(CNN) -- Thailand's King Bhumibol Adulyadej, the world's longest-serving monarch, celebrated his 84th birthday Monday, giving the Southeast Asian country some much-needed cheer after months of devastating flooding nationwide.
Also celebrated as Father's Day, the occasion launched a week of national celebrations, including a birthday speech by Prime Minister Yingluck Shinawatra on behalf of the Thai people, a public audience by the king during a grand state ceremony and the pardon of some 26,000 prisoners.
A new book celebrating his seventh decade as monarch has also hit stores. Titled "King Bhumibol Adulyadej: A Life's Work," and with an editorial advisory board chaired by former Prime Minister Anand Panyarachun, the book offers a look at the king's life, work, laws governing the throne, along with hundreds of pictures.
In a rare appearance, the king on Monday addressed the recent floods that have devastated the country, urging people to overcome divisions and set up sustainable water management. "It is a duty of everyone to cooperate and help each other," he said.
The U.S.-born and Swiss-educated king has reigned since 1950, succeeding his brother King Ananda Mahidol, whose death in 1946 of a gunshot wound in bed remains a mystery.
Also known as Rama IX, the king commands great love, respect and God-like status among Thais despite his lack of direct power under Thailand's constitutional monarchy, in which decision-making rests with the prime minister. The Constitution stipulates that the king "shall be enthroned in a position of revered worship and shall not be violated" and that "no person shall expose the king to any sort of accusation or action."
He has wielded his moral authority to intervene in political crises over the decades, but his failing health -- he has been residing at Bangkok's Siriraj Hospital -- has raised questions about the country's future, as it struggles to recover from the most recent spasms of political unrest in the aftermath of a 2006 military coup.
His son, Crown Prince Vajiralongkorn, is his heir apparent. But talk about the future role of the monarchy -- most especially if it's deemed less than supportive -- has been hampered by Thailand's lese majeste laws, which ban criticism of the monarchy.
Last week, Human Rights Watch urged the amendment of Thailand's lese majeste laws after 61-year-old Ampon Tangnoppakul was sentenced to 20 years in prison for sending four SMS text messages considered offensive to the Queen and the monarchy -- a case that also drew the concern of the European Union.
"The severity of penalties being meted out for lese majeste offenses in Thailand is shocking," said Human Rights Watch's Asia Director, Brad Adams on the HRW web site.
The group pointed to the King's own 2005 birthday speech in suggesting he invited criticism: "If the King can do no wrong, it is akin to looking down upon him because the King is not being treated as a human being. But the King can do wrong," according to a translation by the Thai newspaper, The Nation.
The U.N. Special Rapporteur has recommended the amendment of Thailand's lese majeste laws.
On Monday The Nation released a Dusit survey on the king. Among the findings: 60 percent of those polled most appreciate his kindness for the economy; 78 percent pledged to be honest in honor of his birthday; 61 percent would like to light candles and sing songs to wish him well; and 73 percent believe disunity most upsets the king.
In addition to Crown Prince Vajiralongkorn, King Bhumibol and his wife of more than 60 years, Queen Sirikit, have three other children: Ubolratana, Chulabhorn, and Maha Chakri Sirindhorn, whose work promoting schools, nutrition and health care for the needy has earned her the nickname "Angel Princess."