**3.1 Scope of DRS reverse logistics**

The outbreak of coronavirus disease (COVID-19) from the beginning of the year 2020 has once again emphasized the significant importance of relief supply chain management as the critical items used for personal protection, diagnosis, and clinical care are facing a severe global shortage. On March 3, 2020, the World Health Organization (WHO) has issued a call for industry and governments to increase manufacturing by 40% to meet rising global demand in response to the shortage of personal protective equipment endangering health workers worldwide. Such predicament that produces additional human sufferings forces the relief supply chains to expand their capabilities in preparedness and response. While satisfying the increasing beneficiary needs and wants that generated by highly influential but low frequent disasters and crises, humanitarian decision-makers should think the reverse flow of diverse relief materials in "green" terms to quality-efficiently and cost-effectively manage the relief inventories at least cost to the environment.

There are four classes of DRS items and wastes including the following. (1) Most of the fundamental living necessities, including food, drink, simple tool, and basic medicine stored for disaster rescue and relief purposes are consumable. Take the massively reserved food commodities as an example. The "food waste hierarchy" has been widely discussed in relevant food-management research [8, 9], which indicates that the reuse option for surplus food. (2) The post-disaster relief materials, including medical support, disinfection purpose equipment, and medicine, tent, and clothes, have a longer lifetime but the quality and market quality also deteriorate. (3) Capital items and equipment, including large pieces of machinery used for life-savings, high-value medical equipment, advanced communication equipment, and large electrical generators, are usually expensive in investment but risky in technological obsolescence with relatively low-frequent demand. (4) All types of waste generated in the rescue and relief operations bring harm to the environment as well as increases the overall operational costs, which should be controlled at a minimum level. **Table 1** summarizes the types of DRS reverse logistics.
