The Mono Basin is a land of extremes, and this year’s weather is no exception. Temperatures since January are the warmest on record. October–March precipitation in Lee Vining was the lowest on record. April–September precipitation, on the other hand, already is the highest on record—and we are only halfway through that time period! This water year (October 1, 2014–September 30, 2015) is the first time Apr–Sept precipitation has exceeded Oct–Mar. This reversal of the warm and cold season Mediterranean precipitation patterns has allowed invasive plants like cheatgrass to (more…)
Posts Tagged ‘Hydrology’
A week ago, at mid-month, we excitedly were tallying up the already-record-making Mono Basin precipitation totals for May and the rise in Mono Lake. Who would have thought that it would keep raining and snowing—especially during the driest year of one of the worst droughts on record?
Well, it has kept raining and snowing! (more…)
With May only half over, we have measured almost three inches of precipitation in Lee Vining—surpassing the usual total for all of April-September. This May has already beaten the previous records of 2.23 inches measured in May 1989 and 2.74 inches measured in May 1994. It has also been cold, with over 16 inches of snow already beating the 14.6 inches measured in May 1994. At Cain Ranch, it is already the third-wettest May since 1931.
As Rush Creek above Grant Lake Reservoir nears record-low flows for May, record highs for precipitation are welcome.
A cold May with 400% of average precipitation is very good news for Mono Lake. Reduced evaporation helps slow the declining lake level, and direct precipitation on the lake a week ago raised the level about a tenth of a foot. It now stands at 6379.0 feet above sea level, about a tenth of a foot higher than it was on May 1st. Mono Lake is projected to drop a tenth of a foot this month, but it is now looking like it will remain steady, and it could even have a net rise if the last half of the month is wet.
October to March precipitation was 33% of average—driest on record for Lee Vining and third-driest on record for Cain Ranch. The April 1 snow surveys found only 14% of average snow water content in the Mono Basin after a warm March melted much of the already near-record-low snowpack.
Based on precipitation, snowpack, and recent runoff, the Los Angeles Department of Water & Power (DWP) has run its forecasting equations and issued its runoff forecast: 19% of average runoff is expected for April–September, and 25% over the next year—assuming median precipitation falls. 2015 April–September runoff is not only going to be less than 1977, the driest year on record—it is expected to be less than half of 1977’s runoff.
We are in uncharted territory. It has not been this dry since records began in the Mono Basin. This will be a challenging year for our ecosystems and for water management.
Warm March took snowpack to lowest levels on record; Tioga Pass and Gem Lake have biggest March declines ever measuredFriday, April 3rd, 2015 by Greg, Information & Restoration Specialist
Yesterday I was refreshing the California Cooperative Snow Surveys Webpage almost every hour. Over and over again I saw the dramatic pattern across the state—higher double-digit percentages at the highest elevations of almost every watershed, and lower or zero snowpack at the lower elevations.
Finally, this morning, the rest of the Mono Basin data appeared! The good news is that the snowpack in most of the Mono Basin isn’t as bad as the 6% of average at Tioga Pass and Saddlebag Lake. The bad news is that with only 14% of average snow water content, the snowmelt runoff will be lower than anyone anticipated.
Gem Pass, at the highest elevation, tops the charts with 25% of average snow water content. Everywhere else, snow surveyors measured the lowest snow water content ever measured on April 1st. Ellery Lake is 21% of average, and Gem Lake is 12% of average. Also in the Mono Basin, but reported under the San Joaquin River drainage, is Agnew Pass, which lost 7.5 inches of water in March, and currently is only 3% of average (1 inch of water content).
The following is a summary of the five Mono Basin snow courses:
- Gem Pass lost 2 inches of water in March, and at 8.5″ is about the same as 1977, although not as dry as 1931.
- Gem Lake lost 5.5 inches of water in March, and at 3.5″ is driest on record (beating 5.9″ in 1976).
- Tioga Pass lost 6 inches of water in March, and at 1.5″ is driest on record (beating 7.4″ in 1977).
- Saddlebag Lake lost 6 inches of water in March, and at 2″ is driest on record (beating 9.9″ in 1977).
- Ellery Lake lost 1.5 inches of water in March, and at 6″ is driest on record (beating 9.7″ in 1977).
As early as late February, it seemed likely that this was going to be the driest year on record. Mono Basin snowpack was lower than any year but 1991, and that year had a “Miracle March” that was absent from the long-range forecasts. Sure enough, the dry pattern didn’t change, and March was very dry.
On Thursday I began checking the snow surveys web page for the April 1st snow survey results, which are conducted within a few days of April 1st. On Friday, results for one of the five Mono Basin “snow courses” appeared. And it was a shocking result: Tioga Pass snow water content is at only 6% of average. (more…)
The March 1st snow surveys in the Mono Basin were completed on February 25th, and measured 33% of average snow water content. Even though the snowpack doubled in February, this is only a slight improvement over the February 1st surveys, which found only 23% of average snow water content at the five snow courses where snow is measured. The February 1st surveys, completed at the end of January, found the second-lowest snowpack on record in most places and a record low snowpack at Gem Lake. As of March 1st, the Gem Lake snowpack now ranks the seventh-lowest ever measured (out of 55 years). (more…)
As an almost rainless and snowless January comes to a close, one can’t help but feeling like the seasons are backwards this year. Lee Vining got 1.7 times more precipitation during June through September than it did since October 1st. Normally precipitation during those four fall-winter months is double the summer months (for an average ratio of about 0.5).
Looking back at previous years, 1990–1991 also had a high summer to fall/early-winter precipitation ratio of 4.3—in other words, 4.3 times as much precipitation fell in summer as it did in fall/early-winter. Despite a “miracle March,” 1991 was one of Lee Vining’s driest years on record. 1997–1998 also had a high ratio of 1.5, but then it started snowing (like crazy) in February, and ended up being quite a wet year. Those two years pretty much bookend the options for this year—either it is going to start snowing soon, or it won’t.
Summer thunderstorms can be quite variable, so does this pattern match other precipitation stations? Cain Ranch data confirm this pattern with 1990–1991, however 1997–1998 fails. But the longer record at Cain Ranch allows other years to match: 2013–2014 (1.2), 1976–1976 (1.2), 1976–1977 (4.5), 1967–1968 (1.4), 1960 (1.3). These were all dry years, and most are among the driest years on record.
At this point in the year, with these backward seasons, it will be hard just to catch up to average precipitation for the winter.
In the Mono Basin, the drought continues to press on, as severe as ever. Storms that drench the coast keep splitting apart as they hit the Sierra Nevada.
Storms dropped more December rain on San Francisco and San Jose than those cities have seen in decades. Two and a half feet of water fell on Mt. Tamalpais in the last three weeks and filled all of Marin County’s reservoirs. But in the Mono Basin, these same storms only dropped about half of the average December precipitation at Cain Ranch and a quarter of the average in Lee Vining. Aside from October 2011 and December 2012, Lee Vining hasn’t had a winter season month (October–March) with above-average precipitation since March 2011. That was almost four years ago. (more…)
We were expecting the worst for streamflows this summer. Runoff at 48% of average this year—as forecasted in April, and even lower than the last two dry years—would make 2014 the driest year of the last three, adding up to the three driest consecutive years on record for runoff in the Mono Basin.
But then the summer thunderstorms came, dropping an inch and a half of rain. The late July and early August rains extended the late July streamflows into mid-August, buying about 3–4 weeks of extra time at or above the late July flows. For most creeks, this means that the late July and early August flows this year ended up actually higher than last year. Click on the graphs below to enlarge. (more…)