Added value of solar radiation in snowmelt models: benchmarking
empirical models in the High Atlas Range, Morocco
Abstract
Estimating snow water equivalent (SWE) and snowmelt in semi-arid
mountain ranges is an important but challenging task, due to the large
spatial variability of the seasonal snow cover and scarcity of field
observations. Adding solar radiation as snowmelt predictor within
empirical snow models is often done to account for topographically
induced variations in melt rates, at the cost of increasing model
complexity. This study examines the added value of including different
treatments of solar radiation within empirical snowmelt equations. Three
spatially-distributed, enhanced temperature index models that
respectively include the potential clear-sky direct radiation (HTI), the
incoming solar radiation (ETIA) and net solar radiation (ETIB) were
compared with a classical temperature-index model (TI) to simulate SWE
within the Rheraya basin in the Moroccan High Atlas Range. Extensive
model validation of simulated snow cover area (SCA) was carried out
using blended MODIS snow cover products over the 2003-2016 period. We
found that models enhanced with a radiation term, particularly ETIB
which includes net solar radiation, better explain the observed SCA
variability compared to the TI model. However, differences in model
performance were overall small, as were the differences in basin
averaged simulated SWE and melt rates. SCA variability was found to be
dominated by elevation, which is well captured by the TI model, while
the ETIB model was found to best explain additional SCA variability. The
small differences in model performance for predicting spatiotemporal SCA
variations is interpreted to results from the averaging out of
topographically-induced variations in melt rates simulated by the
enhanced models, a situation favored by the rather uniform distribution
of slope aspects in the basin. Moreover, the aggregation of simulated
SCA from the 100 m model resolution towards the MODIS resolution (500 m)
suppresses key spatial variability related to solar radiation, which
attenuates the differences between the TI and the radiative models.