Droughts in Asian Monsoon Region: Volume 8

Rajib Shaw

Drought is a perennial phenomenon in some parts of the world. Drought is a slow-onset disaster, which is often not initially visible. When it does become visible, it is already too late to respond. Unlike other disasters, drought can be predicted well in advance. Also, most of the drought impacts are prominent in the rural areas, affecting the livelihood options like agriculture, aquaculture, animal husbandry, etc. In developing countries, the key challenge of early warning is its last mile, which means to bring the early warning information to the end users in rural communities. Based on the early warning, the local communities can prepare themselves through shifting the cultivation pattern and looking for the alternative livelihoods. In many communities, the resilience is built through experiences and different indigenous knowledge and practices are developed over time.

The Monsoon Asian region has a much wider rainfall distribution than other regions of the world. The countries in this region are characterized mostly by floods and typhoons, which result from the interplay among the ocean, the atmosphere, and the land. Thus, many factors affect the strength of the rainfall, including sea surface temperatures in the Indian and Pacific Oceans, variations in solar output, land snow cover and soil moisture over the Asian continent, and the position and strength of prevailing winds. The links between these factors and monsoons appear to wax and wane over time, and the observational record is too short to explain this longer-term variability. Precipitation and surface wind maps of Asia during the summer months of June to August show the average spatial patterns of monsoon circulation and moisture.

According to the Intergovernmental Panel on Climate Change (IPCC) special report on the regional impacts of Climate Change (IPCC, 2007a), a drastic change in rainfall patterns in the warmer climate would occur in Bangladesh, and it may experience a 5% to 6% increase of rainfall by 2030 due to glacier melting and more intense monsoons, which will create frequent large and prolonged floods as well as an increase in droughts outside the monsoon season. Furthermore, in the context of global warming, most of the climatic models project a decrease in precipitation in the dry season and an increase during the monsoon season in south Asia (Christensen et al., 2007). This will cause a combination of more extreme floods and droughts in this region. Therefore, the moderately drought-affected areas will be turned into severely drought-prone areas within next 20 to 30 years (IPCC, 2007b).

The country of Cambodia is vulnerable to climate variability and climate change (MoE, 2005). Flood and drought are common in Cambodia, and their impacts include the yearly destruction of infrastructure, property, crops, and livestock, and the loss of lives. Cambodia's adaptive capacity for flood and drought is poorly developed (NAPA, 2006). Cambodia receives most of its rainfall from the southwest monsoon, which occurs from mid-May through November. The coastal regions receive the highest rainfall amounts, about 3,000mm/year, while the highlands and lowlands receive 2,500mm/year and 1,400mm/year, respectively. The monthly distribution of rainfall results in a wet season extending from May through December and a dry season from December through April. On average, the annual rainfall in Cambodia is a bit higher than that of other countries in the region. Although the rainfall distribution in the country is high, drought has still occurred in recent years (MoE, 2005).

While Erratic Distribution of Monsoon is the main cause of abnormal monsoon, the consequences of Early Withdrawal of Monsoon are generally quite serious and can create disastrous situations for the drought-prone areas of the country. It is this intrinsic variability of the rainfall over India, in both time and space that makes India, especially the drier regions thereof, vulnerable to droughts. Although no part of India is immune to the adverse impacts of drought, the arid and ,semi-arid regions in the western, northern and peninsular parts of the country experience more frequent droughts, at times leading to a crippling impact on the national economy. The Indian economy, thus, has been described as a “gamble of monsoon” (Venkateswarlu, 2010). A look at the rainfall departure¹ and the corresponding food-grain production (Table 1) in India from 2000 to 2009 reveals that in the drought years of 2002 and 2009 the All India rainfall departure was −19.2% and −21.8%, respectively, leading to a drastic fall in food-grain production by 13.4 and 6.9%, respectively, as compared to the previous years, which received good monsoon rains.

Myanmar is located between 9deg. 55min. and 28deg. 15min. north latitude and 92deg. 10min. and 101deg. 10min. east longitude. It is the westernmost country in southeast Asia. Its bordering countries are Bangladesh, India, China, Laos, and Thailand. Over 50% of the eastern coastline of the Bay of Bengal and the Andaman Sea constitutes the western border. The country occupies a total land area of 676,577km² and is home to 57.5 million people in 14 states and regions, per 2008 estimate. The general topography of the country is high in the north and the west with north–south-oriented mountain ranges extending from the Himalayas. The eastern side of the country is a wide plateau connected to Yunnan, China. The central area and the more southern parts of the country are relatively low. Rivers run from north to south in most parts of the country. A map of Myanmar's states and regions is shown in Fig. 1.

Chronicles and literary records show that Sri Lanka has been affected by various natural disasters from time to time in the past, as it is now. The sea surge/coastal flooding during King Kelani Tissa's reign, around 190 BC could have been a tsunami. A severe drought and famine known as Beminitiya Seya occurred during the intermittent reign of the Brahmin King Thiya (Tissa) and King Valagamba (89–77 BC). There are also references to droughts prior to this, namely, Akkakayika Seya (it is said that about 24,000 monks died and others left the country, and some of those who remained survived by eating kara leaves). Subsequently, this led King Valagamba to undertake to record the sayings of the Buddha (Tripitaka) for posterity. Duttagamini (161–137 BC), Ekanalika Seya during the reign of King Kunchanaga (187–189 AD) and others, none of which had been as severe as Beminitiya Seya. Apart from these extreme hazard events other incidents have been reported, including the flooding incidents during the British rule (National Disaster Management Plan, 2007).

Thailand's climate is tropical; it has high temperature and humidity and is dominated by monsoons. The average rainfall, recorded from 1950 to 1997, is 1,374mm/year or equivalent to 702,610 Million Cubic Meter (MCM), which is much greater than the global average rainfall of 990mm/year. During the past 10 years, the annual rainfall has been positively deviant from the annual average (Fig. 1). In addition, results from climate-model simulations for the 21st century (Bates, Kundzewicz, Wu, & Palutikof, 2008) show that droughts should not be a problem in Thailand because of increased precipitation, soil moisture, and runoff and Thailand only experiences slight increase in evaporation. Therefore, it can be said that “droughts” change from country to country.

Vietnam is located in the tropical monsoon area, one of five storm hubs of Pacific Asia, and is regularly faced with various disasters. Drought, a normal part of the climate for virtually all regions of Vietnam, is of particular concern, where an interruption of the country already limited water supplies for extended periods of time can produce devastating impacts. Historical records indicate that drought occurs almost everywhere in those places almost every year (Hieu, 2002). However, multiyear droughts are of great concern to water-resource managers, natural-resource managers, and policy makers (Nguyen, 2010b).

Case studies from many countries indicate that even when rainfall is high drought can still occur. Droughts have been recorded in Bangladesh, where the rainfall is 2,300mm per year, and in Luang Prabang, Laos, where the annual rainfall is 3,200mm. Similarly, the highest Standardized Precipitation Index (SPI) value of 2.78 indicates a possibility of floods in Cambodia. Identification of a threshold SPI value is necessary to pinpoint impending drought. Since SPI values reflect only the rainfall situation and not the existing water availability in reservoirs and canal systems, such a detailed impact-assessment study should also compare the duration of a negative SPI value with that of reduction in the available water from various sources, including groundwater, reservoirs, and canal irrigation systems. So drought occurs not only because of lack of rainfall but also because of bad practices of water usage and water management.