Uncertainty in SPI Calculation and its Impact on Drought Assessment in Different Climate Regions over China

Abstract Uncertainty in the calculation of a Standardized Precipitation Index (SPI) attracted growing concerns hydrometeorology research community last decade. This issue is addressed present study from perspective candidate probability distributions, data record length, cumulative timescale and selection reference period with bootstrap Monte Carlo methods using daily precipitation observed four climate regions across China. The impacts uncertainty an SPI on drought assessment are also investigated. Results show that Gamma distribution optimal describing China; among timescales investigated study, minimal appropriate for 20 days humid region, 30 semi-humid/semi-arid region Tibetan Plateau (mostly its eastern part), 90 arid region. decreases increase essentially as consequence decrease confidence interval width parameters length. But there little improvement parameter estimation length longer than 70 years. There greater high absolute values small ones, consequently assessing extreme droughts moderate droughts. Reference has large assessment, especially context change. categorizing droughts, but no impact temporal features variation.