*2.1.4 Winter (December to February) and summer (March to May) rainfall*

The out of 55 years, winter season rainfall was 30 years above the normal rainfall and rest years it was below the normal rainfall (**Figure 1**). The winter season rainfall have recorded slightly increasing trend. However, winter rainy days showing decreasing trend. The characteristics of the winter rainfall are mean rainfall (111.2 mm), highest rainfall (216.5 mm) in the year 2013, and lowest rainfall (13.0 mm) in the year 2016. The highest rainfall in single day (77.0 mm) on 18th February 2003] Likewise, mean winter rainy days (8.3 days); Highest rainy days in a year (15 days) in the year 1975; Lowest rainy days (2 days) in years 1964, 1967 and 2006}]. The summer rainfall in 22 years was above the normal and rest years, was below the normal (**Figure 1**). The summer rainfall and rainy days showed increasing trend (**Figure 1**). The mean rainfall was 136.1 mm, highest rainfall (369.5 mm) in 1983, lowest rainfall (29.0 mm) in 2013 and highest rainfall in single day (57.5 mm) on 7th May 1998. Similarly, mean annual rainy days were 12.4 days, highest rainy days in a year (23 days) in 1990 and lowest rainy days (4 days) in the years 1968, 1984 and 1992.

#### *2.1.5 Monsoon (June to September) and post-monsoon (October to November) rainfall*

The monsoon rainfall out of 55 years, 30 years was below the normal rainfall and it showed decreasing trend (**Figure 1**). The similar trend was observed with regard to rainy days. The mean rainfall was 718.8 mm, highest rainfall (1156.5 mm) in 2010, lowest rainfall (424.2 mm) in 2015 and highest rainfall in single day (167 mm) on 18th September 2010. Whereas, mean annual rainy days (45 days), highest Rainy days (60 days) in a years 1977,1988 and 2010 and lowest rainy days (27 days) in year 2009. The post monsoon rainfall in 36 years was below the normal rainfall and showed an increasing trend (**Figure 1**). The characteristics of post-monsoon rainfall exhibited mean rainfall (29.9 mm), highest rainfall (210.4 mm) in the year 1985, lowest rainfall (0.0 mm) in the years 1964, 1974, 1993, 1994, 2001 and 2017 and highest rainfall in single day (99.8 mm) on 13th October 1985. The mean annual rainy days were 2.0 days, highest rainy days in a year (11 days) in the year 1997 and lowest rainy days in year (0 days) in the years 1964, 1967, 1969, 1974, 1975, 1984, 1988, 1993, 1994, 2001 and 2017.

*Climatic Variation and Its Impacts on Yield and Water Requirement of Crops in Indian Central… DOI: http://dx.doi.org/10.5772/intechopen.94076*

#### **3. Estimation of crop water requirement in study area**

Water requirement of the crops defines the quantity of water needed to meet the water losses through evapotranspiration of a disease-free crop under non restricting soil conditions, including soil, water and fertility and achieving the full potential under a given soil environment in a given time. Water requirement of the main *Kharif* and *Rabi* season crops (*i.e.* Vegetable pea, Barley, Rajma, Tomato, French Bean, Chili, Rice, Wheat, Maize, Soyabean, Okra, Mustard, and Cow pea) were calculated on the basis of Reference crop evapotranspiration (ETo) on the monthly basis by using CROPWAT model based on FAO-Penman-Monteith's semi-empirical equation. The required weather data (min. and max. Temperature, rainfall, sunshine hours, wind speed, etc.) was collected from the automatic weather station. Reference evapotranspiration (ETo) expresses the evaporative index of the atmosphere at a specific location. It is independent of crop type, stage of development and management practices. The reference evapotranspiration had been calculated using this Equation [21] in the following form:

$$\rm{ET}\_o = \frac{\mathbf{0}.408\Delta(R\_n - G) + \gamma \frac{900}{\Gamma + 2\mathcal{T}3} \mathbf{u}\_2 (\mathbf{e}\_s - \mathbf{e}\_a)}{\Delta + \gamma (1 + 0.34 \mathbf{u}\_2)} \tag{1}$$

