This study focuses on understanding and quantifying uncertainties in simulating river discharge in the Upper Indus Basin (UIB) of the Western Himalayas using a macro-scale semi-distributed hydrology model forced with multiple observed precipitation datasets and reanalysis products of near-surface wind-speed, maximum and minimum temperature during 2010–2012. We performed a suite of numerical simulations using a high-resolution setup of the variable infiltration capacity (VIC) hydrology model for the UIB. This model takes into account the balance of both water and surface energy budgets within each grid cell and incorporates sub-grid variability of topography to represent the effects of orographic precipitation and temperature lapse rate essential for hydrological modelling in the complex Himalayan terrain. While river discharges over non-mountainous basins are known to be generally sensitive to precipitation variations, it is noted that both precipitation and snowmelt processes critically influence seasonal river discharge in the UIB during the northern summer through surface temperature and wind-speed variations. Our study found that a marginal difference in temperature forcing can create large difference in snowmelt over UIB during summer season, which in turn increases the uncertainty in the summer monsoon river discharge. This analysis highlights the equally important need for the incorporation of realistic temperature data as that of precipitation product for the better simulation of land surface processes during various seasons, especially during summer, over snow covered UIB. Further analysis of daily simulations of the VIC model during 2010–2012 indicates that low and medium intensity river discharges tend to be associated with relatively lower spread among the ensemble members, as compared to the high intensity discharges which exhibit large ensemble spread. In particular, we noted a large increase in the spread of high flow simulations over the UIB during the flood episodes in the summer of 2010, arising from uncertainties in the precipitation forcing across multiple datasets. Our results emphasize the need for improved representation of precipitation and hydrological processes over the Himalayan region in weather and climate models for better management of water resources and flood forecasting in the UIB region under a changing climate.

中文翻译：

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喜马拉雅西部印度河上游流域模拟的不确定性

这项研究的重点是使用宏观半分布式水文模型，结合多个观测到的降水数据集和近地表风速的重新分析产物，来理解和量化喜马拉雅西部上印度河盆地（UIB）的河流流量模拟中的不确定性。 ，2010-2012年期间的最高和最低温度。我们使用UIB的可变渗透能力（VIC）水文模型的高分辨率设置执行了一组数值模拟。该模型考虑了每个网格单元内水和地面能量收支的平衡，并结合了地形的子网格变异性，以表示地形降水和温度下降速率的影响，这对于复杂的喜马拉雅地形的水文建模至关重要。虽然众所周知，非山区流域的河流流量通常对降水变化敏感，但应注意的是，降水和融雪过程均会通过地表温度和风速变化严重影响北部夏季UIB的季节性河流流量。我们的研究发现，在夏季，温度强迫的边际差异会在UIB上造成很大的融雪差异，这反过来又增加了夏季季风河流量的不确定性。该分析强调了与降雨产品同样重要的实际温度数据的并入需求，以便更好地模拟各个季节（尤其是夏季）积雪覆盖的UIB的地表过程。对2010-2012年期间VIC模型的日常模拟的进一步分析表明，与表现出较大的总体分布的高强度流量相比，低强度和中等强度的河流流量往往与整体成员之间的相对较低扩散相关。特别是，我们注意到，由于多个数据集降水强迫的不确定性，2010年夏季洪水期间高流量模拟在UIB上的传播大大增加。我们的结果强调，有必要在天气和气候模型中更好地表示喜马拉雅地区的降水和水文过程，以便在气候变化的情况下更好地管理UIB地区的水资源和洪水预报。