# Metaheuristics in the Humanitarian Supply Chain
## 2 Humanitarian Supply Chain  
To understand what an HSC is, different definitions can be considered: [PERSON] (1971) first introduced the concept of humanitarian logistics. He proposed that \"humanitarian logistics refers to the process and system of mobilizing human resources, skills and knowledge to help vulnerable groups affected by natural disasters and complex emergencies\". [PERSON] (1971) describes emergency logistics as a process of planning, managing and controlling the efficient flows of relief, information and services from the origin to destination to meet the urgent needs of affected people under emergency conditions. [PERSON] [13] defines a disaster as a disruption that affects a system and its objectives, and considers that the priorities of an HSC are (i) to be a bridge between disaster preparation and response, (ii) in which effectiveness is crucial as well as speed of response in health, food and water distribution, shelter and sanitation; and (iii) it is the most expensive of humanitarian aid efforts. [PERSON] et al. [5] claim that the HCS is \"the process of evacuating people from disaster-stricken areas to safe places and planning, implementing and controlling the efficient, cost-effective flow of goods, meanwhile collecting related information from the point of supply to the point of consumption for the purpose of alleviating the sufferings of vulnerable people\".  
Among the HCS's attributes, it is noted that these kinds of supply chains are clearly unpredictable, turbulent and require flexibility, as well as that they are highly dynamic, innovative and agile [13; 14; 15]; sometimes HSCs are slow to respond to the needs of affected people [16]. In principle, locations are often unknown until demand occurs, short lead times drastically affect inventory availability, sourcing and distribution, and it works with very little real-time information. Consequently, making decisions is more complex than in commercial supply chains [15]. In addition to this, HSCs have uncertainty about the scope of the disaster, the number of victims and the number of urgent needs for rescue items [10].  
There are different classifications of the supply chain. To begin with, for their attributes in logistics, such as [PERSON] et al. [17] who classify it into four groups: Configuration of the epidemic logistics network, collection of medical supplies, triage operations and other approaches; more generally according to the types of problems that are solved: Facility location and distribution model [4; 5; 8] and other types of problems are added such as inventory [4] and mass evacuation [5; 9].  
[PERSON] and [PERSON] [15] mention that the central role in logistics responds to whether disasters are natural or man made. In the United States comprehensive emergency management is commonly described in terms of four programmatic phases: Mitigation, preparedness, response and recovery [5; 18]. It can also be classified as pre-disaster, post-disaster [5] and the period of the disaster management system. The pre-disaster phase covers the mitigation and preparedness phase; mitigation includes the steps to reduce vulnerability to disaster impact; the response phase addresses immediate threats to minimize economic and human losses, while the recovery phase supports the restoration of all the damage caused by the disaster [5; 8]. In Figure 3 the classification of the HSC is shown.  
Figure 3: HSC Classification.  
It is also possible to classify them according to the formulation of the problem in integer and mixed, linear and nonlinear, deterministic and stochastic programming, by the objective function in single or multiple [4; 5; 9; 10]. They can also be categorized according to their solution method in exact, heuristic and metaheuristic methods [8], this classification is shown in Figure 4. Since this focuses mainly on metaheuristics, the following section defines their leading characteristics and methods.