Drought Information for Arizona and Southeast California (Updated December 25, 2018)

 PERIODIC LIGHT RAIN CONTINUES TO AID IN DROUGHT RELIEF IN DECEMBER

Updated on Tuesday, December 25, 2018 - Mark O'Malley

Summary:

After a favorable weather pattern yielded several heavy rainfall events across much of the Southwest United States during the first half of October, conditions became much drier in November with only localized rainfall across the region.  However, a couple beneficial localized rains in western Arizona and SE California have helped drought conditions again in December.

The fall and early winter rains helped both short term rangeland conditions and streamflow through much of the region. Soil moisture profiles and fire weather conditions also correspondingly improved. The seasonably cooler weather has allowed these impact groups to stabilize despite limited rain or snow. Greater improvements to longer term water resources will still require adequate winter rain and snow given the prolonged regional drought.

Local Area Affected:

The National Drought Monitor depicts continued drought improvements over Arizona and SE California this month. Moderate Drought and Abnormally Dry conditions were observed over much of central and southern Arizona while Moderate to Severe drought persists across west central Arizona and much of southeast California. 

Severe Drought (D2) -  parts of west-central Arizona and southeast California

In Arizona: part of eastern La Paz County

In California: western Imperial County

Moderate Drought (D1) -  parts of south-central Arizona and southeast California

In Arizona: southern Gila, eastern Pinal, western Maricopa, and La Paz counties

In California: much of eastern Riverside and eastern Imperial counties

Abnormally Dry (D0) -  parts of south-central Arizona 

In Arizona: western Pinal,central Maricopa, and Yuma counties

Local Climatology:

Below are precipitation totals since the beginning of 2018 from selected locations across Arizona and southeast California:

Rainfall during the first part of October was very impressive with many locations setting records for the month of October. This has also pushed year-to-date percentage near or above 100% for much of central AZ though western Arizona remains lagging near 50-75%. 

Oct-Dec 2018 Percent of Normal Rainfall	2018 Year-to-Date Precipitation Percent of Normal

The long term drought conditions have been exacerbated by the fact that the majority of Arizona (and a good deal of the entire Southwest) has been experiencing one of its warmest year in recorded history (since 1895).

The U.S. Drought Monitor is a weekly collaborative effort between a number of federal agencies including NOAA/NWS, U.S. Department of Agriculture and the National Drought Mitigation Center. Details and explanations of the Drought Monitor can found at the web site:

http://droughtmonitor.unl.edu/ 

The categories of drought are defined as follows:

Abnormally Dry (D0) - Going into drought: short-term dryness slowing planting, growth of crops or pastures; fire risk above average. Coming out of drought: some lingering water deficits; pastures or crops not fully recovered.

Moderate Drought (D1) - Some damage to crops, pastures; fire risk high; streams, reservoirs, or wells low, some water shortages developing or imminent, voluntary water use restrictions requested.

Severe Drought (D2) - Crop or pasture losses likely; fire risk very high; water shortages common; water restrictions imposed.

Extreme Drought (D3) - Major crop/pasture losses; extreme fire danger; widespread water shortages or restrictions.

Exceptional Drought (D4) - Exceptional and widespread crop/pasture losses; exceptional fire risk; shortages of water in reservoirs, streams, and wells, creating water emergencies.

State and Local Actions:

A Drought Emergency Declaration remains in effect for the state of Arizona as signed by the governor in accordance with the Arizona Drought Preparedness Plan. The continuation of this Drought Emergency has been recommended by the Drought Interagency Coordinating Group in their bi-annual meeting on November 28, 2018. This recommendation is based on long term precipitation deficits, along with ongoing negative impacts across the state. 

Additional information concerning the drought in Arizona can be obtained via the Arizona Department of Water Resources web site at:

https://new.azwater.gov/drought

Additional information concerning the drought in California can be obtained via the California Department of Water Resources web site at:

http://www.water.ca.gov/waterconditions

River, Stream Flow, and Reservoir Conditions:

Most rivers and streams responded to the excessive October rainfall with above normal flows, though recently have fallen back from these higher levels. With the lack of more beneficial rain in the short term, some smaller streams are flowing well below normal. However, larger streams and rivers are still flowing within a normal range. 

Reservoir levels remain well below levels at the same time last year, and similar to levels in 2016. October rainfall did little to help reservoir levels as the water contributed primarily to the recharge very dry soils. Better winter rain and snow will be needed to see better reservoir recharge heading into next spring. 

