ASSESSING DROUGHT CONDITIONS BY ANALYZING NDVI WITH SENTINEL-2 IMAGERY USING GOOGLE EARTH ENGINE

Abstract

The Southwest arid region of the United States is facing an unprecedented ‘megadrought’ which has resulted in a water crisis that threatens agriculture production and natural ecosystems. To observe and analyze the consequence of a decline in water availability, Sentinel-2 Images were compiled and analyzed based on NDVI values. These trends were analyzed in the Yuma subcounty in the state of Arizona, which is a center for agricultural production. A time-series was made using the powerful Google Earth Engine (GEE), a free-to-use cloud computing service, which can compile hundreds of images over time for analysis. The time series created plots all average NDVI values from Sentinel-2 images for the study area between January 2019 and June 2022. Additionally, four images were extracted from GEE and analyzed in ArcGIS Pro. Utilizing ArcGIS Pro’s built in raster analysis tools, one image for each year (2019-2022) were modified to display and assess the differences in NDVI values between the images. Based on the time-series, it is evident that NDVI values are trending downwards, indicating a decline in vegetation health for the Yuma subcounty. Observing the individual images, it is also clear that NDVI values are declining across the region, although more data needs to be collected on the ground to confirm this reduced vegetative productivity. Further study can be done annually using the highly detailed Sentinel-2 images to assess the impacts of drought and to analyze what changes can be made to agricultural systems in specific plots that may not be viable with less water availability.