Analysis of the land suitability for paddy fields in Tanzania using a GIS-based analytical hierarchy process

Figures & data

Figure 1. The study area includes the mainland of Tanzania and comprises eight irrigation zones.

Table 1. Scale and its description (Saaty 1977).

Intensity of importance	Definition	Explanation
1	Equal importance	Two activities equally contribute to the objective.
3	Weak importance of one over another	Experience and judgment slightly favor one activity over another.
5	Essential or strong importance	Experience and judgment strongly favor one activity over another.
7	Demonstrated importance	An activity is strongly favored, and its dominance is demonstrated in practice.
9	Absolute importance	The evidence favoring one activity over another is of the highest possible order of affirmation.
2, 4, 6, 8	Intermediate values between the two adjacent judgments	When compromise is needed
Reciprocals	If activity i was assigned one of the above-mentioned numbers compared with activity j, then j has the reciprocal value when compared with i.

Table 2. Random index (RI) table (Saaty 1994).

n	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15
RI	0.00	0.00	0.58	0.90	1.12	1.24	1.32	1.41	1.45	1.49	1.51	1.48	1.56	1.57	1.58

Table 3. List of criteria used for the land suitability assessment and their sources.

Criteria	Source
Soil Type	Based on the Harmonized World Soil Database version 1.2 (FAO/IIASA/ISRIC/ISSCAS/JRC 2012)
Soil Drainage
Soil Organic Carbon
Soil pH
Soil Depth	Based on the FAO–UNESCO Soil Map (FAO 2017a)
Elevation	Topography Mission (SRTM) of the National Geospatial–Intelligence Agency (NGA 2020)
Slope	Calculated based on SRTM data
Land Use	Global Map-Global Land Cover (GLCNMO version 2; Tateishi et al. 2014)
Topographic Wetness Index (TWI)	Calculated based on SRTM data
Temperature	Based on WorldClim 2 data (Fick and Hijmans 2017)
Precipitation	Based on Climate Hazards Group InfraRed Precipitation (CHIRP) version 2 data provided by the Climate Hazard Group (CHG; Funk et al. 2015)

Table 4. Weighting factors for the paddy field suitability (rainfed condition and irrigation priority).

Criteria	ST	S	E	P	T	LU	SD	SOC	SPH	SDR	TWI	W	CI	RI	CR
ST	1	1	7	1	3	5	5	5	5	3	1	0.165	0.072	1.510	0.048
S	1	1	7	1	3	5	7	7	7	3	1	0.181
E	1/7	1/7	1	1/5	1/3	1	1	1	1	1/3	1/9	0.026
P	1	1	5	1	3	5	7	7	7	5	3	0.203
T	1/3	1/3	3	1/3	1	1	3	3	1	1/3	1/5	0.049
LU	1/5	1/5	1	1/5	1	1	3	3	3	1/3	1/7	0.042
SD	1/5	1/7	1	1/7	1/3	1/3	1	1	1/3	1/3	1/7	0.021
SOC	1/5	1/7	1	1/7	1/3	1/3	1	1	1/3	1/3	1/7	0.021
SPH	1/5	1/7	1	1/7	1	1/3	3	3	1	1/5	1/9	0.030
SDR	1/3	1/3	3	1/5	3	3	3	3	5	1	1/3	0.077
TWI	1	1	9	1/3	5	7	7	7	9	3	1	0.185

Note: ST: Soil Type, S: Slope, E: Elevation, P: Precipitation, T: Temperature, LU: Land Use, SD: Soil Depth, SOC: Soil Organic Carbon, SPH: Soil pH, SDR: Soil Drainage, TWI: Topographic Wetness Index, W: Weighting

Figure 2. Criteria used in the land suitability analysis. (a) Precipitation, (b) Topographic Wetness Index, (c) Slope, (d) Soil Type, (e) Soil Drainage, (f) Temperature, (g) Land Use, (h), Soil pH, (i) Elevation, (j) Soil Depth, (k) Soil Organic Carbon.

Table 5. List of criteria and subcriteria used for paddy fields and their scores.

