**4.2 Temporal variation of annual mean streamflow and rainfall**

The variation of streamflow is shown in **Figure 3**. The annual mean streamflow varies from 12.43 m<sup>3</sup> /sec to 55.07 m<sup>3</sup> /sec with annual mean value of 31.53 m<sup>3</sup> /sec, standard deviation of 10.11 m<sup>3</sup> /sec, and coefficient of variation of 0.32.

### **4.3 Variation of seasonal streamflow**

The variation of seasonal streamflow and monthly rainfall was represented in **Figures 4** and **5**, respectively. It clearly shows that the highest value of streamflow was found in the June, July, August, and September (JJAS) seasons, while the March, April, and May (MAM) seasons exhibited the lowest streamflow value.

**Figure 3.** *The annual streamflow analysis (1986 and 2016).*

**Figure 4.** *The seasonal streamflow analysis (1986 and 2016).*

**Figure 5.** *Time series of monthly streamflow.*

These results again corroborate the association between streamflow and rainfall. In this study area, most of the rainfall is received during June and September.

### **4.4 Trend analysis of monthly streamflow and rainfall**

To understand the variations of monthly streamflow behavior, interannual monthly mean streamflow and rainfall were tested using the MK test and Sen's slope (**Table 3**). Similarly, seasonal rainfall and streamflow were analyzed using the MK test and Sen's slope (**Table 4**). The streamflow for all the months shows a decreasing trend at Ramnagar station, although all were not significant.

### **4.5 Characterizing the factors of trends in streamflow**

In this study, we have tried to quantify different drivers for detecting the trend of streamflow. As most of this watershed is under forest land use, we considered urbanization and population growth as the most important factors. It is important to mention that the urban population in Uttarakhand increased from 16.36% of the total in 1971 to 20.7% in 1981, 22.97% in 1991, and 25.59% in 2001 (**Table 5**). The state registered the highest growth of urban population during 1971–1981 (56.38%);


*Trend Analysis of Streamflow and Rainfall in the Kosi River Basin of Mid-Himalaya... DOI: http://dx.doi.org/10.5772/intechopen.107920*

### **Table 3.**

*Overall trend analysis of monthly streamflow and rainfall.*


### **Table 4.**

*Overall trend analysis of annual and seasonal streamflow and rainfall.*

however, decadal urban population growth declined slightly during 1981–1991 (42.20%) and 1991–2001 (32.81%) [39].
