Surface air temperature (SAT) is a key meteorological parameter. Modelling and forecasting of the SAT has vital importance to understand the ecological and agricultural changes. We utilized all India monthly mean SAT, which covers a time span of 1951–2016. We used structural time series (STS) analysis to model and forecast the monthly mean SAT. Forecast during 2006–2016 well matched with the observational data. Further, the forecast of monthly mean surface air temperature patterns for 2017–2019 shows a good agreement with climatological behaviour. Note that we observed an increasing trend 0.0009$^{\circ}$C per year in monthly mean surface air. Further, we noticed slight chance of rise in temperature about 0.1$^{\circ}$C specially for the months of April, May and December in the years 2017–2019.

$\bf{Highlights}$

$\bullet$ An increasing trend of 0.0009$^{\circ}$C per year is evident in the monthly mean surface air.

$\bullet$ Raise in temperature of 0.1$^{\circ}$C is evident during April, May and December.

In the present study, we have demarcated five zones within the Deccan Volcanic Province (DVP): (1) Kutch, (2) Western Ghats, (3) Central Son–Narmada, (4) Eastern Son–Narmada and (5) South- Eastern Deccan (SE DVP) to evaluate spatial geochemical variations within the DVP possibly controlled by different eruption loci. True OIB-type unmixed trace element and isotopic signatures are demon strated by both alkali and tholeiitic basalts from Kutch and a small proportion from Western Ghats. However, large number of tholeiitic basaltic samples from both the zones and Central Son–Narmada zone illustrate sub-continental lithosphere mantle (SCLM) signatures. The Eastern Son–Narmada and SE DVP zones of the DVP show evolved compositions, but are dominantly derived from sub-lithospheric sources. The plume–lithosphere interaction is represented by mixing and/or assimilation and fractional crystallisation (AFC) of plume-derived melts with the sub-continental lithospheric mantle (SCLM)- derived melts, sediments preserved in the SCLM, lower crustal (TTG-type) and upper crustal (granitic) components. We argue that melts from the Archaean sediments preserved in the SCLM, represented by calc-alkaline lamprophyres, are the most suited components that interacted with the plume-derived as well as SCLM peridotite-derived melts. Few Kutch zone basalts require granitic components, while some proportion of Western Ghats zone basalts require TTG-type assimilate to explain their isotopic characteristics. Mixing and/or AFC between the plume-derived and sediment-derived melts and SCLM peridotite-derived and sediment-derived melts played fundamental roles in the observed geochemical heterogeneity of the Deccan basalts. We demonstrate that original sub-lithosphere melts may display apparent SCLM signatures by ${\sim}$10% mixing and/or ${\sim}$20% AFC of lamprophyre source melts and entire Deccan data considered in the present study can be explained by 20% mixing and/or 50% AFC of plumederived melts with calc-alkaline lamprophyre as an assimilate.

$\bf{Highlights}$

$\bullet$ The melts generated from the Archaean sediments preserved in the SCLM, represented by calc-alkaline lamprophyres, are most likely the components that interacted with the plume-derived as well as SCLM-derived partial melts during the formation of DVP.

$\bullet$ Mixing and/or AFC of calc-alkaline lamprophyres, TTGs and granites by plume-derived melts and SCLM peridotite-derived melts explain total geochemical spread of the Deccan basalts.

$\bullet$ Approximately, 10% mixing and/or ~20% AFC of Archean calc-alkaline lamprophyre melts can make original sub-lithosphere melts display apparent SCLM signatures.

$\bullet$ The basalts from the western side of DVP have undergone higher levels of assimilation compared to those from the eastern side.