Simulation of Water–Energy Nexus of the Spatial Patterns of Crops and Irrigation Technologies in the Cascade Pump Station Irrigation District

: Cascade pump station irrigation districts (CPSIDs) consume vast amounts of irrigation water and energy. The aim of this study was to adjust the spatial patterns of crops and irrigation technologies in the CPSID to reduce the consumption of water and energy under the condition of conserving crop irrigation water. The irrigation district (ID) is divided into several sub-districts according to the topography elevation difference and the distribution of cascade pump stations (CPSs). The mathematical models of the irrigation water and energy consumption in each sub-district were established based on the relationship between the spatial patterns of crops and irrigation technologies in each sub-district. According to the present situation of the Jingdian Phase I Irrigation District in the arid region of northwest China, three modes of adjusting the crop planting structure and drip irrigation area were proposed. Based on the combination of these modes, three schemes of the spatial patterns of crops and irrigation technologies were generated. The annual energy consumption and irrigation water consumption of each sub-district in the ID of these three schemes were obtained through simulation. Compared with the present spatial patterns of crops and irrigation technologies in the Jingdian Phase I Irrigation District, Scheme 3 has the best water-saving and energy-saving effects, with an annual water saving and energy saving of 1753 × 10 4 m 3 and 2898 × 10 4 kWh, and the water-saving rate and energy-saving rate were 12.34% and 15.74%, respectively. This paper also shows that the synchronous adjustment of crops and irrigation technologies among the sub-districts of ID can achieve signiﬁcant water-saving and energy-saving effects.


Introduction
With the development of the social economy, the demand for energy and water is increasing, and the demand for environmental protection is also increasing [1,2]. There are many cascade pump station irrigation districts (CPSIDs) in China, Myanmar, India, and Central Asian countries [3,4]. In these irrigation districts (IDs), to irrigate crops, water is sent to the drylands with higher elevations through the cascade pump stations (CPSs) to provide reliable water resources for the development of local agricultural planting and greatly improve the production and living conditions of local farmers. The cumulative head can be up to hundreds of meters in some CPS, and irrigating crops in these IDs consumes a large amount of water and energy.

