Why does the surface wetness anomaly product sometimes disagree with the map of precipitation anomaly on the Drought Watch website?
A9. The surface wetness is affected by many factors, including soil properties, crop cover, precipitation, temperature and wind speed. The surface wetness also has memory from prior weeks, whether it occurred from snow melt, rainfall, or irrigation. It could lag these events by weeks. Moreover, if the soil was dry and moisture is received, the soil will distribute the water through the profile, and it will take substantial moisture to keep the upper soil wet. Conversely, if the soil has been abnormally wet for the last couple of weeks, it may take some time for it to dry out to normal, and if no additional moisture is received, to drop below normal.
