A team of researchers from UCLA and Columbia University have found that the most recent 2012–16 drought had a greater impact on Southern California than it did in parts of the state to the north. Glen MacDonald, a UCLA climate scientist and one of the co-authors of the paper published in Geophysical Research Letters noted, “Southern California is more prone than the northern part of the state to getting severe droughts, but that difference seems to be increasing.”
The study analyzed changes in normalized difference vegetation index (NDVI) which is a calculation of vegetation greenness from satellite data. The health of vegetation, as measured in greenness, can be measured by calculating the ratio of visible light absorbed and near-infrared light reflected by those plants. As vegetation becomes stressed by increased heat and drought, greenness declines. As climate exacerbates drought conditions, particularly in Southern California, satellite data has been able to captured the decline in NDVI.
Dong, C., MacDonald, G. M., Willis, K., Gillespie, T. W., Okin, G. S., & Williams, A. P. (2019). Vegetation Responses to 2012‐2016 Drought in Northern and Southern California. Geophysical Research Letters.