Hourly and forecast river stages out to 90 days can be found at the National Weather Service's (NWS) Advanced Hydrologic Prediction Service (AHPS) web page:

http://water.weather.gov/ahps2/index.php?wfo=psr

Additional Current stream and river stages may be viewed at the following USGS Web Site:

http://waterwatch.usgs.gov/

Agriculture Impacts:

Extensive October rainfall aided in range land and pasture condition improvements though a more extensive recovery was hindered by the longer term drought and extremely dry soils. Reports from around the region indicate stock ponds have mostly refilled. In the beginning of December, 49% of the pasture and range land still is rated poor or very poor. Just one month ago, around 55% of range land was rated poor or very poor versus just 44% at this time last year. 

For additional information on agriculture impacts may be viewed at the United States Department of Agriculture (USDA) National Agricultural Statistics Service NASS Web Site:

        https://www.nass.usda.gov/Statistics_by_State/
index.php

Fire Danger Hazards:

The National Fire Danger Rating: Low to Moderate category for the entire area

The current KDBI: Southwest Arizona and southeast California:

Ranging from High and Extreme in SE California and much of SW Arizona to Moderate and Low in southern Arizona and the higher elevations north and east of Phoenix

Palmer drought severity index (PDSI):
The current weekly PDSI shows slowly improving conditions in Arizona and SE California over the past month. Periods of heavy rain during the first part of October led to vast improvements over much of the area. SE California had missed much of the October rainfall, however recent rains have allowed this region to join in with the improvement. Central Arizona has experienced the most excessive rain and areas that were in Moderate to Severe Drought several months ago are now categorized as Unusually Moist.

The cooler and more humid fall and winter weather have allowed 100-hour dead fuel moisture values to hover around 10% for all of central and eastern Arizona. Some of the shorter term dryness has allowed smaller sized 10-hour dead fuel moisture values to fall back below 7%. Fire weather threat will be muted until the warmer and drier spring weather arrives. 

The Keetch-Byram Drought Index (KBDI) is a drought index that is specifically related to fire potential. The KDBI is broken into four categories which indicate the susceptibility of ground fuels to fire danger. Below are the four categories and a brief description of each.

KBDI and Dead Fuel Moisture data can be found on the Wildland Fire Assessment System (WFAS) web site at:

http://www.wfas.net

Precipitation/Temperature Outlooks:

The 8-14 day temperature outlook for Jan 2-8 period calls for better chances of near average temperatures and near average rainfall. The 30 day outlook for January 2019 (not shown) indicates better chances for above average temperatures and near equal chances of above, below, or near average precipitation. The 90 day outlook for the period January through March 2019 indicates better chances for above average temperatures and slightly enhanced odds of above average precipitation. 

The tropical Pacific is currently transitioning to an El Nino episode and confidence is now high that this El Nino will peak during the middle of the winter and persist into the spring. This episode will reach a weak category, but could briefly touch into the moderate category. While many other factors contribute to the atmospheric circulation pattern, there may be a slight tilting of the odds towards wetter conditions later in the year due to this El Nino cycle. 

For updated temperature and precipitation probabilities consult the following Climate Prediction Center (CPC) Web Sites:

8 to 14 Day Outlook:

http://www.cpc.ncep.noaa.gov/
products/predictions/814day/

30 Day Outlook:

http://www.cpc.ncep.noaa.gov
/products/predictions/30day/

90 Day Outlook:

http://www.cpc.ncep.noaa.gov/products
/predictions/long_range/seasonal.php?lead=01

Questions or Comments:

If you have any questions or comments about this information
please contact:

Mark O’Malley
Climate and Drought Services
National Weather Service-Phoenix
Co-Chair Arizona Drought Monitoring and Technical Committee
mark.omalley@noaa.gov

Acknowledgements:

The Drought Monitor is a multi-agency effort involving NOAA’s National
Weather Service and National Centers for Environmental Information, 
the USDA, state and regional center climatologists and the national
drought mitigation center. Information for this statement has been gathered
from NWS and FAA observation sites, cooperative and volunteer observations,
USDAFS, the USDA and USGS.

Related Websites :

NWS - http://www.weather.gov/phoenix

CPC - http://www.cpc.ncep.noaa.gov

Drought Monitor - http://droughtmonitor.unl.edu/

USGS - http://waterwatch.usgs.gov/

COE - http://www.spk.usace.army.mil/