Frequent, incremental, and uncontrolled changes are classic symptoms of scope creep and weak scope control.
The most effective first step is to strengthen scope management so changes are properly defined, evaluated, approved, and incorporated (or rejected) through a formal process. A detailed scope management plan clarifies how requirements will be collected, how the scope statement and WBS will be developed, how scope will be validated, and-most importantly here-how scope will be controlled. With clear control procedures, the project manager can enforce an integrated change control approach: documenting change requests, analyzing impacts (scope/schedule/cost/risk/quality), obtaining the right approvals, and updating baselines and plans accordingly. While risk, quality, and schedule plans are important, they do not directly address uncontrolled changes. Establishing a strong scope management plan aligns stakeholders on what "done" means, reduces ambiguity, protects baselines, and prevents the team from implementing changes informally.

According to the PMBOK Guide, the project manager should plan the communication to the stakeholders based on the stakeholder communication requirements, the available organizational assets, and the project communication methods1. The project manager should also follow the project communication management plan, which defines how project communications will be planned, executed, and monitored2. In this scenario, the project manager is facing a major risk that could affect the project objectives and the expectations of the stakeholders, especially the local farmers who rely on the water for irrigation. The project manager should not ignore or hide this risk, but rather communicate it to the stakeholders in a timely and transparent manner, with the assistance of the PMO. The PMO can provide guidance, support, and resources to help the project manager deliver the information effectively and address any concerns or issues that may arise. The PMO can also help the project manager coordinate with other stakeholders, such as the project sponsor, the customer, the suppliers, and the regulatory authorities, to ensure a consistent and aligned message. By delivering the information to the stakeholders with the PMO's assistance, the project manager can demonstrate accountability, honesty, and professionalism, and maintain the trust and confidence of the stakeholders. References:
* 1: PMBOK Guide, 6th edition, page 367
* 2: PMBOK Guide, 6th edition, page 376

When a key team member is unexpectedly absent, it's important for the project manager to collaborate with the rest of the team to assess the impact and reprioritize tasks. This is in line with agile principles, which emphasize team collaboration and self-organization1. The team should collectively decide how to redistribute the workload, possibly by sharing responsibilities or adjusting the iteration's scope. This approach maintains the team's agility and ensures that everyone is on board with the revised plan, fostering a sense of ownership and commitment to the project's success.
References:
PMBOK Guide - Seventh Edition2
Professional in Business Analysis (PMI-PBA)3
ExamTopics discussion on PMP topic1