When considering the issue of the sustainability of economic growth, the constraints of natural resources and climate change are always present, and the interaction between climate change and economic growth is of increasing concern [1
]. Technological change, including changes in the utilization efficiency of natural resources, is a possible way to solve the current dilemma of sustainable development [3
], because it has a direct impact on the total scale of natural resource utilization, and thus directly influences whether the regional social economy is in a sustainable development state [5
]. Technological change in agriculture irrigation water use efficiency is of fundamental significance for solving water scarcity and increasing crop productivity, and achieving highly efficient irrigation is crucial to balancing water resources input and sustainable agricultural economic growth [7
The theory of technological change generally distinguishes two types of technological change: technological catch-up and technological diffusion. Technological catch-up concerns the knowledge production function and occurs through the mechanism of learning by doing. It requires continuous additional capital inputs and manufacturers, and the labor force must constantly learn and master new skills in the production process, which brings about extensive progress in social productivity [3
]. Technological diffusion is brought about by technological transmission and is mainly realized through open trade, technology transfer, information flows, and spatial spillover effects [13
]. It is generally believed that technological change will gradually converge to an optimal efficiency level at a certain stage of development. At the same time, the speed of improvement of an advanced region is slower than that of a backward region, which is relevant to the distribution of a conditional convergence model. In this study, the conditional convergence model refers to an exponential model that reflects the long-term changes in technological efficiency of economies with similar structural characteristics [17
The coefficient of the effective utilization of irrigation water is a comprehensive technological efficiency indicator that reflects the quality of irrigation projects, the level of irrigation technology, and the level of water management, which generally refers to the ratio of the amount of water that can be absorbed and utilized by crops in the field and the total amount of water introduced by the canal head from the perspective of irrigation scientists [21
]. The coefficient summarizes the basic data used for evaluating the efficiency and potential of agricultural irrigation, ensuring the scientific allocation of regional resources and undertaking development planning for water-saving irrigation. In addition, it provides an important basis for government departments to make macro decisions [25
]. The influencing factors in water use efficiency involve many disciplines, such as climatology, hydrology, agronomy, engineering, economy, management, and institutions. The following three factors broadly summarize the key influences. (1) Natural conditions: it is recognized that complex and variable natural conditions (including climatic conditions, soil conditions, hydrological conditions, and the evolution of the irrigation area) can have a direct impact on regional water resources, and thus affect the water use efficiency of agricultural irrigation [26
]. A typical example is that of southern China, with its humid climate and abundant rainfall, as well as lack of incentives and motivation to implement water-saving irrigation [30
]. (2) The construction and management of the irrigation area: modernization of the construction and management of the irrigation area (which encompasses engineering construction, management systems and mechanisms, and the application of advanced irrigation technology) is an important component in improving irrigation water use efficiency, extreme natural disaster governance, and regional ecological sustainable development, thus providing strong support for the development of modern water-saving agriculture [25
]. (3) Economic policy: an increasing number of studies have found that economic policy (including subsidy policies, water price policies, and water use restrictions) can affect the preferences and behaviors of peasant households, and provide them with incentives to use water-saving irrigation technology and to change their crop planting structure, which leads to changes in the water use efficiency of agricultural irrigation [36
]. In addition, some scholars have found that other factors such as geographic spatial distribution [30
], irrigation strategies and planting patterns [40
], and crop types [9
] have an impact on the water use efficiency of agricultural irrigation.
The diversity and complexity of influencing factors make it difficult to predict irrigation water use efficiency and, to our best knowledge, there are few predictive studies on irrigation water use efficiency. Most studies take a biological perspective and measure the water use efficiency of specific crops under different irrigation conditions [44
] or predict the irrigation water demand for a period of time in the future through complex multidisciplinary models [47
]. Moreover, because the technological change of water resources utilization efficiency is often determined by exogenous forces, there is no mechanism to support the predictive theoretical derivation.
