Universal recession constants and their potential to predict recession flow

Streamflow prediction during dry or recession periods is crucial for water resources management. The storage-discharge (S -Q) relationship is generally used to model recession flow in the basin. Since storage is practically unobservable, the S -Q relationship is often quantified by analyzing the relationship between -dQ/dt and Q, which Brutsaert and Nieber (1977) observed to be of a power-law type: -dQ/dt = kQ alpha, for natural basins. Integration of the above equation yields an expression for the streamflow at any time, t, during the recession period. However, this approach relies on the availability of the streamflow data and, therefore, cannot be applied directly to ungauged or data-scarce basins. Thus, there exists a necessity for an alternative approach to predict streamflow in the ungauged basins during the recession period. In this study, we investigated recession curves from 413 basins in the United States and determined the existence of a universal relationship (k = kuQ- lambda u N ) between the storage coefficient (k) and the average past discharge (QN) that can serve as a proxy for basin storage. We tested the potential of universal recession constants (ku and lambda u) in predicting the recession flow in both gauged and ungauged basins. It is observed that the median NSEBC, i.e., NSE calculated using the Box-Cox transformation of discharge, was 0.78 for the gauged basins and 0.55 for the ungauged basins. Our findings provide a model-independent method for predicting the recession discharge, which can pave new avenues to-wards improving the predictions in ungauged basins.