Study Area and Analysis
Data for the Jingdian Phase I Irrigation District were obtained from the administrative department of the district, namely the Jingtaichuan Electric Lifting Irrigation Water Resources Utilization Center of Gansu Province.
The Jingdian Phase I Irrigation District is located in the central part of Gansu Province in northwest China, at 103 • 20 -104 • 04 E and 37 • 26 -38 • 41 N. The location of the ID is shown in Figure 1. The terrain of the ID is high in the southwest and low in the northeast. The ID belongs to an extremely arid region. The average annual precipitation and the average annual evaporation are 184 mm and 2289.9 mm, respectively. The soil of the ID is sandy loam. There are 13 pump stations in the Jingdian Phase I Irrigation District. The irrigation area controlled by the last two pump stations is only 212 ha (0.01% of the total area of the ID), so the last two pump stations are incorporated into the 11th pump station; that is, there are 11 pump stations in the ID. The parameters of the pump stations are shown in Table 1. According to the elevation difference and the distribution of the CPSs, the ID is divided into eight sub-districts; the parameters of each sub-district are shown in Table 2. Water from the Yellow River is transported to the farmland through the CPS, water conveyance pipe and channel (WCP&C), as well as the water distribution pipe and channel system (WDP&CS) of each sub-district. The irrigation techniques for the farmland in the ID are surface and drip irrigation. The Jingdian Phase I Irrigation District comprises a complex water source system ( Figure 2) (the Yellow River), 11 CPSs, 11 WCP&C segments, and eight sub-districts. Each sub-district contains WDP&CS, a surface irrigation unit (SIU), and a drip irrigation unit (DIU), as shown in Figure 3. The WDP&CS consists of open channel systems and pipe networks. Water from the WCP&C is diverted to the SIU by the open channel system for surface irrigation. The water from the WCP&C is sent to the DIU through pipe networks. There are eight crops in the SIU and five crops in the DIU, as shown in Figure 3 and Table 3.  There are 13 pump stations in the Jingdian Phase I Irrigation District. The irrigation area controlled by the last two pump stations is only 212 ha (0.01% of the total area of the ID), so the last two pump stations are incorporated into the 11th pump station; that is, there are 11 pump stations in the ID. The parameters of the pump stations are shown in Table 1. According to the elevation difference and the distribution of the CPSs, the ID is divided into eight sub-districts; the parameters of each sub-district are shown in Table 2. Water from the Yellow River is transported to the farmland through the CPS, water conveyance pipe and channel (WCP&C), as well as the water distribution pipe and channel system (WDP&CS) of each sub-district. The irrigation techniques for the farmland in the ID are surface and drip irrigation. The Jingdian Phase I Irrigation District comprises a complex water source system ( Figure 2) (the Yellow River), 11 CPSs, 11 WCP&C segments, and eight sub-districts. Each sub-district contains WDP&CS, a surface irrigation unit (SIU), and a drip irrigation unit (DIU), as shown in Figure 3. The WDP&CS consists of open channel systems and pipe networks. Water from the WCP&C is diverted to the SIU by the open channel system for surface irrigation. The water from the WCP&C is sent to the DIU through pipe networks. There are eight crops in the SIU and five crops in the DIU, as shown in Figure 3 and Table 3.           The first pump station pumps water from the Yellow River, and the design discharge of each pump station decreases successively (Table 1) due to two reasons. One reason is the loss of water that occurs in each WCP&C segment connecting the two pump stations.
Another reason is that the WCP&C supplies water to various sub-districts for crop irrigation. The efficiency of the WCP&C segment represents the water loss degree of the segment between 2 pump stations, which can be represented as the ratio of its outflow and inflow (Table 4). From the 4th pump station, water from the WCP&C is fed into the WDP&CS of the sub-districts to irrigate the crops in the farmland. The water supply of each subdistrict should cover two parts. The first part is the irrigation water for crop growth in the sub-district, which is related to the net irrigation quota (Table 3) based on the type of irrigation technologies and crops. The other part is the water loss through the WDP&CS in the sub-district and the water loss in the farmland, which is related to the irrigation technology. Table 2 shows the irrigation efficiency of different irrigation units (SIU and DIU) in each sub-district. The irrigation area of the Jingdian Phase I Irrigation District was 21,951 ha in 2020, the annual irrigation water is 14,210 × 10 4 m 3 , the annual energy consumption of the CPS and DIU is 18,412 × 10 4 kWh. The present situation of the spatial patterns of crops and irrigation technologies in 2020 (Scheme 0) is shown in Table 5.  Table 5. Present situation of the spatial patterns of crops and irrigation technologies (ha, Scheme 0). 1  64  112  20  24  30  27  36  18  26  0  0  0  0  2  415  726  127  155  194  174  233  116  0  166  0  0  0  3  1176  2058  359  439  549  494  659  329  0  0  200  270  0  4  428  748  131  160  199  179  239  120  0  0  0  0  171  5  145  254  44  54  68  61  81  41  0  58  0  0  0  6  730  1277  223  272  341  306  409  204  182  0  110  0  0  7  622  1088  190  232  290  261  348  174  0  100  0  149  0  8  372  651  114  139  174  156  208  104  0  0  148  0  0 Note: Crop abbreviation as shown in Table 3.

Sub-District Surface Irrigation Unit Drip Irrigation Unit
The focus of this study is to reasonably determine the spatial patterns of crops and irrigation technologies in each sub-district. A good arrangement will reduce the total consumption of energy and irrigation water in the whole ID. This involves the present situation of the ID, the cumulative head of each sub-district, the irrigation water consumption of various crops, and the water efficiency of various irrigation technologies.

Sub-District Surface Irrigation Unit
The annual irrigation amount of sub-district i is calculated by: where w i is the annual irrigation water consumption of sub-district i (m 3 ); s ijk is the area of crop k in unit j of sub-district i (ha), as shown in Table 5.
The annual irrigation amount of the ID is calculated by: where W is the annual irrigation amount of the ID (m 3 ). As shown in Figure 2, in the process of irrigation, water from the Yellow River should be pumped to sub-district i through pump station p = 1, 2, . . . , i + 3. The annual energy consumption per unit area of crop k of an SIU (j = 1) in sub-district i is calculated according to Equation (4) [6,25]: where e i1k is the annual energy consumption per unit area of an SIU (kWh/ha); p is the number of pump stations, H p is the head of pump stations (m), α p is the efficiency of pump stations (%). The above data can be obtained from Table 1.
The annual energy consumption per unit area of crop k of a DIU (j = 2) in sub-district i is calculated according to Equation (5): where e i2k is the annual energy consumption per unit area of a DIU (kWh/ha); H 2 is the head of the pump station of the drip irrigation system (m), H 2 = 50 m. The 50 m head should meet the requirements of two aspects: firstly, the working head of the drip emitter is 10 m; secondly, the head loss of the pipe network system of drip irrigation is 40 m. α 2 is the efficiency of the pump station of the drip irrigation system (%, α 2 = 82%). Table 7 shows the annual energy consumption per unit area of crops under different irrigation technologies. Table 7. The annual energy consumption per unit area of various crops (kWh/ha). Drip Irrigation Unit   W  M  F  A  P1  V  P2  O  A  P1  V  P2  O   1  5668  5744  4745  4481  4284  6037  4759  5209  2188  2080  3062  2310  2538  2  6347  6432  5314  5018  4797  7062  5329  5833  2410  2292  3374  2546  2797  3  7212  7309  6039  5703  5452  8025  6056  6629  2694  2561  3771  2845  3126  4  8353  8465  6993  6604  6314  9295  7014  7677  3068  2917  4295  3240  3560  5  9574  9703  8016  7570  7237 10,654  8039  8800  3469  3298  4855  3663  4025  6 10,749 10 The annual energy consumption of sub-district i is calculated according to Equation (6):

