ICG Agenda - May 29, 2018
This water year (WY) has been very dry across the western U. S. and Arizona received very little rain and snow, which exacerbated short-term drought conditions. Monsoon storms were almost entirely limited to the month of July, and from October through December, less than 25% of average precipitation was received. Snow cover is typically highest across the Southwest on March 1st; however, snow cover observed this March was minimal to non-existent, putting the entire basin in a snow drought. As of late May, 3% of the State was in Moderate Drought, 24% in Severe Drought, 57% in Extreme Drought and 16% in Exceptional Drought. This is a stark contrast to May of last year in which the northern half of Arizona was completely free of drought and the southern part was partly in abnormally dry and in moderate drought conditions. This exceptionally dry winter has extended the wildfire season, decimated forage, and led to many wells going dry. Even native desert vegetation, such as creosotes, appear to be dying in some locations. Over the past month, there has been an increase in water hauling, supplementing feed for livestock, and culling of herds. These drought conditions have also led to drought emergency declarations in Yuma County and the Navajo Nation. Long-term statewide average precipitation in WY 2017 seemed to be nearing the mean (12.59 inches) of recorded data, however that trend is now sloping downwards with less than 10 inches of rain in WY 2018 thus far.
NOAA’s Climate Prediction Center’s outlook for Summer 2018 suggests slightly enhanced odds for wetter than normal monsoon season due to warmer than average East Pacific waters and likelihood that the typical summer subtropical high-pressure system will be favorably located to frequently bring moisture into the State. However, summer thunderstorms are usually quite erratic and may only provide partial and local relief to long-term drought conditions. Temperatures this summer are likely to be warmer than average based on consistent trends in recent years. The weak to moderate La Niña conditions, which existed last Fall and Winter and were partially responsible for the poor rain and snow in the Southwest, are now transitioning into a neutral state. Based on past winters’ trend, there are better odds for above normal temperatures this winter. There is no large tilt in odds for above, below or near normal precipitation for the upcoming winter.
Salt River & Verde River Watersheds – Water Supply Status
Salt-Verde watershed cumulative precipitation for August through April amounted to 5.17 inches, which is 33% of normal and the driest on record (since 1896). Salt River, Tonto Creek, and Verde River spring runoff from 2011 to 2018 indicate the driest consecutive 8-year period on record. Inflow from January to May amounts to 99,000 acre feet compared to last year’s 970,440 acre feet. Since 2010, reservoir storage has declined 57% from 2.311 million acre feet (MAF) to 1.337 MAF. Utilizing both the gaged record and the University of Arizona’s Tree Ring Laboratory record from 1361 to 2005, SRP has determined that the last 23-years (1996—2018) have been the driest in the entire record (1361—2018), officially making the last few decades the worst megadrought in recorded history for the Salt and Verde basins. Despite the dry conditions, total system storage of Salt River Project (SRP) reservoirs amounts to 1.309 MAF (57% of maximum capacity) as of mid-May due to calculated water management.
Colorado River – Water Supply Status
This winter was exceptionally dry on most of the Colorado River basin, and the entire system reservoirs are at 51% of maximum capacity or 30.434 million acre feet (MAF). This is only a decrease of roughly 1% from last May. Lake Powell and Lake Mead are at 52% (12.679 MAF) and 39% (10.247 MAF) of capacity, respectively. Lake Mead’s elevation is just below 1,083 feet, eight feet above Tier-1 shortage. In the Upper Basin, this year’s snow water equivalent reached 12 inches at its peak, which is 4 inches below the 1981-2010 median, and only 51% (5.5 MAF) of unregulated inflow is projected for Lake Powell. Projected elevations for Lake Powell and Mead by year-end are approximately 3590.43 feet or 45% of capacity (a 13% decrease from December 2017) and 1079.1 feet or 38% of capacity, respectively. Though no shortage on the Lower Basin is currently predicated for 2019, the Bureau of Reclamation predicts a 52% probability of a Tier-1 shortage in 2020. Furthermore, this is the first time that the probability of a double-digit Tier-3 shortage has been projected within a 5-year outlook period.
Impacts of Drought on Wildlife
In the Pinetop Region, 110,150 gallons of water were already hauled so far this spring to 41 catchments. Increased salinity in SRP reservoirs and urban lakes due to low inflows cause growth of golden algae bloom, which is toxic to fish. Low spring inflow into one of the endangered Gila topminnow habitat cause the disappearance of one of its population as the habitat could no longer support the fish.
Forest Health and Wildfire Season Update
Many of last year’s burned acres regrew before the State launched into 120 days of dry weather providing ample fine fuels that invite greater opportunity for fire activity. As of May 20, there have been 611 fires: 604 of these were caused by human activity while 7 by natural conditions. Many state lands are currently closed to recreation, which have helped reduce wildfire occurrence. Drought stress in forest and urban vegetation render trees vulnerable and less capable of deterring pests. Increased juniper mortality due to drought stress has been observed this year. In addition, 80,469 acres of forest trees were killed or damaged due to bark beetles and defoliators/sap feeders in 2017. Yet these figures pale in comparison to the extremely dry years of 2002 and 2003 when bark beetles decimated 570,000 to 763,000 acres of ponderosa pine forest.
Northern Arizona Forest Fund Efforts
The Northern Arizona Forest Fund (NAFF), a regional initiative of the National Forest Foundation, supports watershed restoration projects across five forests in Northern Arizona. Over $2.5 million have already been invested over 4 years, engaging 24 donors and 200 volunteers who donated over 1500 hours. So far, 21 restoration projects have been completed in non-market-value, high-priority locations where restoration work would not have otherwise been funded. The NAFF is working on improving hydrologic functions through restoration of springs, wetlands, streams, and meadows. NAFF projects also focus on minimizing severe fire risk through prescribed burning, small-diameter tree thinning and sediment and erosion control improving the flow and quality of waterways and reservoirs. In program year 2017, NAFF efforts have reduced 31 tons of sediment on 37 miles of roads and trails, replenished 2.3 million gallons of water, and reduced fire risk by 27% on 3,500 acres.
Spring 2018 Drought ICG Recommendation Letter to the Governor
- Drought Status Update & Monitoring Technical Committee Activities, Nancy Selover, State Climatologist, Drought Monitoring Technical Committee Co-Chair
- Summer 2017-2018 Weather Outlook, Mark O'Malley, National Weather Service, Drought Monitoring Technical Committee Co-chair
- Colorado River - Water Supply Update, Jeff Inwood, Arizona Department of Water Resources
- Salt River & Verde River Watershed - Water Supply Update, Charlie Ester, Salt River Project
- Forest Health & Wildfire Season Update Jeff Whitney, John Richardson, Steve Mckelvey, Arizona Department of Forestry and Fire Management
- Northern Arizona Forest Fund Efforts Rebecca Davidson, National Forest Foundation