Status of climate change/variability studies and potential impacts of climate change/variability on national and regional agriculture, rangelands, forestry and fisheries in RA-II region by H. P. Das Division of Agricultural Meteorology India Meteorological Department
Major risks due to climate change The following are the major risks in Asia apprehended from climate change: • The frequency of forest fires is expected to increase in boreal Asia. • Increased precipitation intensity, particularly during the summer monsoon, could increase flood prone areas in temperate and tropical Asia. There is a potential for drier conditions in arid and semi-arid Asia during summer, which could lead to more severe droughts. • Crop production and aquaculture would be threatened by a combination of thermal and water stresses, sea level rise, increased flooding, and strong winds associated with intense tropical cyclones.
Present trend and variabilities in key climatic variablesSurface air temperature
Present trend and variabilities in key climatic variablesPrecipitation
Status of extreme and severe weather systems There is some evidence of increase in the intensity or frequency of some of extreme weather events like heat waves, extratropical and tropical cyclones, prolonged dry spells, intense rainfall, tornadoes, snow avalanches, thunder storms, dust storms etc on regional scales in widely separated areas of Asia throughout the 20th century. Boreal Asia • Increases in climate extremes in the western Siberia-Baikal region and eastern parts of boreal Asia have been reported in recent decades. • Some mountains in Asia have permanent glaciers that have vacated large areas during the past few decades, resulting in increases in glacial runoff. As a consequence, an increased frequency of events such as mudflows and avalanches affecting human settlements has occurred. • As mountain glaciers continue to disappear, the volume of summer runoff eventually will be reduced as a result of loss of ice resources. Consequences for downstream agriculture, which relies on this water for irrigation, will be unfavorable in some places. For example, low and mid-lying parts of central Asia are likely to change gradually into more arid, interior deserts. Temperate Asia • In China, droughts in 1972, 1978, and 1997 have been recorded as the most serious and extensive. A large number of severe floods also have occurred in China, predominately over the middle and lower basins of the Yangtze (Changjiang), Huanghe, Huaihe and Haihe rivers. • In Japan, drought disasters are significantly more frequent during years following ENSO warm events than in normal years.
Status of extreme and severe weather systems(Contd..) Tropical Asia • No identifiable variability in the number, frequency, or intensity of tropical cyclones or depressions has been observed in the northern Indian Ocean cyclone region (Bay of Bengal and Arabian Sea) over the past 100 years, although there was some evidence of decadal scale variations with a rising trend during 1950-75 and a declining trend since that time. • No conclusive increasing or decreasing trends in time series data of flooded areas has been noticed in various river basins of India and Bangladesh. • In India, Laos, the Philippines, and Vietnam drought disasters are more frequent during years following ENSO events. At least half of the severe failures of the Indian summer monsoon since 1871 have occurred during El Niño years. • It is found that the 1891-1920 and 1961-80 periods witnessed frequent droughts while few droughts occurred during 1930-1960 and 1980-2000. This suggests some kind of low frequency oscillation of the monsoon system on the decadal scale. • There are also reports of an increase in thunderstorms over the land regions of tropical Asia. Arid and Semi-arid Asia • Over arid and semi-arid regions of India there have been periods in the last decades of the nineteenth century and first two decades of twentieth century when drought frequencies have been markedly higher than in recent years, although individual recent droughts may have been intense ones in some regions. • The frequency and severity of wild fires in grassland and rangelands in arid and semi-arid Asia have increased in recent decades. • Coupled with the conversion of grazing lands to farming, the arid regions of India is undergoing an aggravation of desertification through erosion of lands and aeolian shifting of soil particles. In some locations, there has been a rise in water table with simultaneous increase of salinity and deterioration of soil regime. • The variation of the aridity index line, computed by Penman method, over arid regions of India reveals a possible spread of arid conditions in southeast direction.
Table 1 Possible changes in area-averaged surface air temperature over Asia and its sub-regions as a result of future increases in greenhouse gases. Numbers in parenthesis are area-averaged changes when direct effects of sulphate aerosols are included.
Table 3 Precipitation
Extreme events – Future scenario • Recent observations suggest that there is no appreciable long term variation in the total number of tropical cyclones observed in the north Indian, southwest Indian, and southwest Pacific Oceans east of 160 0E . • The frequency of typhoons and the total number of tropical storms and typhoons has been more variable since about 1980. Some studies suggest an increase in tropical storm intensities with carbon dioxide (CO2) induced warming. • Some of the most pronounced year-to-year variability in climate features in many parts of Asia has been linked to ENSO. • Future seasonal precipitation extremes associated with a given ENSO event are likely to be more intense in the tropical Indian Ocean region; anomalously wet areas could become wetter, and anomalously dry areas could become drier during ENSO events. • The intensity of extreme rainfall events is projected to be higher in a warmer atmosphere, suggesting a decrease in return period for extreme precipitation events and the possibility of more frequent flash floods in parts of India Nepal, and Bangladesh. • No significant change is found in the number and intensity of monsoon depressions (which are largely responsible for the observed interannual variability of rainfall in the central plains of India) in the Bay of Bengal in a warmer climate.
