Agroclimatic Zones and Cropping Systems in the Southwestern Regions of the Kingdom of Saudi Arabia: Characterization, Classification and Improvement Potential

Abstract

The southwestern regions of the Kingdom of Saudi Arabia (KSA) are geographically and agriculturally diverse. Over millennia, crop production in these regions has evolved to use renewable water resources sustainably. This study analysed environmental and crop production data for 58 governorates in KSA’s four southwestern regions: Al Baha, Aseer, Jazan and Makkah. The biplot analysis generated six clusters of cropping systems: sorghum, cereals, dates, watermelon, vegetables and fruits, and mixed. The main biophysical factors shaping these systems are topography, altitude, rainfall, air temperature and soils. Sorghum, grown on more than half of the cultivated land, dominates the two main systems. Fruits (subtropical and temperate) and open field vegetables are important elements in most systems. The main challenge is combining a moderate use of water with greater crop diversity. Cereals consume relatively little water, but their dominance within the systems reduces overall diversity. Another important issue is the low-input technologies used to cultivate sorghum and other cereals. Landraces or older varieties are planted and little, if any, fertilizers and pesticides are applied. The introduction of sustainable intensification packages is needed, which can begin with making improved varieties accessible to farmers, promoting conservation agriculture, and integrated pest management practices.

1. Introduction

The Kingdom of Saudi Arabia (KSA) covers 2,150,000 km² in the Arabian Peninsula. Its population exceeds 35 million people. The country is characterized by desert terrain and an extremely dry climate. Moisture availability represents a major challenge for arable farming. Food security is a priority for KSA. Increasing uncertainties related to food imports have created a need to strengthen the agriculture potential across the country. According to FAOSTAT (The Food and Agriculture Organization Corporate Statistical Database), in 2018, the country imported almost 14 million tonnes of grain (barley, wheat, rice and maize). This is ten times higher than domestic production. The government strategic framework, Vision 2030, calls for the improvement of local production to reduce this imbalance.

The structure of agricultural production is driven by two major factors: food security and the availability of land and water. According to the Ministry of Environment, Water and Agriculture [1], the total arable area in the country was more than 770,000 ha in 2020. Most of the arable land is irrigated. The main crops grown in 2020 were alfalfa (146,514 ha), Rhodes grass (54,200 ha), wheat (86,963 ha), barley (81,520 ha), sorghum (67,466 ha), and vegetables (88,644 ha), mainly potato, watermelon and tomato. In addition, date palms are grown on around 152,704 ha; olives on 30,960 ha; and fruit trees on 24,705 ha. Greenhouses for vegetables and flowers cover around 6000 ha. Livestock is an extremely important sector in the country. There is a total of 21.7 million sheep, 6.7 million goats; 1.5 million camels; and 0.4 million cows being raised. Around 200 million chickens are kept for poultry production.

Since the 1960s, KSA has been focusing on the north and central regions of the country for cereal and crop production. In these areas, crop cultivation is based on irrigation [2]. The recent government policy is to limit the use of irrigation to preserve water, and at the same time, maintain the production of critically important crops. The use of desalinated and treated water has been increasing, as has the application of water-saving irrigation technologies.

Until recently, limited attention was given to rainfed crop production. For millennia, producers in the southwestern administrative regions of the country (Al Baha, Aseer, Jazan and Makkah) have practiced rainfed agriculture. The key geographic feature of these regions is the Aseer Mountains, stretching from the southeast to the northwest. Westerly air currents bring moisture from the Red Sea, which falls as precipitation on the slopes and valleys, creating suitable conditions for crop production. The air temperature in the mountains and foothills is cooler than on the coastal plains.

According to the 2015 Agricultural Census, there were more than 285,000 farms with land (https://www.stats.gov.sa/en/22, accessed 20 November 2021). The four southwestern regions had more than 162,000 farms or 57.1% of the national total. However, the area under cultivation on these farms was only 10–12% of the total land registered as being under farms in the country. The land size per farm is below 1 ha in the Aseer and Al Baha regions. The main cereal crops grown in these regions are sorghum, wheat and millet. Sesame is popular and in high demand by consumers. Landraces or older varieties of these crops are grown using conventional technologies with few, if any, inputs. As a result, yields and farmers’ profits are low, which has contributed to the area falling into decline.