The shared socioeconomic pathways (SSPs) recently proposed by the Intergovernmental Panel on Climate Change can assist in analyzing the change and future evolution of the effective utilization coefficient of irrigation water, a key indicator of water resources technological change, from the broader perspective of climate change and the selection of socioeconomic development pathways. Thus, it can provide a new basis for the prediction of irrigation water efficiency [51
]. The SSPs quantitatively describe five typical development pathways of the future social economy and distinguish coping capacity and adaptive capacity for different emission concentrations and climate change scenarios caused by the different development pathways. Thus, they can assist in predicting the change in the effective utilization coefficient of irrigation water in the future from the perspective of different social and economic development pathways [52
]. At present, studies considering the impact of economic policy and development patterns on technological change under the influence of climate change are relatively rare, and the setting of future scenarios is subjective. There is no systematic and comparable unified standard for setting scenarios. Moreover, in terms of model settings, the classification of the simulated objects involved is oversimplified. For example, often, the simulated objects are only grouped by income level, without establishing a multi-dimensional index system to evaluate and group the simulated objects [55
The Water Futures and Solutions (WFaS) extended the original SSPs framework and proposed the hydro-economic (HE) classification method, which can be combined with the scenario settings of the SSPs to group regions by their different economic and water resources conditions [58
]. The extended SSPs–HE framework inputs more important features into the model, and assists in accurately setting optimal efficiency target values, convergence speeds, convergence time, and other parameters for the different regions. It also assists in simulating the curves demonstrating the technological change in water resources utilization in different regions under various scenarios, and thus lays a solid scientific foundation for predicting water resources utilization. Compared with the previous studies, which focused excessively on small-scale water-saving effects and the field of engineering, the extended SSPs–HE framework combines a broad perspective on the entire hydrographic basin with comprehensive management of water resources to evaluate different social and economic pathways selections from the angle of water use efficiency. It assists in choosing a suitable way to realize the Chinese Government’s requirements for a strict water resource management system. It can also be used to analyze the influence of different socioeconomic development pathways on water use efficiency and to determine suggestions for socioeconomic improvement [47
The scale of agricultural production in China is large and agricultural water accounts for 61.4% of total water use [61
]. The study of irrigation water efficiency is of profound significance for solving the complex water resources problem in rural areas and realizing sustainable economic and social development. Since the implementation of the strict water resources management system was clearly proposed in the No. 1 document of the Communist Party of China (CPC) Central Committee in 2011, China has attached great importance to water use efficiency for agricultural irrigation, and it has been elevated to the macro and strategic level of national economic development. In the specific implementation opinions subsequently issued by the CPC, three red bottom lines on water resources management were clearly established, one of which requires China’s effective utilization coefficient of irrigation water to be raised to more than 0.6 by 2030 [62
]. In 2015 and 2016, the national average coefficients were 0.536 and 0.542, respectively [63
]. To put this in context, in Israel, which has advanced water-saving irrigation technology, the effective utilization coefficient of irrigation water is above 0.9 [65
The objective of this study is to group 31 Chinese provinces according to their different economic and water resources conditions by HE classifications. The water use scenario and parameters can be determined combined with the SSPs scenario settings and HE classification characteristics. The equation of technological diffusion mechanism, the conditional convergence model, is the core tool to predict irrigation water use efficiency. The principle is to set the optimal efficiency target value, the convergence speed, convergence time, and other parameters, in order to simulate the curve for the effective utilization coefficient of irrigation water. The parallel aim is to understand the technological level of the water resources utilization of each province under different scenarios for specific years in the future, and find the improvement pathways for irrigation water use efficiency for specific regions.
This study attempts to solve three key scientific problems: (1) establishing an HE classification method for the evaluation of each province, (2) combining the HE classification results with the SSPs framework to set parameters for the future scenarios, and (3) establishing a conditional convergence model and using the parameters in the model for simulations.
4. Simulation and Results Analysis
4.1. Prediction of the Irrigation Water Use Efficiency of Each Province
On the basis of the HE classification results for each province and the description of irrigation water use scenarios under different socioeconomic pathways, we can further predict the effective utilization coefficients of irrigation water in each province under different SSPs, as shown in Figure 3
Taking an overall view of the five development pathways, the effective utilization coefficients of irrigation water in half of the provinces converge to 0.6 under SSP1, SSP2, and SSP5 by 2030, whereas only nine provinces reach 0.6 under SSP3 and 11 provinces do under SSP4. The HE-3 class has the highest proportion (100%) of provinces that can achieve the irrigation water use efficiency target under every development pathway in 2030, followed by the HE-4 class (64%), and then the HE-2 class (53%). The HE-1 class has the lowest proportion (9%) of provinces successfully reaching the 0.6 target. Provinces with severe hydrological conditions generally have higher water use efficiency than do provinces with low hydrological challenges.
Comparing the simulation values in 2016 and 2030, HE-3 provinces present the largest improvement in efficiency. All HE-3 provinces have a coefficient of more than 0.6 under each pathway in 2030. Indeed, with the except of Liaoning, the coefficients of these provinces are above 0.7, with Shanghai close to 0.9. Moreover, the differences in the coefficients between the five pathways are relatively small for the HE-3 provinces, with a standard deviation below 0.02.
