Tropical cyclone-induced water and suspended sediment discharge delivered by mountainous rivers into the Beibu Gulf, South China

Small mountainous rivers can deliver considerable freshwater discharge and suspended sediment discharge (SSD) to the ocean during tropical cyclones (TCs), and this has received special attention worldwide. However, little information is available on how TCs impact variations in water discharge and SSD delivered by mountainous rivers into the ocean. Here, based on the daily water discharge and SSD at the gauging stations of the tidal limit in July and August from 1965 to 2017, the Qin River (QR) and Nanliu River (NR), 2 small mountainous rivers located in the north of the Beibu Gulf, South China, were selected to quantify variations in water discharge and SSD into the Beibu Gulf during the TC period. The main results show that the net TC-induced water discharges in the QR and NR during July and August are larger than those of non-TC days, respectively. The net SSD increases in the QR and NR induced by TCs are far larger than those of normal days, respectively. Meanwhile, the water discharge and SSD in the flood season can be dominated by TC-associated rainfall, but the impacts on water discharge and SSD are influenced by the TC characteristics and basin environment. Moreover, it is found that in these 2 mountainous rivers, high water discharge delivers high SSD, but extremely high water discharge caused by TCs fails to produce extremely high SSD. It is expected that TCs will produce great impacts on SSD and water discharge of the mountainous rivers in South China behind global climatic change with increasing TCs events.