**1. Introduction**

The prominent challenge being faced by the Indian Himalayan region (IHR) is climate change [1]. Study in connection with climate change is of great importance for the Kumaon region of Uttarakhand [2]. Changing temperature and precipitation patterns and their impact on water resources, glaciers, ecology, and agriculture are the results of changing climate over the Himalayas region [3]. Several researchers have studied the impact of climate change on Himalayan region and found that temperature is showing an increasing trend in the western Himalayas, while precipitation is showing a decreasing trend during winter and summer periods [4–8]. The nonuniform distribution of rainfall in the mountains results in differential rainfall

trends within small distances [9]. For example, the central Himalayas receives 80% of annual precipitation due to the Indian summer monsoon (ISM), while the western Himalayas receives 30% due to western disturbances [10–12].

It has been observed that low rainfall or shift in rainfall patterns at different altitudes had resulted in crop failure, declining in food grain yield. It was reported that traditional crops will soon be replaced with cash crops in the Kumaon region [13].

The impact of change on land use and land cover (LULC) plays an important role in climate change on local to regional scale. Increased urbanization or changes in LULC is known to alter changes in LULC directly affecting the rainfall and mesoscale convective system [14–19]. Therefore, understanding rainfall variability in the Himalayan region becomes extremely critical for holistic Himalayan spatial planning for water resource management.

A growing literature suggests that the Western Himalayas region is witnessing above normal increasing temporal trend in temperature and decreasing trend in rainfall. The worst case is the large-scale devastation owing to the Nanda Devi glacier burst in Uttarakhand's Chamoli district, which triggered a mass of snow, ice, and rocks falling speedily down a mountainside known as an avalanche that led to the water level rising in the river Rishiganga and heavy flood in Dhauliganga [19].

Finding variability and trend in long-term historical streamflow is of crucial importance for the appropriate management and planning of water resources. Some of the important reasons for trend analysis of streamflow are to understand the design flow rate for hydraulic structure and assigning water rights beyond the capacity of river supply.

This study applies Mann–Kendall (MK) test, the Sen's slope (SS) estimator, and nonparametric tests for evaluating the trends in streamflow time series. The MK checks whether the trend increases or decreases with time by examining whether to reject the null hypothesis or accept the alternative hypothesis. SS indicates the median of all pairwise slope values of a set of observed data. These two parameters have been employed in several studies for hydrological assessment of trends over various regions of globe for last decade.

There are several factors that impact the hydrology of a river basin, such as land use, climate change, and hydraulic infrastructure management [20, 21]. Therefore, investigating the hydrological characteristics from the historical time series of discharge data is considered one of the most important objectives in the field of water resource planning [22]. Salarijazi [23] reported that in several published research studies, the hydrological time series from different regions describe significant nonconsistency or non-stationary. Due to this concern, trend analysis and change point detection in streamflow time series and other climatic variables (rainfall, evapotranspiration, and temperature) have been studied by many researchers in different watersheds or river basins at different time scales throughout the globe. Hyvärinen [24] analyzed streamflow data from 1913 to 2008 using Mann–Kendall test. He reported a significant decrease in high flow trend in Hawaii. Trend analysis and change point detection are two important tests, which have been popularly used at same time as mentioned by [23]. There is loss of spatial information of the hydro-climatic variable at large scale. Hence, it is recommended to analyze hydro-climatic variables at a small scale [24]. In the present study, the Kosi river watershed was undertaken to investigate the trend in measured streamflow data and the possible linkage for the observed changes in streamflow with rainfall and anthropogenic factors.

According to the published literature, no research study has addressed the trend in stream flow and rainfall, and their association with each other in the Kosi river

watershed. Therefore, this study investigates trend of stream flow and rainfall data of this watershed at Ramnagar station during the last 31 years from 1986 to 2016.
