A numerical modelling study of the hydroclimatology of the Niger River Basin, West Africa

Figures & data

Figure 1. Model domain and topography used in this study. The regions designated as Guinea, Savanna and Sahel over West Africa are indicated. The Niger River Basin is shown with a blue line.

Figure 2. Observed (a, c) and simulated (b, d) rainfall (mm d^-1) for January–March (a, b) and July–September (c, d). The Niger River Basin is shown with a blue line.

Figure 3. Observed (a, c) and simulated (b, d) evapotranspiration (mm d^-1) for January–March (a, b) and July–September (c, d). The Niger River Basin is shown with a blue line.

Figure 4. Observed (a, c) and simulated (b, d) temperature (°C) for January–March (a, b) and July–September (c, d). The Niger River Basin is shown by a blue line.

Table 1. Evaluation statistics for validating regional climate model (version 3, RegCM3) simulations with ERA-Interim reanalysis (ERAIM). Values shown in parentheses are for comparison with CRU (Climate Research Unit) data and river discharge in the case of runoff.

Variable	Evaluation statistics*
	R	MBE
Precipitation (mm d^-1)	0.95 (0.93)	−0.31 (−0.25)
Evapotranspiration (mm d^-1)	0.82	−0.72
Runoff (mm d^-1)	0.66 (0.73)	0.06 (−0.42)
Soil moisture (%)	0.88	−4.45
Air temperature (°C)	0.70 (0.88)	−1.21 (−1.45)
Relative humidity (%)	0.94 (0.93)	8.00 (−5.13)
Shortwave radiation (W m^-^2)	0.91	8.49
Longwave radiation (W m^-^2)	0.85	21.01

*R: correlation coefficient, MBE: mean bias error.

All correlation coefficients are significant at the 0.01 level.

Figure 5. Simulated and observed annual cycle of (a) rainfall (mm d^-1), (b) evapotranspiration (mm d^-1), (c) runoff (mm d^-1), and (d) soil moisture (%).

Figure 6. Simulated and observed annual cycle of (a) temperature (°C), (b) relative humidity (mm d^-1), (c) shortwave radiation, and (d) longwave radiation.

Figure 7. Observed (a, c) and simulated (b, d) moisture flux (arrow) and moisture flux convergence (shaded) for January–March (a, b) and July–September (c, d). The Niger River Basin is shown by a blue line.

Table 2. Atmospheric water flux at the boundaries of Niger River Basin. F_in denotes flux into the basin and F_out flux out of the basin estimated from regional climate model (version 3, RegCM3) output and ERA-Interim reanalysis (ERAIM) data.

Month	Fin (mm d^-1)		Fout (mm d^-1)
	RegCM3	ERAIM	RegCM3	ERAIM
January	5.1	7.0	6.2	8.1
February	4.1	6.1	5.2	6.8
March	5.0	7.3	5.7	6.6
April	7.0	8.4	8.0	8.3
May	11.6	11.4	12.0	11.1
June	10.3	10.2	11.5	9.9
July	10.4	10.0	8.8	8.8
August	10.9	11.0	9.2	9.7
September	11.0	12.3	10.8	12.0
October	16.0	14.6	15.5	14.8
November	11.9	12.2	13.0	13.3
December	7.3	8.3	8.5	9.6

Table 3. Evaluation statistics for validating computed moisture fluxes and recycling ratios from regional climate model (RegCM3) output.

Parameter	Evaluation statistics
	R	MBE
Fin (mm d^-1)	0.85	−0.68
Fout (mm d^-1)	0.88	−0.38
Precipitation recycling (%)	0.47	−2.07
Precipitation efficiency (%)	0.97	−3.79
Moistening efficiency (%)	0.52	−7.13

Correlation is significant at the 0.05 level (normal face).

Correlation is significant at the 0.01 level (bold face).

Figure 8. Simulated and observed annual cycle of (a) moisture recycling, (b) precipitation efficiency, and (c) moistening efficiency.

Table 4. Annual average of parameters for the regional precipitation cycle over the Amazon, Mississippi, Nile and Niger. Values in parentheses are computed with ERA-Interim reanalysis (ERAIM) data.

Parameter	Amazon*	Mississippi*	Nile*	Niger
Precipitation recycling, β	29	14	19	20 (22)
Precipitation efficiency, ρ	83	22	28	32 (36)
Moistening efficiency, m	48	17	24	28 (35)
Runoff coefficient, c	42	22	14	19 (9)
Evaporation coefficient, γ	58	78	86	81 (91)

*Values for Amazon, Mississippi and Nile after Mohamed et al. (2005).

Mohamed, Y.A., et al., 2005. Impact of Sudd wetland on the Nile hydroclimatology. Water Resources Research, 41, W08420. doi:10.1029/2004WR003792

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