| Water quantity and water quality are inseparable in water resources management;the realization of the value of water resources lies in their unity.Two-dimensional water trading(2DWT),which consists of the simultaneous trading of water rights and discharge permits,tends to be effective for water resource management.However,there have been few studies on the quantitative description of the two-dimensional water trading scheme and its impact on the system.The interaction between water rights trading and effluent trading is not yet clear,which affects the scientific integrity of decision-making in two-dimensional water trading.Water resources,water environment,and water ecology are referred to as the "three waters".They are fundamental components of the two-dimensional water trading system and are closely related.However,previous researches on two-dimensional water trading have often neglected the important interdependent relationships among them.This makes it difficult to coordinate the improvement of water resource utilization,water ecology,and water environment.Additionally,various uncertainties and factors within the system can cause great difficulties for water resources management.For example,the stochastic characteristics of precipitation,surface runoff,and pollutant emissions are sources of uncertainties,and decisions have to be made in the face of an uncertain and risky future.In this study,the Daguhe Basin in Qingdao,Shandong Province,is selected as the study area.The chemical oxygen demand is used as a water quality factor in twodimensional water trading.This study aims to combine an inexact two-stage stochastic robust programming model with 2DWT and develop a risk-aversion optimization twodimensional water trading scheme model group(RAO-2DWTMs).Furthermore,the interdependent relationships among the "three waters" and government participation mechanisms are introduced.Based on the interval stochastic bi-level programming method,a hybrid "three waters" government participation based two-dimensional water trading rule model(TWG-2DWTM)is proposed.Then,the model groups are used to research medium and long-term(2023-2042)two-dimensional water trading mechanisms and planning.The main contributions include:(1)The interaction between water rights trading and effluent trading in twodimensional water trading has been analyzed.Water rights trading can increase the possessed water rights for some livestock users,thereby increasing their production scale and demand for discharge permits.Consequently,the trading volume of discharge permits is increased.Effluent trading can increase the possessed discharge permits for some livestock users,increasing their production scale and demand for water rights,and increasing the trading volume of water rights.Under 2DWT,water trading and effluent trading would promote each other.(2)The impacts of the two-dimensional water trading scheme and risk control level on the system have been revealed.2DWT would bring the most system benefit and the least risk cost.The non-trading scenario(NTS)brings the least system benefit and the most risk cost.The two-dimensional water trading,based on water rights trading and effluent trading,can fully utilize the available water resources and environmental capacity in the watershed.As the risk control level increases,decision-makers tend to be more conservative and reduce production scale,resulting in decreased system benefits,increased streamflow,and improved water quality.Under the highest risk control level,the average system risk cost of each trading mode decreases by [3.78%,9.74%].(3)The optimal two-dimensional water trading scheme and risk-aversion plan have been obtained.Based on the multi-criterion comprehensive evaluation of the twodimensional water trading scheme and risk control level,the optimal trading scheme is determined using the Technique for Order Preference by Similarity to an Ideal Solution(TOPSIS),which is the two-dimensional water trading at the risk control level of 0.80.(4)The effects of two-dimensional water trading rules on the system have been revealed.Ecological runoff guarantees in river regions would increase the sale or decrease the purchase of water rights in river regions where meeting ecological runoff requirements is difficult.Concentration control for monitoring sections would improve water quality and lead to decline in the purchase or increase in the sale of twodimensional water rights for certain users upstream of monitoring sections where water quality standards are difficult to meet.When government participation is considered,there is transformation from water rights to discharge permits.Government participation can realize the full use of two-dimensional water rights to increase production scale,promoting the economy under the guarantee of water environment and water ecology.As the water-saving percentage increases,the system benefit would increase by [22.84%,23.40%],water consumption would decrease by [20.86%,22.02%],and the water environment and ecology would improve.(5)The optimal two-dimensional water trading rules and trading schemes have been obtained.The optimal trading rule is determined based on TOPSIS,and the optimal trading rule is conducting ecological runoff guarantees in river regions,concentration control of monitoring sections,and government participation mechanism under water-saving percentage of 50%. |
