but concentrated in high-risk areas such as the coast or river basins. In this section we present flood exposure estimated disaggregated to subnational regions, the number of which can vary across countries. World Bank household surveys are sampled to be statistically representative at different subnational levels – in this study we adopt these statistically representative subnational units which enable us to compare flood exposure estimates with socio-economic characteristics, such as income levels and poverty (Section 3.4).

The disaggregation of exposure estimates highlights several subnational regions with high risks (Figure 9). Punjab, Pakistan, with a population of 120 million people, frequently experiences heavy flooding and ranks highest in terms of the absolute population headcount exposed to significant flood risk; approximately 48 million people are exposed, which is 38% of the total population. Several of the populous regions in China and India are also among the world’s subnational regions with the highest number of people exposed to flood risk. In China for instance, high population exposure tends to be close to the coast and around the Yellow River valley. However, the sub-national region with the highest population exposure in China is Guangdong in the southeast, on the South China Sea, where 43 million people are exposed across Hong Kong SAR, China; Macao SAR, China; Shenzhen; and the rest of the region. In India, the three sub-regions with the highest population exposure to flood risk (Uttar Pradesh, Bihar, and West Bengal) are all situated in the Ganges basin. Maharashta, which spreads across the central and western regions of India, experiences heavy monsoon seasons and ranks fourth in India in terms of absolute population exposure.

|Punjab (Pakistan)|48.0m (37.6%)|
|---|---|
|Guangdong (China)|43.1m (34.5%)|
|Uttar Pradesh (India)|41.1m (17.4%)|
|Jiangsu (China)|37.4m (45.0%)|
|Bihar (India)|35.0m (27.4%)|
|Shandong (China)|30.5m (30.1%)|
|Henan (China)|29.2m (29.8%)|
|West Bengal (India)|22.3m (21.9%)|
|Upper Delta (Egypt)|18.0m (46.6%)|
|Maharashtra (India)|17.6m (13.6%)|

_Figure 9. Top 10 countries: Number of people exposed to significant flood risk (and as share of total regional population)_ Considering the absolute population exposure figures above biases attention towards large and populous regions. Notably, Uttar Pradesh, Maharashtra, and Bihar are the three most populous sub-national regions in the world. Instead, considering relative population exposure, i.e. the share of the overall population that is exposed to flood risks, can help identify regions in which flood risks are prevalent across large parts of the population. Figures 10 and 11 present relative flood exposure estimates, which demonstrate that in various regions the vast majority of the population is facing significant flood risks.

The sub-national region with the highest relative exposure to flood inundation risk is the Pool region in the Republic of Congo. The region, home to Pool Malebo, has a population of approximately 360,000 people, 91% of whom are exposed to significant flood risk. In all of the top 10 subnational regions in terms of relative population exposure, over two-thirds of the population are estimated to face significant flood risks. Strikingly, regions with high flood exposure can be found in all regions, and in low- and high-income 15