Congo Basin Hydrology, Climate, and Biogeochemistry. Группа авторов

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Congo Basin Hydrology, Climate, and Biogeochemistry - Группа авторов


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series of GRACE‐derived TWS and model‐derived SWS during the 2002–2017 period. Spatial distribution of trends in TWS obtained from three GRACE solutions (including TWS solutions that have been smoothen with a 150 km Gaussian filter) are generally consistent (Figure 5.3a–f). The distribution of positive trends in TWS in the basin is weak unlike the surrounding regions (East and South Africa), where considerable rise in TWS is observed (Figure 5.3a–c). The negative trends around the Cuvette centrale and northern section of the basin could result in a possible unfavourable hydro‐climatology of the Congo Basin if the trends persist (Figure 5.3a–f). The root mean square error (RMSE) values summarizing the monthly errors (68% confidence level) in the aerial averaged time series are 23.70 mm, 22.84 mm, and 26.00 mm for CSR, GSFC, and JPL, respectively (Figure 5.4). The linear rates over during the period (April 2002 to June 2017) were estimated using weighted least‐squares method (including their uncertainties). These linear rates show mass changes of approximately 0.33 ± 0.94 mm/yr (CSR), 0.73 ± 0.95 mm/yr (GSFC), and 1.95 ± 0.93 mm/yr (JPL) but they are statistically insignificant (Figure 5.4a–c). Overall, the temporal variations of TWS and their corresponding RMSEs observed over the Congo suggest low uncertainties amongst products. From the averaged TWS time series for the Congo Basin (Figure 5.4), the three mascon solutions depict the same overall seasonality while the error bars represent the monthly uncertainties of TWS and was estimated following Scanlon et al. (2016). First, the residual series were considered as the difference between the observed TWS series and the best fit considering constant, trend, annual, and semi‐annual terms. Secondly, the residual series from the previous step were smoothed using a 13‐month moving average, which was considered as the monthly errors for the GRACE series. The RMSE of the smoothed residual series is approximately 23.70 mm, 22.84 mm, and 26.00 mm for CSR, GSFC, and JPL, respectively. This suggests the GSFC GRACE product is relatively better over the Congo basin. The time temporal patterns summarizing the overall mass changes within the Congo Basin are indicated in Figure 5.4a–c and show a slight rise between 2012 and 2016, though not significant.

Schematic illustration of spatial distribution of trends in GRACE-derived TWS (2002–2017) over the Congo basin. Schematic illustration of aerial averaged temporal series of TWS (2002–2017) estimated from three different GRACE mascon products. Gaps in the time series are periods with missing data. Schematic illustration of leading modes of TWS (2002–2017) over the Congo basin. Averaged spatial patterns (a, c, and e) corresponds to the temporal series (b, d, and f).

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