**3. Analysis of rainfall pattern**

The rainfall pattern over the study areas were analysed with data received from the metrological department of India (http://www.imd.gov.in). The analysis is done for the data between years 1951 and 2014. The monthly rainfall over Kerala, and weighted average rainfall across India were analysis to find the relationship between the rainfall over the state Kerala and Indian subcontinent. **Figure 3** shows the comparison of rainfall over Kerala with the weighted average rainfall across India. While **Figure 3(b, c)** corresponds the histogram of rainfall occurred during 1951–2014. It is clear from the histogram that out of 64 years used for study every year having rainfall more than 2000 cm overall across Kerala while more than 90% of years having rainfall over 1000 cm on weighted average scale across India. Hence it is evident that the overall rain pattern over the Indian subcontinent almost kept the same.

**Figures 4**–**7** shows the rainfall comparison of Kerala and weighted average across India for the four seasons that predominantly occurs across the subcontinent; namely summer, winter, rainy season and autumn. Major finding is that overall changes in the rain pattern are not visible along the study duration. From **Figure 4** it is clear that during summer season only traces of rain across the country occurs in all parts of India. These summer rains do not follow a specific pattern also across India as well as Kerala state too.

Upon analysing **Figures 5**–**7** it is clear that state of Kerala is getting more rainfall when compared to the weighted average across India. Another interesting fact is that if the rainfall across is less in certain years then the overall weighted average across India is also in the

reduced level. The detailed study using histogram it is clear that even during summer Indian subcontinent receives some amount of rain at least some parts or some traces of rain in other

Rainfall Pattern Analysis over India in Relation to the State of Kerala

http://dx.doi.org/10.5772/intechopen.72870

23

parts, which is a common trait of along any region which lies along the equator.

**Figure 3.** (a) Yearly rainfall comparison 1951–2014, (b, c) histogram.

**Figure 4.** Rainfall comparison during summer season.

Rainfall Pattern Analysis over India in Relation to the State of Kerala http://dx.doi.org/10.5772/intechopen.72870 23

**Figure 3.** (a) Yearly rainfall comparison 1951–2014, (b, c) histogram.

Kerala even with its closeness to equator when compared to other states in the country, has a composed and pleasing climate with temperature lies between 28–35°C throughout the year. The presence of sea in its west side and Western Ghats in the west side are the major reason for this pleasing climate. Kerala lies between north latitudes 8°.17′.30" N and 12°. 47′.40" N and east longitudes 74°.27′47″ E and 77°.37′.12″ E. The climate is mainly tropical wet due the presence heavy monsoon which starts from June and extends till September (https://www.mapsofindia.com/maps/kerala/geography-and-history/). **Figure 2** shows the physical map of Kerala. Kerala can be divided into three climatically distant regions namely, hot and wet coastal areas along the west, central midlands and eastern highlands. The region lies in the centre of Indian tectonic plate with gradual increase in altitude from coastal areas to western highlands. Kerala experiences mainly three seasons; south west Monsoon, north east Monsoon and summer [25, 26]. The south west monsoon is the most prominent source of rainfall across the region with almost 65% of the total rain received during this season. The southwest monsoon, which is known as "Edavapathi" in the colloquial language, means mid of Malayalam month Edavam, start during the end of May or first of June with support of southwest monsoon wind [27–29]. Across the state 42 rivers flow from Eastern Ghats to the Arabian Sea which are fed by these rains. Northeast monsoon, known as "Thualavarsham", occurs during the retarding of southwest monsoon. This occurs during October and November. The main characteristics of this rainy season are the prudential rains with lighting and thunder. Summer starts towards the start of March with reaching higher temperature around 40°C at certain places [30–33].

The rainfall pattern over the study areas were analysed with data received from the metrological department of India (http://www.imd.gov.in). The analysis is done for the data between years 1951 and 2014. The monthly rainfall over Kerala, and weighted average rainfall across India were analysis to find the relationship between the rainfall over the state Kerala and Indian subcontinent. **Figure 3** shows the comparison of rainfall over Kerala with the weighted average rainfall across India. While **Figure 3(b, c)** corresponds the histogram of rainfall occurred during 1951–2014. It is clear from the histogram that out of 64 years used for study every year having rainfall more than 2000 cm overall across Kerala while more than 90% of years having rainfall over 1000 cm on weighted average scale across India. Hence it is evident that the overall rain pattern over the Indian subcontinent almost kept the same.