Sub-District Surface Irrigation Unit
where E i is the annual energy consumption of the sub-district i (kWh). The annual energy consumption of the ID is calculated according to Equation (7): where F is the annual energy consumption of the ID (kWh).

Calculation Method of Irrigation Water Consumption and Energy Consumption
According to the above models, the irrigation water and energy consumption of each sub-district are calculated. Combined with the present situation (Table 5, Scheme 0), the calculation steps are as follows: (1) The data in Tables 2-4 were substituted into Equation (1) to obtain the gross irrigation quota q ijk (Table 6). (2) The data in Tables 5 and 6 were substituted into Equation (2) to obtain the annual irrigation water consumption of sub-district w i (Table 8). According to Equation (3), the annual irrigation amount of the ID is 14,210 × 10 4 m 3 (Scheme 0). (3) The data in Tables 1-4 were substituted into Equations (4) and (5) to obtain the annual energy consumption per unit area e ijk (Table 7). (4) The data in Tables 5 and 7 were substituted into Equation (6) to obtain the annual energy consumption E i of each sub-district (Table 9). According to Equation (7), the annual energy consumption of the irrigation district is 18,412 × 10 4 kWh (Scheme 0).

Adjustment and Evaluation of the Spatial Patterns of Crops and Irrigation Technologies
The spatial patterns of crops and irrigation technologies in the ID will be adjusted based on the present situation (Scheme 0). Different adjustment schemes of the spatial patterns of crops and irrigation technologies will be formed according to certain adjustment principles. Taking Scheme 0 as the baseline, the effect of water saving and energy saving of each adjustment scheme will be evaluated. This research provides a basis for optimizing the spatial patterns of crops and irrigation technologies in the CPSID. This principle is to avoid the deterioration of the ecological environment in arid regions caused by blindly expanding irrigation areas. The area of each sub-district shall meet Equation (8):

The Principles of the Adjustment
where S i is the area of the sub-district (ha), as shown in Table 2.
• Principle 2: The adjustment is integrated with existing irrigation facilities.
In the process of adjustment, to reduce the project investment, the WCP&C and CPS remain the status quo, and the pre-existing crop types and areas of drip irrigation in the DIU in each sub-district remain unchanged.

•
Principle 3: Adjusting the spatial pattern based on the net irrigation quotas.
Different crops use different irrigation technologies; their net irrigation quotas are also different. The net irrigation quota is ranked in ascending order, as shown in Table 3. In the process of adjusting the spatial patterns of crops and irrigation technologies, the crops with the smallest net irrigation quota for drip irrigation are placed in the sub-district with the highest cumulative head, and the crops with the largest net irrigation quota for surface irrigation are placed in the sub-district with the lowest cumulative head. According to this principle, the spatial patterns of each sub-district are adjusted to reduce the water and energy consumption in the CPSID.

Adjustment Modes
The ID is composed of several sub-districts ( Figure 2). Each sub-district has an SIU and DIU; each unit contains several crops with a different irrigated area (Figure 3). To achieve water and energy savings, the following adjustment modes are formed.

•
Mode 1: Adjust the spatial patterns among sub-districts.
Following Principles 1, 2, and 3, adjust the spatial patterns of crops and irrigation technologies among sub-districts.

•
Mode 2: Adjust the crop planting structure within the unit in each sub-district.
According to Principles 1 and 2, part or all of the crop areas with the higher net irrigation quota are transferred to those with the lower net irrigation quota within the unit (SIU or DIU) in each sub-district.

