Rapid Assessment for Resilient Recovery and ... - GFDRR

1
THE DISASTER
1.1 Introduction
Thailand is no stranger to natural disasters. The country has a long history of drought and
flood cycles in seasonal variance. Flooding occurs every year in the Chao Phraya River
Basin. Tropical storm cycles come from the east through Laos and Vietnam and touchdown
in the northern parts of the country where water collects and flows downstream into
the basin. With a changing climate and increasing variance and severity of weather, events
similar to this flood may no longer be only 50 years in frequency.
Thailand has dealt with catastrophic floods in the past. In 1942, the flood level in Ayuthaya
reached 5.51 m and inundated Bangkok for two months; 1983 brought a cyclone that inundated
the country for five months, causing THB 6.6 billion in damage; and unprecedented
rainfall in 1995 inundated the largest recorded area of 5,400 m3. Though the 2011 flood
area was smaller than the area affected in 1995, the impact it had on life and the cost of
damage – more than 100 times the 1983 damage costs – was unprecedented. These
factors contributed to the 2011 floods registering on the magnitude of roughly a once in
every 50 or 100 years event.
1.2 Overview of the Floods
The floods that affected 66 of the country’s 77 provinces started in June in the northern
regions with storm Haima, which brought 128 percent of the average rainfall for June.
Haima was quickly followed by tropical storm Nock-Ten throughout parts of July and
August, which resulted in rainfall of more than 150 percent of the average for both months.
Though rains slowed slightly, storms continued to hit the country from the north to the east
and rainfall remained above average throughout September and October (135 and 116
percent respectively). The accumulated water from months of storms and above average
precipitation resulted in the flooding of the central regions.
Over time, the water drained slowly from the north downstream to the central plains in the
Chao Phraya River Basin, eventually reaching Bangkok in early November. The period
of September 14 to October 3 saw 10 major flood control systems overflow or breach 4 .
Though the geographical peak of flooding (in terms of number of provinces affected) was
in late August – after the storms, the impact was most heavily felt in terms of the number
of people affected, when large parts of Bangkok were flooded in mid-November – peaking
at over five million flood-affected people at one time.
4 See flood breach maps in Annex 5.
10 THAI FLOOD 2011 RAPID ASSESSMENT FOR RESILIENT RECOVERY AND RECONSTRUCTION PLANNING