Technological innovations to improve the current production systems in the southwestern regions of the country need to be based on a detailed analysis of the environmental and soil resources as well as the cropping systems. The cropping patterns in the country have been analysed by Alzahrani et al. [3] as part of a process to optimize local production while reducing water use at the national level. The study recommended altering the existing cropping pattern by encouraging the production of different crops in regions with the highest productivity. For example, the production of cereals could be concentrated in the Jouf and Tabuk areas, whereas vegetable production could be in the central-eastern region and the Asser area. The study by Alabdulkader et al. [4] applied a mathematical model to optimize cropping patterns based on yields, market prices, production costs, commodity prices, crop water requirements, and national demand. The optimized cropping pattern in KSA would achieve a 53% saving in water use and about a 48% reduction in the arable land use compared to the base-year cropping pattern. The proposed allocation of land to crop groups was 48.4% for cereals, 35.4% for fruits, 13.1% for forages, and 3.2% for vegetables. Both studies targeted the whole country without placing a specific focus on the southwestern regions.

Cropping system analyses have evolved into a modern tool for supporting decision-making for specific purposes, including environmental and economic sustainability assessment [5]; agroecosystem management [6]; and soil health improvement [7]. The input data used for the analyses, and the statistical and modeling tools largely depend on the specific purpose of the cropping system analysis and vary broadly from study to study. The objectives of the current study were to describe agroclimatic zones; classify and map the cropping systems, identify their interaction; and identify the main sustainable development options with a clear geographic focus on the four regions in the southwestern part of the country. The study provides a field-based analysis of the potential of the agriculture sector in the southwestern regions to contribute to national food security.

2. Materials and Methods

The study analysed environmental and crop production data for 58 administrative units (governorates) that cover the four studied regions: 10 in Al Baha; 15 in Aseer; 16 in Jazan and 17 in Makkah. The governorates vary in size from 992 km² in Al Baha to 9000 km² in the Makkah region. The population also varies from 47,000 in Al Baha to almost 150,000 in the Aseer region. The following environmental data was utilized: prevalent agroclimatic subzones based on the MoEWA classification (

Table 1. Characteristics of the main agroclimatic zones of the southwestern regions of the Kingdom of Saudi Arabia.

Agroclimatic Zone	Agroclimatic Subzone	Subzone Code *	Elevation, Meters above Sea Level	Mean Temperature Range, °C		Annual Rainfall, mm	Dominant Soil Types **:
				January	July		1	2	3
Najd	Southwestern Najd	3.2	950	16	32	68	Arenosols	Leptosols	Regosols
Hijaz highlands	Southern Hijaz	5.3	500	21	31	162	Andosols	Leptosols	Arenosols
	Makkah Basin	5.5	500	23	35	98	Arenosols	Leptosols	-
Aseer mountains	Aseer Scarp	6.1	1200	19	29	302	Leptosols	Arenosols	Solonchaks
	High Aseer	6.2	2000	15	25	431	Leptosols	Anthrosols	-
	Central-eastern Aseer	6.3	1500	15	27	268	Leptosols	Anthrosols	Regosols
	Eastern Aseer	6.4	1300	15	29	78	Leptosols	Arenosols	Cambisols
	Bishah Plateau	6.5	1100	17	31	108	Leptosols	Arenosols	Andosols
Red Sea coast	Northern Tihamah	7.1	30	23	33	51	Arenosols	Regosols	Andosols
	Southern Tihamah	7.2	50	21	33	85	Cambisols	Arenosols	Solonchaks

*—refers to code on map, Figure 1. **—Soil types are classified according to the World Reference Base for Soil Resources [8]. Andosols are found in volcanic areas and formed in volcanic tephra. They are relatively young soils and generally very fertile and can support intensive cropping. Anthrosols are formed or heavily modified due to long-term human activities. They are often found in shifting sand dunes and contain unconsolidated sand deposits and have no distinct soil horizons. Their water-holding capacity is very low, and they are extremely low in all essential nutrients. Arenosols are sandy-textured soils that lack any significant soil profile development. They exhibit only a partially formed surface horizon (uppermost layer) that is low in humus, and they are bereft of subsurface clay accumulation. Cambisols are at the beginning stage of soil formation, and their horizon differentiation is very weak. They develop in medium and fine-textured materials from alluvial sedimentations and make for good agricultural land. Leptosols are very shallow and extremely gravelly and/or stony. They are not suitable for rainfed agriculture because of their inability to hold water, but they have the potential for tree crops. Regosols are weakly developed, extensively eroded and can be used for grazing. Solonchaks are found in arid to subhumid environments, and in poorly drained conditions, which limit the root growth of plants, as there is a high concentration of soluble salts.

