Weiguang Wang

Emergy evaluation of the contribution of irrigation water, and its utilization, in three agricultural systems in China

Emergy theory and method are used to evaluate the contribution of irrigation water, and the process of its utilization, in three agricultural systems. The agricultural systems evaluated in this study were rice, wheat, and oilseed rape productions in an irrigation pumping district of China. A corresponding framework for emergy evaluation and sensitivity analysis methods was proposed. Two new indices, the fraction of irrigation water (FIW), and the irrigation intensity of agriculture (IIA), were developed to depict the contribution of irrigation water. The calculated FIW indicated that irrigation water used for the rice production system (34.7%) contributed more than irrigation water used for wheat (5.3%) and oilseed rape (11.2%) production systems in a typical dry year. The wheat production with an IIA of 19.0 had the highest net benefit from irrigation compared to the rice (2.9) and oilseed rape (8.9) productions. The transformities of the systems’ products represented different energy efficiencies for rice (2.50E + 05 sej·J−1), wheat (1.66E + 05 sej·J−1) and oilseed rape (2.14E + 05 sej·J−1) production systems. According to several emergy indices, of the three systems evaluated, the rice system had the greatest level of sustainability. However, all of them were less sustainable than the ecological agricultural systems. A sensitivity analysis showed that the emergy inputs of irrigation water and nitrogenous fertilizer were the highest sensitivity factors influencing the emergy ratios. Best Management Practices, and other agroecological strategies, could be implemented to make further improvements in the sustainability of the three systems.

Can China achieve food security through the development of irrigation

China faces the dual challenge of water scarcity and food security with continued population growth. This paper explores methods to meet that demand without increasing agricultural water usage. The results show that China’s grain yield increased from 1.09 to 5.38xa0t/ha in 1949–2014 and may reach 6.13xa0t/ha in 2030. Further, food production increases can be achieved by increasing crop yield and enhancing irrigation efficiency (the ratio of crop irrigation water consumption to water diversion, IE). According to forecast scenarios, future grain yield will reach 5.86xa0t/ha if the ratio of total irrigated areas increases by 12.3%, while the IE will reach 0.583, lower than the planning goal of 0.600. The increase of water productivity proves that China can ensure its food security by improving IE and expanding irrigation areas with the water that is saved. The basic premise to ensure food security is to ensure that future investments in agricultural water and arable land are not reduced. The future should focus on provinces in the South, which is the major grain-producing area, in developing irrigation. The Northern regions have limited potential to develop irrigation and should therefore maintain the current scale of agricultural production to lay a solid foundation for food security in the future.

Prediction of the Reference Evapotranspiration Using a Chaotic Approach

Evapotranspiration is one of the most important hydrological variables in the context of water resources management. An attempt was made to understand and predict the dynamics of reference evapotranspiration from a nonlinear dynamical perspective in this study. The reference evapotranspiration data was calculated using the FAO Penman-Monteith equation with the observed daily meteorological data for the period 1966–2005 at four meteorological stations (i.e., Baotou, Zhangbei, Kaifeng, and Shaoguan) representing a wide range of climatic conditions of China. The correlation dimension method was employed to investigate the chaotic behavior of the reference evapotranspiration series. The existence of chaos in the reference evapotranspiration series at the four different locations was proved by the finite and low correlation dimension. A local approximation approach was employed to forecast the daily reference evapotranspiration series. Low root mean square error (RSME) and mean absolute error (MAE) (for all locations lower than 0.31 and 0.24, resp.), high correlation coefficient (CC), and modified coefficient of efficiency (for all locations larger than 0.97 and 0.8, resp.) indicate that the predicted reference evapotranspiration agrees well with the observed one. The encouraging results indicate the suitableness of chaotic approach for understanding and predicting the dynamics of the reference evapotranspiration.

Emergy evaluation of a pumping irrigation water production system in China

The emergy concept was used to evaluate a pumping irrigation water production system in China. A framework for emergy evaluation of the significance of irrigation water and its production process was developed. The results show that the irrigation water saved has the highest emergy value (8.73E + 05 sej·J−1), followed by the irrigation water supplied to farmlands (1.72E + 05 sej·J−1), the pumped water (4.81E + 04 sej·J−1), with the lowest value shown from water taken from the local river (3.72E + 04 sej·J−1). The major contributions to the emergy needed for production are the inputs of soil and water. This production system could contribute to the irrigated agriculture and economy, according to several calculated emergy indices: emergy yield ratio (EYR), emergy investment ratio (EIR), environmental load ratio (ELR), and environmental sustainability index (ESI). The comparative analysis shows that the emergy theory and method, different from the conventional monetary-based analysis, could be used to evaluate irrigation water and its production process in terms of the biophysical account. Additional emergy evaluations should be completed on different types of water production and irrigated agricultural systems to provide adequate guidelines for the sustainability of irrigation development.

Scarce water resources and priority irrigation schemes from agronomic crops

Global environmental change places unavoidable pressure on water resources and agronomic crop production systems. Irrigation development is a credible measure to alleviate the challenge of food safety under water shortages, but it needs sufficient basis. The aim of this study is to address the problem of balancing water scarcity with food requirements, which are the key components of water security in regions with population growth. Marginal water productivity (MWP) indices for irrigation water performance and productivity evaluation were established in the current study. Based on the analysis of the regional water-crop relationship and spatial differences of MWP in China, the priorities for developing irrigation areas in different types of regions are discussed in this study. The results show that high MWPs are mainly in semi-arid regions with precipitation (P) between 500 and 1000xa0mm, while low MWPs mostly occur in areas with P more than 1000 and less than 500xa0mm. The significance and spatial distribution patterns of MWP are different than those of conventional irrigation water use efficiency evaluation indices, so its role cannot be replaced for the real production capacity of irrigation water evaluation. The strategies for global environmental change adaptation suggested in this study are taking MWP for irrigation water productivity evaluation and the priority irrigation schemes for agronomic crop determination; increasing MWP by means of irrigation efficiency and crop variety improvement worldwide; and raising global food production through the expansion of irrigation area in the regions hold high MWP and abundant water resources.