Where,

*2.1.4 Winter (December to February) and summer (March to May) rainfall*

*Mann- Kendall test statistics for annual and rainfall data of different seasons.*

in 1983, lowest rainfall (29.0 mm) in 2013 and highest rainfall in single day (57.5 mm) on 7th May 1998. Similarly, mean annual rainy days were 12.4 days, highest rainy days in a year (23 days) in 1990 and lowest rainy days (4 days) in the

*2.1.5 Monsoon (June to September) and post-monsoon (October to November) rainfall*

The monsoon rainfall out of 55 years, 30 years was below the normal rainfall and it showed decreasing trend (**Figure 1**). The similar trend was observed with regard to rainy days. The mean rainfall was 718.8 mm, highest rainfall (1156.5 mm) in 2010, lowest rainfall (424.2 mm) in 2015 and highest rainfall in single day (167 mm) on 18th September 2010. Whereas, mean annual rainy days (45 days), highest Rainy days (60 days) in a years 1977,1988 and 2010 and lowest rainy days (27 days) in year 2009. The post monsoon rainfall in 36 years was below the normal rainfall and showed an increasing trend (**Figure 1**). The characteristics of post-monsoon rainfall exhibited mean rainfall (29.9 mm), highest rainfall (210.4 mm) in the year 1985, lowest rainfall (0.0 mm) in the years 1964, 1974, 1993, 1994, 2001 and 2017 and highest rainfall in single day (99.8 mm) on 13th October 1985. The mean annual rainy days were 2.0 days, highest rainy days in a year (11 days) in the year 1997 and lowest rainy days in year (0 days) in the years 1964, 1967, 1969, 1974, 1975, 1984,

years 1968, 1984 and 1992.

**Figure 1.**

*Agrometeorology*

1988, 1993, 1994, 2001 and 2017.

**14**

The out of 55 years, winter season rainfall was 30 years above the normal rainfall and rest years it was below the normal rainfall (**Figure 1**). The winter season rainfall have recorded slightly increasing trend. However, winter rainy days showing decreasing trend. The characteristics of the winter rainfall are mean rainfall (111.2 mm), highest rainfall (216.5 mm) in the year 2013, and lowest rainfall (13.0 mm) in the year 2016. The highest rainfall in single day (77.0 mm) on 18th February 2003] Likewise, mean winter rainy days (8.3 days); Highest rainy days in a year (15 days) in the year 1975; Lowest rainy days (2 days) in years 1964, 1967 and 2006}]. The summer rainfall in 22 years was above the normal and rest years, was below the normal (**Figure 1**). The summer rainfall and rainy days showed increasing trend (**Figure 1**). The mean rainfall was 136.1 mm, highest rainfall (369.5 mm)

ETo = reference evapotranspiration [mm day�<sup>1</sup> ]. u2 = wind speed at 2 m height [m s�<sup>1</sup> ]. Rn = net radiation at crop surface [MJ m�<sup>2</sup> day �<sup>1</sup> ]. G = soil heat flux density [MJ m�<sup>2</sup> day �<sup>1</sup> ]. T = mean daily air temperature at 2 m height [°C]. *γ* = psychrometric constant [kPa °C�<sup>1</sup> ]. Δ = slope of vapor pressure curve [kPa °C�<sup>1</sup> ]. es � ea = saturation vapor pressure deficit [kPa].

#### **3.1 Crop coefficient**

The crop evapotranspiration, (ETc) is calculated by multiplying the reference crop evapotranspiration, (ETo) by crop coefficient (Kc). Consequently, different crops will have different crop coefficients. Kc value varies with the type of crop, climate, soil evaporation and crop growth stages [21].

$$\rm ET\_c = K\_c \times ET\_o \tag{2}$$

Where,

ETc = crop evapotranspiration [mm day�<sup>1</sup> ]. Kc = crop coefficient [dimensionless]. ETo = reference crop evapotranspiration [mm day�<sup>1</sup> ].

#### **3.2 Gross irrigation requirement**

The gross irrigation requirement (GIR) accounts for losses of water included during conveyance and application of irrigation water to the field. The gross irrigation requirement is calculated by the ratio of net irrigation requirement to the irrigation efficiency.