•
Mode 3: Adjust crop irrigation technology between the units in the sub-district.
According to Principles 1 and 2, change part or all of the crop areas in the SIU to the DIU in the sub-district.

Evaluation Indexes of Water-Saving and Energy-Saving
To analyze and evaluate the effects of water and energy savings of each scheme, the following evaluation indexes of water and energy savings are proposed based on the present situation (Scheme 0).
The water-saving rate of each sub-district for Scheme r (r is the number of spatial patterns schemes, r = 1,2,3) is calculated as: where θ ri is the water-saving rate of sub-district i in Scheme r (%); w ri is the irrigation water consumption of sub-district i in Scheme r (m 3 ); w 0i is the irrigation water consumption of sub-district i in Scheme 0 (m 3 ). The water-saving rate of the ID for Scheme r is calculated as: where Θ r is the water-saving rate of the ID in Scheme r (%); W r is the irrigation water consumption of the ID in Scheme r (m 3 ); W 0 is the irrigation water consumption of the ID in Scheme 0 (m 3 ). The energy-saving rate of each sub-district is calculated as: where ϕ ri is the energy-saving rate (%) of sub-district i in Scheme r (%); E ri is the annual energy consumption of sub-district i in Scheme r (kWh). E 0i is the annual energy of sub-district i in Scheme 0 (kWh). The energy-saving rate of the ID in each scheme is calculated as: where Φ r is the energy-saving rate of the ID in Scheme r (%); F r is the annual energy consumption of the ID in Scheme r (kWh); F 0 is the annual energy consumption of the ID in Scheme 0 (kWh).

Results Analysis
Three different schemes of spatial patterns were formed based on the different combinations of the three modes above.

Scheme 1 (Mode 1)
According to Mode 1, Scheme 1 is adjusted based on Scheme 0 ( Table 5). The adjustment starts from sub-district 8 with a cumulative head of 479.10 m (the highest). According to Principles 2 and 3, SN (sequence number) 1-5 of the net irrigation quotas (Table 3) are the crops of the DIU in Scheme 0, which already satisfy the requirements. All 1845 ha of pear trees (SN 6) in the SIU are transferred to sub-district 8, while the 73 ha of apple trees (SN 7) in the SIU are transferred to sub-district 8, and 148 ha of vegetables in the DIU of Scheme 0. The sum of these three terms is 2066 ha, which is equal to the area of sub-district 8 ( Table 2) and meets the requirement of Principle 1 and Equation (8). Then sub-district 7 with the cumulative head of 451.99 m is adjusted. According to Principles 2 and 3, the following adjustments are made: transfer all the other 1402 ha of apple trees (SN 7) of the SIU to sub-district 7, transfer the 1208 ha of flax (SN 8) of the SIU to sub-district 7, transfer the 595 ha of potatoes (SN 9) to sub-district 7, as well as 100 ha of pear trees and 149 ha of potatoes in the SIU of Scheme 0. The sum of the above five items is the area of sub-district 7, totaling 3454 ha (Table 2), which meets the requirement of Principle 1. Following the same principles, the spatial patterns of crops and irrigation technologies in sub-districts 1-6 are adjusted. Thus, the spatial patterns of Scheme 1 are formed (Table 10). To obtain the annual irrigation water consumption in each sub-district and the whole ID for Scheme 1, the data in Tables 5 and 6 are substituted into Equations (2) and (3) (Table 8). The data in Tables 5 and 7 are substituted into Equations (6) and (7) to obtain the annual energy consumption of each sub-district and the whole ID for Scheme 1 ( Table 9). The data in Table 8 are substituted into Equations (9) and (10) to obtain the water-saving rate of each sub-district and the whole ID for Scheme 1 (Table 11). Substitute the data in Table 9 into Equations (11) and (12) to obtain the energy-saving rate of each sub-district and the whole ID for Scheme 1 ( Table 12). The irrigation water consumption and energy consumption in sub-districts 6-8 of Scheme 1 are all smaller than that in Scheme 0, while the irrigation water consumption and energy consumption in sub-districts 1-5 are both larger than that in Scheme 0. The water-saving rate and energy-saving rate in the ID for Scheme 1 are 0.53% and 2.51%, respectively (Tables 11 and 12).  Table 3. Table 11. Water-saving rate of each sub-district and irrigation district in each scheme (%).  According to Modes 2 and 3, Scheme 2 is adjusted based on Scheme 0 (Table 5). First, according to Mode 2, the 50% area of corn with the highest net irrigation quota (SN 12) is adjusted to flax (SN 8) in the SIU of each sub-district, and the rest sub-districts are adjusted accordingly. Then, according to Mode 3, all the areas of apple trees and vegetables in the SIU in each sub-district of Scheme 0 are adjusted to the DIU in the same sub-district. Then form the spatial patterns of Scheme 2 ( Table 13). The results show that synchronous adjustment of crop and irrigation technology can achieve a more obvious effect of water and energy savings than a single adjustment of the crop planting structure or irrigation technology. The water-saving rate and energy-saving rate in each sub-district of Scheme 2 are positive (Tables 11 and 12). Table 13. The spatial patterns of crops and irrigation technologies of Scheme 2 (ha).