, Figure 1); prevalent soil types based on the Ministry of Environment, Water and Agriculture (MoEWA) soil map (Figure 1); the monthly rainfall and average monthly maximum air temperature, based on the data from 18 weather stations distributed across the regions. Crop production data for 2020 was provided by MoEWA and was based on an annual agricultural survey. The data included governorate-level information for the area under cultivation of specific crops and estimates on water use. General validation of the data took place through visits to 25 governorates and surveys of the cropping systems.

Biplot and cluster analyses were used to group agroclimatic zones and governorates based on environmental and crop production data. The R Studio software, version 3.4 [9], was used for this purpose. The Simpson Diversity Index for cropping systems was calculated using the formula adopted by Swarnam et al. [10] (2016):

$$\mathrm{DI}=1-{\displaystyle \sum }_{\mathrm{n}=1}^{\mathrm{S}}{\left({\mathrm{n}}_{\mathrm{i}}/\mathrm{N} \right)}^2$$

In this formula, S is the number of crops that are present; n_i (for i = 1 to S) is the area devoted to the ith crop and N (=Sum of n_i) is the total area across all crops. For a region with only one crop and no diversity, the Simpson Diversity Index value is zero. As crop diversity increases, the Simpson Diversity Index approaches one.

3. Results

3.1. Characterization and Classification of Agroclimatic Zones

The southwestern regions of KSA have four agroclimatic zones and ten subzones (Table 1, Figure 1 and Figure S1). The main factors that define these zones are their geographic location and topography, which determine two key weather parameters: rainfall and air temperature. The Red Sea coastal plains (northern and southern Tihamah) are lowlands stretching along the sea. They have very low rainfall, warm winters and hot summers. Cambisols are dominant in southern Tihamah, which makes this area suitable for arable farming. To the east, the coastal plains give way to the sudden rise of mountains: the Aseer Scarp, which reaches an altitude of 1000 masl and then to the High Aseer subzone, which rises above 2000 masl. The lower temperatures and higher rainfalls (up to 400–450 mm per year) at the higher altitudes create conditions for more diverse vegetation. However, in this zone, the predominant leptosols, which are made up of gravel and stones, are poorly suited for crop production. Anthrosols in the highlands of Aseer are heavily modified and degraded due to long-term human activity. Further to the east, the mountain range flattens into an arid and hot plateau with an average altitude of 500–1000 masl. The dominant soils here are arenosols and leptosols, which are not suitable for arable farming. The profile of the Aseer region across the main agroclimatic subzones, presented in Figure S2, clearly indicates the abrupt changes in altitude and related variations in the landscape.

The long-term variation in monthly air temperature and rainfall in the main agroclimatic subzones is presented in Figure 2. The temperature differences between southern Tihamah and the Aseer Scarp on one hand, and the high and central-eastern Aseer on the other, exceeds 10–12 °C. Consequently, these two areas have highly contrasting environments for crop production. There are also clear differences in the amount and distribution of rainfall. The coastal southern Tihamah plain receives limited rainfall (below 70 mm/year) with rain spikes in July and October. For the other zones, there are pronounced rainfall maximums in April and again in August and September (the Aseer Scarp and central-eastern Aseer subzones) or in November and December (High Aseer). The rainfall in the Aseer Mountains is of fundamental importance for cropping systems in the whole region, as a diverse range of ancient rainwater harvesting techniques is used to capture the rain and make it available for crop production.

There were 51 commodity crops grown across the southwestern regions, including 7 cereals, 6 forages, 18 fruits, 4 aromatic plants and flowers, 14 field vegetables and 7 greenhouse vegetables. Similarities between the agroclimatic subzones were evaluated using cluster analysis based on the physical area where all of the crops are grown in the subzones (Figure 3). The central-eastern Aseer and southern Tihamah subzones emerged as being distinctly different from the other agroclimatic subzones. However, six subzones (southwestern Najd, southern Hijaz, the Makkah basin, eastern Aseer, the Bishah Plateau and northern Tihamah) were found to be very similar and formed one cluster. The High Aseer subzone was clustered with these six subzones as it demonstrated certain similarities. The Aseer Scarp subzone was similar to both the High Aseer and southern Tihamah subzones. It is, in fact, a transitional subzone between the two.

