"It's obviously a blow to lose Pop, but we're hoping Al will prove a massive acquisition for us," Bears director of cricket Dougie Brown told BBC Sport.
Alan Richardson's first-class haul
1 match, three wkts
63 matches, 165 wkts at 32.87
43 matches, 142 wkts at 27.02
60 matches, 254 wkts at 22.07
1 match, six wkts at 16.66
1 match, 1 wkt at 44.00
TOTAL 569 wickets at 26.37
"He has enormous respect from everyone within the game and will fit in well."
After an initial brief foray with Derbyshire in 1995, following which he played Minor Counties cricket for his native Staffordshire, Richardson made the full-time move to the first-class game with the Bears when he arrived at Edgbaston in 1999.
After five seasons with Warwickshire, he then moved on to Lord's in 2004 to spend the next five, somewhat injury-hit years with Middlesex.
In his four-year stay at New Road, Richardson took 254 wickets in 60 first-class matches, being named as one of Wisden's five cricketers of the year for 2011 after a career-best summer haul of 73.
He was contracted to play one final season with Worcestershire this summer, but admitted: "I have been working on my coaching qualifications for some time and this is a fantastic opportunity for me.
"I have thoroughly enjoyed my time at New Road and am grateful for the understanding that the management and coaching team at Worcestershire have shown since I informed them of my decision to retire early.
"I am looking forward to the challenge ahead and cannot wait to get stuck into working with one of the finest bowling attacks in the country."
Brown added: "I know they say you're a long time retired, but this really feels like Al has made his decision at just the right time.
"All the members of our bowling unit are now back in full training following the various injuries we suffered last summer. And Al's experience and knowledge will help continue the excellent work that Pop has done."
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