ICG Agenda - November 12, 2019
Drought Status Update
Winter 2018-2019, followed by some spring precipitation in May and June, improved short-term drought conditions throughout the state. However, multiple consecutive years with higher than average precipitation are needed to improve long-term drought conditions. There were very few monsoon storms during the 2019 summer, exacerbating drought conditions throughout the northeast part of the state. By October, about 55% of Arizona experienced Moderate Drought (D1), 26% Severe Drought (D2), 14% Abnormal Dry (D0), and only 5% experienced No Drought conditions. As of November 12th, there has been less than 25% of average precipitation throughout the state for Water Year 2020.
Winter 2019-2020 Weather Outlook
The increased spring precipitation and delayed onset of monsoon thunderstorm activity was the result of lingering El Niño conditions in the Pacific. The relatively dry summer and early fall resulted in dry soils, which may reduce the amount of winter runoff even if an average amount of precipitation occurs. Although forecast models for Arizona depict neutral El Niño-Southern Oscillation (ENSO) conditions through spring 2020, water temperature forecasts in the Pacific and forecast model output suggest that conditions may shift towards a drier and warmer than normal winter.
Colorado River Water Supply Update
Winter 2018-2019 was wetter than average in the Upper Colorado River Basin leading to 120% of average unregulated inflow into Lake Powell, which helped improve Upper Basin reservoir levels. Lower Basin side inflows into Lake Mead were well above average for the beginning of Water Year 2019, but well below average since July 2019. The total Colorado River system reservoir contents increased from 45% (25.84 million acre-feet (MAF)) capacity at the end of Water Year 2018 to 52% (29.45 MAF) at the end of Water Year 2019. According to the United States Bureau of Reclamation October 24-month study, the end of Water Year 2020 projections indicate that Lake Mead and Lake Powell levels will increase, reducing the probability of shortage conditions. However, under the Colorado River Drought Contingency Plan (DCP), Lake Mead will be in Tier Zero, under which Arizona is obligated to contribute 192,000 AF to Lake Mead.
Salt River & Verde River Watersheds Water Supply Update
2018-2019 winter precipitation was much wetter than average, which led to a substantial inflow (210% of median or 1,121,000 AF) in the Salt River and Verde River watersheds. This is a significant improvement from spring 2018, which followed a very dry winter that produced the lowest inflow on record (17% of median or 100,000 AF). As of May 2019, which marks the end of the spring inflow season, the total Salt and Verde system storage was at 81%, compared to 58% in May 2018. Total precipitation over the watersheds during Water Year 2019 was higher than average (114% of normal), with some reservoirs reaching full capacity and spilling. A tropical system in September caused a significant flood event (6-8 inches) on the lower Salt River Watershed and generated some runoff, however, the rest of the monsoon season was the driest on record for some areas of the state and fall inflow was 45% of median. According to tree ring records, the current megadrought is the most severe from the 16th Century to the present.
2019 Wildfire Season Update
There was a total of 1,781 state and federal fires in 2019, which was relatively similar to 2018 with a total of 1,937 fires. However, the number of impacted acres increased from 157,070 in 2018, to 371,940 in 2019 mainly due to the occurrence of 69 significant fires (extending beyond 100 acres) that covered a total of 353,814 acres. The fire season has been prolonged due to the meager monsoon precipitation and wildfires continue to burn across the state in November.
2019 Forest Health Update
Winter 2018-2019 precipitation reduced drought conditions throughout the state, improving forest and woodland health. The observed tree mortality from bark beetles in Water Year 2019 increased by only 65% (compared to 513% last year), from 275,933 to about 455,053 acres. However, this moisture also caused a foliar blight infestation that defoliated approximately 34,000 acres of native aspen across northern Arizona. The Pinyon-juniper woodlands in particular have become increasingly affected by bark beetles and continue to show significant population decline, which is a major point of concern. The minimal 2019 monsoon activity and the remaining bark beetle populations from Water Year 2018 have the potential to continue deteriorating forest and woodland health.
Although the 2018-2019 winter precipitation alleviated drought conditions throughout the state, the monsoon season precipitation was insufficient, and Arizona remains in a long-term drought. A few consecutive wet winters are needed to eliminate the long-term drought conditions that have impacted Arizona since the mid-1990s. The Drought Interagency Coordinating Group unanimously recommends that both drought declarations be kept in place.
Fall 2019 Drought ICG Recommendation Letter to the Governor
- Drought Status Update & Monitoring Technical Committee Activities, Nancy Selover, State Climatologist, Drought Monitoring Technical Committee Co-Chair
- Winter 2019-2020 Weather Outlook, Mark O'Malley, National Weather Service, Drought Monitoring Technical Committee Co-chair
- Colorado River Water Supply Update, Bret Esslin, Arizona Department of Water Resources
- Salt River & Verde River Watersheds Water Supply Update
- 2019 Wildfire Season Update, Byron Kimball, Arizona Department of Forestry and Fire Management
- 2019 Forest Health Update, John Richardson, Arizona Department of Forestry and Fire Management