IDACORP's 2020 fourth quarter earnings per diluted share were $0.74, a decrease of $0.19 per share over the last year's record fourth quarter.
IDACORP's earnings per diluted share for the full year 2020 were $4.69, an increase of $0.08 per diluted share from 2019.
Today, we also issued our full year 2021 IDACORP earnings guidance estimate to be in the range of $4.60 to $4.80 per diluted share with our expectation that Idaho Power will not need to utilize in 2021 any of the additional tax credits that are available to support earnings in Idaho under its regulatory settlement stipulation.
Our nearly 2,000 employees were challenged daily as we continued to carry out our mission as an essential service provider.
And our reliability numbers remained among the best in the industry as we capitalized on 99.96% of the time.
We're pleased to continue to share the successes of the company with our owners by increasing IDACORP's quarterly common stock dividend again in 2020 from $0.67 to $0.71 per share, marking our 9th consecutive year with an increase to the dividend.
According to U.S. News & World Report and the United States Census Bureau, Idaho was once again the fastest growing state in the country during 2020 and Idaho Power's customer base grew 2.7%.
A national study by United Van Lines also ranked Boise as the number 3 metropolitan area for inbound moves during 2020.
Idaho Power now serves more than 587,000 customers and we view the reliable, affordable, clean energy our company provides as an important factor in continuing to attract the business and residential customers to Southern Idaho and Eastern Oregon.
It does not seem that long ago that we crossed the 500,000 customer mark.
On Slide 9, you'll see the highlighted notable milestones, including the announcement of a 240,000 square foot True West Beef facility, the opening of Amazon's 2.5 million square foot fulfillment center and the announcement of a 90,050,000 square foot expansion to an existing Lamb Weston potato processing plant.
Moody's predicts sustained economic growth going forward after experiencing a GDP decrease of 1.7% in 2020 with Moody's forecast calls for growth of 6.1% in 2021 and 6.8% in 2022.
Unemployment within Idaho Power's service area is at 4.7%, an increase over recent years, but still well below the 6.7% reported at the national level.
As I mentioned earlier, IDACORP was pleased to announce a dividend increase of 6% this past fall.
Going forward, management expects to recommend the Board of Directors future annual increases in the dividend of 5% or more with the intent of keeping the company within our target payout ratio of between 60% and 70% of sustainable IDACORP earnings.
Idaho Power's goal to achieve a 100% clean energy by 2045 fits well into our overall strategy as we expected to meet the new investment in system improvements that will enhance the customer experience.
Idaho Power has previously ended its participation in 1 unit at the North Valmy coal-fired plants in Nevada at the end of 2019.
Our most recent integrated resource plant calls for a full exit from coal-fired generation by 2030.
Last quarter, we stated Idaho Power did not plan to file a general rate case in Idaho or Oregon in the next 12 months.
We expect to spend approximately $47 million in incremental WMP and wildfire-related O&M expenses and $35 million in incremental capital expenses over the next five years.
First up on the table is our strengthening customer growth of 2.7%, which added $14 million to operating income.
Higher usage per residential and irrigation customer of 1% and 11% respectively more than offset the negative used impacts of the pandemic, which contributed to decreased commercial and industrial sales volumes by a respective 4% and 1% during the year.
The net result was a relatively modest $0.9 million increase in overall usage per customer.
Also on the table you will see that the increase in residential sales was offset by a $1 million decrease in fixed cost adjustment revenues.
Next, changes in net power supply expenses led to a $2.6 million decrease in retail revenues per megawatt hour largely due to fewer opportunities processed in sales than in the prior year.
Transmission wheeling-related revenues also decreased $2.2 million primarily due to a 13% decline in Idaho Power's open access transmission tariff rate in October of 2019.
This decrease was partially offset by an increase in wheeling volumes this past summer related to warmer weather in the Southwest, U.S. and California as well as roughly 10% increase in tariff rate beginning October 1 of 2020.
Next on the table, other operating and maintenance expenses decreased by $3.7 million.
Finally, our higher pre-tax earnings led to an increase in income tax expense of $2.1 million this quarter.
The changes collectively resulted in an increase to Idaho Power's net income of $8.8 million.
IDACORP's full year net income for 2020 was a net $4.5 million higher than 2019.
Cash flows from operations were about $22 million higher than the prior year.
At this time, we do not anticipate issuing additional equity in 2000 -- or in 2021 other than nominal amounts under our compensation plans.
As we did last year, Idaho Power contributed $40 million to its pension plan during 2021, which would be above its required contribution.
We currently expect IDACORP's 2021 earnings to be in the range of $4.60 and $4.80 per diluted share.
At or above the midpoint of this guidance range, IDACORP would achieve its 14th consecutive year of growth in earnings per share, which approaches a 5% cumulative average growth over the past five years.
Our strong, consistent financial results and sustained cost management efforts during the past decade have preserved the full $45 million of tax credits available to support our current Idaho jurisdictional return on equity support level of 9.4% under our regulatory stipulation and we plan to continue our efforts to preserve as many of those credits as we can going forward.
Our full year O&M expense guidance is expected to be in the range of $345 million to $355 million.
Our capex spending is expected to increase to the range of $320 million to $330 million, and our expectation of hydropower generation is expected to be in the range of 6 to 8 million megawatt hours, the upper end of which could be close to our normal annual generation over the past 30 years.
We now expect our capital expenditures over the next five years to approach $2 billion and it shows roughly at 7% compound average growth over our previous five-year plan.

Summary:
IDACORP's 2020 fourth quarter earnings per diluted share were $0.74, a decrease of $0.19 per share over the last year's record fourth quarter.
Today, we also issued our full year 2021 IDACORP earnings guidance estimate to be in the range of $4.60 to $4.80 per diluted share with our expectation that Idaho Power will not need to utilize in 2021 any of the additional tax credits that are available to support earnings in Idaho under its regulatory settlement stipulation.
We currently expect IDACORP's 2021 earnings to be in the range of $4.60 and $4.80 per diluted share.