Applicability of a combined drought index to monitoring drought in Jordan

The present study explores and evaluates the potential of using a combined drought index (CDI) based on precipitation (PDI), temperature (TDI), and vegetation (VDI) drought indices, to characterize drought variability and trends in Jordan based on 1-, 2-, 3-, 6-, and 12-month timescales. Drought is a complex natural hazard with variable patterns and severity that has become a trending phenomenon in all countries across the globe, impacting all sectors negatively. Due to the importance of drought monitoring and early warning in terms of enhancing drought resilience and preparedness, drought characterization and vulnerability have been investigated repeatedly during the last decade, leading to the development of various drought indices. However, a single drought index may not provide a clear understanding of drought spatial and temporal patterns and the impacts on various sectors; thus, a combination of various indices could provide a key to better interpolation and forecasting.

The CDI was computed as a weighted average of the PDI, TDI, and VDI indicators as derived from daily rainfall, air temperature, and NDVI data respectively for 21 meteorological stations for dates from 1980 to 2017. Although the CDI is simply a statistical index that measures how much present conditions deviate from the reference level, CDI applicability to monitoring and its correlation with sector impacts is much better than for any single drought indicator. Generated CDI maps also provide better interpolation for national and local drought characteristics in terms of severity, amplitude, and duration, and, as such, the CDI can clearly trace the footprints of droughts in Jordan. However, the relative weights of the PDI, TDI, and VDI may require further assessments through sensitivity analyses for improved sector-based responses (specific crop yields, groundwater recharge, etc.). The use of timescale CDI also enables the potential use of indicators for detailed short duration investigations for the development of an early warning system or long-term forecasting for adaptation planning and capacity building. Keywords: Drought index, precipitation, temperature, vegetation, combined index, Jordan.