Effect of El Niño and La Niña on seasonal and annual rainfall in different districts of Chhattisgarh state

Introduction

The term El Niño refers to the large-scale ocean-atmosphere climate phenomenon linked to a periodic warming in sea-surface temperatures across the central and east central equatorial Pacific (between approximately the dateline and120°W). The inter-annual variability of seasonal precipitation over India is influenced by El Niño-Southern Oscillation (ENSO) phenomenon. The ENSO is negatively El Niño episodes on crop production or productivity at district level (Rao et al., 2011 and Patel et al., 2014) [5,4] . La Niña is a climatological phenomenon akin to El Niño, but with opposite tendencies in the tropical Pacific Ocean and atmosphere. La Niña is characterized by stronger than normal trade winds and colder than normal tropical Pacific Sea surface temperatures. It is also characterized by unusually high surface atmospheric pressure in the eastern tropical Pacific and low surface pressure in the western tropical Pacific in association with the Southern Oscillation. The cooling phase (La Niña episodes) is also termed as anti ENSO period. These signals resulted in ecological/economical disasters like heavy rains and floods in Pacific Coast of South America (Nicolls, 1991) [3] . La Niña's effects on global weather are roughly opposite to those of El Niño. La Niña is the reverse of El Niño event and is triggered due to alteration of Sea Surface Temperature (SST) in Pacific Ocean. The La Niña cycle is a complex interaction between random atmospheric phenomenon and oceanic processes. In the La Niña event the trade winds push warm water to ward west and cause it to accumulate in the western Pacific. El Niño and La Niña Years and intensities have been shown in Table-1. period (1960-2023) were collected from the Department of Agricultural Meteorology, College of Agriculture Raipur (Chhattisgarh). El Niñoand La-NiñaYears and Intensities (Based on Oceanic Nino Index (ONI) data for the period 1951-2023 were downloaded from the website of Golden gate weather services 2023. (https://ggweather.com/enso/oni.htm). The mean and per cent change for both seasonal as well as annual rainfall was calculated for all districts of Chhattisgarh in Excel.

Normal rainfall (Mean)

It is average of long-term rainfall in a region. 2). Total 11 weak El Niño events, 7 strong El Niño events, 6 moderate El Niño events and 3 very strong El Niño events were observed. Weak El Niño events are more frequently occurring El Niño events followed by moderate El Niño years. The El Niño events adversely affect the Indian and Chhattisgarh monsoon rainfall and negatively impacts are usually seen in food grain production.

El Niño and La Niña events generally last between 5-19 months.

In the northern hemisphere, they develop during the winter season and therefore they take extensions often to about two calendar years. It is noticeable that El Niño events during the last fift y years of the twentieth century occurred in 19 calendar years while La Niña happened during the same period in 15 calendar years. Radi (2004) [6] also reported similar results.

Characteristics of the La Niña phenomena in terms of span, duration, intensity and impact

During the year 1951-23 we observed three different categories of occurrence (weak, moderate and strong) of La Niña events (Fig. 1, Table 3). There are 12 week La Niña events, 6 moderate La Niña events and 7 strong La Niña events. Weak La Niña events are more frequently occurring La Niña events than other La Niña events followed by strong La Niña events. The La Niña events positively affect the Indian and Chhattisgarh monsoon rainfall and these positively impacts are usually seen in Indian food grain production. Overall Chhattisgarh state showed negative deviation in southwest monsoon rainfall by about 3 per cent (Table 4). [7] have also reported similar results.

Seasonal and annual rainfall during all La Niña years

The most crucial southwest monsoon (SWM) season rainfall (June-Sept) is major crop growing season and important for crop growing periods. Positive deviation in rainfall ranging from 1 per cent in Balodabazar, Bilaspur, Janjgir-Champa, Mungeli, Surguja, Kondagaon to 7 per cent in Kabirdham was observed. However, no change in rainfall in Bemetara, Raipur, Rajnandgaon and Surajpur district were observed. Chhattisgarh Plains ACZ showed no change in southwest monsoon rainfall, Northern Hills ACZ showed positive deviation in rainfall by 1 per cent and Bastar plateau ACZ showed negative deviation in rainfall by 1 per cent (Table 5). Percent change in district-wise annual rainfall during all La Niña years irrespective of its intensity were presented (Table 5). It can be seen from the results that during all La Niña years, positive deviation in annual rainfall varied from 1 per cent in Bemetara/ Bilaspur/ Dhamtari/ Mungeli to 6 per cent in Kabirdham district was observed. Some districts like Balod, Durg, Gariaband, Raigarh, Kanker, Narayanpur and Sukma showed negative deviation in annual rainfall. Rainfall at Agro-Climatic Zones (ACZs) level was analyzed and there is no change in annual rainfall in Bastar Plateau ACZ. Positive deviation in annual rainfall by 1 per cent and 2 per cent was observed in Chhattisgarh Plains ACZ and Northern Hills ACZ, respectively. Overall Chhattisgarh state for this category showed slightly positive deviation in annual rainfall by about 1 per cent.

References

1. Anonymous. El Niño/southern oscillation. Geneva: World Meteorological Organization (WMO); 2014.
2. Null J. El Niño and La Niña Intensities [Internet]. 2023 [cited 2025 Sep 24]. Available from: http://ggweather.com/enso/oni.htm
3. Nicolls N. Teleconnection and Health-Teleconnection linking worldwide climate anomalies. Cambridge: Cambridge University Press; 1991. p. 493-510.
4. Patel HR, Lunagaria MM, Pandey V, Sharma PK, Rao BB, Rao VUM. El Niño episodes and agricultural productivity in Gujarat. Technical Report No. 01/2014-15. Anand, Gujarat: Department of Agricultural Meteorology, AAU; 2014.
5. Rao VUM, Subba Rao AVM, Bapuji Rao B, Ramana Rao BV, Sravani C, Venkateswarlu B. El Niño effect on climatic variability and crop production: a case study for Andhra Pradesh. Research Bulletin No. 2/2011. Hyderabad: CRIDA; 2011. p. 36.
6. Radi FA. Foundations of climatic and vegetative geography. Beirut, Lebanon: Arab Renaissance House; 2004.
7. Rishma C, Katpatal YB. Variability in rainfall and vegetation density as a response to ENSO events: a case study in Venna river basin of Central India. J Agrometeorol. 2016;18(2):300-305.