**Figures 4**–**7** shows the rainfall comparison of Kerala and weighted average across India for the four seasons that predominantly occurs across the subcontinent; namely summer, winter, rainy season and autumn. Major finding is that overall changes in the rain pattern are not visible along the study duration. From **Figure 4** it is clear that during summer season only traces of rain across the country occurs in all parts of India. These summer rains do not follow

Upon analysing **Figures 5**–**7** it is clear that state of Kerala is getting more rainfall when compared to the weighted average across India. Another interesting fact is that if the rainfall across is less in certain years then the overall weighted average across India is also in the

a specific pattern also across India as well as Kerala state too.

**3. Analysis of rainfall pattern**

22 Engineering and Mathematical Topics in Rainfall

**Figure 4.** Rainfall comparison during summer season.

reduced level. The detailed study using histogram it is clear that even during summer Indian subcontinent receives some amount of rain at least some parts or some traces of rain in other parts, which is a common trait of along any region which lies along the equator.

**Figure 5.** Rainfall comparison during autumn season.

#### **3.1. Effect of solar cycle over rainfall**

Solar cycle is the most significant activity of Sun over earth which changes the solar radiation levels. Solar irradiance is the power per unit area received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument. Irradiance is measured in space or at the Earth's surface after atmospheric absorption and scattering. It is measured perpendicular to the incoming sunlight), ejection of solar materials along with the Sun's appearance (changes in number and size of sun spots). The changes occurred in the Sun forces changes in the atmosphere, space and earth's surface. The solar cycle mostly is of 11 years' duration. The solar cycle has its maximum activity and minimum activity period based on the number of sunspots occurrence. Sun spots are developed over the sun's surface when Sun's magnetic field welling up to the photosphere of the sun which creates powerful active regions on the Sun. This sun spots form over duration of few days extends up to months. Sun spot number is used to measure this solar activity which in turn a major cause for variations in earth's climate, satellite failures, etc. Sun spot number counted by counting individual sun spots and sun spots groups. Mathematically sun spot number is the sum of individual sun spots and ten times the sun spot groups. **Table 1** shows the details of solar cycle over the study

Rainfall Pattern Analysis over India in Relation to the State of Kerala

http://dx.doi.org/10.5772/intechopen.72870

25

time. This table describes solar cycles occurred during the phase of our study [32–34].

**Solar cycle No. Starting time Finished time Duration (yrs.)**

Solar cycle 18 Jan 1944 Feb 1954 10.2 Solar cycle 19 Feb 1954 Oct 1964 10.5 Solar cycle 20 Oct 1964 May 1976 11.7 Solar cycle 21 May 1976 March 1986 10.3 Solar cycle 22 March 1986 June 1996 9.7 Solar cycle 23 June 1996 Jan 2008 11.7

Solar cycle 24 Jan 2008 Still going

**Table 1.** Solar cycle between 1951 to 2014.

**Figure 7.** Rainfall comparison during winter season.

**Figure 6.** Rainfall comparison during rainy season.

Rainfall Pattern Analysis over India in Relation to the State of Kerala http://dx.doi.org/10.5772/intechopen.72870 25

**Figure 7.** Rainfall comparison during winter season.

**3.1. Effect of solar cycle over rainfall**

24 Engineering and Mathematical Topics in Rainfall

**Figure 6.** Rainfall comparison during rainy season.

**Figure 5.** Rainfall comparison during autumn season.

Solar cycle is the most significant activity of Sun over earth which changes the solar radiation levels. Solar irradiance is the power per unit area received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument. Irradiance is measured in space or at the Earth's surface after atmospheric absorption and scattering. It is measured perpendicular to the incoming sunlight), ejection of solar materials along with the Sun's appearance (changes in number and size of sun spots). The changes occurred in the Sun forces changes in the atmosphere, space and earth's surface. The solar cycle mostly is of 11 years' duration. The solar cycle has its maximum activity and minimum activity period based on the number of sunspots occurrence. Sun spots are developed over the sun's surface when Sun's magnetic field welling up to the photosphere of the sun which creates powerful active regions on the Sun. This sun spots form over duration of few days extends up to months. Sun spot number is used to measure this solar activity which in turn a major cause for variations in earth's climate, satellite failures, etc. Sun spot number counted by counting individual sun spots and sun spots groups. Mathematically sun spot number is the sum of individual sun spots and ten times the sun spot groups. **Table 1** shows the details of solar cycle over the study time. This table describes solar cycles occurred during the phase of our study [32–34].


