Drought Indices in Decision-Making Process of Drought Management

Drought indices are one of the most important elements of an effective drought monitoring and early warning system. They help to characterize drought and guide appropriate responses to reduce drought impacts. Drought indicators are more useful than raw data in decision-making process, even though each index has specific use and limited by its strengths and weaknesses. The literature review showed the evaluation of drought conditions by decision-makers as an important issue, but so far no research has been done to understand how decision-makers use diverse and often conflicting values of drought indices to make drought declarations. This research studies how drought declarations by decision-makers relate to drought indices to measure past two droughts in South Carolina. The South Carolina Drought Response Committee (DRC), the state's major drought decision-making body, evaluates climate data and drought indices to issue drought status declarations for each county of the state. The case of South Carolina's drought management program is particular beneficial because the state has one of the largest number of drought indicators among other state-level programs in the nation. My research determines similarities and differences in measures of drought between the DRC and multiple drought indices, such as Palmer Drought Severity Index (PDSI), Palmer Hydrological Drought Index (PHDI), Z-index, Standardized Precipitation Index (SPI), Crop Moisture Index (CMI), Keetch-Byrum Drought Index (KBDI) and the U.S. Drought Monitor (USDM). Nine years of monthly values of each index are compared with the DRC declarations in evaluating drought onset, duration, severity and recovery. The results show that a cumulative approach is more useful in measuring drought conditions rather than one or two indices. The DRC measures drought onset 3-4 months later than the majority of indices. The drought duration of the DRC for overall study period is similar to most drought indices and longer in comparison to drought indices within two drought periods 2000-2002 and 2007-2008. The severity, measured by the DRC is typically has more moderate months than other indices. The DRC consistently identifies drought recovery after drought indices and tends to agree with drought indices in measuring drought recovery more often than in measuring drought onset. This research aims to benefit the decision-making process for drought and water managers, government officials, and stakeholders, as it informs drought assessment in the use of major drought indices. This research is an assessment of drought indicators for policy purposes and can be used in advisement for drought triggers in other regions of the country and the world. Effective use of drought indices in decision-making process enhances proactive drought management policies (risk management approaches) and helps to reduce drought impacts with an ultimate goal of creating drought resilient societies.