After the recent rains many are wondering what is means for the status of the drought-
Long-term rainfall data indicate that, on average, the Napa Valley receives 14% of its annual rainfall during the month of March. Based on the data collected from the Napa County ALERT rain gauging stations during March 2016, the Napa Valley received 35% of its annual average. In total, since October 1 we have received 96% of our mean annual precipitation, more than the average of 88% for this time of year. Rainfall amounts recorded at these stations during March ranged from 8.58-16.70 inches. Rainfall totals for Water Year 2015-16 range from 22.85 inches on Mt. George to 51.30 inches on Mt. St. Helena.
In February of 1991, Napa Valley, along with the rest of California, were in the midst of a major drought. The city of Napa had received only 5.27 inches so far that year. The future looked bleak, but then, that March, Napa received 10.64 inches! It seemed like a miracle, and although Napa ended the year at just 70% of its annual average, it was enough to avoid disaster. Conditions improved after that, but the drought persisted until the 1992-93 season, which kicked off an extended wet period. Rainfall was above-average for 11 of the next 14 years, and enough to cause serious Napa River flooding in 1995, 1997, and 2005. The wet period came to an end with the 2006-07 year, which saw only 62% of annual rainfall. Since that time, 7 of 9 years have been below average, and last month, it seemed like we might be in for another underachieving year unless a “Miracle March” was in store.
Two very wet storm systems brought a lot of rain to the Napa Valley in the first half of March 2016, and pushed rainfall totals into above-average territory. In this sense, we got the March rains we needed. The wet March has given us what is likely to be a slightly above-average rainfall year and topped off our local reservoirs, but the drought persists. It was not the miracle drought-busting March many of us were hoping for given the strong El Nino conditions present off the coast. However, drought conditions in Napa County are currently classified mostly as “Abnormally Dry,” a much-improved situation compared with the “Extreme Drought” classification we had a year ago.
On average, we get 10% of our annual rainfall during the months of April and May, which is beneficial because we need a bit more to ensure an above-average year. Although our local reservoirs are full and spilling, more spring rain will continue to recharge groundwater supplies, provide additional flow for our streams, and help fill Lake Berryessa, which remains at only 65% capacity.
– Paul Blank, Senior Hydrologist, paul@naparcd.org