Monitoring and Assessment of Global Patterns of Subnational droughts using Combined Drought Indicator and Geocoded Disaster Dataset

Agro-climatological droughts have been a dominant driver of various socio-economical losses. However, the association between drought hazards & their socio-economic impacts is still less explored on a global scale. The objective of this study is to understand this linkage by globally analyzing drought hazards and their socio-economic impacts during 2001-2021.

To monitor the agro-climatological drought hazard, we have developed a new combined drought indicator (CDI) integrating satellite and reanalysis model-based four input variables (i.e., precipitation- CHIRPS data, temperature, and soil moisture – ERA5-Land data, normalized difference vegetation index – MODIS data). In CDI, the Principal Component Analysis was applied to combine all the variables. To examine the socio-economic impacts of drought hazard, we used the Geocoded Disaster (GDIS) dataset, which provided the location information of subnational-level drought events. Since GDIS shows the actual impact of drought events on socio-economic conditions, the drought vulnerability at a sub-national level can be quantified by performing a comparative analysis between CDI and GDIS.

Based on CDI, the maximum frequency of severe drought events (> 7) is observed over sub-Saharan Africa, followed by parts of south Asia. During these events, the CDI values ranged between -1.5 to -3, signifying the critical hydrometeorological conditions in the respective region. The comparative analysis shows that the CDI-based drought clusters can represent the GDIS drought events at a statistically significant level. Both CDI and GDIS methods noticed that the parts of Argentina, Brazil, the horn of Africa, western India, and north China are continuously under the grips of severe droughts. In these regions, even less severe agro-climatological (CDI) droughts have caused substantial socio-economical (GDIS) losses making these areas highly vulnerable to drought. In contrast, the outcomes of CDI also indicated extreme drought cases over parts of North America and Europe, but these events were inconsistent with GDIS, meaning that developed countries are less vulnerable to drought.

This study highlighted the importance of GDIS data for accurate drought impact assessment at the subnational level and in validating CDI. The proven subnational level association between CDI and GDIS from this study could help to identify the socio-economically vulnerable areas to drought on a finer scale and priorities the regions that demand more concern.