Simulating Hawaiian Microclimates
C. Zhang1, Y. Wang1, A. Lauer2 and K. Hamilton1
1IPRC, 2Institute
for Advanced Sustainability Studies (IASS)
Annual mean rainfall rate for the period 1994−2009: (left) derived using rain gauge observations, (middle) from the 1-km simulation,
and (right) from the 3-km simulation (mm/day). Contours show the model topography at 250 m intervals.
The high, steep mountains of the main Hawaiian
islands lead to a climate with sharp gradients. Annual
mean rainfall can vary by an order of magnitude over a
few
kilometers.
Simulating
such
small-scale
microclimatic features is a challenge. Adapting the
Weather Research and Forecasting (WRF) model to
Hawaii, IPRC researchers have conducted simulations
using observed sea surface temperatures and horizontal
boundary conditions taken from reanalyses.
The figure compares the observed long-term mean
rainfall over the island of Maui with results from a doubly
nested, 3-km horizontal resolution version and results
from a triply-nested 1-km resolution version.
The simulated rainfall features are a maximum on the
northeast slope of Haleakala, which looms over East
Maui; a maximum at the topographic high point at the
center of West Maui; and a very dry area in between. The
3-km simulation captures these basic features, but
significantly under predicts West Maui rainfall and misses
the northwest-southeast orientation of the rainfallmaximum on East Maui. The 1-km simulation reproduces
better the peak rainfall in west Maui and the rainfall
distribution on the northeast slope of Haleakala. The
results reveal the demanding computations in resolving
adequately the dynamics of the Hawaiian microclimates.