Revisiting the composite drought index for improving drought monitoring

Abstract

Well-known natural disasters (i.e., drought) are notably difficult to control and have far-reaching effects. The identification and evaluation of drought are essential for designing water scarcity management plans. Studies have shown that a single drought index has a limited ability for drought monitoring. Therefore, the composite drought index (CDI) was revised by integrating a moisture index that represents the degree of dryness/wetness, reference, and actual and potential evapotranspiration, including advection and radiation component-based water balance and rainfall anomalies. The revised indices were subsequently compared with the original CDI and composite index (CI) developed by the National Climate Center, China, and well-known traditional drought indices (e.g., the standardized precipitation index (SPI) and standardized potential evapotranspiration index (SPEI)). The results revealed that the revised CDIs, especially those with potential and actual evapotranspiration-based moisture and water balance, were well correlated with soil moisture and crop water requirements. The correlation coefficient was statistically significant and greater than 0.5 in most of the grid cells. The indices demonstrated a good ability to determine drought events and characteristics (duration and severity). For example, a one-month drought duration was captured by the CDI (based on actual and potential evapotranspiration); in contrast, the CI presented no drought duration in a similar region. Additionally, the CDIs robustly captured dryness, whereas the CI, SPEI, and SPI reflected a greater amount of wetness. As drought severity has a major impact on crops, these findings emphasize the potential of revised CDIs in drought monitoring and management.