By Madhavan Nair Rajeevan

This year has already seen significant rainfall events during the months of August and September, leading many to question the impacts of global warming on seasonal weather patterns, particularly the El Niño and La Niña phenomena. These climatic changes are influencing the variability of monsoon conditions, as explained in detail by Madhavan Nair Rajeevan.

Recent Heavy Rainfall Events

Throughout the monsoon season, regions such as Andhra Pradesh, Telangana, Gujarat, and Rajasthan experienced heavy rainfall, a pattern consistent with past observations. Notably, the increase in the frequency of intense rainfall events, such as those producing over 150 mm of precipitation in a single day, is discernibly influenced by global warming. Statistical analysis indicates an uptick of approximately two heavy rainfall events per decade in the Indian subcontinent. Increasing atmospheric temperatures enable the atmosphere to retain more moisture, thereby fostering greater cloud development. This monsoon season has seen numerous severe rain events resulting in flash floods and landslides reminiscent of the dramatic weather observed in Kerala.

Current numerical weather prediction (NWP) models frequently struggle to accurately estimate heavy rainfall amounts, often underestimating these extremes while overestimating lighter rainfalls. However, employing model-based methodologies such as the Extreme Forecast Index (EFI) can lead to more precise predictions of extreme weather patterns. For instance, during the recent severe rainfall occurrences in Andhra Pradesh and Telangana, estimates generated by the IMD/IITM model and the ECMWF model indicated anticipations of extreme weather conditions, highlighting the EFI’s effectiveness in forecasting.

Has the Distribution Pattern Changed?

A comprehensive analysis of observational data dating back to 1875 suggests that there is no discernible long-term trend in national average monsoon rainfall across India. Nevertheless, significant spatial variability persists in the long-term rainfall trends. For example, regions in east-central India, parts of the northeast, and states like Kerala have exhibited a downward trend in seasonal rainfall, whereas certain areas within North Karnataka, Maharashtra, and Rajasthan show a marked increase. Multi-decadal variability characterizes Indian monsoon rainfall patterns, with fluctuations over epochs that yield varying levels of precipitation. Presently, it appears that we have entered a period marked by heightened precipitation levels. Recent monthly analyses reveal a rising trend of rainfall in September contrasted with a decreasing trend in July. Additionally, the onset of the monsoon in central India has been delayed, coupled with a similarly delayed retreat in northwest India. This is accompanied by a reduction in the frequency of monsoon lows and a notable delay in the formation of the first monsoon depression over the Bay of Bengal.

Role of El Nino and La Nina

The dynamics of El Niño and La Niña have been increasingly dictating precipitation patterns across India. Over the past five to six years, we have witnessed three consecutive La Niña events, while last year was characterized as an El Niño phase, which has swiftly transitioned back into La Niña conditions this year. This pattern is atypical; usually, these phenomena recur every three to seven years. The ramifications of El Niño and La Niña cycles introduce considerable variability into India’s monsoon rainfall, creating a cycle of unpredictability. One year may bring heavy rains and flooding, while the following year may result in widespread drought conditions. Although the total monsoon rainfall in 2023 was not critically deficient, several districts recorded inadequate rainfall levels. This variability demands robust attention, as enhancing early warning systems and establishing adaptive measures are imperative. The acceleration of global warming trends suggests that the incidence of El Niño and La Niña events is poised to increase significantly, further amplifying monsoon variability in the future.

Impact on Farming Practices

The rising frequency of extreme weather events and alterations in monsoon dynamics are poised to significantly impact agricultural practices. Recent data points to an increase in the length of dry spells while the duration of wet spells is on the decline. In stark contrast, the frequency of extreme rainfall events has surged in recent times, with approximately half of the seasonal rainfall occurring over a brief 20-30 hour span as heavy rain (representing only 20% of the time). The remaining 50% of rainfall is delivered through lighter to moderate showers, which occur 80% of the time. Such intense rainfall events result in substantial runoff, with lighter rains evaporating quickly, emphasizing the necessity for effective water management strategies. Increased hiatus days — representing the number of days the monsoon does not progress — have been recorded due to the growing influence of mid-latitude weather systems. Therefore, it is crucial to educate farmers about these evolving weather patterns and assist them in devising new, adaptive farming methodologies that adequately respond to these climatic changes.

Need to Be a Climate-Resilient Nation

According to projections by the Intergovernmental Panel on Climate Change (IPCC), there are four notable trends anticipated for the Indian region: a slight increase in seasonal monsoon rainfall averages, a significant rise in the frequency of heavy rainfall events, an increasing incidence of dry periods throughout the monsoon season, and a delayed monsoon withdrawal from northwest India. It is essential for us to proactively prepare for the repercussions of these climatic shifts, instigating appropriate policy measures to respond accordingly. Our urban infrastructure is largely unprepared for the growing frequency of heavy rainfall and subsequent flooding. Frequently, urban flooding can be attributed to inadequate drainage systems; moreover, urban expansion often leads to the elimination of water bodies in favor of new constructions. Thus, the time has come for us to establish a weather-ready and climate-resilient nation, and this preparation must commence immediately.

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The writer is former secretary, ministry of earth sciences.