The cropping pattern of each of the five subzone clusters is presented in

Table 2. Crops cultivated area across the main agroclimatic zones in the southwestern regions of Saudi Arabia, 2020.

Crops	Cultivated Area across Agroclimatic Subzones Clusters, ha
	1 Central Eastern Aseer	2 Southern Tihamah	3 Aseer Scarp	4 High Aseer	5 Southwestern Najd, Southern Hijaz, Makkah Basin, Eastern Aseer, Bishah Plateau, Northern Tihamah	Total
Cultivated land	5711	69,327	14,551	2216	16,345	108,150
Cereals	2736	40,756	9754	1457	706	55,410
Barley	266	2	79	137	103	587
Maize	101	1206	263	0	66	1636
Millet	199	1413	838	0	99	2549
Sesame	33	2334	442	0	13	2822
Sorghum	1105	35,753	8027	429	151	45,465
Wheat	981	48	106	891	272	2298
Forages	132	894	177	23	1128	2353
Alfalfa	86	0	3	17	231	338
Hijazi clover	0	863	5	0	93	960
Fruits	1120	8070	1391	445	10,807	21,833
Almonds	54	506	0	11	42	613
Apricots	58	0	0	20	1	79
Bananas	8	1008	136	16	181	1349
Citrus	84	80	111	41	78	393
Coffee	40	0	171	11	1	222
Dates	98	50	36	1	9137	9321
Figs	92	473	14	41	63	683
Grapes	180	0	6	109	379	674
Mango	27	5825	334	10	90	6286
Pomegranates	236	58	485	109	769	1657
Aromatic-All	5	262	107	5	0	378
Jasmin	0	115	13	0	0	128
Cut flowers	2	0	3	5	0	11
Vegetables-field	1550	20,501	3406	202	4785	30,443
Beans	240	100	7	1	59	407
Eggplant	23	1455	213	13	195	1899
Leafy vegetables	235	817	71	57	773	1952
Okra	0	507	102	7	122	737
Pepper	50	316	365	9	202	941
Pumpkins	111	177	852	30	34	1204
Tomato	395	2107	769	40	967	4279
Watermelon	250	14,862	938	12	2040	18,102
Zucchini	14	67	31	0	292	404
Vegetables-greenhouse	305	0	0	112	48	465
Tomato	175	0	0	67	15	258

. The Red Sea coastal area of southern Tihamah is a major agricultural production subzone with almost 70,000 ha or 64% of the total land under cultivation. The Aseer Scarp accounts for more than 14,500 ha of agricultural land. In both these subzones, cereals are the most important crop, extending over 58–67% of all cultivated land, with sorghum being the most widely cultivated cereal crop (48–58% of the cultivated land). Tropical fruits (banana and mango) are also cultivated in southern Tihamah (10% of the cultivated land). Subtropical fruits (pomegranate and citrus) are more common in the Aseer Scarp (4% of the cultivated land). Watermelon is the most popular in southern Tihamah followed by eggplant and tomato. In the Aseer Scarp, watermelon, pumpkin and tomato are the main vegetable crops. For central-eastern Aseer and High Aseer, arable farming is of less importance, with the total cultivated area being less than 8000 ha. In both subzones, cereals dominate crop production, but temperate crops such as wheat and barley are cultivated over the same area as sorghum. In the cluster 5 subzones (southwestern Najd, southern Hijaz, the Makkah Basin, eastern Aseer, the Bishah Plateau, northern Tihamah), fruits are dominant, with dates being the main commodity crop (66% of the cultivated land).

The seasonal use of water for crop production in all 58 governorates consumes 651 million m³ (

Table 3. Total yearly water consumption (1000 m³) for different crops across the agroclimatic subzones of the southwestern regions of KSA, 2020.

Crops	Agroclimatic Zones Clusters
	Central Eastern Aseer	Southern Tihamah	Aseer Scarp	High Aseer	Southwestern Najd, Southern Hijaz, Makkah Basin, Eastern Aseer, Bishah Plateau, Northern Tihamah	Total
Cereals	7293	29,870	14,730	4828	2395	59,117
Millet	178	1118	1614	0	99	3009
Sesame	26	1967	1505	0	11	3508
Sorghum	1908	22,871	8499	1119	209	34,608
Wheat	2982	234	404	3191	1061	7873
Forages	5252	38,468	7500	846	50,666	102,732
Fruits	11,614	75,184	19,825	4688	120,728	232,038
Bananas	175	10,619	2179	393	1531	14,896
Dates	1112	517	373	4	95,297	97,303
Mango	330	51,566	3486	130	990	56,503
Vegetables-field	15,800	173,764	17,689	1960	41,405	250,619
Eggplant	175	13,420	1960	78	2207	17,841
Leafy vegetables	3598	7988	709	728	8260	21,283
Tomato	4185	19,585	2946	371	9587	36,676
Watermelon	3173	122,647	2200	113	15,177	143,312
Total	42,056	319,335	60,471	13,135	216,644	651,643