Scheme 3 (Mode 2 + Mode 3 + Mode 1)
According to Modes 2, 3, and 1, Scheme 3 is adjusted based on Scheme 2. According to Mode 1, the crops with the smallest net irrigation quota in Scheme 2 are adjusted downward from the sub-district with the highest cumulative head, then form the spatial patterns of Scheme 3 (Table 14). Compared with Scheme 0, the water-saving rate and energy-saving rate in sub-districts 1-3 of Scheme 3 are negative, while the water-saving rate and energy-saving rate in sub-districts 4-8 of Scheme 3 are positive. The water-saving rate and energy saving rate in the ID are 12.34% and 15.74%, respectively (Tables 11 and 12), which are superior to Scheme 2. The results showed that coordinated adjustment of the spatial patterns of crops and irrigation technologies among the sub-districts has a more significant effect on water and energy savings.   Table 3.

Discussion
In some large-scale IDs, to achieve the purpose of reducing irrigation water consumption, pressure pipes are used to replace open channels, and water-saving irrigation systems (such as sprinklers or drip irrigation systems) are taken for irrigation [26,27], but it increases the energy consumption and cost [6,28,29]. To reduce the energy consumption of the irrigation pressure pipe networks, a large amount of research has been carried out [30][31][32]. The research in this paper shows that drip irrigation technology can reduce the consumption of water and energy in the high lift CPSIDs.
There are two main reasons for drip irrigation to save water in the CPSIDs. One reason is that the net irrigation quota of surface irrigation is higher than that of drip irrigation for the same crop, because the wetting range of drip irrigation is limited to the soil near the crop root layer, while the soil evaporation of drip irrigation is much less than that of surface irrigation. For example, for an apple tree, the net irrigation quotas of surface irrigation and drip irrigation are 3226 m 3 /ha and 1784 m 3 /ha, respectively ( Table 3). The net irrigation quota of drip irrigation is 45% lower than that of surface irrigation. The other reason is that the leakage and evaporation loss of the irrigation water by surface irrigation and drip irrigation are different in water transportation. For the same crop in the same sub-district, the gross irrigation quota of surface irrigation is much higher than that of drip irrigation. The water loss during the transportation is divided into two parts. The first part is the water loss from the water source to the sub-district in each WCP&C segment. According to Equation (1) and Table 3, the loss ratio of the two irrigation technologies is the same. The second part is to send water from the WCP&C segment to the field; in this part, the loss ratios of the two irrigation technologies are very different because the irrigation water of the SIU is sent to the field through the channel system, while that of the DIU is sent to the crops through the pressurized pipe network and drip emitters. For example, in sub-district 1 (the cumulative head is 270.80 m), the gross irrigation quotas of surface irrigation and drip irrigation for the apple tree are 5227 m 3 /ha and 2168 m 3 /ha, respectively ( Table 6). The gross irrigation quota of drip irrigation is 58% lower than surface irrigation. The higher the cumulative head of the sub-district, the greater the difference in the gross irrigation quota between the surface and drip irrigation technology for the same crop. Because the higher the cumulative head of the sub-district to which the water is sent, the more WCP&C segments are traversed, the longer the distance of water delivery and the higher the proportion of water is lost. For example, in sub-district 8 (the cumulative head is 479.10 m), the gross irrigation quotas of surface irrigation and drip irrigation for apple trees are 6474 m 3 /ha and 2657 m 3 /ha, respectively ( Table 6). The gross irrigation quota of drip irrigation is 59% lower than surface irrigation.
Drip irrigation saves energy mainly because it saves water. In the high lift CPSIDs, water saving means energy saving. The process of lifting the irrigation water from the source to the field through the pump station can be divided into two stages. The first stage is from the water source to the sub-districts. The second stage is to transfer water from the WCP&C segment of each sub-district to the fields of the SIU and the crops of the DIU, respectively. According to the data in Tables 3 and 6, the net irrigation quota or gross irrigation quota for the same crop irrigated by drip irrigation technology is less than surface irrigation; therefore, in the first stage, water is lifted from the water source to a certain sub-district through CPSs; surface irrigation will increase more water per unit area than drip irrigation, so the energy consumption of surface irrigation will be higher. In the second stage, water flows through the channel system into the field by the SIU. As shown in Equation (4), to ensure the normal operation of the drip irrigation system, the irrigation water from the WCP&C segment should be pressurized 50 m through the pump stations.
Although the drip irrigation system requires pressure, it consumes far less energy than surface irrigation in the CPSID. There are two reasons: (1) drip irrigation saves a lot of energy compared to surface irrigation. (2) The amount of water required by drip irrigation is much lower than that of surface irrigation. Although the drip irrigation system requires an increase of 50 m water head, its proportion in the cumulative head is relatively low. The 50 m water head required by drip irrigation is 18.46% of the cumulative head (270.80 m) in sub-district 1. The annual energy consumption per unit area of surface irrigation and drip irrigation for the apple tree in sub-district 1 is 4481 kWh/ha and 2188 kWh/ha, respectively. Drip irrigation is 51.17% lower in energy consumption than surface irrigation. In sub-district 8, the 50 m head is 10.43% of the cumulative head (479.10 m). The energy consumption per unit area of surface irrigation and drip irrigation for apple trees is 10,302 kWh and 4602 kWh, respectively. Drip irrigation is 55.33% lower than surface irrigation, which also indicates that a higher cumulative head of drip irrigation in the sub-district is more energy efficient.
It is necessary to increase the investment to expand the drip irrigation area in the CPSID [12,13]. Changing surface irrigation to drip irrigation and adjusting the crop planting structure will improve the crop output value in the CPSID [14]. Water and energy savings in the CPSID will also produce economic and ecological environmental benefits. The benefit analysis of the input and output of the CPSID caused by the above reasons should be further studied.