For HE-2 provinces, Zhejiang has the highest effective irrigation water use coefficient, followed by Fujian and Guangdong. Under SSP3, the coefficients of these three provinces are all lower than the target of 0.6 in 2030. However, under the other pathways, Zhejiang and Fujian do achieve coefficients higher than 0.6, although Guangdong still fails to reach 0.6 by 2030.
For HE-1 provinces, only Jilin and Hainan reach the 0.6 target under SSP1, SSP2, and SSP5. The other provinces in the HE-1 class have relatively low efficiency compared with all the HE provinces because abundant resources mean there is no pressure to reduce water use and there is limited investment in water-saving facilities.
Provinces in HE-4 are facing large uncertainties regarding water use efficiency in the future owing to their backward economies and strong pressure on scarce water resources. HE-4 provinces have the largest fluctuations in water use efficiency under the different pathways of all four HE classifications, with a standard deviation of more than 0.02 in 2030. The standard deviation in Hebei and Shandong is even higher, at 0.03. The effective water use coefficient of most provinces in the HE-4 quadrant would be above 0.6 in 2030 under SSP1, SSP2, SSP4, and SSP5. Only Ningxia and Inner Mongolia would be below 0.6, but both would be very close to reaching this target.
4.2. Analysis for Typical HE Provinces
On the basis of the relative location of the provinces in HE quadrant space, Hubei, Guangdong, Jiangsu, and Gansu are selected as representatives of all provinces in HE-1, HE-2, HE-3, and HE-4 quadrants, respectively, and used to illustrate the convergence of the effective utilization coefficients of irrigation water in these four classes under different pathways from 2016 to 2030 (Figure 4
Jiangsu, a province with high pressure on water use and a strong economy, has a high effective utilization coefficient of irrigation water under the five pathways, and easily reaches the national standard of 0.6 by 2030. Jiangsu irrigation water use efficiency is highest under SSP1 and SSP4 (as the two curves coincide), and Jiangsu would remain in the efficient growth period with adequate potential for technological change. Its irrigation water use efficiency under SSP5 is the third-best case, with the coefficient reaching 0.68 in 2030, but with relatively narrow scope remaining for technological change improvements compared with SSP1 and SSP4. Under SSP3, the efficiency of irrigation water converges quickly but essentially remains unchanged after reaching 0.68, and there is no room for further technological improvement.
Gansu, which is under strong pressure to reduce water use and has a weak economy, has a generally lower irrigation water use efficiency compared with that of Jiangsu. Owing to adequate capital and open channels for technological transmission, the irrigation water use efficiency is at a relatively high level under SSP1 and SSP5 (the two curves coincide). Not only would the irrigation water use efficiency target be reached by 2030, but there would remain room for improvement in the future, although the improvement rate would be lower than that in Jiangsu. Under SSP2, because recent policies have placed strong emphasis on water saving, the irrigation water use efficiency would improve rapidly and then converge to 0.6. However, it would then remain unchanged because of a lack of financial support and slow technological diffusion. For the highly unbalanced SSP4 scenario, backward provinces such as Gansu are at a disadvantage because they lack capital and talent. The demonstration effect of advanced provinces and the diffusion effect of advanced technologies means that the irrigation water use efficiency can be improved slowly through partial catch-up. The national target will not be reached by 2030, however, and irrigation water use efficiency in Gansu remains basically stagnant under SSP3.
Hubei is in the third place among the four provinces in terms of the overall irrigation water use efficiency situation, performing below Jiangsu and Gansu, but better than Guangdong. Because it has abundant water resources, Hubei lacks the motivation to improve water use efficiency and it will not meet the national target by 2030 under any pathways. It is similar to Gansu province in regard to the low coefficient for the effective utilization of irrigation water and other conditions.
Among the four provinces with different HE classifications, Guangdong in the HE-2 class has the lowest irrigation water use efficiency because of the absence of pressure on its water resources, which limits improvements in water use efficiency. The speed of improvement is highest under SSP1 and SSP4 (the two curves coincide), but even under these pathways, Guangdong is unable to meet the national target by 2030. Under SSP5, the next best scenario, which is based on fossil fuels, it fails to reach the convergence state by 2030. Guangdong reaches convergence soonest under SSP2 and its coefficient value (0.55) is close to SSP5 by 2030. Under SSP3, the province is in a stable state in which irrigation water use efficiency is stagnant and always lower than 0.5 up to 2030.
