Assessing two precipitation data sources at basins of special interest to hydropower production in Brazil

ABSTRACT Accurate estimates of precipitation amounts are necessary to evaluate river flows, assess water-related risks (floods and drought) and quantify water availability for a broad range of water uses, such as water supply, agriculture, navigation and energy production. Especially in the context of operations in the Brazilian electricity sector, where the electrical system is essentially hydrothermal and more than 65% of its production comes from hydroelectric generation, real-time observed precipitation plays a key role as a primary input for hydrological models and river flow forecasting. It is thus crucial to build knowledge on and quantify river basin precipitation and its uncertainties. In this paper, we evaluate two sources of real-time (or near real-time) precipitation data, the TRMM-MERGE dataset from the CPETC and the CPC dataset, distributed by NOAA. Our assessment is based on 41 river basins in South America and covers the period 1997-2017. We investigated differences for different time resolutions (daily, monthly and annual precipitation) and their impact on the simulation of streamflows. Substantial differences were found between the two data sources, which seem to be amplified in the second decade. A spatial trend was found towards higher TRMM-MERGE precipitation values than CPC values when moving from north and west in the study area. We also found evidence that differences in precipitation propagate to simulated flows, with large percent differences in precipitation resulting in even larger percent differences in streamflow.

摘要 精准的降水量估算，是评估河道径流量、研判涉水风险（洪涝与干旱）以及量化供水、农业、航运、能源生产等多类用水场景下水资源可获取量的必要前提。尤其在巴西电力行业运营场景中，该国电力系统以水火电混合架构为主，超65%的发电量来自水力发电，此时实时观测降水作为水文模型与河道径流量预报的核心输入要素，发挥着关键作用。因此，构建流域降水相关研究认知并量化其不确定性，具有重要意义。本文针对两类实时（或近实时）降水数据源开展评估：其一为来自CPETC的TRMM-MERGE数据集，其二为美国国家海洋和大气管理局（NOAA）发布的CPC数据集。本次评估以南美洲的41个流域为研究对象，时间覆盖1997年至2017年。我们分析了不同时间分辨率（日、月、年降水量）下两类数据的差异，及其对河道径流量模拟的影响。研究发现两类数据源间存在显著差异，且该差异在研究时段的第二个十年内呈现放大趋势。研究还揭示了空间分布特征：在研究区域内，从北部与西部向其余区域移动时，TRMM-MERGE的降水量估算值普遍高于CPC数据集。此外，我们发现降水数据的差异会传导至径流量模拟结果中，降水量的较大百分比差异会引发径流量百分比差异的进一步放大。