A simple formula for estimating approximate values of return levels for sub-daily rainfall is presented and tested. It was derived from a combination of simple mathematical principles, approximations and fitted to 10 year return levels taken from intensity-duration-frequency (IDF) curves representing 14 sites in Oslo. The formula was subsequently evaluated against IDF curves from independent sites elsewhere in Norway. Since it only needs 24 h rain gauge data as input, it can provide approximate estimates for the IDF curves used to describe sub-daily rainfall return levels. In this respect, it can be considered as means of downscaling with respect to timescale, given an approximate power-law dependency between temporal scales. One clear benefit with this framework is that observational data is far more abundant for 24 h rain gauge records than for sub-daily measurements. Furthermore, it does not assume stationarity, and is well-suited for projecting IDF curves for a future climate.

提出并测试了一个简单的公式，用于估算次日降雨的返回水平的近似值。它是由简单的数学原理，近似值结合而成，并根据代表奥斯陆14个地点的强度-持续时间-频率（IDF）曲线得出的10年回报水平进行拟合。随后根据挪威其他地方独立站点的IDF曲线对该公式进行了评估。由于它仅需要24小时雨量计数据作为输入，因此它可以为用于描述次日雨量返回水平的IDF曲线提供近似估计。在这方面，考虑到时间尺度之间的近似幂律相关性，可以将其视为相对于时间尺度缩减的手段。该框架的一个明显好处是，24小时雨量计记录的观测数据比次日测量的观测数据丰富得多。此外，它不具有平稳性，非常适合预测未来气候的IDF曲线。