Regional variation of recession flow power-law exponent

Recession flows of a basin provide valuable information about its storage-discharge relationship as during recession periods discharge occurs due to depletion of storage. Storage-discharge analysis is generally performed by plotting -dQ/ dt against Q, where Q is discharge at time t. For most real world catchments, -dQ/ dt versus Q show a power-law relationship of the type: -dQ/ dt = kQa. Because the coefficient k varies across recession events significantly, the exponent a needs to be computed separately for individual recession events. The median a can then be considered as the representative a for the basin. The question that arises here is what are the basin characteristics that influence the value of a? Studies based on a small number of basins (up to 50 basins) reveal that a has good relationship with several basin characteristics. However, whether such a relationship is universal remains an important question, because a universal relationship would allow prediction of the value of a for any ungauged basin. To test this hypothesis, here, we study data collected from a relatively large number of basins (358 basins) in USA and examine the influence of 35 different physio-climatic characteristics on a. We divide the basins into 2 groups based on their longitudes and test the relationship between a and basin characteristics separately for the two groups. The results indicate that a is not identically influenced by different basin characteristics for the two datasets. This may suggest that the power-law exponent a of a region is determined by the way local physio-climatic forces have shaped the landscape.