). Cereals are grown on 51.2% of total cultivated land but use only 9.3% of the total water. Vegetable production uses the largest share of water for agriculture (39%), with watermelon cultivation alone accounting for 23%. Fruits use 36% of the water for agriculture with dates using 15.4%. There are substantial differences between the subzones. The southern Tihamah region grows 64% of all the crops but uses only 50 percent of all the water. The share of cluster 5 of the total cultivated land is 15%, but it consumes 34% of the total water. Banana cultivation uses, by far, the most water, with the seasonal average exceeding 15,000 m³/ha. The cultivation of leafy vegetables, watermelon, mango, dates, tomato and eggplant uses 10,000 m³/season/ha. Sorghum, millet and sesame use the lowest amount of water (less than 2000 m³/season/ha). Wheat production is an intermediate water user (5000 m³/season/ha).

3.2. Classification of Cropping Patterns

Individual governorates were used as the units of classification. The following eight variables were selected: total area of the cultivated land per governorate; the percentage of land under cereals, feed, fruits and vegetables; the number of crops grown, the Simpson Diversity Index; and the seasonal water use per unit area (Table S1). Biplot analyses were conducted using data from the 58 governorates for these eight variables. Biplot graphs allow the information for both the samples (governorates) and the variables (production parameters) to be clearly displayed. Governorates are displayed as points separated into six clusters, whereas the production factors are displayed as vectors that are grouped into five clusters (Figure 4). The relationship between the variables is reflected by their relative position: vectors pointing in the same direction and close to each other have a high positive correlation, while vectors facing opposite directions have a strong negative correlation. When the relative position of vectors is at 90°, there is a lack of association. The length of a vector reflects the relative contribution of this variable to overall variation. The position of the governorates clusters relative to the production vectors reflects their relationship.

The biplot analysis presented in Figure 4 accounts for 55.3% of the total variation of the eight production variables across the 58 governorates. The area under vegetable feed crops and seasonal water use was closely associated and was assigned to the same cluster. The number of crops grown in each governorate and the Simpson Diversity Index was also closely correlated and grouped in cluster 3. The share of the fruit vector is aligned with water use. The share of the cereals vector points in the opposite direction, which indicates low seasonal water use, as was noted earlier. The share of vegetables has a positive effect on cropping system diversity (Simpson Diversity Index), whereas the share of cereals has a negative effect.

The main outcome of the biplot analysis is the clustering of governorates according to eight selected variables. The analysis generated six clusters that represent distinct cropping patterns practiced in the southwestern regions of KSA: (1) sorghum; (2) cereals; (3) dates; (4) watermelon; (5) vegetables and fruits; and (6) mixed (

Table 4. Description of the main cropping systems in the southwestern regions of KSA.

Cropping Parameters	Cropping Systems Clusters *
	1—Sorghum	2—Cereals	3—Dates	4—Watermelon	5—Vegetables and Fruits	6—Mixed
Agroclimatic subzones	6.1, 7.2	6.1–3	3.2, 5.3, 6.5, 7.1	5.5, 6.1	3.2, 5.3, 6.1–4	3.2, 5.2–3, 6.1, 7.2
Yearly rainfall (mm)	122	208	84	85	150	145
Average yearly T max (°C)	36.4	30.8	34.0	36.1	30.7	35.9
Number of governorates	13	14	5	2	14	10
Total culivated area (ha)	54,090	16,535	8353	14,359	8272	9645
Cultivated area per governorate (ha)	4161	1181	1670	7179	591	964
% of cereals (total)	84.6	63.5	3.6	1.8	12.5	16.8
Sorghum	72.3	28.8	0	0.6	6.6	13.2
Millet and sesame	8.7	9.0	2.8	0.9	0.2	1.0
Wheat and barley	0.1	20.6	0.8	0.1	4.7	4.7
% of feed grown	0.6	2.2	2.1	0.7	3.2	26.8
% of fruits (total)	5.8	16.5	88.5	3.5	37.5	20.0
Dates	0	0.5	88.0	1.2	14.9	9.1
Tropical (banana and mango)	5.1	3.7	0.3	0.1	3.3	5.5
Temparate (pomegranate, figs, grape)	0.9	5.2	1.0	0.4	13.3	7.5
% of field vegetables (total)	8.3	16.4	5.7	94.0	41.9	34.4
Watermelon	0.1	3.8	0	91.7	4.4	11.3
% of greenhouse vegetables	0.3	0	0	0	3.4	0
Aromatic crops and flowers	0.5	0	0	0	0	0.9
Average number of crops per governorate	14.7	20.1	10.8	17.0	21.8	15.3
Simpson Diversity Index	0.426	0.759	0.206	0.157	0.833	0.738
Water use (m3/season/ha)	2228	6133	10,184	11,000	9731	13,117