**Table 1.** Solar cycle between 1951 to 2014.

Every solar cycle has its maximum activity period and minimum activity period. It depends on the number of sun spots occurrence during a specific time. Sun spots are dark patches over the photosphere of sun, which forms due to the reduction of surface temperature which is due to concentration of magnetic flux because of convection. These sun spots usually appear in pairs of opposite magnetic polarity and may be active for a few days to over a month period with varying sizes. The study has recorded the rainfall over these solar cycles and analysed for identifying any similarity or dissimilarity occurs over the solar cycle. **Table 1** shows the details of Solar cycles 18 to 24. Solar cycle 24 is currently running. All solar cycles have a time duration of around 11 years. The study tabulated and analysed the rainfall received across Indian subcontinent and state of Kerala for solar cycles 18 to 23. The data was analysed for all the four seasons namely; winter, summer, rainy and autumn. The data analysed on the overall rainfall across Kerala and also the weighted average rainfall across India respectively. **Tables 2** and **3** shows the maximum and minimum values of both weighted average of rainfall across India and rainfall over Kerala these for each solar cycle with respect to each season.

**Solar cycle Minimum rainfall Maximum rainfall**

**Table 3.** Weighted average maximum and minimum across India.

**Figure 8.** Rainfall during summer season across solar cycles.

**Figure 9.** Rainfall during rainy season across solar cycle.

**Season 1 Season 2 Season 3 Season 4 Season 1 Season 2 Season 3 Season 4**

Rainfall Pattern Analysis over India in Relation to the State of Kerala

http://dx.doi.org/10.5772/intechopen.72870

27

 16.5 791 3229 91.3 74.9 153.1 1052 206.1 25.3 526 2711 74.4 50.5 138.6 1003.4 151.2 31.2 502.1 2274 86.6 55.9 170.5 727.6 167.4 30.7 548.3 2515.6 87.7 60.7 210.7 1049.6 165.3 16.1 741.8 2786.2 66.4 69.9 159.2 947.9 167

The above data was analysed based upon the four seasons; summer, winter, rainy and autumn and its variation among the solar cycles 19 to 23. Based on the solar cycles, the available data was fitted into solar cycles 19 to 23. Solar cycle 19 started in February 1954 and solar cycle 23 ended in January 2008. **Figures 8**–**11** shows the graphical representation of rainfall across Kerala and the weighted average across India over these solar cycles. These graphs state that over the period of solar cycle these areas receive almost the same quality of rain.

The third set of analysis is done with respect to the rainfall received in maximum sun spot activity year with the overall average rainfall received between the years 1951 and 2014 for the four different seasons. The maximum sun spot occurred in years 1958, 1968, 1979, 1989 and 2001 during the solar cycles 19 to 23 respectively.

**Figure 12a** shows the average of maximum rainfall occurred during the four seasons in the above said years, **Figure 12b** shows the average rainfall received in years 1951 to 2014. On comparison it is clear that there is no specific impact on the maximum rainfall received with respect to the above stated years. **Figure 12c** and **d** shows the minimum rainfall received during the above two cases. There also no significant change was identified.


**Table 2.** Maximum and minimum rainfall over Kerala.


**Table 3.** Weighted average maximum and minimum across India.

Every solar cycle has its maximum activity period and minimum activity period. It depends on the number of sun spots occurrence during a specific time. Sun spots are dark patches over the photosphere of sun, which forms due to the reduction of surface temperature which is due to concentration of magnetic flux because of convection. These sun spots usually appear in pairs of opposite magnetic polarity and may be active for a few days to over a month period with varying sizes. The study has recorded the rainfall over these solar cycles and analysed for identifying any similarity or dissimilarity occurs over the solar cycle. **Table 1** shows the details of Solar cycles 18 to 24. Solar cycle 24 is currently running. All solar cycles have a time duration of around 11 years. The study tabulated and analysed the rainfall received across Indian subcontinent and state of Kerala for solar cycles 18 to 23. The data was analysed for all the four seasons namely; winter, summer, rainy and autumn. The data analysed on the overall rainfall across Kerala and also the weighted average rainfall across India respectively. **Tables 2** and **3** shows the maximum and minimum values of both weighted average of rainfall across India and rainfall over

