## 1 Introduction  
Across the world, there are more than 260 rivers and lakes shared by countries, and they account for 40% of the Earth's land surface and 60 percent of the global freshwater [1; 2]. Transboundary rivers play a critical role in economic development by supporting the income and livelihood of roughly two billion people globally [3]. In recent decades, a number of large dams, which are indicated as being higher than 15 m or storing over 3 mcm [4], have been constructed in transboundary regions, such as the Toktogul dam (Kyrgyzstan, Central Asia), the Adjarala dam (Togo and Benin, West Africa), Hwanggang dam (North Korea, East Asia), the Tipaimukh dam (India, South Asia), and the Lower Sesan II dam (Cambodia, Southeast Asia), etc., providing many benefits for the regions, such as the supply of drinking and irrigation water, the generation of electric power, and flood protection. However, these constructions have shown not only their positive impacts but also the potential to create major flood waves capable of causing damage when a dam fails [5]. Failure of a dam could have disastrous consequences in downstream regions and countries [6]. Because of their advantages and disadvantages, as well as their far-reaching and often irreversible social and environmental impacts, dams have become the subject of controversy and debate [4]. In addition, due to a wide range of existing water resource issues, it is not possible to find a one-size-fits-all approach to basin management in the transboundary regions [7]. These problems are incurred from the differences in political, social, economic, and ecological drivers. The lessons from past dam failures in transboundary regions have been rarely learned, but their serious consequences have been recorded. For instance, in July 2018, flooding due to water released by a collapsed dam in southeastern Laos ruined thousands of hectares of agricultural land in An Giang, Dong Thap, and Long An provinces (Vietnam). As a result, water levels in Mekong tributaries have been rising seven to ten centimeters a day, and 27 Laotians were killed and thousands of people were displaced [8]. In September 2009, North Korea released a massive amount of water from Hwanggang dam without warning, causing extreme floods in South Korea and the death of 6 people; an estimated 40,000,000 short tons of water was dumped during the flood, causing the water level at the border of Gyeonggi-do to jump from 2.3 m to 4.6 m [9]. Furthermore, the physical characteristics of catchments increasingly change due to human activity, meaning dam failure disasters that threaten life are set to increase [10]. Hence, the evaluation of dam impacts on the discharge in downstream regions, especially in case of dam failures, is vital to take necessary response actions. Recently, research topics related to modelling of catastrophic floods due to dam failure have become more attractive along with the explosion of large dam construction [11; 12], gaining more attention in water management in the transboundary regions [13]. Floods due to dam failure are generally significantly larger than natural floods because of unexpected high peak in a very short duration and presence of an extremely high velocity flow due to large quantities of water being suddenly released [14]. Additionally, the impact of large dam outflow may cause changes in downstream hydrology and geomorphology such as change in total flows, change in seasonal timing of flows, short-term fluctuations in flows, change in extreme high and low of flow, channel erosion and deposition, riverbed composition, etc. [15; 16; 17], leading to more difficulty in flood forecasting and protection. The precision modelling of dam failure can lead to the development of an appropriate emergency action plan to minimize the impact of flooding. However, the model setup is challenging due to lack of data sharing among the countries occupying the transboundary rivers [18]. In fact, the absence of information sharing among riparian countries has led to many tensions in the past [19].