Exploring landscape sensitivity to the Pacific Trade Wind Inversion on the subsiding island of Hawaii

Abstract

AbstractThe interaction of the subsiding limb of the Hadley circulation and the easterly North Pacific Trade Winds establishes a persistent thermal inversion at about 2000 m above sea level in the subtropical Pacific. The inversion restricts convective rainfall to the lower elevations of the windward flank of the island of Hawaii, creating an order‐of‐magnitude vertical rainfall gradient, as well as high interbasin variability in precipitation. In the high‐rainfall zone, streams are incised tens to hundreds of meters below the surface of the volcanic shield. We use a digital elevation model and 1‐D numerical modeling to assess whether deep incision on the flank of Mauna Kea is tied to the elevation of the trade wind inversion. The 83 channels examined can be well fit in aggregate by all models that account for differences in precipitation between basins; specifically, the maximum depth of incision in each drainage is a power function of precipitation‐weighted drainage area with an exponent of ~ ½. Individual longitudinal stream profiles are generally better fit by models that acknowledge both along‐channel precipitation variability and the subsidence of the island through that gradient, but this relationship is not clearly demonstrable for many channels. We argue that island subsidence through the dry‐to‐wet precipitation gradient has resulted in less cumulative discharge in the lower reaches of the drainages over their lifetime, relative to a nonsubsiding case. This reduces differential erosion between the wet and dry reaches by 20–30% over 300 kyr, making the longitudinal profiles less sensitive to the very strong climate gradient.