*—numbers refer to governorates clusters according to Figure 4.

and Table S1).

3.3. Characterization and Mapping of Cropping Systems

The sorghum cropping system is predominant in the southwestern regions, covering more than 54,000 ha or half of the total cultivated area. This system extends over most of the coastal Southern Tihamah and the Aseer Scarp agroclimatic subzones (Figure 5). Sorghum is the main crop, covering 85% of the total area. It is a unique commodity crop grown primarily during the winter season (October to April) using river valley spate flood irrigation with a supplementary water supply during the summer. The crop is harvested two to four times for biomass, and the first harvest also produces a reasonable grain yield. Conventional tall varieties or landraces are cultivated without any inputs or crop protection. Millet is also cultivated, primarily under rainfed conditions with limited or no irrigation. Sesame is a traditional high-value crop grown during the winter season. Extensive low-input farming is practiced for millet and sesame, and again, older traditional varieties are grown for production. Tropical fruits (banana and mango) are grown as cash crops on approximately 5% of the cultivated land using constant irrigation with water drawn from on-farm wells. Vegetables, which are grown on 8.3% of the cultivated land, are important for both household consumption and as a market commodity. Overall, the sorghum cropping system is characterized by low water use (2200 m³/season/ha) and relatively low diversity, as indicated by the Simpson Diversity Index (0.426).

The cereal cropping system is found on the western slope of the Aseer Mountains (Aseer Scarp), the narrow plateau (High Aseer) and the eastern slope (central-eastern Aseer). The share of cultivated land under sorghum is less extensive (almost 30%), while temperate cereals, primarily wheat, are grown on around 20% of the cultivated land. Millet and sesame cover almost 10% of the land in this system. The key environmental characteristic of this region is its higher altitude, which causes more rainfall and cooler temperatures that allow for the cultivation of more temperate crops. In the mountainous topography, terrace farming has been established to capture rainwater and enable crop production. Despite the availability of rainwater and additional irrigation sources, flat land and suitable soil for farming are limited to the established terraces. Fruits and vegetable crops each occupy 16% of the cultivated land, and as a result, the whole system is much more diverse. The average number of crops grown in each governorate is 20.1, and the Simpson Diversity Index is relatively high (0.759). Seasonal water use in this system exceeds 6000 m³/ha. All cereals are grown with little, if any, inputs, which are limited to organic fertilizer. For sorghum and millet, conventional varieties or landraces are grown. For wheat, both improved semi-dwarf varieties and older landraces are planted.

The date production system is situated in the arid and hot interior subzones of southwestern Najd, eastern Aseer and the Bishah plateau. Date palm is the traditional oasis farming commodity crop in the area. Its production has expanded over the last 30–40 years, owing to the establishment of irrigation schemes that draw water from dams and underground wells. Vegetables, which are grown on 5.7% of the cultivated land, are the other significant commodity crop cultivated in this system. The date production system is the least diverse (Simpson Diversity Index—0.206) and uses high volumes of water (more than 10,000 m³/season/ha.)

Watermelon is an important commodity in the governorates south of Jeddah in the Makkah region. Al Lith is the main watermelon producing governorate with more than 12,000 ha. The watermelon cropping system is primarily based on coastal desert rainfed production. The farmers wait for a substantial rainfall in late fall or early winter and then plant the crop at low densities to take advantage of the residual moisture in the soil. The crop takes 90–120 days to mature and produces good quality fruits that are sold in wholesale markets. Some watermelon production uses spate flood irrigation or underground water sources. Improved watermelon varieties and hybrids are planted. The main production constraint is viral and fungal diseases, which can devastate the crop if they appear early in the season. Rainfall variability is an important challenge, as most watermelon production is entirely dependent on rainfall.

