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Recent studies have shown that climate change is having severe impacts on production of the tea plant [Camellia sinensis (L.) Kuntze], an important woody cash crop. Quantitative production figures are necessary to provide tea stakeholders and policy makers with evidence to justify immediate action. We used data from Zhejiang Province, China, and the economic output model of four tea plant cultivars (Jiaming 1, Longjing 43, Baiye 1, and Jiukeng) in spring and the yield output model of one tea plant cultivar (Jiukeng) in summer and autumn, and analyzed the impact of climate change on tea production from 1985 to 2018. The results showed that the effects of high temperature and drought on tea production have increased significantly. Temperature was the main factor effecting the economic output of tea plants in spring. Climate change has resulted in the start date of tea buds and leaves plucking period to have become significantly earlier in spring. The risk of frost damage and economic loss, caused by frost, decreased significantly in the period of spring tea production. Among the five bud and leaf grades, the length of plucking periods for superfine, Grades 1 and 2 decreased significantly. High temperatures and drought were the main factors impacting tea production in summer and autumn, and effected the economic output of spring tea in the following year. The economic losses caused by daytime rainfall decreased significantly in spring tea production. This study has provided essential evidence that climate change has already had a significant impact on tea plant output. [ABSTRACT FROM AUTHOR]

Summer drought is one of the main natural disasters in Zhejiang Province, China. To explore the characteristics of summer drought in Zhejiang Province during 1973-2013, the standardized precipitation evapotranspiration index (SPEI) is calculated based on 10-day precipitation and temperature data, and the summer drought index (DI) is defined. The Mann-Kendall test and Sen's trend test are used to analyze changes of DI and drought area. Temperature is the main effect on changes of summer drought intensity and drought area. Significant increasing trends are observed for drought intensity, drought area, and extreme drought area, and their linear trend rates in northeast Zhejiang Province are larger than that in the southwest Zhejiang Province. DI and drought area time series have significant mutations in 2003. County-average DI and drought area during 2003-2013 are significantly larger than that during 1973-2002. The aforementioned SPEI could quantify, monitor and analyze summer drought onset, extent, and end. [ABSTRACT FROM AUTHOR]

The uncertainty of generation and load increases in the transmission network in the power market. Considering the transmission congestion risk caused by various uncertainties of the transmission network, the optimal operation strategies of the transmission network under various operational scenarios are decided, aiming for the maximum of social benefit for the evaluation of the degree of scenario congestion. Then, a screening method for major congestion scenario is proposed based on the shadow price theory. With the goal of maximizing the difference between the social benefits and the investment and maintenance costs of transmission lines under major congestion scenarios, a multi-stage transmission network planning model based on major congestion scenarios is proposed to determine the configuration of transmission lines in each planning stage. In this paper, the multi-stage transmission network planning is a mixed integer linear programming problem. The DC power flow model and the commercial optimization software CPLEX are applied to solve the problem to obtain the planning scheme. The improved six-node Garver power system and the simplified 25-node power system of Zhejiang Province, China are used to verify the effectiveness of the proposed multi-stage planning model. [ABSTRACT FROM AUTHOR]

With the increasing penetration of renewables into the AC–DC hybrid distribution system, it is necessary to develop a security-constrained planning approach to address the uncertainty brought by renewables. Motivated by the urgent need to accommodate high penetration of renewable energy resources in weak grids, this paper presents a novel planning approach for AC–DC hybrid distribution systems considering the N-1 security criterion. Network reconfiguration is incorporated as a method to improve the flexibility of the system under normal and post-contingency conditions. To alleviate the burden of computing all possible N-1 contingencies, a novel solving strategy with a nested loop structure is proposed. In the inner loop, a novel contingency screening method is designed for the fast identification of high-risk contingencies under a given planning solution. In the outer loop, the obtained high-risk contingency set is adopted to refine and filter the security constraints, so that the planning solution can be improved iteratively. The superiority and effectiveness of the proposed planning model and solving strategy are tested on a real-world distribution network in Zhejiang Province, China. Numerical results verify that the proposed planning approach is able to deal with the installation of large-scale renewable energy while ensuring the security of the system. • Network reconfiguration is considered to ensure the security of the system. • A novel contingency screening approach is designed to identify high-risk N-1 contingencies. • Case studies are conducted on a real-world distribution system in Zhejiang Province, China. [ABSTRACT FROM AUTHOR]