# The Role of Environmental Assumptions in Shaping Requirements Technical Debt
## 1 Introduction
The literature increasingly emphasizes the importance of explicitly managing assumptions during requirements engineering, particularly in environments characterized by uncertainty and change. [PERSON] et al. [14] found that when developers face incomplete or ambiguous requirements, they frequently introduce implicit assumptions to fill knowledge gaps. However, these assumptions often remain undocumented and unvalidated, which contributes to rework and misalignment during later development stages. [PERSON] et al. [15] emphasize the role of models at runtime in managing evolving environmental uncertainty in self-adaptive systems. The authors suggest that systems should continuously monitor and revise their assumptions to remain aligned with operational realities. Similarly, [PERSON] et al. [16] and [PERSON] [17] argue that uncertainty stemming from assumptions must be addressed during development, as deferring resolution increases the risk of downstream failures and costly rework. Expanding this view, [PERSON] et al. [18] provide a comprehensive mapping of challenges associated with architectural assumptions, showing that unmanaged assumptions often lead to flawed requirements and safety failures. In cyber-physical systems, where software interacts tightly with sensors, actuators, and physical processes, invalid or outdated assumptions about sensor accuracy, timing behavior, or hardware reliability can undermine system correctness and safety [19; 20; 21]. This body of work underscores that failure to document and manage assumptions early in the requirements phase not only increases the likelihood of design inconsistencies and integration issues but also leads to frequent requirements changes and costly rework as systems evolve. This work examines how environmental assumptions contribute to the emergence of RTD, extending earlier work introduced at the TechDebt conference [9]. Building on that foundation, this article presents an in-depth analysis of a real-world case study and offers the following contributions:  
* A case study from the field of small uncrewed aerial systems (sUASs) is analyzed based on safety requirements and their associated environmental assumptions. * This analysis illustrates how missing or incorrect environmental assumptions lead to different types of RTD. * A new classification of RTD is proposed based on environmental assumptions. Specifically, various types of RTD that emerge due to incomplete, incorrect, or evolving environmental assumptions are highlighted. * An initial attempt is made to relate these RTD types to the RTD quantification model (RTDQM), in order to show how environmental assumptions can influence measurable dimensions of debt. The remainder of the paper is organized as follows. Section 2 provides background information on environmental assumptions and RTD, including related work. Section 3 presents the methodology. The results and analysis are reported in Section 4. The discussion can be found in Section 5. Section 6 discusses threats to validity. Finally, Section 7 concludes the paper and outlines future work.