Impact of climate variability and change on agriculture(Contd…)
Impact of climate variability and change on agriculture(Contd…)
Impact of climate variability and change on agriculture(Contd…)
Table 4 Yield impact of selected climate change studies for rice in Tropical Asia.
Table 5 Increase in yield (%) of different cultivars under modified climate of northwest India S-I :current climates S-II: Tmax + 1.00C, Tmin+1.50C, 2 x CO2 S-III: Tmax + 2.00C, Tmin+2.50C, 2 x CO2
Table 6 Possible impacts due to different climate scenarios in 2050s (billion Yuan)
Impact of climate variability and change on forestry Impact on boreal forests • Climate change may affect the biodiversity in boreal forests of Asia through a myriad of processes and effects like local mortality of boreal species and replacement by northern hardwoods or prairies, migration of boreal species northward and coastward, increased probability of fire; increased or decreased soil nutrients availability, increased emissions of green house gases particularly methane from wetlands etc. • Major alterations in vegetation could be expected, specially in the mountains of the northern boreals subzones and the subarctic forest – tundra ecotone in northeast Siberia. • In the middle and southern boreals subzones, vegetation changes may be more limited because of more resistant species interaction in the forest communities of the continental area and the isolated islands of the Kuril, Shantar and Kommander groups.
(Contd..) Impact on temperate forests • Studies on projected impacts of climate change suggest that northeast China may be deprived of the conifer forests and its habitat and broad leaved forests in east China may shift northward by approximately 3 0 of latitude. These results are based on a 2 0C increase in annual mean temperature and a 20% increase in annual precipitation. • Although the area of potential distribution of temperate forests in Temperate Asia is to a large extent, cleared and used for intensive agriculture, global warming can be considered to trigger structural changes in remaining temperate forests. The nature and magnitude of these changes depend on associated changes in water availability, as well as in water use efficiency. • Shifts in temperature and precipitation in temperate rangelands may result in altered growing seasons and boundary shifts among grasslands, forests and shrublands.
(Contd..) Impact on tropical forests • Results of research from Thailand suggest that climate change would have a profound effect on the future distribution, productivity, and health of Thailand’s forests. The area of subtropical forest could decline from the current 50 % to either 20 % or 12 % of Thailand’s total forest cover (depending on the model used), whereas the area of tropical forests could increase from 45 % to 80 % of total forest cover. • A decrease in tropical rainforest of 2-11 % and an increase in tropical dry forest of 7-8 % in Sri Lanka. • A projected depletion of soil moisture would likely cause teak productivity to decline from 5.40 m3/ha to 5.07 m3/ha in India. The productivity of moist deciduous forests also could decline from 1.8 m3/ha to 1.5 m3/ha.
(Contd..) Impact on Arid and Semi-Arid rangeland • With an increase in temperature of 2-3 0C combined with reduced precipitation as projected for the future in the semi-arid and arid regions of Asia, grassland productivity is expected to decrease by as much as 40-90 %. • Rangelands in Nepal also have been subjected to degradation in recent years. Climate change is likely to represent an additional stress to rapid social change in many of Asia’s rangelands. • Shifts in temporal biomass patterns due to changed climate have potentially significant implications for grazing management. • Forest fires alter the structure of vegetation and affect nutrient cycling. By making nitrogen and other nutrients more available to soil microorganisms, fire may result in enhanced emissions of nitrous oxide (N2O) from soil.
Effect on Fisheries • Climate change impacts on fish species generally will be positive through faster growth, low winter mortality rates, reduced ice cover, and reduced energy costs as a result of expanded regions of warmer water. Cultivation of warm water species also may expand. Warming will require greater attention to possible oxygen depletion, fish diseases, and introduction of unwanted species. • For marine fisheries, slight changes in environmental variables such as temperature, salinity, wind speed and direction, ocean currents, strength of upwelling, and predators – can sharply alter the abundance of fish population. Rises in sea level also may cause saline water fronts to penetrate further inland, which could increase the habitat of brackish – water fisheries. Coastal inundation also could damage the aquaculture industry. • Fisheries at higher elevations may be particularly affected by lower oxygen availability resulting from increases in temperature. In the plains, the timing and amount of precipitation may affect the migration of fish species from the river to the flood plains for spawning, dispersal and growth. If the magnitude and extent of floods increase, more flood control projects would further deplete flood plain fisheries.
Effect on Fisheries (Contd..) • Marine productivity is greatly affected by temperature changes that control plankton shift, such as seasonal shifting of sardine in the sea of Japan and induced during the cyclic occurrence of the ENSO in low latitudes. The impact of global warming on fisheries will depend on the complicated food chain, which would be disturbed by sea level rise, changes in ocean currents, and alteration of mixing layer thickness. • The rise in the SST will shift the southern limit of salmon species further to the north. It is also suggested that the Sea of Japan bottom water will become anoxic within a few hundred years; a decreased oxygen supply will lead to major losses in biological productivity in deep waters. • Increased frequency of El-Nino events, which are likely in the warmer atmosphere, could lead to measurable declines in plankton biomass and fish larvae abundance in coastal waters of south and southeast Asia. Such declines in lower levels of the food chain will have negative impacts on fisheries in Asia.