How to find green growing plants in Arizona, a state famous for its long droughts and intermittent, but torrential, rains? Previously I reviewed the available public models for drought, NDVI, and rainfall, and concluded that rainfall was most useful. However, the most important factor for plant growth is regular consistent rain. Not drought, but also not deluge. I hypothesized that a consistent "drip" of at least 1/4 inch of rain each week would yield the best plant growth, and I created a GIS model to map this.
Methods
Download data files from NOAA: https://water.noaa.gov/resources/downloads/precip/stageIV/2025/03/04/
lots more info at the bottom link for PDF: NWPS Products and User Guide
GeoTIFF The new QPE GeoTIFFs generated from the NCEP Stage IV data are multi-band GeoTIFF. The bands they contain are:
● Band 1 - Observation - Last 24 hours of QPE spanning 12Z to 12Z in inches
● Band 2 - PRISM normals - PRISM normals in inches (see Appendix A- Normal Precipitation)
● Band 3 - Departure from normal - The departure from normal in inches
● Band 4 - Percent of normal - The percent of normal
I only use Band 1, for the previous week, not 24 hours.
I download the data using a Power Automate FTP query for: concat('https://water.noaa.gov/resources/downloads/precip/ ', variables('Date2'), '/nws_precip_', 'last 7-days_', variables('CurrentDate'), '_conus.tif')
In GIS, I Clip rasters to extent and calculate threshold (0.25") for each week:
Then I use Cell Statistics to add all threshold files for a several month period.
Results
10/13-12/01, each week gets 1 point for rain over 0.25"
12/8 to 3/5, each week gets 1 point for rain over 0.25"
The highest mountains in UT and CO got regular precipitation, as did northern CA. NM did not continue wetter than AZ. This winter period is important for desert spring ephemeral flowers. While some areas of the Mojave did get rain, there was basically no rain in the Sonoran desert during this period.