The vegetables and fruit cropping system is found in the central-western agroclimatic subzone of the Al Baha region and the central and northern areas of the Makkah Region, including the very large Taif governorate. The percentage of the cultivated land under vegetable production exceeds 40%. Fruits are grown on more than 35% of the cultivated land, with date palm accounting for 15%. Mixed cereals are also grown on 12% of the cultivated land. This is the only system in which vegetable production in greenhouses extends over a relatively significant share (3.4%) of the cultivated land. It is the most diverse cropping system (Simpson Diversity Index—0.833) and is almost entirely irrigated.

The mixed cropping system is characterized by a relatively high area (26.8%) of the cultivated land devoted to feeding crops, which is not common in any other system. Vegetables remain an important commodity. They are grown on 34.4% of the cultivated land, with watermelon accounting for 11.3%. In this system, a diverse range of fruits, including tropical and temperate, are grown on 20% of the cultivated land. The governorates where this farming system is practiced are spread across several subzones from the Red Sea coast and the Aseer Scarp to the arid interior regions. This system requires full irrigation and has by far the highest seasonal water use (more than 13 000 m³/ha.)

The distribution of cropping systems across the four administrative regions in the southwestern part of the country is important because many agricultural activities are managed by regional administrations. The sorghum cropping system is almost entirely located in the Jazan region. The Aseer and Al Baha regions have cereal cropping systems based on terrace farming. Dates and watermelon systems are almost exclusively located in the Makkah region. The vegetable and fruit cropping system is shared primarily between the Al Baha and Makkah regions. The mixed system is spread across all four regions. Jazan is the region with the largest areas of cultivated land, followed by Makkah, Aseer and Al Baha.

4. Discussion

In the 2020 Global Food Security Index (https://foodsecurityindex.eiu.com, accessed 20 November 2021), KSA was ranked 38th overall. The country ranked 8th in food availability; 40th in food quality and safety; 42nd in food affordability; and 112th in natural resources and resilience. The country’s strengths are the low percentage of the population under the global poverty line; the presence and quality of food safety net programmes; access to financing for farmers; nutritional standards; heightened food safety; price stability for average food costs; low rates of food loss; and low agricultural import tariffs. Its weakness is insufficient public expenditures on agricultural research and development. The government policy supports rural and agricultural development in regions with traditional sustainable production systems. The southwestern regions of KSA, which have a long history of the production of field crops, as well as vegetables and fruits, have emerged as an important area in this regard.

The regions account for 10–15% of the total cultivated land and more than half of all agricultural holdings. The four regions in the southwestern part of the country (Al Baha, Aseer, Jazan and Makkah) are home to 14 million people or 40% of the national population. Therefore, their contribution of locally produced crops to the regional and national food supply is extremely important. This is especially true, given the observed trend of increasing rainfall in the Aseer Mountains demonstrating region potential [11].

Until recently, no systematic analysis of the cropping systems in the southwestern regions had been conducted. The current study represents the first attempt at a focused analysis of the crops grown in the southwestern regions that take into account natural resources and environmental conditions. The study was based on extensive crop production data, the characterization of agroclimatic conditions, and soil and weather data. Realizing the importance of taking a farming system approach, the current study entirely focused on cropping patterns. The many existing socio-economic approaches and instruments were not included in the scope of this study. However, the current analysis of the agroclimatic zones and cropping systems and their interaction has produced important outcomes.

The cropping systems described in the study have been evolving over thousands of years. They are largely based on older traditional crop varieties and landraces, which are cultivated using low-input technologies and limited mechanization [12]. Even though farmers continue to use traditional technologies and practices, the farming and cropping systems appear to have a relatively high degree of sustainability. Water resources and their efficient use for crop production remain a key component of the sustainability of cropping systems throughout the entire country. Farmers in the southwestern regions make use of millennia-old rainwater harvesting practices (e.g., spate flood irrigation and terraces). A careful evaluation of the current status of these practices is needed, as is the development of support programmes, especially targeting the improvement of infrastructure. A detailed and focused analysis of all sustainability components on farms and in villages is entirely justified and should be considered as a step toward the development of technological interventions for the enhancement of the existing cropping systems.

