**5. Conclusions**

The time series of rainfall and streamflow data of the Kosi river watershed for the last 31 years (1986*–*2016) was statistically analyzed to determine the trend and understand the changes in the streamflow regime. Based on this study, following conclusions were drawn:

• The rainfall is assumed to be the dominant component in the streamflow of the Kosi river watershed.


### **Table 5.**

*Trends of urban growth in Uttarakhand (1901–2011).*

• The Mann*–*Kendall analysis of mean monthly streamflow data for last 31 years showed a nonsignificant decreasing trend during monsoon with a significance level of 10%.

The opposite trends observed between the streamflow and rainfall in majority of the watershed area suggest that endogenous change in the catchment dominates over exogenous changes. Abeysingha et al. [40] reported that the trend in annual streamflow for different rivers primarily was driven by changes in rainfall. In addition, Tiwari et al. [41] evaluated the actual evapotranspiration, runoff, and potential evapotranspiration for the past century by using monthly water balance model, and their analysis indicated that rainfall has been the primary factor of variability in the runoff.

The decreasing trend of streamflow in the downstream area of the river may be partly caused by the variations in rainfall and partly by other anthropogenic factors. Human activities such as water consumption, land use, and land cover changes caused by forest disturbances, soil and water conservation projects, new drain construction and city expansion, soil water infiltration, and surface evapotranspiration result in significant hydrological alteration [42, 43]. Nune et al. [44] also found a declining trend in streamflow without significant changes in rainfall Himayat Sagar catchment in India over 24 years (1980–2008). They also reported that streamflow trends declined mainly due to anthropogenic factors, such as changes in land use, watershed development, groundwater abstraction, and storage. Regarding the trend in the seasonal distribution of rainfall, we found that the pre-monsoon seasonal rainfall is increasing significantly, particularly in the month of May. In contrast, post-monsoon rainfall is decreasing significantly, especially in the downstream area.
