Filling gaps in measured discharge series with model-generated series

Gaps in measured discharge series are common in Iceland, especially during winter, but reconstructed series are needed for a number of applications. Modeled series are therefore sometimes used to fill the gaps to create a continuous series, but the modeled inserts may have different statistical characteristics from the observed series, whilst their initial and final values rarely coincide with the corresponding measured values. Where gaps are numerous, individual treatment of each gap is time-consuming and often impractical. A method for adjusting modeled sequences to be inserted into gaps was therefore designed with the objective of reducing the difference between model-generated inserts and recorded series. This paper reports on the performance of the method and shows how an improved fit can be attained by adjusting the model-generated inserts so as to smoothly match the discharges observed before and after a gap.