Abstract
Most areas around the world lack fine rainfall records which are needed to derive Intensity-Duration-Frequency (IDF) curves, and those that are available are in the form of daily data. Thus, the disaggregation of rainfall data from coarse to fine temporal resolution may offer a solution to that problem. Most of the previous studies have adopted only historical rainfall data as the predictor to disaggregate daily rainfall data to hourly resolution, while only a few studies have adopted other historical climate variables besides rainfall for such a purpose. Therefore, this study adopts and assesses the performance of two methods of rainfall disaggregation one uses for historical temperature and rainfall variables while the other uses only historical rainfall data for disaggregation. The two methods are applied to disaggregate the current observed and projected modeled daily rainfall data to an hourly scale for a small urban area in the United Kingdom. Then, the IDF curves for the current and future climates are derived for each case of disaggregation and compared. After which, the uncertainties associated with the difference between the two cases are assessed. The constructed IDF curves (for the two cases of disaggregation) agree in the sense that they both show that there is a big difference between the current and future climates for all durations and frequencies. However, the uncertainty related to the difference between the results of the constructed IDF curves (for the two cases of disaggregation) for each climate is considerable, especially for short durations and long return periods. In addition, the projected and current rainfall values based on disaggregation case which adopts historical temperature and rainfall variables were higher than the corresponding projections and current values based on only rainfall data for the disaggregation.
Highlights
Intensity-Duration-Frequency (IDF) curves indicate maximum rainfall events for certain frequencies and durations and this information is crucial for the flood analysis step in designing hydrosystems
There is an urgent need to (1) check whether the current IDF curves used in the design of urban stormwater collection systems are still appropriate in terms of their level accuracy and uncertainty in light of the impact of climate change and (2) consider future projections based on sub-daily rainfall durations for the design of these curves
The first example was a climate ensemble member for the year 2074 and a daily rainfall value of 49.91 mm. When this daily rainfall value was disaggregated to an hourly scale by using the two cases of rainfall disaggregation, case 1 gave a rainfall temporal pattern with a peak of 25.1 mm and case 2 gave a temporal pattern with a peak of 13.6 mm. (It is worth noting that the peaks in this example and the rest of the examples were the annual maximum (AM) values for the duration of 1 h since the concentration time was found to be 1 h)
Summary
Intensity-Duration-Frequency (IDF) curves indicate maximum rainfall events for certain frequencies and durations and this information is crucial for the flood analysis step in designing hydrosystems. According to the Intergovernmental Panel on Climate Change (IPCC) [9], the return period for annual maximum (AM) precipitation will decrease significantly by the end of the 21st century, extreme rainfall events will occur more frequently, and the risk of flooding will increase [10]. Action needs to be taken to ensure that stormwater collection systems for urban areas can accommodate these anticipated changes in extreme rainfall events [11]. There is an urgent need to (1) check whether the current IDF curves used in the design of urban stormwater collection systems are still appropriate in terms of their level accuracy and uncertainty in light of the impact of climate change and (2) consider future projections based on sub-daily rainfall durations (hourly or sub-hourly) for the design of these curves
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