Conclusions (Cont. a)

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TABLE 92 Comparison of the figures on soil and land suitability for irrigation with the figures on irrigation potential. by basin

Basin No.	Basin	Total area of basin(ha)	Land suitable for surface irrigation(ha)	Irrigation potential of basin(ha)	Irrigation potential as % of suitable land
	(1)	(2)	(3)	(4)	*(5)=100(4)/(3)**
01	Senegal	48 318 100	3 645 800	420 000	11.52
02	Niger	227 394 600	28 943 400	2 816 510	9.73
03	Lake Chad	238 163 500	36 524 600	1 163 200	3.18
04	Nile	311 236 900	92 019 000	8 000 000	8.69
05	Rift Valley	63 759 300	13 946 700	844 010	6.05
06	Shebelli-Juba	81 042 700	25 847 900	351 460	1.36
07	Congo/Zaire	378 905 300	109 815 500	9 800 000	8.92
08	Zambezi	135 136 500	37 632 500	3 160 380	8.40
09	Okavango	32 319 200	6 612 100	208 060	3.15
10	Limpopo	40 186 400	9 736 100	295 400	3.03
11	Orange	89 636 800	14 140 500	390 000	2.76
12	South Interior	64 582 600	15 421 800	54 000	0.35
13	North Interior	580 446 300	48 325 700	71 000	0.15
14	Mediterranean Coast	67 952 500	11 897 700	850 000	7.14
15	North West Coast	67 062 100	12 565 200	1 200 000	9.55
16	West Coast	143 019 600	29 567 400	5 112 750	17.29
17	West Central Coast	70 477 400	16 335 000	835 000	5.11
18	South West Coast	51 620 000	13 792 500	1 807 900	13.11
19	South Atlantic Coast	36 548 500	4 041 900	84 200	2.08
20	Indian Ocean Coast	66 378 500	14 853 200	1 500 000	10.10
21	East Central Coast	102 625 200	24 913 500	1 927 460	7.74
22	North East Coast	72 570 200	11 779 100	78 050	0.66
24	Madagascar	58 704 000	14 497 400	1 500 000	10.35
25	Islands	934 600	105 500	34 990	33.17
Total		3 029 020 800	596 960 000	42 504 370	7.12

While this study was based on average annual discharges, important seasonal variations do exist. In all cases full development of the whole irrigation potential would require important storage works and collaboration between countries on the management of shared waters within individual basins.

TABLE 93 Irrigation potential, irrigated areas and possibilities for irrigation expansion, by basin

Basin No.	Total area Basin	Irrigation of basin (ha)	Irrigation potential of basin (ha)	Area potential as % of basin area	Irrigation under irrigation (ha)	Possibility for as % of irrigation potential	irrigation expansion(ha)
	(1)	(2)	(3)	*(4) =100(3)/(2)**	(5)	(6) -100-(5)/(3)	(7) =(3)-(5)
01	Senegal	48 318 100	420 000	0.87	118 150	28.1	301 850
02	Niger	227 394 600	2 816 510	1.24	228 240	8.1	2 588 270
03	Lake Chad	238 163 500	1 163 200	0.49	113 296	9.7	1 049 904
04	Nile	311 236 900	8 000 000	2.57	5 078 604	63.5	2 921 396
05	Rift Valley	63 759 300	844 010	1.32	193 496	22.9	650 514
06	Shebelli-Juba	81 042 700	351 460	0.43	199 000	56.6	152 460
07	Congo/Zaire	378 905 300	9 800 000	2.59	35 767	0.4	9 764 233
08	Zambezi	135 136 500	3 160 380	2.34	146 869	4.6	3 013 511
09	Okavango	32 319 200	208 060	0.64	0	0.0	208 060
10	Limpopo	40 186 400	295 400	0.74	241 381	81.7	54 019
11	Orange	89 636 800	390 000	0.44	302 722	77.6	87 278
12	South interior	64 582 600	54 000	0.08	250	0.5	53 750
13	North Interior	580 446 300	71 000	0.01	232 500	327.5	- 161 500
14	Mediterran. Coast	67 952 500	850 000	1.25	1 606 700	189.0	- 756 700
15	North West Coast	67 062 100	1 200 000 1.79	1 000 750	83.4	199 250
16	West Coast	143 019 600	5 112 750	3.57	310 883	6.1	4 801 867
17	West Central Coast	70 477 400	835 000	1.18	28 450	3.4	806 550
18	South West Coast	51 620 000	1 807 900	3.50	70 000	3.9	1 737 900
19	South Atlant. Coast	36 548 500	84 200	0.23	84 000	99.8	200
20	Indian Ocean Coast	66 378 500	1 500 000	2.26	862 110	57.5	637 890
21	East Central Coast	102 625 200	1 927 460	1.88	178 610	9.3	1 748 850
22	North East Coast	72 570 200	78 050 0.11	24 574	31.5	53 476
24	Madagascar W+E	704 000	1 500 000	2.56	1 087 000	72.5	413 000
25	Islands	934 600	34 990	3.74	30 109	86.1	4 881
Total	3 029 020 800	42 504 370	1 40	12 173 461	28.6	30 330 909

(6) + (7): In estimating the irrigation potential only renewable water resources are taken into consideration. If >100% (6) or negative (7) either non-renewable water resources are already being used for irrigation or the quantities of water used per hectare are less than the quantities recommended for the potential area.

The present study concentrated on long-term averages. Climate fluctuations, however, may greatly influence the possibilities for irrigation development. In the Niger basin, for example the 1980s were much drier than earlier years: the average annual discharges of the 1980s were 20 to 40% less than those before the 1980s. The average annual discharge of the White Nile entering Sudan from Uganda during the period 1961-1980 (50 km�/year) was nearly twice the average annual discharge during the period 1905-1960 (27 km /year). The recent drought years in Southern Africa will also lead to different averages depending on the period of reference considered.

Figure 18 and Tables 93 to 95 show the part of irrigation potential by basin which is already under irrigation at present¹. As expected, it is much lower in the humid regions than in the dry regions. In a few basins, figures higher than 100% mean that the area already under irrigation is larger than the potential. This is due to the fact that either fossil water is used for irrigation (northern Africa) or that the quantity of water used per hectare is less than the irrigation potential in Africa 153 irrigation water requirement figure used in the computation of the irrigation potential (both northern and southern Africa). Figure 19 shows the remaining possibilities for irrigation expansion, which are greatest in the humid regions and smallest or even negative (for the reasons explained above) in the dry regions.

^{1This is the area occupied by irrigation schemes with full or partial control
(11.5 million ha), spate irrigation (0.5 million ha) and wetlands and inland valley
bottoms that are equipped for water control (0.2 million ha).}

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