To cite package ‘chirps’ in publications use:

  de Sousa et al., (2020). chirps: API Client for the CHIRPS
  Precipitation Data in R. Journal of Open Source Software, 5(51),
  2419, https://doi.org/10.21105/joss.02419

A BibTeX entry for LaTeX users is

  @Article{,
    title = {{chirps: API Client for the CHIRPS Precipitation Data in R}},
    doi = {10.21105/joss.02419},
    url = {https://doi.org/10.21105/joss.02419},
    year = {2020},
    author = {Kauê {de Sousa} and Adam H. Sparks and William Ashmall and Jacob {van Etten} and Svein Ø. Solberg},
    journal = {{Journal of Open Source Software}},
  }