Sorghum has emerged as the key component in several cropping systems, owing to its use as both grains for human consumption and as forage for livestock. Because of its unique biological suitability for the dry and hot climate of the coast and mountain foothills, sorghum is at the core of the two most widespread cropping systems. It is grown all year, using harvested rainwater and supplementary irrigation. However, according to FAOSTAT, the area under sorghum has been decreasing over the last 10–15 years. There is no sorghum breeding or applied research programme in the country, and there is limited capacity for extension work with farmers. Establishing a targeted applied research and extension programme for sorghum and other cereal crops, especially millet, sesame and wheat, would contribute to increasing the productivity and profitability of these commodity crops. The key pathways for the sustainable development of the current cropping systems based on sorghum and cereals involve improvements in water-use efficiency, conservation agriculture and integrated pest management. The introduction, testing, selection and promotion of improved varieties can provide the basis for steady progress toward the enhancement of all aspects of these cropping systems.

The current study has demonstrated the relationship between different commodity crops and water use. The cultivation of cereals is associated with the lowest water use, whereas bananas, dates, watermelon and vegetables consume substantial amounts of water. However, the sorghum-dominated system has very low crop diversity, which is an important criterion for determining the sustainability of a system [13]. One of the general challenges for the cropping system in the southwestern regions is to maintain a relatively high diversity while keeping a medium level of water use. Although water-use efficiency was not included in this study, it is an important issue and another key component of system sustainability.

The southwestern regions of KSA have become the focus of a large government programme, titled The Sustainable Rural Agricultural Development (SRAD), which was initiated in 2019. The SRAD programme aims to enhance the production of rainfed cereals, subtropical fruits, rose oil and coffee Arabica; improve beekeeping and honey production; and augment production from the livestock and fisheries sectors. This will be achieved through several interventions that include innovative technologies and practices to increase productivity, and the enhancement of the capacities of rural agriculture institutions and small producers to access resources, services and markets. The outcomes of the current study may contribute to identifying the SRAD programme’s geographical priority areas and pilot governorates for different commodities. It can also contribute to designing the SRAD programme’s technical interventions, which will be integrated into existing cropping systems. For example, addressing issues related to water use and crop diversity in cropping systems will be a critical consideration. Finally, the current study calls for an integrated analysis of the cropping and farming systems and an assessment of their sustainability. The analysis should take into consideration economic, production and environmental aspects, as has been done by several studies and reviews [14,15,16]. Long-term rainfed farming traditions and the farmers’ commitment to their crops remain important factors in the design and implementation of interventions.

5. Conclusions

The southwestern regions of KSA are geographically and agriculturally diverse. Over millennia, crop production in these regions has evolved in ways that utilize the available natural resources (soil and rainfall) to satisfy the needs of local populations, support livestock, and generate profit from commercial production. They are the only regions of the country where crops are grown using sustainable and renewable water resources. The regions which produce cereal crops (sorghum, millet, sesame) and fruits (banana, mango, papaya) that are not grown in other regions, make a substantial contribution to national food security. In these regions, the study defined for the first time six cropping systems based on the share of different crops, their diversity and their water consumption. The main biophysical factors that shape the cropping patterns are topography, altitude, rainfall, air temperature and soils. Sorghum, which is grown on more than half of the total land under cultivation, has emerged as the dominant crop. Fruits (both subtropical and temperate) and open field vegetables are important for generating income for farmers. The main challenge facing the existing cropping systems in these regions is combining a more moderate use of water with greater crop diversity. Cereal production is associated with low water use, but the dominance of cereals within cropping systems reduces the systems’ overall diversity. On the other hand, fruit and vegetable production, which can serve to diversify cropping systems, is associated with high water consumption. Rainwater harvesting and irrigation efficiency can be improved to address this challenge. Another important issue is the low-input production technologies used in the cultivation of sorghum and other cereals. Landraces or older varieties are planted and very little if any, fertilizers and pesticides are applied. Often, only manual labour is used. This limits the adoption of modern technologies and practices and reduces the potential for increasing production and achieving greater profits for farmers. The introduction of sustainable intensification packages is needed. This process can begin with making new improved varieties accessible to farmers, adopting conservation agriculture and following integrated pest management practices. The cropping area in the southwestern regions can be substantially expanded in the future using the available fertile land if technologies that increase water-use efficiency and enhance production are applied. Sustainability remains an essential objective in the transformation of the cropping systems.