Complexity is inherent to the policy processes and to more and more domains such as environment or social policy. Complexity produces unexpected and counterintuitive effects, in particular, the phenomenon of policy regimes falling short of expectations while made by refined policies. This paper addresses this phenomenon by investigating the process of policy integration and its nonlinearities in the long run. We consider that the increase in the number of policies unexpectedly impacts the policy coherence within a policy regime. We argue that, depending on the degree of policy interactions, this impact varies in direction and intensity over time, which explains nonlinearities in integration. The impact turns negative when the regime is made of numerous policies, which favors non-coordinated policy interactions. Finally, the negative impact prevents further integration as stated by the Institutional Complexity Trap hypothesis and explains the contemporary paradoxical phenomenon of ineffective policy regimes made of refined policies. Empirically, we draw on a relational analysis of policies in the Swiss flood risk policy regime from 1848 to 2017. We study the co-evolution of the number of policies and of their de facto interlinkages, i.e., the co-regulations of a common issue. Findings support that the Institutional Complexity Trap is a structural and long-term dynamic punctuated by periods of policy learning and policy selection. We identify three main phases in the evolution of the regime: the start (1848–1874), the development (1874–1991), and the Institutional Complexity Trap (since 1991).

复杂性是政策过程和越来越多的领域（如环境或社会政策）所固有的。复杂性会产生意想不到的和违反直觉的影响，特别是政策制度因精细化政策而达不到预期的现象。本文通过研究政策整合过程及其长期非线性来解决这一现象。我们认为政策数量的增加出乎意料地影响了政策制度内的政策一致性。我们认为，根据政策互动的程度，这种影响的方向和强度会随着时间的推移而变化，这解释了整合中的非线性。当制度由众多政策组成时，影响就会变成负面，这有利于非协调的政策互动。最后，正如制度复杂性陷阱假设所言，负面影响阻止了进一步的整合，并解释了由精细政策构成的无效政策制度的当代矛盾现象。从经验上讲，我们对 1848 年至 2017 年瑞士洪水风险政策制度中的政策进行了相关分析。我们研究了政策数量及其事实上的相互联系的共同演变，即共同问题的共同监管. 研究结果支持制度复杂性陷阱是一种结构性和长期动态，其间断有政策学习和政策选择时期。我们确定了政权演变的三个主要阶段：开始（1848-1874 年）、发展（1874-1991 年）和制度复杂性陷阱（自 1991 年以来）。