5. Conclusions and Suggestions
This study uses a conditional convergence model for predicting technological change combined with the SSPs scenario settings and HE classification to group 31 Chinese provinces by their different economic and water resources conditions. On this basis, it presents the results from a new extended SSPs–HE framework for predicting the change in irrigation water use efficiency of 31 Chinese provinces by 2030. The conclusions are as follows.
The effective utilization coefficients of irrigation water in half of the provinces converge to 0.6 under SSP1, SSP2, and SSP5 by 2030, whereas SSP3 and SSP4 are generally inefficient development pathways. The HE-3 class has the highest proportion (100%) of provinces that can achieve the irrigation water use efficiency target under every development pathway in 2030, followed by the HE-4 class (64%), and then the HE-2 class (53%). The HE-1 class has the lowest proportion (9%) of successful provinces.
Provinces with severe hydrological conditions generally have higher water use efficiency than do provinces with low hydrological challenges. Substantial regional hydrological challenges are the most important incentive or internal driving force to improve water use efficiency. In addition, HE-3 provinces present the largest improvement in irrigation water use efficiency, reflecting the great importance of economic capacity in improving water use efficiency.
The curves for the effective utilization coefficients of irrigation water have different trajectories in the different scenarios. Coefficient curves increase rapidly in various provinces under SSP1 and SSP5, but these pathways do not result in provinces reaching the convergence state by 2030 and room for further improvement remains. Coefficient curves have the fastest convergence rate under SSP2 among all the pathways, but this pathway lacks the potential for further development and provinces remains stagnant once they converge to a certain level. The coefficient curves present an inefficient situation under SSP3, in which the irrigation water use efficiency is at a low level and does not significantly improve for a long time. Under SSP4, the coefficient curves reflect a highly imbalanced situation with coefficient curve trajectories depending on the economic strength of the provinces. The coefficient curves of the provinces with strong economic capacity rise quickly, whereas those of the provinces with weak economic capacity rise slowly (i.e., the strong get stronger, but the weak become weaker).
On the basis of the analysis of the results and conclusions above, we put forward the following suggestions for improving the irrigation water use efficiency of each province.
A water-saving development pathway for specific regions should be selected in line with the local conditions. HE-3 provinces have both the motivation and the economic capacity for water-saving actions, with strong endogenous water-saving powers making SSP1 a suitable pathway for HE-3 provinces. HE-4 provinces are facing the dual pressures of capital shortages and severe hydrological challenges, and they require policy and financial support from the central government, including access to the limited funds designated for water-saving projects. SSP2 is likely to be the most suitable pathway for HE-4 provinces because of its cost-effectiveness. For HE-1 provinces with abundant water resources but weak economies, efforts should be made to enhance economic capacity under SSP1 or SSP5, with efficiency improved slowly, but continuously over the long term. For HE-2 provinces with strong economic capacity and water security, a harmonious relationship between maintaining human living standards and environmental water resources should be the goal of future development, which aligns with the development concept of SSP1.
Regional rivalry and fragmentation are not wise development choices. It is important to increase connectivity and openness among the regions and narrow the technological and income gaps. China is a vast country with complex national conditions and its development is inadequate and unbalanced, as evidenced by the great variation in hydro-economic conditions among regions and provinces. Although the hydro-economic conditions of backward regions cannot be changed in the short term, these regions can benefit from technological diffusion and spillovers, which requires overall irrigation water use planning at the national level and an open, inclusive, and shared development concept among all regions to change the situation of imbalance and even regional rivalry.
It is always good to be prepared, even in a province in which pressure on water resources is low, by improving the management of irrigation and the application and popularization of related technologies. The low-pressure pipeline water delivery irrigation is likely to be the most suitable technology for HE-1 provinces (low economic capacity, low hydrological challenges) because of its cost-effectiveness. For a province in which economic capacity is strong, more advanced technologies can be considered, such as the sprinkler irrigation and the micro irrigation. Considering that substantial regional hydrological challenges are the most important incentive or internal driving force to improve water use efficiency and water resources is so valuable in arid and semi-arid regions in northern China, efforts should be made continuously to develop highly efficient water-saving irrigation, such as the micro irrigation, despite the fact that some provinces have a weak economy. In addition to increasing capital investment in water-saving technology, it is very important to strengthen the belief in technological innovation and green development [75
] and to build a policy and social environment that encourages technological innovation and water and energy conservation.