# Dynamic Relief Items Distribution Model with Sliding Time Window in the Post-Disaster Environment
## 2 Related Works
### Periodic Distribution Aspects in RID  
Another concern in the disaster distribution plan is \"how long the distribution should be operated\"? Studies have shown that the multi-period or periodic distribution models had a better impact on the disaster regions in comparison to single period distribution [40]. [PERSON] and [PERSON] [41] had applied dynamic distribution in terms of the static distribution of relief items in multiple time-periods. The multiple time-period distributionsraised another issue regarding the inclusion of the disaster information in the distribution plan for a future time-period. The forecasting approach has been applied as one of the ways to represent a dynamic condition where the information was anticipated with the change of time [42]. Estimation methods [5; 7; 8] have also been applied to approximate the relief demand based on the affected population in particular disaster regions. [PERSON] [43] applied a dynamic relief items distribution model by utilising an estimation method for the future time-period demand. However, in disaster environments, the distribution strategies are often far from the estimation or forecasting because of the complexities such as unpredictability and uncertainty associated with the next period. To deal with unpredictability and uncertainty in a disaster environment, the probabilistic risk factor has been analysed for prioritising distribution tasks considering the delay time crucial in defining priority [44]. A robust optimisation approach has been applied as one of the alternative methods to deal with the uncertainty and find feasible solutions for humanitarian relief operations [45]. In any RID model, if real-time updates have not been included in the distribution plan for multiple time periods, it may hinder the efficiency of the model [46; 47].  
By analysing different models and corresponding challenges, it has been noted that there is a need for a RID model that generates the dynamic relief items distribution schedules considering future information, the availability of vehicles and other resources, which is challenging. It has also been argued, in the literature, that the proper selection of resources, transportation fleet and vehicle routing routes are the key components in dynamic relief items distribution management. For effective dynamic modelling, the distribution model needs to be comprised of past information and available current information along with any future predictable or anticipated updates [48]. Additionally, for quick and efficient relief distribution, it has been important to prioritise the disaster regions based on victims' severity [49]. These studies have also highlighted that static models have been found to be less effective in disaster scenarios as these models have not been able to update the distribution task with the information update. From the analysis of the relief distribution models in different disaster environments (case studies) operated in different cities, it has also been discovered that there is a need for a dynamic optimised RID model to improve the distribution of relief items tasks in disaster environments, considering the management perspectives and more realistic relief operations. In the dynamic model, relief items distribution management should consider the changing conditions as a basic requirement for effective relief operations in disaster environments. In other words, dynamic relief items distribution is the key to having effective distribution operations in disaster environments as the information related to relief demand, available resources and travel routes change with time.