National Weather Service United States Department of Commerce

Continued Monsoon Rainfall Results in Additional Drought Improvement



Updated on Sunday, September 19, 2021


 

Summary:

Numerous rounds of widespread thunderstorms with heavy rainfall were common in July and August resulting in many parts of Arizona experiencing their wettest monsoon in decades. In fact, a few
locations have been flirting with all-time monsoon records, although extended dry periods in September have tempered this possibility. While most areas enjoyed this beneficial wet weather, some communities along the Colorado River, northeast and north-central Arizona, as well as parts SE California have missed out on the most prolific storms. Nevertheless, rainfall amounts around the region have been so abundant that excess runoff has resulted in local reservoir inflow. The most serious short term drought impacts in relation to ranching efforts, wildfire, and forest and wildlife
health have been significantly reduced this monsoon, though long term regional drought impacting hydrologic stability still exists.  

 

 Drought Monitor Arizona

 

 Drought Monitor California

Local Area Affected:

The National Drought Monitor depicts continued modest improvements in drought measures across Arizona and SE California.

Extreme Drought (D3) - part of SE California

In SE California: eastern Riverside County

Severe Drought (D2) -  parts of southwest Arizona and SE California

In Arizona: northern La Paz County

In SE California: part of Riverside County

Moderate Drought (D1) - south-central and southwest Arizona and SE California

In Arizona: Gila, Pinal, most of Maricopa, southern La Paz and northern Yuma counties

In SE California: Imperial County

Abnormally Dry (D0) - southwest Arizona

In Arizona: far southern Yuma County, and small portions of Maricopa and Gila counties

 

Local Climatology:

Below are precipitation totals since the beginning of the 2020-21 Water Year from selected locations across Arizona and southeast California (Please note Normals have been adjusted to reflect the new 1991-2020 official climate period):

Location

 Precip since Oct 1st

Normal fm Oct 1st

Departure fm Normal

% Normal

Rank

Driest

Phoenix

5.50

7.03

-1.53

78

49th

Scottsdale

10.01

8.47

+1.54

118

N/A

Globe
15.85
15.22
+0.63
104
N/A

Yuma

2.32

3.06

-0.74

76

84th

Blythe, CA

1.26

3.45

-2.19

37

11th

Tucson

13.85

10.23

+3.62

135

101st

Flagstaff

20.02

19.93

+0.09

101

88th

 

 

6-month temperature ranking Past 12 months temperature ranking
6-month Precip ranking Past 12 months precip ranking

 

Expansive heavy monsoon rainfall has resulted in one of the wetter spring/summer seasons for the southern half of Arizona. However given the long term drought over the past year, communities with the heaviest rain have only recovered to near normal for the past 12 months,  In northern Arizona and the Upper Colorado basin, long term shortages still exists. Record or near record heat over the past year have only exacerbated drought intensity though extra evapotranspiration. 

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 11, 2021. This recommendation is based on long term precipitation deficits and impacts experienced across the state. 

 

AZ Drought Preparedness

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:

Smaller streams throughout Arizona experienced substantial responses from the repeated heavy rainfall events this summer. Some unregulated smaller streams are still flowing well above average, however extended drier periods this September have resulted in some streams falling back to minimal flow. The more highly regulated larger rivers mostly remain in a near normal flow rates due to continual management efforts.

 Stream Flow

 

Early monsoon rainfall helped replenish soil moisture across  much of the Salt/Verde basin, then periods of heavier rain in August actually resulted in reservoir inflow. It`s common to see minor bumps in reservoir levels during the monsoon, but the notable
increases in reservoir storage this monsoon is not often experienced. In fact, inflow to Salt/Verde reservoirs this monsoon was the 2nd greatest on record. 

 

Reservoir

09/18/2021

09/18/2020

09/18/2019

Roosevelt

69

85

66

Horse Mesa

93

93

92

Mormon Flat

94

95

96

Steward Mtn

92

94

94

Total Salt  

74

87

71

 

 

 

 

Horseshoe

26

1

7

Bartlett

67

91

83

Total Verde  

51

57

54

 

 

 

 

Total System

71

83

69

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/

 

AZ Reservoir storage

Despite adequate storage levels within the Salt-Verde basin, the greater Colorado
River basin has been hit by multiple years of drought and overextended usage. As 
a result, the Bureau of Reclamation officially declared a basin shortage condition for
2022 cutting water deliveries to the state
. Farmers around the state, in particularly in
Pinal County, will experienced the greatest water cuts from this delivery shortage.

Lower Colorado reservoirs


 

Agriculture Impacts:

Only 4% of the Arizona range and pasture land rated as poor to very poor in mid September versus 57% in August and 78% in July. Widespread beneficial monsoon rainfall has helped alleviate the most severe impacts for ranchers. In addition to forage growth, stock ponds have refilled in many areas. 

 

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 Very High category across the region

The current KDBI: Southwest Arizona and southeast California: Ranging from Extreme lower elevations of SE California and southwest Arizona and Low in eastern Arizona.

Palmer drought severity index (PDSI):
The current weekly PDSI shows another round of large improvements across southern Arizona as heavy rainfall over much of the summer has contributed to lessening drought. The worst PDSI measure continues to be spread over northeast Arizona and SE California where monsoon rainfall has been more spotty and drier than normal conditions have been prevalent over the past several years.  

 

Palmer Index

After a spring season of unusually dry fuels and expansive wildfire coverage, persistent and copious amounts of monsoon moisture abruptly ended the fire season in early summer. However because of the amount of area burned and intensity of the fire activity, flooding and debris flows from these burned areas were a tremendous hazards for downstream communities over the monsoon.

As drier weather has been more prevalent in September, 100-hour dead fuel moisture has fallen below 10% after surging above 16% range in much of Arizona in August. Similarly, 10-hour dead fine fuels have deteriorated slightly with values under 5% for most lower elevation locations, and upwards of 7-10% at higher terrain locations of central Arizona. 

 

 100-hr dead fuel

10-hour dead fuel moisture

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.

Keetch-Byram Drought Index (KDBI)

KBDI Value

Description of Fire Potential

0 to 200

Low - Wet with little danger of fire initiation

201 to 400

Moderate - Drying occurring with some fire danger

401 to 600

High - Ground cover dry and will burn readily

601 to 800

Extreme - Dead and live fuels will burn readily

 

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 Sep 27-Oct 3 period calls for better chances of above average temperatures and best odds for near normal rainfall. The 90 day outlook for the period October through December 2021 indicates better chances for above average temperatures and enhanced odds for below normal precipitation. 

8-14 day temp prob

8-14 day precip prob

 

Long Lead 3-month Temp Prob

Long Lead 3-month Precip Prob

Tropical Pacific sea surface temperatures were near average through much of the summer (ENSO neutral), however have already exhibited widespread cooling suggestive of another La Nina winter. There is approximately an 80% chance of La Nina returning this winter 2021-22 with odds favoring another cool season of below normal precipitation throughout the region. 

ENSO Forecast

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:

w-psr.webmaster@noaa.gov

Other Contacts:

For state climate impacts:


http://www.stateclimate.org

 


 

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/