The above data was analysed based upon the four seasons; summer, winter, rainy and autumn and its variation among the solar cycles 19 to 23. Based on the solar cycles, the available data was fitted into solar cycles 19 to 23. Solar cycle 19 started in February 1954 and solar cycle 23 ended in January 2008. **Figures 8**–**11** shows the graphical representation of rainfall across Kerala and the weighted average across India over these solar cycles. These graphs state that

The third set of analysis is done with respect to the rainfall received in maximum sun spot activity year with the overall average rainfall received between the years 1951 and 2014 for the four different seasons. The maximum sun spot occurred in years 1958, 1968, 1979, 1989 and

**Figure 12a** shows the average of maximum rainfall occurred during the four seasons in the above said years, **Figure 12b** shows the average rainfall received in years 1951 to 2014. On comparison it is clear that there is no specific impact on the maximum rainfall received with respect to the above stated years. **Figure 12c** and **d** shows the minimum rainfall received dur-

**Season 1 Season 2 Season 3 Season 4 Season 1 Season 2 Season 3 Season 4**

 8.9 245.3 1720 377.6 83.1 791 3229 637.6 0.3 263.7 1509 206.7 50.1 526 2711 688.2 0.8 90 1297 302.7 96.8 502.1 2274 805.4 1.4 169.8 1347 166.6 51.4 548.3 2516 631.2 3.6 213 1322 361.4 69.5 741.8 2786 675.7

over the period of solar cycle these areas receive almost the same quality of rain.

ing the above two cases. There also no significant change was identified.

**Solar cycle Minimum rainfall Maximum rainfall**

Kerala these for each solar cycle with respect to each season.

26 Engineering and Mathematical Topics in Rainfall

2001 during the solar cycles 19 to 23 respectively.

**Table 2.** Maximum and minimum rainfall over Kerala.

**Figure 8.** Rainfall during summer season across solar cycles.

**Figure 9.** Rainfall during rainy season across solar cycle.

**4. Conclusion**

not affect the rainfall pattern at all.

Address all correspondence to: shajimonkalayil@gmail.com

[1] Chowdhury's guide to planet earth. In: The Water Cycle. USA: WestEd; 2005

Jet Propulsion Laboratory: Chinese University of Hong Kong; 2006

[2] Timothy Liu W, XiaosuXie, Tang W. Monsoon, orography, and human influence on Asian rainfall (PDF). In: Proceedings of the First International Symposium in Cloud-Prone & Rainy Areas Remote Sensing (CARRS). National Aeronautic and Space Administration

[3] Meehl GA, Stocker TF, Collins WD, Friedlingstein P, Gaye AT, Gregory JM, Kitoh A, Knutti R, Murphy JM, Noda A, Raper SCB, Watterson IG, Weaver AJ, Zhao Z-C. Precipitation and Surface Water, Global Climate Projections. Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. UK: Cambridge University Press; 2007

[4] Peel MC, Finlayson BL, McMahon TA. Updated world map of the Köppen-Geiger climate classification. Hydrology and Earth System Sciences. 2007;**11**:1633-1644. DOI: 10.5194/

Saintgits College of Engineering, Kottayam, Kerala, India

hess-11-1633-2007 ISSN 1027-5606

**Author details**

Shajimon K John

**References**

The study was mainly done on comparing the rainfall received across the Indian subcontinent to the specific state of India named Kerala. It has found that the amount of rain received across the state of Kerala has a direct impact on the overall rain received across subcontinent. The rainfall pattern was also analysed for the four predominant climatic patterns prevailing over India. It was also found that except the summer season, all three other seasons of the subcontinent follows the same pattern that prevails over the state of Kerala. Summer rainfall does not follow any specific pattern. Another interesting conclusion is that the overall rainfall does not show any significant change during the study duration. The second part of study was done with respect to the solar cycles. Based on the available data the solar cycles 19 to 23 were mapped based on the based criteria to verify significant changes if any. But there also no major changes identified. The last work was on comparing the maximum and minimum rainfall received during the maximum sun spot years to the average rainfall received between the years 1951 to 2014. This study also concludes that both average correlates very highly. This study points to the fact that the overall rainfall pattern across Indian subcontinent has not change much for the last 60 years or so and also that the solar activities like sun spots do

Rainfall Pattern Analysis over India in Relation to the State of Kerala

http://dx.doi.org/10.5772/intechopen.72870

29

**Figure 10.** Rainfall during winter season across solar cycle.

**Figure 11.** Rainfall during autumn season across solar cycle.

**Figure 12.** Comparison chart.
