A Python Reference Implementation of Standard Drought and Climate Indicators

The Palmer Drought Severity Index (PDSI), Standard Precipitation Index (SPI), Standard Precipitation Evapotranspiration Index (SPEI), and Percentage of Average Precipitation (PAP) are important climate indicators used to monitor hydrological trends and drought severity. NOAA and the National Integrated Drought Information System (NIDIS) are producing a new reference implementation of these algorithms in Python, through the code rejuvenation of existing legacy code developed in multiple languages throughout the community over the previous three decades. This implementation provides NCEI and the drought and climate science community an easy-to-use and well documented codebase to support future product creation. The new implementation has many additional benefits, including:

• Support for multiple formats including NetCDF.
• Flexibility to process any source of time series data, including NetCDF grids, stations, climate divisions, states and counties.
• The initial implementation in Python, which has become widely used in the climate science community.
• Code availability in the public domain and hosted on Drought.gov, utilizing Jupyter notebooks for step-by-step documentation and interactive execution of the code.
• Scientific validation from NCEI and NIDIS subject matter experts and collaborators.
• Test datasets and unit tests used to validate the code on an ongoing basis.
• Additional product features including a self-calibrated component to the PDSI.

This new codebase is presented as a reference implementation of these various climate indicators and provides common, standard and transparent computational procedures that are reusable, extensible, and faithful to the published literature.