Reply on EC1

Benjamin Kitambo

doi:10.5194/hess-2021-315-ac3

Abstract

The Congo River Basin (CRB) is the second largest river system in the world, but its hydroclimatic characteristics remain relatively poorly known. Here, we jointly analyze a large record of in situ and satellite-derived observations, including long term time series of Surface Water Height (SWH) from radar altimetry (a total of 2,311 virtual stations) and surface water extent (SWE) from a multi-satellite technique to better characterize CRB surface hydrology and its variability. Firstly, we show that SWH from radar altimetry multi-missions agree well with in situ water stage at various locations, with root mean square deviation varying from 10 cm (with Sentinel-3A) to 75 cm (with European Remote Sensing-2). SWE from multi-satellite observations also shows a good behavior over a ~25-year period against in situ observations from sub-basin to basin scale. Both datasets help to better characterize the large spatial and temporal variability of hydrological patterns across the basin, with SWH exhibiting annual amplitude of more than 5 m in the northern sub-basins while Congo main-stream and Cuvette Centrale tributaries vary in smaller proportions (1.5 m to 4.5 m). Furthermore, SWH and SWE help better illustrate the spatial distribution and different timings of the CRB annual flood dynamic and how each sub-basin and tributary contribute to the hydrological regime at the outlet of the basin (the Brazzaville/Kinshasa station), including its peculiar bi-modal pattern. Across the basin, we jointly use SWH and SWE to estimate time lag and water travel time to reach the Brazzaville/Kinshasa station, ranging from 0–1 month in its vicinity downstream the basin up to 3 months in remote areas and small tributaries. Northern sub-basins and the central Congo region highly contribute to the large peak in December–January while the southern part of the basin supplies water to both hydrological peaks, in particular to the moderate one in April–May. The results are supported using in situ observations at various locations in the basin. Our results contribute to a better characterization of the hydrological variability in the CRB and represent an unprecedented source of information for hydrological modeling and to study hydrological processes over the region.

Highlights

The Congo River Basin (CRB) is located in the equatorial region of Africa (Fig. 1)
In order to evaluate the performance of the different satellite missions, we choose the nearest virtual station (VS) located in the direct vicinity of the different gauges
Similar results in CRB were found by Paris et al (2020) where the comparisons were done at seasonal time scale with few tens of centimetersof standard error

Summary

Introduction

The Congo River Basin (CRB) is located in the equatorial region of Africa (Fig. 1). It is the second largest river system in the world, both in terms of drainage area and discharge. Increasing evidences suggest that change s in land use practices such as large scale mining, deforestation, pose significant threat to the basin water resources availability, including hydrological, ecological, and geomorphological processes in the basin (Bele et al, 2010; Ingram et al, 2011; Nogherotto et al, 2013; Tshimanga and Hughes, 2012; Plisnier et al, 2018). Thereis still insufficient knowledge of CRB hydro-climatic characteristics and processes and their spatial-temporal variability This is sustained by the lack of comprehensive and maintained in situ data networks that keep the basin poorly monitored at 70 large scale, limiting our understanding of the major factors controlling freshwater dynamics at proper space and time scales. Their findings have highlighted the important regulatory function of the Cuvette Centrale which receives contributions from the upstream Congo River (33 %), 115 effective precipitation inside the Cuvette Centrale (31 %), and other tributaries (36 %)

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