Global Warming Responsible For Floods In Wayanad, Kerala

IMAGE COURTESY : SKYMET WEATHER

As Wayanad district in Kerala reels from destruction wreaked by one of the most devastating landslides triggered by incessant Monsoon rains. During the wee hours of July 30, multiple landlines swept away several villages in the district. The tragedy has claimed over 100 lives and injured several. Experts believe that climate change is the culprit for this.

Geographically, Kerala is bounded by Arabian Sea to its west and the Western Ghats to its east. It receives the second-highest monsoon rainfall in India after its northeastern states. It records an average annual rainfall of about 3,107 mm of which 75% is received during the monsoon months of June-September studies have established that the rise in global average temperatures due to human-induced climate change has led to an increase in the number of extreme rainfall events associated with monsoon.

The rainfall potential

The region increases from the coastal belt towards the Western Ghats, reaching a maximum on the windward side of the Ghats and rapidly decreases on the leeward side. The rainfall characteristics over Kerala are unique because of the influence of isolated steep-sloped structures separated by the wide Palghat gap. Contrary to this climatology, the state has experienced severe floods in recent times due to intense precipitation during the SW monsoon. However, experts suggest that factors beyond the meteorological factors, such as climate change and unplanned development, are to blame for the catastrophic landslides.

“Whilst rainfall in Kannur district has been 21% above the average between 1st June and 30th July, it is 14% below the average in the neighbouring district of Wayanad, and up to 25% below average in Idukki and Ernakulam districts. The co-occurence of two extreme scenarios (landslides and rainfall deficit) in the same state reflect a strong spatial variability in this year’s monsoon rainfall. The expectation is that such a pattern would become more intense in the future if global warming continues,” said Dr Akshay Deoras, Research Scientist, National Centre for Atmospheric Science and the Department of Meteorology, University of Reading, UK.

There has been a steady rise in extreme events in the state over the last decade. For example, Cyclone Ockhi wreaked havoc in 2017, followed by devastating floods in 2018, which were among the worst in the state’s history. In August 2019, the state experienced another spell of extremely heavy rainfall.

According to a report, ‘Climate Change Assessment over the Indian Region’, the inter-annual variability of summer monsoon rainfall is projected to increase throughout the twenty-first century. The increased frequency of localized heavy rainfall on sub-daily and daily timescales has enhanced flood risks across India. Role of Climate Change and the science behind it Numerous studies have established that the rise in global average temperatures due to human-induced climate change has led to an increase in the number of extreme rainfall events (ERE) associated with monsoon, thunderstorms and short-spanned local cloudbursts.

These events, ranging from a few hours to a few days, have become more frequent in the recent decades over the subcontinent. The effects of climate change have led to changes in monsoon trends due to the weakening of synoptic activity within the Indian monsoon and the moistening of the tropical troposphere. The meteorological factors behind extremely heavy rainfall include: “Climate change is drastically changing rainfall patterns in Wayanad. What was once a cool, humid environment with year-round drizzles and monsoon rains, is turning into one marked by drier, hotter summers and intense downpours during the monsoons. This change has increased the risk of landslides. Dry soils absorb less water and heavy rainfalls cause run-offs that can lead to landslides, such as the ones we’ve seen this week,” said Mariam Zachariah, Research Associate, Imperial College London.

Citing similar views, Mahesh Palawat, Vice President – Meteorology and Climate Change, Skymet Weather said, “Monsoon patterns have definitely changed and they now behave in an erratic manner. Earlier during the Monsoon season, we used to witness uniform rains and no convective activity, but now we see rains which are more of pre-Monsoon characteristics that include thundershowers. Kerala has not been witnessing typical Monsoon rains and has been struggling to achieve its average rainfall. Despite these heavy showers, it is yet to surpass its average rainfall so far. Also, with the rise in air as well as ocean temperatures, there has been a drastic increase in the moisture. The Arabian Sea has been warming at a faster rate, pumping moisture in the atmosphere, making it unstable. All these factors are directly linked to global warming.”

Over 90% of the global warming is observed by oceans, which has led to significant rise in ocean heating. As per a new research by Nature, oceans have warmed by more than 1.5 °C since the beginning of the industrial era, challenging previous estimates. The Indian Ocean is a hotspot for climate change and has seen the fastest surface warming since the 1950s.

This rapid warming of the Indian Ocean has led to an increase in marine heat waves, which impact the monsoon by reducing the rainfall over the central Indian subcontinent while enhancing it over the southern peninsula. The cumulative rainfall for Kerala from June 1 to July 30 stands at 1,222.5 mm against the normal average of 1,283.5, resulting in a deficit of -5%. According to meteorological criteria for districts during monsoon, a departure of +/-19% is considered to be normal rainfall. According to the report ‘A review on the extreme rainfall studies in India,’ the frequency and intensity of extreme monsoon downpours in India have increased over the past 50 years, despite significant inter-annual variability.

Trends indicate that extreme rainfall events are likely to continue increasing in the coming decades. The intensification of extreme sub-daily rainfall is driven by convective feed back and changes in regional circulation, as temperatures exceed Clausius-Clapeyron scaling in both localized and larger regions. The number of heavy rainfall events is increasing, while the number of rainy days during the monsoon is decreasing. Contributing factors include the variability of low-level monsoon westerlies over the Arabian Sea, which drive surges of moisture supply, the trailing strength of monsoon circulation and the variation of vertical wind shear from the break phase to the active phase of an Indian Summer Monsoon (ISM) cycle. Deforestation, rapid urbanization, unplanned development and poor planning are significant factors exacerbating the climate crisis in India. It is evident that development plans and human interference are not complementing the ecological balance of the mountainous 0terrain.

The writer of this article is Dr. Seema Javed, an environmentalist & a communications professional in the field of climate and energy