Standardized Precipitation Evapotranspiration Index (SPEI)
Index name: Standardized Precipitation Evapotranspiration Index (SPEI).
Ease of use: Yellow.
Origins: Developed by Vicente-Serrano et al. at the Instituto Pirenaico de Ecologia in Zaragoza, Spain.
Characteristics: As a relatively new drought index, SPEI uses the basis of SPI but includes a temperature component, allowing the index to account for the effect of temperature on drought development through a basic water balance calculation. SPEI has an intensity scale in which both positive and negative values are calculated, identifying wet and dry events. It can be calculated for time steps of as little as 1 month up to 48 months or more. Monthly updates allow it to be used operationally, and the longer the time series of data available, the more robust the results will be.
Input parameters: Monthly precipitation and temperature data. A serially complete record of data is required with no missing months.
Applications: With the same versatility as that of SPI, SPEI can be used to identify and monitor conditions associated with a variety of drought impacts.
Strengths: The inclusion of temperature along with precipitation data allows SPEI to account for the impact of temperature on a drought situation. The output is applicable for all climate regimes, with the results being comparable because they are standardized. With the use of temperature data, SPEI is an ideal index when looking at the impact of climate change in model output under various future scenarios.
Weaknesses: The requirement for a serially complete dataset for both temperature and precipitation may limit its use due to insufficient data being available. Being a monthly index, rapidly developing drought situations may not be identified quickly.
Resources: SPEI code is freely available at the SPEI website by the Consejo Superior de Investigaciones Científicas (CSIC) and the calculations are also described in the literature. Additional resources are available at the Flood and Drought portal developed by GEF, UN Environment, IWA and DHI.
Reference: Vicente-Serrano, S.M., S. Begueria and J.I. Lopez-Moreno, 2010: A multi-scalar drought index sensitive to global warming: the Standardized Precipitation Evapotranspiration Index. Journal of Climate, 23: 1696–1718. DOI: 10.1175/2009JCLI2909.1.
Currently used by: Peru, Switzerland.
Is there any python code for calculation of SPEI. Please send.
You can find python package for SPEI here: https://pypi.org/project/spei/
i am asnke enawagw amoognehen
Hello, how many years of data is needed for calculating SPEI?
Thank you for your question. The SPEI is calculated in analogy to the SPI. The resulting values are sensitive to the quantity and reliability of the data used to fit the distribution. A time series of 30-50 years is recommended.
Hello, I surfed the internet in search of the Intensity scale for SPEI, then I stumbled on this interactive group. Could you please send me the intensity scale. Thanks
Dear Vincent Uche
Thank you for your question. The SPEI is calculated in analogy to the SPI, but the SPEI uses the weekly or monthly difference between precipitation and PET. Therefore, the values of both indices can generally range from -2 to 2. The lower the value, the higher the precipitation/PET deficit. The severity of a drought however is also connected with the recorded impacts at a certain SPEI value.
I got all procedure from the Vicente-Serrano et al 2010 paper, I am trying to following it to my station but struggling with no success. Can someone provide a simple example of one year in excel to use the formulas and calculate SPEI?
Dear Francisco Saimone
Please refer to to the SPEI package for the R statistical software (freeware). This package will allow you to calculate the SPEI and there are also several data examples included: https://cran.r-project.org/web/packages/SPEI/.
I really appreciate your services
and I’m interested if you can expand the calculation area for 2019 and 2020.
Please for Romania (NE): weather stations: Cotnari, Iasi, Botosani and Roman.
All the best !
My name is: Papaghiuc Lidia Maria, Iasi, Romania
The above-mentioned web page (https://spei.csic.es/home.html) was blocked.
Could you please check the page?
Thanks in advance.
We just checked. The web page is still there. This is a link to a IDMP partner page but not directly under the management of IDMP.
I can’t visit the page and it shows Web Page Blocked too. How may I resolve this issue?
Why we calculate difference between precipitation and potential evapotranspiration?
Thank you for your comment to the SPEI. The SPEI uses the basis of the standardized precipitation index (SPI), which permits to identify the deviation of precipitation values from a long-term average. By adding a temperature component, the SPEI accounts for the effect of temperature on the development of drought conditions – high temperatures have been empirically shown to aggravate drought conditions. Temperature is included into the SPEI as a proxy for potential evapotranspiration (PET). By calculating the difference between precipitation and PET a simple climatic water balance is established, providing a simple measure of the water surplus or deficit of a month (if calculated on a monthly basis).
You can find more information on this by visiting the SPEI website: https://spei.csic.es/home.html
please send SPEI index for me.
with the best wishes
Dear M.H. Gholizadeh,
The SPEI code is freely available and the calculations are also described in the literature at http://sac.csic.es/spei/.
The reference paper is: Vicente-Serrano, S.M., S. Begueria and J.I. Lopez-Moreno, 2010: A multi-scalar
drought index sensitive to global warming: the Standardized Precipitation Evapotranspiration
Index. Journal of Climate, 23:1696–1718.
This information is also find on page 23 of the Handbook and n the SPEI page.