High-resolution rainfall maps from commercial microwave links for a data-scarce region in West Africa

Abstract

We present high-resolution rainfall maps from commercial microwave link (CML) data in the city of Ouagadougou, Burkina Faso. Rainfall was quantified based on data from 100 CMLs along unique paths and interpolated to achieve rainfall maps with a 5-minute temporal and 0.55km spatial resolution for the monsoon season of 2020. Established processing methods were combined with newly developed filtering methods, minimizing the loss of data availability. The rainfall maps were analyzed qualitatively both at a five-minute and aggregated daily scale. We observed high spatio-temporal variability on the five-minute scale which cannot be captured with any existing measurement infrastructure in West Africa. For the quantitative evaluation only one rain gauge with a daily resolution was available. Comparing the gauge data with the corresponding CML rainfall map pixel showed a high agreement with a Pearson correlation coefficient of over 0.95 and an underestimation of the CML rainfall maps of around ten percent. Because the CMLs closest to the gauge have the largest influence on the map pixel at the gauge location, we thinned out the CML network around the rain gauge synthetically in several steps and repeated the interpolation. The performance of these rainfall maps dropped only when a radius of 5 km was reached and around half of all CMLs were removed. We further compared ERA5 and GPM-IMERG data to the rain gauge and found that they show much lower correlation than data from the CML rainfall maps. This clearly highlights the large benefit that CML data can provide in the data scarce but densely populated African cities.