Climate Variability in South Asia V. Niranjan, M. Dinesh Kumar, and Nitin Bassi Institute for Resource Analysis and Policy
Contents • Introduction • Rainfall variability in South Asia • Temporal variability in rainfall • Variability in climate in South Asia • Spatial variability in climate • How South Asian rainfall has been changing over time? • Conclusions
Introduction • It is well understood that from a utilitarian perspective, ‘climate variability’ has significant implications for the way climate change predictions need to be made • Understanding of ‘climate variability’ (spatial and temporal) and its impact on hydrological systems would also help understand the likely impact of the change in climate over time on the hydrological system and water resources • Unfortunately, these concerns were very narrowly addressed by the advocates of climate change, with the key contention being the variability in precipitation would increase with greater frequency of extreme events such as floods and droughts.
Introduction • There are several other important climate parameters one needs to deal with for analyzing climate variability issues which include the following – number of rainy days; – wind speed; – wind directions; – humidity; – temperature and – solar radiation
Rainfall variability in South Asia • The mean annual rainfall across South Asia varies from 100mm to 3200mm • India has diverse climates (hyper-arid to arid to semi arid to sub-humid to humid) • Srilanka being an island country, has coastal climate in many parts • Pakistan has true humid conditions after the rainfall increases to 750mm in plains and 625mm in highlands
Rainfall variability in South Asia (Contd..) • Nepal (Alpine to sub-alpine in higher Himalayas to temperate in lesser Himalayan region to sub-tropical in the Terai and Siwalik regions • Afghanistan has the central highlands, which are part of the Hindukhush Himalayan range, northern plains and south western plateau, which consists of sandy desert and semi desert. • Bangladesh has tropical monsoon climate characterized by high seasonal rainfall, high temperature and high humidity.
Temporal variability in rainfall • Analysis of monsoon rainfall carried out by Physical Research Laboratories shows that the inter-annual variability (expressed in terms of CV) in annual rainfall is high in regions of low rainfall and low in regions of high rainfall • In regions such as western Rajasthan and Kachchh, the CV in the rainfall is as high as 50 per cent and above. • In the northeastern and western Ghat regions the CV in rainfall is very low, meaning high dependability
Variability in climate in South Asia • Climate is the net effect of the interplay of precipitation, humidity, temperature of the atmosphere and winds (speed) and rainfall • Humidity is a measure of the amount of vapor in the air, and is measured in terms of vapor pressure of the air (measured in KPa/m 2 ) • The relative humidity (RH) is the measure of the vapor pressure of the air measured as a percentage of the saturated vapor pressure and this RH ranges from <25% to 100% across South Asia
Variability in climate in South Asia (Contd..) • Atmospheric temperature change is a result of change in energy balance, which is the net effect of the incident and reflected solar radiations • Speed of winds , which occur as a result of atmospheric pressure gradients, is an important climate parameter as it can change the humidity of an area. • There is significant variation in solar radiation flux across South Asia
Spatial variability in climate • Potential evaporation (expressed in mm), the amount of water an open water body can evaporate in a year, for a particular location is a net result of the solar radiation flux, wind speed and relative humidity experienced in that location and • to a lesser extent the temperature, and is a strong indicator of the location’s climate, along with rainfall. • The variations in solar radiation, air temperature, wind speed and relative humidity across space ultimately results in significant variation in potential evaporation (PE).
How South Asian rainfall has been changing over time? • Understanding how the monsoon will change in the face of global warming is a challenge for climate science • The general circulation models still have difficulty simulating the regional distribution of monsoon rainfall • Historical and Projection of South Asia monsoon rainfall (1860 – 2100) • The analysis by IITM is the only work which comprehensively examines the long term variations in Physiographic rainfall across India
Conclusions • We have seen that there is substantial inter-annual and inter- regional variations rainfall. • There is also substantial variation in the annual potential evaporation rates, which is the result of variations in key climate variables with respect to space. • We have also seen that there is significant variation in climate variable such as relative humidity, temperature and wind speed across seasons and years.
Conclusions • These together can induce major changes in the physical and biophysical processes such as evaporation from soils and water bodies, and evapo-transpiration from plants, grass and trees. • Understanding these characteristics is important as it has significant implications for the way climate change predictions need to be made for the sub-continent. • Understanding of the impact of ‘climate variability’ on water resources and water demand would also help understand the likely impact of the change in climate over time on the hydrological system and water resources
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Figure1: Monthly Mean Rainfall and Temperature in India Figure2: Monthly Mean Rainfall and Temperature in Srilanka 400 40 (1900 - 2009) 450 40 (1900 - 2009) 350 35 400 35 Temperature in o C Temperature in o C 300 30 350 30 Rainfall in mm Rainfall in mm 300 250 25 25 250 200 20 20 200 150 15 15 150 100 10 10 100 50 5 5 50 0 0 0 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Monthly Mean Rainfall Monthly Mean Temperature Monthly Mean Rainfall Monthly Average Temperature Figure4: Monthly Mean Rainfall and Temperature in Nepal Figure3: Monthly Mean Rainfall and Temperature in Pakistan (1900 - 2009) (1900 - 2009 ) 500 40 60 40 35 35 400 Temperature in o C 50 30 Temperature in o C Rainfall in mm 30 Rainfall in mm 25 40 300 25 20 30 20 200 15 15 20 10 100 10 5 10 5 0 0 0 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Monthly Mean Rainfall Monthly Mean Temperature Monthly Mean Rainfall Monthly Mean Temperature Figure5: Monthly Mean Rainfall and Temperature in Afghanistan Figure6: Monthly Mean Rainfall and Temperature in Bangladesh (1900 - 2009) (1900 - 2009) 600 40 80 40 35 70 500 Temperature in o C 30 Temperature in o C 30 60 Rainfall in mm Rainfall in mm 400 25 50 20 300 20 40 15 10 200 30 10 20 100 0 5 10 0 0 0 -10 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Monthly Mean Rainfall Monthly Mean Temperature Monthly Mean Rainfall Monthly Mean Temperature
Relative Humidity: Aurangabad (2009 and 2010) 100 90 80 70 Relative Humidity % 60 50 40 30 20 10 0 1 13 25 37 49 61 73 85 97 109 121 133 145 157 169 181 193 205 217 229 241 253 265 277 289 301 313 325 337 349 361 RH%-AM-2009 RH%-AM-2010 RH%-PM-2009 RH%-PM-2010
Temperature and Rainfall of Aurangabad (2009 and 2010) 50.0 160.0 45.0 140.0 Temperature in degrees C 40.0 120.0 35.0 Rainfall in mm 100.0 30.0 25.0 80.0 20.0 60.0 15.0 40.0 10.0 20.0 5.0 0.0 0.0 1 12 23 34 45 56 67 78 89 100 111 122 133 144 155 166 177 188 199 210 221 232 243 254 265 276 287 298 309 320 331 342 353 364 Daily Max Temp-2009 Daily Max Temp-2010 Daily Min Temp-2009 Daily Min Temp-2010 Daily Rainfall-2009 Daily Rainfall-2010
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