Modeling Daily Floods in the Lancang‐Mekong River Basin Using an Improved Hydrological‐Hydrodynamic Model

Abstract

Daily floods including event, characteristic, extreme and inundation in the Lancang‐Mekong River Basin (LMRB), crucial for flood projection and forecasting, have not been adequately modeled. An improved hydrological‐hydrodynamic model (VIC and CaMa‐Flood) considering regional parameterization was developed to simulate the flood dynamics over the basin from 1967 to 2015. The flood elements were extracted from daily time series and evaluated at both local and regional scales using the data collected from in‐situ observations and remote sensing. The results show that the daily discharge and water level are both well simulated at selected stations with relative error (RE) less than 10% and Nash‐Sutcliffe efficiency coefficient (NSE) over 0.90. Half of the flood events have NSE exceeding 0.76. The peak time and flood volume are well reproduced while both peak discharge and water level are slightly underestimated. The results tend to worsen when the characteristics of flood events are extended to annual extremes. These extremes are generally underestimated with NSE less than 0.5 but RE is within 20%. The simulated rainy season inundation area generally agrees with observations from remote sensing, with about 86.8% inundation occurrence frequency captured within the model capacity. Ignoring the regional parameterization and reservoir regulation can both deteriorate flood simulation performance at the local scale, resulting in lower NSE. Specifically, systematically higher water levels and up to 27% overestimation of peak discharge are found when ignoring regional parameterization, while ignoring reservoir regulation would cause up to 23% overestimation for flood extremes. It is expected that these findings would contribute to the regional flood forecasting and flood management.

Changes in China's Snow Droughts Characteristics From 1993 to 2019

“…Due to strong seasonal characteristics, changes in snow droughts are likely to impact the downstream runoff and water usage. Especially in spring, the runoff of the Brahmaputra, and Lancang–Mekong Rivers around the QTP is strongly mediated by the meltwater of the snowpack upstream, although snowmelt runoff only represents a relatively lower fraction than that of rainfall‐runoff over the total runoff (Irannezhad & Liu, 2022; Liu et al., 2021; Wang et al., 2021). Considering the continuous changes in drought characteristics, policymakers must develop different adaptation strategies and manage water resources in the spring to mitigate the drought and agricultural risks associated with the changing snowpacks (Huning & AghaKouchak, 2020).…”

Quantitative assessment of the impacts of climate and human activities on streamflow of the Lancang-Mekong river over the recent decades

“…Although this study provides a quantitative evaluation of the impacts of climatic variation and human activities on streamflow changes in the integrated form in LMRB, some shortcomings remain. While this study took the effects of climate, topography, soil, vegetation, and other spatial-temporal variability on streamflow into consideration, the parameter values, sensitivity, and scale effects of those factors on streamflow process were not systematically investigated and further detailed studied are required (Ahn and Merwade, 2014;Gao et al, 2020;Andaryani et al, 2021;Wang et al, 2021).…”

Future Change Projections of Extreme Floods at Catchment Scale and Hydrodynamic Response of Its Downstream Lake Based on Catchment‐Waterbody Relationship Simulation

“…The changes in the intensity and frequency of the extreme precipitation due to climate change (Hanel & Buishand, 2010; Kendon et al., 2014) can strongly influence catchment hydrological processes and result in increasing flood risk for the low‐lying areas (Jahn, 2015; Monier & Gao, 2015). For example, the large‐scale heavy precipitation in the summer of 2020 induced massive floods over the central and eastern China, which threatened the lives of over 63 million people and caused a direct economic loss of 179 billion RMB (Wang, Yun, et al., 2021). Even the countries with mature infrastructure systems, such as the United States (Afshari et al., 2018; Zhou et al., 2017) and Germany (in den Baumen et al., 2015), may suffer from severe losses from large‐scale flood inundation.…”

“…Hoch et al (2019) enhanced the accuracy of the peak discharge simulations through a globally applicable framework for integrated hydrologic-hydrodynamic modeling (PCR-GLOBWB, CaMa-Flood, and LISFLOOD-FP). Wang, Yun, et al (2021) simulated the daily flood dynamics of the Mekong River Basin using a coupled hydrological-hydrodynamic model (VIC and CaMa-Flood), with a relative error of less than 20% and Nash-Sutcliffe efficiency over 0.90 at their selected stations. Nonetheless, it is still difficult to simulate the complicated nonlinear response of flood regimes to extreme precipitation using the widely adopted catchment hydrological models (e.g., SWAT, VIC), especially in the human-disturbed catchments including agricultural irrigations and dam regulations (Borah & Bera, 2004;Brunner et al, 2021;Zhang, Shao, Ye, et al, 2016).…”