Conclusions
Based on the water-energy nexus of the Jingdian Phase I Irrigation District, two methods to reduce the consumption of energy and irrigation water in the ID are proposed: the first method is to adjust the planting pattern of crops, that is, to change the crops with high water consumption to the crops with low water consumption; the second method is to adjust the pattern of irrigation technologies, which means to change surface irrigation to drip irrigation. According to the two methods proposed, combined with the characteristics of the CPSIDs, three regulating principles and three modes are proposed to regulate the spatial patterns of crops and irrigation technologies. Three adjustment schemes have been formed by the combination of the three modes. The proposed mathematical model for energy consumption and irrigation water consumption, as well as water and energy-saving evaluation indicators, are the basis for the adjustment of the spatial patterns of crops and irrigation technologies in the CPSIDs. The application of drip irrigation technology in the CPSIDs saves both water and energy. In the CPSIDs, the higher the cumulative head, the more significant the water-saving and energy-saving effect of drip irrigation technology. Simultaneously, adjusting the spatial pattern of crops and irrigation technologies in each sub-district has a better effect than adjusting crop planting structure alone or expanding drip irrigation area alone. According to Principle 3, adjusting the spatial patterns of crops and irrigation technologies among the sub-districts of the ID is better than adjusting the spatial pattern within the sub-districts. The results of this research show that adjusting the spatial patterns of crops and irrigation technologies has great potential for water and energy savings in the CPSIDs, which is of great significance to the sustainable development of the CPSIDs.
Author Contributions: Data curation, C.B., Y.Z. and W.P.; writing-original draft preparation, C.B.; writing-review and editing, C.B., L.Y. and C.W.; conceptualization, methodology, and supervision., L.Y. All authors have read and agreed to the published version of the manuscript.
Funding: This study is supported by National Natural Science Foundation of China (41571222).
Institutional Review Board Statement: Not applicable.

Informed Consent Statement: Not applicable.
Data Availability Statement: The data are available on request.

Acknowledgments:
The authors appreciated the editor and anonymous reviewers for their constructive comments and suggestions on the revision of this paper.

Conflicts of Interest:
The authors declare no conflict of interest.

CPSID
cascade pump station irrigation district CPS cascade pump station ID irrigation district WCP&C water conveyance pipe and channel WDP&CS water distribution pipe and channel system SIU surface irrigation unit DIU drip irrigation unit SN sequence number