Socio-Hydrologic Modeling of the Dynamics of Cooperation in the Transboundary 1 Lancang-Mekong River 2 3

Abstract. The transboundary Lancang-Mekong River Basin has experienced dynamics of cooperation over the past several decades, which is a common emergent response in transboundary human-water systems. Downstream countries rely on Mekong River for fisheries, agriculture, etc., while upstream countries have been constructing dams to generate hydropower. The dam construction and operation in upstream countries have changed the seasonality of streamflow in downstream countries, affecting their economic benefits. More recently, cooperation between upstream and downstream countries has been enhanced throughout the river basin. In this study, we introduce a quantitative socio-hydrological model to simulate hydrological processes, reservoir operations, economic benefits, policy feedbacks and therefore dynamics of cooperation within the Lancang-Mekong River basin. The model reproduces the observed dynamics of cooperation in the basin revealed by sentiment analysis of news articles. Hydrological variability such as droughts and human activities associated with reservoir operations affect dynamics of cooperation between the riparian countries, with importance attached to indirect political benefits of upstream playing an important role in the enhancement of cooperation. In this way, our study generated understanding of emergent cooperation dynamics in this transboundary river basin, and the socio-hydrological model used here provides a useful new framework to investigate and improve transboundary water management elsewhere.


Outcomes of sentiment analysis of newspaper articles are used to evaluate the modeled 277 cooperation demand. The calculation step length of the model is one month. Each of these 278 components of the model is discussed in detail in the following sections. 279

Hydrological simulation 280
We use the distributed hydrological model THREW to simulate natural runoff of mainstream 281 and tributaries without impacts of reservoir operations, i.e., Qn in Figure 3. The THREW model 282 has been applied to many river basins successfully, including rivers derived from mountainous 283 areas and consisting of snow and glacier melt, and large-scale basins (Tian et al., 2006;Tian et 284 al., 2008;Li et al., 2012;Mou et al., 2008). Based on the Representative Elementary Watershed 285 (REW) approach (Reggiani et al., 1998), the THREW model uses the REW as the sub-286 catchment unit for hydrological simulations (He et al., 2015). The main runoff generation 287 processes include surface runoff, groundwater flow, and snow and glacier melt. 288 In this study, we divide the Lancang-Mekong basin into 651 REWs on the basis of DEM data, 289 as shown in Figure 1. The precipitation data is retrieved from TRMM data of 1998-2018. The 290 https://doi.org/10.5194/hess-2020-388 Preprint. Discussion started: 10 August 2020 c Author(s) 2020. CC BY 4.0 License. runoff observations of 6 stations on the mainstream of the Lancang-Mekong river include data 296 of Jinghong (1998-2013), Chiang Saen (1998-2015), Luang Prabang (1998-2015), Nong Khai 297 (1998-2007, Nakhon Phanom (1998Phanom ( -2015 and Pakse (1998Pakse ( -2006. 298 The hydrological model is used to provide simulations of natural runoff without the impacts of 299 water withdrawal and reservoir operations. Therefore, we use the runoff data in the period 300 before large reservoir construction for parameter calibration, i.e., runoff data of the period of 301 Laos has aimed to be the "battery of Southeast Asia" (Stone, 2016) and has started hydroelectric 317 dam construction on the mainstream of the Mekong river in line with this ambition. Before that, 318 Laos constructed many dams on its tributaries, which also impact the streamflow regimes of 319 the Mekong River. According to MRC (2018), the expected live storage of reservoirs in Laos 320 will ultimately reach 24,257 MCM, accounting for 73% of the flows left for the four 321 downstream countries. For simplicity, we only consider the completed tributary reservoirs in 322 Laos. They are aggregated by one proxy reservoir in the upper reaches, including some 323 reservoir storages located in the relatively lower reaches in Laos (Li et al., 2019;WLE, 2018). 324 In the model, the proxy reservoir used is assumed to have live storage from 5,074 MCM in 325 2000 to 21,066 MCM in 2018, which was linear interpolated and represents continuous dam 326 construction in Laos. 327 Overall, these simplifications through lumping the effects of many reservoirs is deemed 328 reasonable for the purposes of this study, because three reservoirs (Xiaowan and Nuozhadu in 329 China and the aggregated Laos Reservoir) shown in Figure 4 capture most of the effects of 330 reservoirs within the entire river basin. As shown in Figure 4, the river system and its water 331 diversion configuration are also simplified, where T0, T1 to T6 indicate natural runoff of 332 upstream and tributaries, W4, W5, W6 are the water withdrawal for irrigation in Laos, Thailand, 333 Cambodia and Vietnam. For each node, runoff flowing to the next node is calculated by water 334 https://doi.org/10.5194/hess-2020-388 Preprint. Discussion started: 10 August 2020 c Author(s) 2020. CC BY 4.0 License.
where, QN3 is runoff flowing to Thailand from the upstream node, Laos, T5 is inflow from 337 tributaries in Thailand, W4 is irrigation withdrawal in Thailand, and QN4 is runoff flowing to 338 the downstream node, Cambodia. 339 For the operation of constructed dams, we consider two basic scenarios. The first scenario is 340 the self-interested scenario (non-cooperation scenario, abbreviated by NC), in which the 341 upstream countries, China and Laos, operate the dams considering only their own hydropower 342 benefits ℎ . 343 where, ph is the electricity price, is the monthly water release from the reservoir, Δh is 345 the water head difference between the upstream and downstream, which is related to the actual 346 storage , and η is hydropower generation efficiency. storage of t-1 period , −1 is less than these two values the reservoir will store water to reach 352 the amount; otherwise, the reservoir will release water. There are also constraints of minimum 353 ecological release flow to satisfy the requirements of ecosystem and navigation. Actual 354 water release under the self-interested scenario , is calculated using Equations (3) and (4). 355 The actual storage of next month , is calculated based on water balance equation. and that under the altruistic scenario , , we obtain the weighted average scenario (WA 365 scenario) and final actual water release by calculating their weighted average. 366 where 1 + 2 = 1 , and 2 is calculated using the cooperation equations while 1 is 368 calculated as the residual 1 − 2 , which will be introduced in section 3.4. It should be noted 369 that the calculated by equation (5)

