Wireless Sensor Network (WSN) is one of the Internet-of-Things (IoT) paradigms which provide monitoring services for natural disasters such as volcanoes eruption and earthquake which can affect the life of human being. As such, the Quality-of-Service (QoS) of the underlying applications is of important issue in order to ensure its effectiveness and robustness. Besides its undoubtedly services and contributions in monitoring systems, WSN's limited resources can severely degrade the QoS in IoT applications. Congestion in WSN will further reduce the expected QoS of the associated applications. In this case, efficient used of the scarce resources is important to ensure seamless data transmission. The power consumption of a sensor node can be reduced by reducing the rate of packet retransmission which is caused by congestion. In this paper, a selective packet discarding method which is known as Packet Discarding based Node Clustering (PDNC) is introduced. All nodes deployed in the targeted area will be clustered into several groups and a cluster head will be selected at a time. The packet discarding process will then be carried at each node to reduce the number of packets contributing to congestion. Simulation analysis using NS-2 shows that the proposed technique is able to reduce congestion thus improve the overall performance.