Multi-model analysis of historical runoff changes in the Lancang-Mekong River Basin-Characteristics and uncertainties

Runoff changes are critical to the sustainable water resource in the Lancang-Mekong River Basin (LMRB). Changes in the LMRB's runoff over the past decades are unclear because of inadequate streamflow observations. The advancement of global hydrological models (GHMs) has facilitated the understanding of runoff change worldwide. However, it is required to evaluate the performance of GHMs in simulating historical runoff change in the LMRB before assessing the runoff changes. This study aims to conduct a multi-model analysis of temporal -spatial changes in runoff in the LMRB for 1971-2010 using ten GHMs from the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP) and evaluate the corresponding uncertainties among models. Results show that the model ensemble mean has the best performance than the individuals when compared with the reference data. Based on the model ensemble mean, large spatial heterogeneity of runoff is found in the LMRB, with an overall slightly positive trend (8.03%). Besides, the models perform better in estimating the trends of high flow than low flow. As to the trend of runoff in the wet and dry seasons, about 32% (70%) of the basin became drier (wetter) in the dry (wet) season. Meanwhile, 17% of the basin has experienced a trend of drier dry seasons and wetter wet seasons. Overall, our results highlight the uncertainty of the runoff changes in the LMRB in the low flow simulation, particularly requiring more attention in future model improvement. The complex change patterns of the runoff suggest the importance of accurate runoff observations and projections for better water management.