writing—review and editing, R.T., Y.-J.Z., P.R.-B., B.H. and K.B.; visualization, R.T. and Y.-J.Z.; supervision, Y.-J.Z.; project administration, Y.-J.Z.; funding acquisition, Y.-J.Z. All authors have read and agreed to the published version of the manuscript.

**Funding:** This project was supported by the USDA National Institute of Food and Agriculture, Hatch Project Number ME0-21832 and ME0-22021, through the Maine Agricultural and Forest Experiment Station. This research was also supported by the Wild Blueberry Commission of Maine, the Maine Department of Agriculture, Conservation and Forestry (SCBGP), and the UMaine Faculty Summer Research Award.

**Data Availability Statement:** Please refer to "Section 2.2" in this article for the sources of the publicly archived data products used in this study. Any data and codes used in this study are available upon request from the corresponding author (yongjiang.zhang@maine.edu).

**Acknowledgments:** We would like to acknowledge David Yarborough, Horticulture and Wild Blueberry Specialist, the University of Maine, for providing us with the KMZ file containing the wild blueberry field polygons in Maine to conduct this study.

**Conflicts of Interest:** The authors declare no conflict of interest.