Priority Ranking	Criteria	Subcriteria	Scoring (Rainfed Condition)	Scoring (Irrigation Priority)
1	Precipitation (mm/yr)	>2000	5	1
		1200–2000	4	3
		800–1200	3	5
		600–800	2	4
		≤600	1	2
2	Topographic Wetness Index	>15.7	5	5
		12.2–15.7	4	4
		8.7–12.2	3	3
		5.3–8.7	2	2
		≤ 5.3	1	1
3	Slope (°)	≤ 3	5	5
		3–15	3	3
		>15	1	1
4	Soil Type	Cambisols; Luvisols	5	5
		Fluvisols; Vertisols	4	4
		Gleysols; Chernozems	3	3
		Phaeozems; Planosols; Nitisols; Andosols; Ferralsols; Acrisols; Histosols; Arenosols; Solonetz	2	2
		Lixisols; Leptosols; Regosols; Solonchaks	1	1
5	Soil Drainage	Very Poor	5	5
		Poor	4	4
		Imperfect; Moderately Well	3	3
		Well	2	2
		Somewhat Excessive	1	1
6	Temperature (°C)	>25	5	5
		20–25	3	3
		≤20	1	1
7	Land Use	Sparse vegetation; Paddy field	5	5
		Natural vegetation	4	4
		Cropland; Cropland/other vegetation mosaic	3	3
		Bare area	2	2
		Forest; Wetland; Urban; Waterbody	1	1
8	Soil pH	<4.5 and >8.0	1	1
		7.5–8.0	2	2
		4.5–5.0 and 7.0–7.5	3	3
		5.0–5.5 and 6.5–7.0	4	4
		5.5–6.5	5	5
9	Elevation (m)	>2000	1	1
		1500–2000	2	2
		1000–1500	3	3
		500–1000	4	4
		≤500	5	5
10	Soil Depth (cm)	150–300	5	5
		100–150	4	4
		50–100	3	3
		10–50	2	2
		≤10	1	1
11	Soil Organic Carbon (% weight)	>3.0	1	1
		2.0–3.0	4	4
		1.2–2.0	5	5
		0.6–1.2	3	3
		0.2–0.6	2	2
		≤0.2	1	1

Table 6. Rainfall distribution in the study area.

Rainfall Amount (mm/yr)	Area (km^2)	Area (ha)	Area (%)
≤600	69,611	6,961,129	7.4
600–800	171,135	17,113,519	18.3
800–1200	563,924	56,392,444	60.1
1200–2000	131,970	13,197,041	14.1
>2000	920	91,966	0.1
Total	937,561	93,756,100	100.0

Table 7. Acreage of land use/cover in the mainland of Tanzania.

Class	Area (km^2)	Area (ha)	Area (%)
Forest	302,396	30,239,600	32.3
Natural vegetation*	164,557	16,455,700	17.6
Cropland*	84,707	8,470,700	9.0
Wetland*	5240	524,000	0.6
Bare area and sparse vegetation*	571	57,100	0.1
Urban	151	15,100	0.02
Water	60,846	6,084,600	6.5
Protected Area	319,093	31,909,300	34.0
Total	937,561	93,756,100	100.0
Potential Agriculture Land*	255,075	25,507,500	27.2

The * indicates classes that represent potential agricultural land.

Figure 3. Land suitability distribution for paddy fields under the rainfed condition scenario. (a) whole study area (b) within potential agricultural land.

Table 8. Acreage of land suitability classes (rainfed condition) in the mainland of Tanzania.

Class	Area (km^2)	Area (ha)	Area (%)
Very high	80,083	8,008,289	8.5
High	496,876	49,687,568	53.0
Moderate	311,597	31,159,692	33.2
Low	48,094	4,809,353	5.1
Very low	912	91,197	0.1
Total	937,561	93,756,100	100.0

Table 9. Acreage of land suitability classes (rainfed condition) within potential agricultural land in the mainland of Tanzania.

Class	Area (km^2)	Area (ha)	Area (%)
Very high	25,917	2,591,681	2.8
High	139,178	13,917,801	14.8
Moderate	80,666	8,066,641	8.6
Low	9171	917,113	1.0
Very low	142	14,225	0.02
Unsuitable	682,486	68,248,639	72.8
Total	937,561	93,756,100	100.0

Figure 4. Percentages of land suitability classes under the (a) rainfed condition and (b) irrigation priority scenarios distributed within the eight irrigation zones.

Figure 5. The land suitability distribution for paddy fields under the irrigation priority scenario (a) whole study area (b) within potential agricultural land.

Table 10. Acreage of land suitability classes (irrigation priority) in the mainland of Tanzania.

Class	Area (km^2)	Area (ha)	Area (%)
Very high	281,854	28,185,440	30.1
High	388,550	38,854,988	41.4
Moderate	200,776	20,077,624	21.4
Low	65,407	6,540,723	7.0
Very low	973	97,325	0.1
Total	937,561	93,756,100	100.0

Table 11. Acreage of land suitability classes (irrigation priority) within potential agricultural land in the mainland of Tanzania.

Class	Area (km^2)	Area (ha)	Area (%)
Very high	76,476	7,647,563	8.2
High	123,958	12,395,822	13.2
Moderate	48,074	4,807,433	5.1
Low	6528	652,822	0.7
Very low	39	3860	0.004
Unsuitable	682,486	68,248,600	72.8
Total	937,561	93,756,100	100.0

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Data availability statement

Data not available due to legal restrictions. Due to the nature of this research, participants of this study did not agree for their data to be shared publicly, so supporting data is not available.