How can climate adaptation policy enhance urban climate resilience? Empirical evidence from China

PLOS One | https://doi.org/10.1371/journal.pone.0335736 November 6, 2025 11 / 21 4.2. Robustness tests 4.2.1. Parallel trend test. While the Synthetic DID results do not rely heavily on the parallel trend assumption, this paper employs the event study method to conduct a parallel trend test, ensuring its validity. In order to ensure that there is a specific sample size before and after the pseudo-policy treatment, and in line with the Synthetic DID method on the characteristics of the control group of the spatiotemporal fit, we need to retain the sample size of a few years before the pseudo-policy treatment, so we choose 2013, 2014, 2015 and 2016 as the year of pseudo-policy implementation. We generated the pseudo-policy treatment variables for each year from 2013 to 2016. Then, we used the Synthetic DID method to carry out four estimations and got the pseudo-policy treatment estimation results, as shown in Fig 4. The results show that, before the policy implementation, from 2013 to 2016, the estimated policy effect was consistently close Fig 2. Empowerment of the control group. https://doi.org/10.1371/journal.pone.0335736.g002 Fig 3. Dynamics of policy effects. https://doi.org/10.1371/journal.pone.0335736.g003