Abstract
Abstract. Increasing urbanization makes it more and more important to have accurate stormwater runoff predictions, especially with potentially severe weather and climatic changes on the horizon. Such stormwater predictions in turn require reliable rainfall information. Especially for urban centres, the problem is that the spatial and temporal resolution of rainfall observations should be substantially higher than commonly provided by weather services with their standard rainfall monitoring networks. Commercial microwave links (CMLs) are non-traditional sensors, which have been proposed about a decade ago as a promising solution. CMLs are line-of-sight radio connections widely used by operators of mobile telecommunication networks. They are typically very dense in urban areas and can provide path-integrated rainfall observations at sub-minute resolution. Unfortunately, quantitative precipitation estimates (QPEs) from CMLs are often highly biased due to several epistemic uncertainties, which significantly limit their usability. In this manuscript we therefore suggest a novel method to reduce this bias by adjusting QPEs to existing rain gauges. The method has been specifically designed to produce reliable results even with comparably distant rain gauges or cumulative observations. This eliminates the need to install reference gauges and makes it possible to work with existing information. First, the method is tested on data from a dedicated experiment, where a CML has been specifically set up for rainfall monitoring experiments, as well as operational CMLs from an existing cellular network. Second, we assess the performance for several experimental layouts of ground truth from rain gauges (RGs) with different spatial and temporal resolutions. The results suggest that CMLs adjusted by RGs with a temporal aggregation of up to 1 h (i) provide precise high-resolution QPEs (relative error < 7 %, Nash–Sutcliffe efficiency coefficient > 0.75) and (ii) that the combination of both sensor types clearly outperforms each individual monitoring system. Unfortunately, adjusting CML observations to RGs with longer aggregation intervals of up to 24 h has drawbacks. Although it substantially reduces bias, it unfavourably smoothes out rainfall peaks of high intensities, which is undesirable for stormwater management. A similar, but less severe, effect occurs due to spatial averaging when CMLs are adjusted to remote RGs. Nevertheless, even here, adjusted CMLs perform better than RGs alone. Furthermore, we provide first evidence that the joint use of multiple CMLs together with RGs also reduces bias in their QPEs. In summary, we believe that our adjustment method has great potential to improve the space–time resolution of current urban rainfall monitoring networks. Nevertheless, future work should aim to better understand the reason for the observed systematic error in QPEs from CMLs.
Highlights
Water-related issues are one of the major challenges of modern cities
We only find a slight underestimation of high intense peaks (Fig. 3), which might be due to mismatch between point and path-averaged observations
Quantitative precipitation estimates (QPEs) from Commercial microwave links (CMLs) as rainfall sensors are, affected by various uncertainties, which are still too poorly understood to build effective signalprocessing algorithms based on CML observations alone
Summary
Water-related issues are one of the major challenges of modern cities. More than 54 % of the world’s population lives in urban areas and the number is continuously growing (United Nations, 2014). Increasing urbanization, together with undergoing weather and climatic changes, stresses the importance of efficient urban water management for preventing flooding and at the same time controlling pollution and ensuring sanitation. Rainfall is the main driver for many urban hydrological processes. Reliable rainfall observations are crucial to informed decision making. Rainfall is very variable in both time and space, which makes it challenging to observe reliably. This is especially true for rainfall monitoring for urban stormwater management. Urban catchments usually consist of many small subcatchments with diverse land use characteristics
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