Economic benefit calculation 374
In this study, we consider the hydropower benefits ℎ of China and Laos, and agriculture 375 benefits and fishery benefits of Thailand, Cambodia and Vietnam. The hydropower 376 benefits calculation of China and Laos were introduced in section 3.2. Here agriculture benefits 377 only include irrigated rice without consideration of rain-fed crop production. Agricultural 378 https://doi.org/10.5194/hess-2020-388 Preprint. Discussion started: 10 August 2020 c Author(s) 2020. CC BY 4.0 License.
where is a shape parameter ranging from 0 to 1, is the benefit of cooperation, and 447 is the benefit without cooperation. 448 Similarly, for upstream countries, if they choose not to cooperate, their benefit will be 449 hydropower generation benefits under self-interested scenario ℎ, and benefits from other 450 sectors. If they choose to cooperate, besides the hydropower benefits under the altruistic 451 scenario ℎ, and benefits of other sectors, the upstream country will also gain indirect 452 political benefits, which is related to the cooperation demands of downstream countries. Here 453 we assume that the political benefit is proportional to cooperation demand and a political 454 factor . If the upstream country values the political relations with downstream countries and 455 regards diplomatic benefits as important, as China has demonstrated in recent years, the value 456 of political factor will be higher. Therefore, the equation to calculate the actual cooperation 457 level for China is as described below, and the cooperation level for Laos should consider 458 agriculture benefits additionally. 459 We used the Lexis-Nexis database to extract relevant information in English newspapers in 478 Thailand (Weaver and Bimber, 2008), sorted the data manually and conducted sentiment 479 analysis. Although the English newspapers could omit some information when compared to 480 local language newspapers, they are important sources to analyze the dynamics of local public 481 opinions. Firstly, key words for search (e.g., Mekong, water, dam, etc.) and search limitations 482 (e.g., location of publisher) are set for this study, and data retrieval is conducted automatically. 483 Secondly, manual data sorting was used to remove duplicates and irrelevant news. Thirdly, the 484 sorted data was analyzed through coding to get the sentiment of each piece of news and 485 corrected manually. This method has been used widely to explore the perspectives towards