A long-term database of the Integrated Drought Index for Brazil from 2003 to 2023
Description
The Integrated Drought Index (IDI) was developed at the National Center for Monitoring and Early Warning of Natural Disasters (Cemaden, www.cemaden.gov.br), in Brazil, to support the monitoring of agricultural drought. The index is a combination of three components: the 3-month Standardized Precipitation Index (SPI3), the Root Zone Soil Moisture (RZSM), and the Vegetation Health Index (VHI). The SPI3 is calculated from a long-term dataset of precipitation records in Brazil with a spatial resolution of 10 km (https://ftp.cptec.inpe.br/modelos/tempo/MERGE/). The RZSM is obtained from NASA's Gravity Recovery and Climate Experiment (GRACE; 2002-2017) and GRACE Follow On (GRACE-FO; 2018-present) satellites (https://nasagrace.unl.edu). The product is released weekly since 2003 with a spatial resolution of 25 km. The VHI is obtained from NOAA's polar-orbiting satellites, available weekly with a spatial resolution of approximately 4 km (https://www.star.nesdis.noaa.gov/smcd/emb/vci/VH/vh_ftp.php). The IDI is used in Cemaden's continuous monitoring activities of drought over Brazil, including monthly meetings with stakeholders, preparing of reports on drought conditions, and updates of an online platform (https://mapasecas.cemaden.gov.br). A previous version of IDI without RZSM was already used in reports of droughts over Brazil, such as in Cunha et al. (2019, https://doi.org/10.3390/atmos10110642). The current version of IDI is routinely assessed against reports of yield losses and other drought indicators. A publication is currently being prepared to assess its spatial and temporal accuracy when compared with other indices. Preliminary results indicate good agreement with the Standardized Precipitation Evapotranspiration Index (SPEI). This dataset contains a netCDF file (IDI3.nc) with the index in the variable IIS3. The variable has values ranging from 1 to 6, corresponding to the following drought classes: Exceptional, Extreme, Severe, Moderate, Weak, and Normal conditions.
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Steps to reproduce
The SPI3 is used as a metric of meteorological and agricultural drought in IDI. For this reason, the weekly data of RZSM and VHI are averaged for the current and previous 2 months, so that all components refer to the same three-month period. Previously studies have indicated that monthly VHI has a high correlation with the SPI at a 3-month scale. Then, the SPI3 and RZSM are resampled to the same spatial resolution of VHI (4 km). Next, each component is converted into 6 classes (from 1 to 6), according to the following ranges: -2,-1.6,-1.3,-0.8,-0.5,6, for SPI; 0,3,6,11,20,30,100, for RZSM; and 0,6,12,20,30,40,100, for VHI. The final value of IDI is then calculated as the average of the classified components.