The visible impacts of climate change in South Asia
El Niño is a phase of the El Niño-Southern Oscillation (ENSO) when warm ocean water develops in the central and east equatorial region of the Pacific Ocean. Under the El Niño phase, warm water and atmospheric conditions move eastward. It also makes deeper thermocline and warm upwelling water near South America.
This year, an El Niño was fully developed in the Pacific, which was began last fall. In a conventional El Niño condition, low-pressure zone forming near the eastern Pacific region near Peru and rising air forms cloud and rains after condensed. In such conditions, above average rainfall can be observed in the Eastern Pacific near to the equator and lower than average rainfall can be observed over the Western Pacific.
However, the El Niño formed this year is different.
Observation data over the Pacific shows that heavy rainfall occurred in the Central Pacific but not in the Eastern Pacific. This type of condition is known as El Niño “Modoki.”
The impact of Modoki events significantly influences the temperature and precipitation patterns over many parts of the globe. Through teleconnections, Modoki can generate atmospheric changes. Teleconnections exist with atmospheric conditions of many maritime countries such as Indonesia, Malaysia, Singapore, etc.
Such teleconnection can be extended up to India and Bangladesh.
The eastern tropical Pacific usually receives more than average rainfall, whereas tropical Western Pacific receives deficit rainfall in El Niño years. However, during Modoki, north-western America receives excessive rainfall, which is opposite to the El Niño years.
There is limited confidence on the impact of Modoki on the precipitation over Central and Eastern India compared to Southern India.
During El Niño years, air temperature over land surface will be higher in the North American region. In South Asia, Central Asia, and East Africa, the air temperature will be higher in El Niño years.
It is expected that El Niño will cause lower than normal rainfall, warmer than normal temperatures, drier than normal climate, and higher than normal cyclonic activities over this region.
However, there has been no work done on the impact of El Niño Modoki on the rainfall patterns of Bangladesh. Based on studies over India and other regions, it can be suggested that warm temperature, drier climate, and intense cyclones can be formed over this region in Modoki years.
The occurrence of more rainfall during March and April than May in recent years can provide some indications on the changes in the seasonal rainfall patterns.
The occurrence of frequent flash floods in the northeast haor regions of Bangladesh also provide indications of changes in extreme events.
Based on recent studies using climate projections, the frequency and duration of heat waves over the Indian sub-continent in the future will be increased.
In the future, heat waves will increase due to strengthening mid-tropospheric high and associated subsidence over central and northwest India.
Considering the impacts of climate change on the weather systems, it can be expected that more heatwaves, intense cyclones, and extreme rainfall will be observed over this region in the future.
AKM Saiful Islam is a Professor of the Institute of Water and Flood Management, BUET.