The choice of the baseline period, intentionally chosen or not, as a reference for assessing future changes of any projected variable can play an important role for the resulting statement. In regional climate impact studies, well-established or arbitrarily chosen baselines are often used without being questioned. Here we investigated the effects of different baseline periods on the interpretation of discharge simulations from eight river basins in the period 1960–2099. The simulations were forced by four bias-adjusted and downscaled Global Climate Modelsunder two radiative forcing scenarios (RCP 2.6 and RCP 8.5). To systematically evaluate how far the choice of different baselines impacts the simulation results, we developed a similarity index that compares two time series of projected changes. The results show that 25% of the analyzed simulations are sensitive to the choice of the baseline period under RCP 2.6 and 32% under RCP 8.5. In extreme cases, change signals of two time series show opposite trends. This has serious consequences for key messages drawn from a basin-scale climate impact study. To address this problem, an algorithm was developed to identify flexible baseline periods for each simulation individually, which better represent the statistical properties of a given historical period.

中文翻译：

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一次模拟，不同的结论 - 基线期有所不同！

基准期的选择，无论有意选择与否，作为评估任何预测变量未来变化的参考，都可以对结果报表发挥重要作用。在区域气候影响研究中，经常使用既定的或任意选择的基线，而不会受到质疑。在这里，我们调查了不同基线期对 1960 年至 2099 年期间八个流域的排放模拟的解释的影响。在两种辐射强迫情景（RCP 2.6 和 RCP 8.5）下，模拟是由四个经过偏差调整和缩小规模的全球气候模型强制进行的。为了系统地评估不同基线的选择对模拟结果的影响程度，我们开发了一个相似性指数，用于比较两个预测变化的时间序列。结果表明，25% 的分析模拟对 RCP 2.6 下的基线期选择敏感，RCP 8.5 下的 32% 对基线期的选择敏感。在极端情况下，两个时间序列的变化信号呈现相反的趋势。这对从流域尺度气候影响研究中得出的关键信息产生了严重的影响。为了解决这个问题，开发了一种算法来单独识别每个模拟的灵活基线期，这更好地代表了给定历史时期的统计特性。