Drought Information for Arizona and Southeast California (Updated August 30, 2018)

CONTINUED MODERATE IMPROVEMENTS TO DROUGHT CONDITIONS AS BENEFICIAL MONSOON RAINS AFFECT THE REGION

Updated on Thursday, August 30, 2018 - Mark O'Malley

Summary:

Over the past month, numerous showers and thunderstorms have spread across the region yielding locally generous rainfall. Parts of central Arizona have been the largest beneficiaries of the heaviest rains resulting in some moderate drought relief. However as is typical with summer thunderstorms, rainfall coverage has not been uniform and not all aspects of drought impacts are alleviated by these brief, heavy rains.

In addition, precipitation deficits and impacts from drought have been so extreme since last year, this beneficial rain has only started the drought relief process. As a result, extreme and exceptional drought conditions have persisted over much of the area with only modest improvements where the heaviest rainfall has occurred. A continuation of frequent, widespread rain will be necessary the remainder of the summer with a good followup fall and winter for more expansive improvement in drought conditions to be realized. 

Local Area Affected:

The National Drought Monitor depicts more moderate improvements to drought conditions this month. Although Extreme and Exceptional drought conditions continue to persist over a large part of Arizona, the areal coverage has been decreasing. Severe drought conditions exist much of the remainder Arizona, except the far northwest and southeast parts of the state where Moderate drought conditions exist. Extreme drought remains in parts of far southeast California with Severe drought holding firm through the rest of the southeast California deserts. 

Extreme Drought (D3) - across much of central and western Arizona, as well as Southeast California

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

In California: much of Imperial and far southeastern Riverside counties

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

In Arizona: parts of central and southern Maricopa, and western Pinal counties

In California: far western Imperial and much of eastern Riverside counties

Local Climatology:

Below are water year precipitation totals since October 2017 and totals
since the beginning of 2018 from selected locations across Arizona and
southeast California:

The drought conditions have been exacerbated by the fact that the majority of Arizona (and a good deal of the entire Southwest) is experiencing its warmest Water Year (Oct 1st-July 31st) 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 May 29, 2018. This recommendation is based on long term precipitation deficits, along with ongoing negative impacts across the state. In northeast Arizona, the Navajo Nation has issued an emergency drought declaration to deal with extreme drought conditions. 

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:

Many smaller unregulated streams have responded to the generous monsoon rainfall, though there is a wide range in flows obviously depending on proximity to the more prolific storms. This range of much below to much above seasonal flow rate is quite typical during the monsoon season. Otherwise, much of the Colorado River and other highly regulated rivers remain in a near normal flow rates due to ongoing management efforts.

Reservoir levels remain well below levels at the same time last year, and similar to levels in 2016. Runoff has been near record low levels and additional reservoir re-charge will be minimal this year as monsoon season rains typical only offer limited benefits. 

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:

With prolonged drought conditions, impacts have included increased water hauling necessary for farmers and ranchers, distressed vegetation, and loss of forage acreage.  Livestock on regional ranches have suffered the greatest impacts from drought and many ranchers are selling off higher amounts of their herds this year. 

With recent rainfall, range land and pasture conditions have shown local improvements, and some stock ponds are beginning to refill. However, 76% of the area pasture and range land still is rated poor or very poor. Just one month ago, around 88% of range land was rated poor or very poor versus just 12% 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: Moderate to High category for the entire area

The current KDBI: Southwest Arizona and southeast California:

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

Palmer drought severity index (PDSI):
The current weekly PDSI shows improvement across the central part of Arizona as a result of recent monsoon rainfall. However despite occasional good rains in the northeast portion of Arizona, prolonged dryness has kept Extreme Drought (-4.0 or greater) conditions valid per this PDSI measure. 

Recent rainfall and larger increases in humidity levels have allowed 100-hour dead fuel moisture values to be maintained around 5% for lower elevations of SE California and central Arizona. Smaller sized 10-hour dead fuel moisture values have been oscillating around 5% for the past month, though recently have fallen due the current bout of dry weather. 

The spring wildfire season was somewhat more active this year. However, preventative efforts such as closing large portions of state lands along with fairly tranquil weather conditions precluded a worse fire season with no single large acreage, high intensity incidents. The increased rainfall and humidity levels of the monsoon season have allowed state lands to be re-opened, and minimal fire activity should be expected for the remainder of the summer. 

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 Sept 7-13 period calls for better chances of above average temperatures and the best chance of near average rainfall. The 30 day outlook for September 2018 (not shown) indicates only a modest chance for above average temperatures and above average precipitation. The 90 day outlook for the period September through November 2018 indicates better chances for above average temperatures and enhanced odds of above average precipitation. 

With a healthy 2/3rds of the monsoon season over, model based evidence continues to suggest the remainder of the monsoon season could trend towards wetter than normal over a larger scale. However as is typical with summer thunderstorms, rainfall amounts can be highly variable over small distances and not everyone should expect plentiful rainfall for the remainder of the summer.

ENSO has had little overall impact on monsoon season patterns, through the current neutral state is already beginning to transitioning to an El Nino episode. Confidence is growing that equatorial Pacific sea surface temperatures will reach El Nino thresholds by the fall season and peak during the winter. It is likely that weak to moderate El Nino conditions will exist later this year. 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. 

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/