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.
- 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
In May 2018, 60% of the state was in either Extreme Drought (D3) or Exceptional Drought (D4), and little relief was provided by the monsoon season. In October 2018, heavy rainfall, which lasted well into the winter months, saturated the soil and vegetation throughout Arizona. Precipitation from January through March 2019 improved short-term drought conditions significantly and 83.3% of Arizona became drought-free. Long-term drought, however, is still present in many areas of the State, including, extreme and exceptional drought conditions in the west and northeastern Arizona. As the summer season approaches with higher temperatures, snowmelt is likely to improve soil moisture and may bring further drought relief to these areas.
Monsoon activity in the summer will be influenced by the steering of moisture from northern Mexico and by weather disturbances in Arizona. Snow cover and drought conditions since October may have an influence on summer rainfall; high levels of soil moisture may suppress monsoon development while warmer water temperatures in the eastern Pacific Ocean may bring more tropical systems and potential moisture surges into Arizona. Since last summer, equatorial Pacific waters have been warmer than normal, and weak El Niño conditions have aided in the development of frequent storms affecting the Southwest United States. If these conditions persist through the 2019-2020 summer and winter seasons, the odds for above average temperatures and precipitation are likely.
Colorado River – Water Supply Status
As of May 8, 2019, total Colorado River reservoir system content equates to 46% of capacity or 27.63 million acre feet. Unregulated inflow into the Colorado River Basin (CRB) for Water Year 2019 is expected to reach 112% of average. Snowpack accumulation this season peaked on April 8 at 130% of the median with 21 inches of snow water equivalent. Due to the recent wet winter, a first level shortage is not expected for the Lower CRB in 2019 or 2020. However, according to the United States Bureau of Reclamation April 24-Month Study, storage in Lake Mead is projected to decrease to 38% of capacity by January 1, 2021.
Colorado River Drought Contingency Plan Update
Colorado River Drought Contingency Plan Update
The purpose of the Drought Contingency Plan (DCP) is to reduce the probability that Lake Mead will decline to critically low elevations (below 1,020 ft). Implementing the DCP will reduce the probability of a third level shortage by as much as 34% by 2026. Under the DCP, total reductions in Colorado River water use from Arizona, Nevada, California, Mexico, and the U.S equate to 1.475 million acre feet at various elevations. This number more than doubles the reductions outlined in the 2007 shortage guidelines. Congressional approval for the Colorado River DCP Authorization Act (H.R. 2030) was granted on March 19, 2019.
Salt River & Verde River Watersheds – Water Supply Status
The weather in Water Year 2019 brought wetter than average conditions throughout the Salt River and Verde River watersheds with nearly 15 inches of cumulative precipitation as of March 30 (129% of normal). Verde River inflow peaked at 68,500 cubic feet per second after a heavy storm in mid-February, which led to an increase from 30% to 64% in Verde River system reservoir storage levels. In late February, elevations of as low as 2,500 feet received snow with an average snow depth of 12 inches throughout both watersheds, a snow water equivalent of 1.4 million acre feet. Cumulative inflow from January to May is projected to reach 1.1 million acre feet, which is double the median value for this time of year. As of May 7, total Salt River and Verde River reservoir system storage is at 81% of capacity.
Forest Health and Wildfire Season Update
Forest Health and Wildfire Season Update
The 2018 aerial and ground survey conducted by the Department of Forestry and Wildfire Management detected 275,934 acres of trees impacted by bark beetles compared to 45,003 acres in 2017, an increase of 513%. This drastic increase is largely attributed to the dry winter of 2017-2018, which stressed many trees and made them more susceptible to pests. This past wet winter improved forest health across Arizona and because healthier trees are better able to defend against bark beetle activity, reduction in tree mortality levels is anticipated. Drought impacts are starting to ease but still present in the form of dead vegetation, particularly in the White Mountains. Fine fuels (i.e. grasses, pine needles, and small herbaceous growth) that help fire spread quickly and intensely are observed at normal to above normal levels.
Impacts of Drought on Wildlife
Precipitation over the winter has filled water catchments for wildlife and there was no need for water hauling. Aquatic habitats have improved significantly since last year.
Impacts of Drought on the Navajo Nation
The Navajo Nation received average to above average precipitation in Water Year 2019 thus far, with a heavy storm in February which brought precipitation levels to above 200%. This led to a notable recovery in the drought conditions experienced in 2018.
Despite short-term drought improvements, these updates confirm that Arizona remains in a long-term drought and that the drought is expected to continue. The Drought Interagency Coordinating Group unanimously recommends that both drought declarations be kept in place.
- Drought Status Update and Monitoring Technical Committee Activities, Nancy Selover, State Climatologist, Drought Monitoring Technical Committee Co-Chair
- Winter 2018-2019 Weather Outlook, Mark O'Malley, National Weather Service, Drought Monitoring Technical Committee Co-chair
- Colorado River Water Supply Status, Rabi Gyawali, Arizona Department of Water Resources
- Colorado River Drought Contingency Plan Update, Thomas Buschatzke, Arizona Department of Water Resources
- Salt River & Verde River Watershed Water Supplies, Stephen Flora, Salt River Project
- Forest Health Update, John Richardson, Arizona Department of Forestry and Fire Management
- Wildfire Season Update, Byron Kimball, Arizona Department of Forestry and Fire Management
- Impacts of Drought on Wildlife, David Weedman, Arizona Game & Fish
- Impacts of Drought on the Navajo Nation, Carlee McClellan, Navajo Nation Department of Water Resources