Impacts of Climate Change Modelling activities

In the ADAPT project, the SWAP 2.0 model is applied to analyse the variation of food production at field-scale level. SWAP is a one-dimensional physically based model for water, heat and solute transport in the saturated and unsaturated zones, and also includes modules for simulating irrigation practices and crop growth (see Chapter 3). The SLURP model has been used for hydrological modelling on the basin scale (Kite, 2000). SLURP is a hydrological basin model that simulates the hydrological cycle from precipitation to runoff, including the effects of reservoirs, regulators, water extractions and irrigation schemes. It first divides a basin into sub-basins using topography from a digital elevation map.

In this study, we used the previously described data from climate change scenarios comprising three data sets for 1961-1990, 2010-2039 and 2070-2099. However, since the SLURP model requires daily climate data, the SRES scenarios (provided at a monthly time step) were interpolated to daily scenario values. The process was applied for two main parameters (temperature and precipitation). To analyse the effects of climate change, values of other factors such as land cover area, reservoir, etc. are kept the same as in the previous SLURP/MRB study (Kite, 2000).

Impacts of climate change

Projected climate changes in the MRB include strengthening of monsoon circulation, increases in temperature and increases in the magnitude and frequency of extreme rainfall events (IPCC, 2001). Climate-related effects also include sea-level rise. These changes could result in major impacts on the region's ecosystems and biodiversity; hydrology and water resources; agriculture, forestry and fisheries; mountains and coastal lands; and human settlements and human health. The following are major features of climate changes that affect the MRB.

• The monsoons bring most of the region's precipitation and are the most critical climatic factor in the provision of drinking water and water for rain-fed and irrigated agriculture. As a result of the seasonal shifts in weather, a large part of Tropical Asia, including the MRB, is exposed to annual floods and droughts.

• Tropical cyclones, frequency and related floods may increase.

• Other extreme events include high-temperature winds.

• In the megacities and large urban areas, high temperatures and heat waves also occur. These phenomena are exacerbated by the urban heat-island effect and air pollution.

• The El Nino-Southern Oscillation (ENSO) phenomenon becomes geographically much more extensive, which has an especially important influence on the weather and interannual variability of climate and sea level, especially in the western Pacific Ocean and South China Sea around the MRB.

The main current water issues in the MRB may be accelerated through climate change (WUP, 2001).

Water shortages in Thailand: the level of irrigation development in the Northeast Thailand region, as well as in neighbouring, agriculturally important Chao Phraya Basin in Thailand, has resulted in a lack of water during the dry season.

• Salinity intrusion in delta: the extent of the intrusion of saline water into the Mekong Delta depends on the magnitude of the dry-season flows from upstream and the level of abstractions for irrigation.

• Floods: the flood in 2000 was the highest flood in over 40 years, with significant loss of life and high damage to crops and infrastructure in Cambodia and Vietnam.

Impacts of climate change on food production

Changes in climate will have significant effects on agriculture in many parts of the MRB, particularly on low-income populations that depend on isolated agricultural systems. These effects are due to frequent floods, droughts, cyclones, sea-level rise, higher temperature that can damage life and property and severely reduce agricultural production. Two additional factors increase the vulnerability of the agricultural sector in the LMB under climate change: (i) only about 7-10% of the cultivated land in the LMB is irrigated (Ringler, 2001). Yields for rice under rain-fed conditions in the LMB are low, compared with those of irrigated rice yields, due to many factors, including floods, droughts, temporary inundation from rainfalls, and tidal flows and coastal salinity (Hossain and Fischer, 1995); (ii) the region supports a large human population per hectare of cropland, from 2.4 in North-east Thailand to 11.5 in the Vietnamese Mekong Delta.

Impacts of climate change on the environment

As in other regions in Tropical Asia, climate change represents an important additional external stress on the numerous ecological and socio-economic systems in the MRB that already are adversely affected by air, water or land pollution, as well as increasing resource demands, environmental degradation and unsustainable management practices (IPCC, 2001). The main current environmental issues related to climate change in the MRB are closely linked to water usage, particularly regarding availability of water for agriculture, but also to flooding, and storage and release of water from hydropower dams.

Indicators

Knowing the major hydrological, food and environmental issues related to climate change, we now can identify a set of indicators that allows for a quantitative impact assessment exercise. In this study we focus on a set of indicators for the general basin hydrology. An increase in maximum flows, in particular daily flow, means a higher risk of flood, while a decrease in minimum or average monthly flow means a risk of water shortage for certain land use types and deeper salt intrusion into the Delta. Furthermore, we used two indicators that measure the state of food security in the MRB and two indicators that measure the quality of the environment. The selected indicators are listed in Table 8.4. It is noted that this list is not final and many more important indicators could be considered in subsequent studies.

Table 8.4. List of selected indicators for the MRB.

Group

Indicator

Description

Hydrological indicators

Indicators for food security

Indicators for environment

Maximum daily flow (m3/s) Maximum, minimum and average monthly flows (m3/s)

Total rice production (t/year)

Farm income index (relative to 1)

Number of people affected by floods

Output from the SLURP model Outputs from the SLURP model

Estimated from current production with the assumption that it will alter in proportion with changes in yield predicted by SWAP model and crop intensification Equal to 1 for 1961-1990 and will alter in proportion to yield increased by climate changes and crop intensification

Estimated from current people affected in each country with the assumption that it will alter in proportion to the increment in maximum daily flow

Qualitatively evaluated based on minimum monthly flow into the delta

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