Water supply forecasts in the Sierra Nevada using ground-based measurements of snow water
equivalent
(SWE) are uncertain because neither point measurements nor transects adequately explain spatial or
temporal vari- ability in mountainous terrain. To address this problem, we combine satellite-based
retrievals of fractional snow cover in 2006 with energy balance calculations to reconstruct the SWE
values throughout the melt season. Model estimates when compared to snow pillows at maximum
accumulation are unbiased and have an RMS error of 297 to 417 mm. We compare this retrospective
calculation of distributed SWE with two real-time models: (i) interpola- tion from pillows,
courses, and satellite snow cover, and (ii) the Snow Data Assimilation System (SNODAS). The
interpolation and SNODAS models show complete melt out more than a month earlier than
reconstruction, and their total SWE volumes are 68% and 87% of the reconstructed volume. At
elevations below 1500 m, the recon- struction model has less total SWE because of early season
melt. Above 3000 m, the reconstruction shows more SWE than the real time models, which depend on
surface measurements that do not sample the higher elevations. The results indicate that spatial
patterns from the reconstruction could improve estimates of snow accumulation and duration.Funded by Naval Postgraduate School.NASACooperative Agreement NNG04GC52A (NASA)Award N00244-07-1-0013 (NPS)Earth Systems Science Fellowship program (NASA
