EGU24-12175, updated on 09 Mar 2024
EGU General Assembly 2024
© Author(s) 2024. This work is distributed under
the Creative Commons Attribution 4.0 License.

Evaluation of daily SPI and SPEI indices for near-real time drought monitoring over CONUS

Olivier Prat1, David Coates1, Scott Wilkins1, Denis Willett1, Ronald Leeper1, Brian Nelson2, Michael Shaw3, and Steve Ansari4
Olivier Prat et al.
  • 1North Carolina State University (NCSU), Cooperative Institute for Satellite Earth System Studies (CISESS), Asheville, NC, USA (
  • 2NOAA/NCEI/Center for Weather and Climate (CWC), Asheville, NC, USA
  • 3ISciences, L.L.C., National Centers for Environmental Information (NCEI), Asheville, NC, USA
  • 4NOAA/NCEI/National Integrated Drought Information System (NIDIS), Asheville, NC, USA

Two drought indices; the Standardized Precipitation Index (SPI) and the Standardized Precipitation Evapotranspiration Index (SPEI) are computed over CONUS using daily precipitation and temperature estimates from the NOAA Daily U.S. Climate Gridded Dataset (NClimGrid-Daily). The NClimGrid-Daily dataset consists of four climate variables derived from the GHCN-D dataset: maximum, minimum, and average temperatures and precipitation from 1951 to the present with a 5-km grid resolution. While SPI only uses precipitation as an input to assess drought conditions, SPEI uses both precipitation and potential evapotranspiration (PET). The daily SPI and SPEI are computed over various time scales (30-, 90-, 180-, 270-, 365-, 730-day). The differences between the two indices are being evaluated focusing on the influence accumulation period, differing period of record, and various SPI (McKee et al 1993, Guttman 1999) and daily PET (Thornthwaite and Mather 1957, Camargo et al. 1999, Pereira and Pruitt 2004) formulations. The impact of the period of reference is analyzed to account for the impact of precipitation and temperature changes over time (i.e., 1952-present, 1960-1990, and 1990-2020 for instance). For the most recent period (2000-present), the NClimGrid-SPI and NClimGrid-SPEI are compared against existing droughts monitoring resources such as the weekly US Drought Monitor (USDM). The use of cloud-scale computing resources reduces considerably the computation time and allows for the near-real time computation of daily SPI and SPEI indices. The effort to transfer the SPI and SPEI from research to operation (R2O) and to provide near-real time drought monitoring capabilities is also presented.

How to cite: Prat, O., Coates, D., Wilkins, S., Willett, D., Leeper, R., Nelson, B., Shaw, M., and Ansari, S.: Evaluation of daily SPI and SPEI indices for near-real time drought monitoring over CONUS, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12175,, 2024.

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