Precipitation samples of various spatio-temporal scales were collected from coastal, midland and urban regions of Greater Cochin, Ernakulam district, Kerala for a period of 1 yr (2015–2016). The collected samples were analysed for stable water isotopes (SWI) ($\delta\rm{D}$ and $\delta^{18}\rm{O}$), to understand these variations in the precipitation source and the factors governing its isotopic characteristics during precipitation. The $\delta^{18}O$ in rainwater varies from -8.73 per thousand to 0.29 per thousand in urban, -12.21 per thousand to 2.59 per thousand in midland and -9.99 per thousand to 0.97 per thousand in lowland regions. Spatio-temporal variations in SWI were observed in various regions, suggesting altitude and continental effect followed by the establishment of a regional overall local meteoric water line (LMWL) $\delta\rm{D}$ = $8.06 (\pm0.15)\delta^{18}O + 12.5 (\pm0.68)$. Among the coastal, midland and urban regions, the highest slope ($\sim8.3$) and intercept($\sim13.0$) were observed in the urban region, which designates the variations in temperature along spatial and different layers of the atmosphere in the urban region, resulting in the deviation of isotopic characteristics.The overall deuterium excess ($d$-excess) value is $\sim10$ per thousand during the south-west monsoon (June–September), suggesting a moisture source of marine origin. A $d$-excess of $\sim13$ per thousand is observed during the north-east monsoon, indicating a moisture source from the continental contribution (October–December). The results of the moisture source obtained from the $d$-excess value are also supported by back-trajectory analysis. Thus, the present study on isotopic characterisation of precipitation and its controlling factor may enhance our understanding of the Indian monsoon and its dynamics in the west coast region of India.

Glacier systems are important components of the hydrological cycle and a major source of meltwater and sediment flux that controls the river ecology, water quality, and hydropower generation in the Indian Himalayan Region (IHR). Thus, understanding short- and long-term changes in water and suspended sediment (SS) dynamics is crucial in highly sensitive pro-glacial Himalayan Rivers. In the present study, the Chandra River basin in Western Himalaya was chosen to study river discharge, SS transport dynamics, physical erosion rate, and their governing factors for the 2017 melting season (May–September). The daily mean water discharge and SS concentration in the Chandra River was 260.7 m$^{3}$ s$^{-1}$ and 775.5 mgL$^{-1}$ with maximum discharge and SS flux in the month of July. The air temperature showed significant relationship with the river discharge ($R^{2}$= 0.67; n = 156; p <0.001), which in turn controlled the SS export in the basin ($R^{2}$ =0.86; n = 130; p <0.001). An anticlockwise sediment-discharge hysteresis during peak flow conditions suggest exhausted sediments or large distance of sediment transport (>100 km) from the upper glacierized region to the end of the basin. Statistical analysis of SS particle size showed poorly sorted immature grains with a dominance of silt particles (85%), followed by sand (8.5%) and clay (6.5%). The SS estimates revealed a total suspended sediment yield of 1285 tons km$^{-2}$ yr$^{-1}$ and physical erosion rate of 0.47 mm yr$^{-1}$. Considering the socio-economic importance of the Himalayan region, the present study will help to evaluate the water and sediment budget of the Chandra River, Western Himalaya and to establish their relationship to the meteorological conditions in the basin.

$\bf{Highlights}$

$\bullet$The total water discharge and suspended sediment flux during ablation period (May–September 2017) in the Chandra River were 3536 MCM and 3 million tons.

$\bullet$Overall, the suspended sediment were composed of silt size particles (85%) followed by sand (8.5%) and clay size (6.5+%) particles.

$\bullet$The suspended sediment estimates revealed a total suspended sediment yield of 1285 tons km$^{3}$ yr$^{-1}$ and physical erosion rate of 0.47 mm yr$^{-1}$

$\bullet$ This study will be useful in understanding the SS cycling from the Himalayan region and to build robust models for future projections.