INTRODUCTION

Water supply demand is increasing rapidly with increasing human population with changes in land use land cover (LULC). In land use types such as forest, hydrology plays an important role in studying the link between water movements through the forest. The major challenge in the 21st century is the proper management of the forest and water supply. Land cover (LC) of the tropics is now becoming more fragmented and highly complex, and secondary forest is now emerging as the dominant forest type interspersed with remnants of old-growth forest and other intermediate LCs (Giambelluca, 2002; Drigo, 2004; Holscher et al., 2004; Cuo et al., 2008). The dynamics of changes in forest and its hydrological effect on the rivers is also determined by land use (LU), its extent and climate of the area. Rivers in south India receive runoff due to rainfall and have good flow only during monsoon unlike rivers in northern part of India which are perennial since they receive snow melt runoff in summer. The knowledge of soil formation, recharge of streams and lakes, rainfall pattern, cropping patterns, etc. are required in understanding the hydrogeology of an area.  In other words, the hydrological study helps in the assessment, development, utilization and management of water resources. The storm runoff hydrology of the intermediate LCs from many decades of human occupancy, and ‘forestation’ (afforestation–reforestation, defined in Scott et al., 2004; Wiersum, 1984) of land in various states of degradation, have been much less studied across a range of soils and scales (Giambelluca, 2002; Bruijnzeel, 2004; Holscher et al., 2004; Scott et al., 2004).

In forests LU types, most water transactions in the atmosphere are mainly due to interception, evaporation, transpiration, and evapotranspiration from irrigated and cropped land. Transpiration is the process by which water vapour escapes from the living plant leaves and enters the atmosphere. Interception is due to the water held up by the surface of the leaves and buildings, which are in turn returned to the atmosphere by evaporation without reaching the ground surface. Evapotranspiration is the total water lost from the cropped land due to evaporation from the soil and transpiration by the plants or used by the plants in the formation of the plant tissue. Climatological factors like percentage sunshine hours, wind speed, mean monthly temperature and humidity, cropping factor and the moisture level of the soil affects evapotranspiration. How much these man-induced impacts have been influential on climate –water relations, as against the effects of inherent climatic variability and predicted climate change scenarios, still remains a major challenge to quantify. Thus embedded within the global warming issue are these additional LULC change that impacts climate-rainfall-storm runoff across scales which also require consideration under the broader mandate of ‘global change’ (Mike et. al., 2010). Water entering the soil at the ground surface is called infiltration, which replenishes the soil moisture deficiency and excess water seeps and build up the water table. The infiltration depends on the duration of rainfall, temperature, soil type, vegetation cover, LU, etc. Rainfall  is  one  of  the  important climatic  parameter  influencing  the  cropping  pattern,  productivity,  flooding  and  drought hazards, erosion and sedimentation (Kusre et. al.,2012). In case of perennial streams, ground water table never drops below the bed of the streams and therefore flows throughout the year. Ground water is widely distributed in the ground and is replenishable resource unlike other resources in the earth. During a storm, portion of rain water seeps into the soil and some may evaporate and the rest may flow over the land surface which is the overland flow. Run off is the balance of rain water, which flows or run over the natural ground surface after losses by evaporation, interception, and infiltration. Rain helps in the recharge of ground water as it seeps down through soil and rock layer of the ground from surface water sources. The entire area of the river basin whose surface runoff due to rain drains into the river in the basin is considered as a hydrological unit and is called drainage basin, watershed or catchment’s area of the river flowing. When the storm water infiltrates in the ground then some portion of it evaporates and the rest flows as a thin sheet of water over land surface termed as overland flow.

Climatic and human activities can influence land cover status and eco-environment quality (Hao et.al., 2012). On the other hand, dramatic changes in the humid tropics of LC and LU have occurred (Drigo 2004) from the mid- 20th century to the present that have resulted in rapid rates of forest conversion and an expansion of ‘land and forest degradation’ (Lal 1987; Scott et al. 2004; Safriel 2007). To a large extent, afforestation and deforestation are major human activities responsible for these enormous environmental changes. Indiscriminate cutting of trees have decreased the storage of ground water sponge, leading to water shortages during dry seasons and, in wet seasons, to brief destructive floods, during which very little water is absorbed by the soil. Large productive land becomes desert when vegetation cover is removed. Therefore, there is a need to study the linkages between LULC, forest fragmentation, rainfall and stream flow (seasonal and perennial). In this context, remote sensing data coupled with other primary data such as rainfall, amount of vegetation and forest, and other ground level information, etc. can be used to analyse this relationship in watersheds.

In this study, we attempt to study the Kali river basin in Uttara Kannada district, Karnataka state, India. The river basin has been divided into ten subbasins based on the tributaries (drainage network) to study dynamics of LULC change and establish a relationship between stream flow and other parameters. LU analysis (agriculture, evergreen forest, plantation, built up, waste land and water bodies) is carried out for each basin and forest fragmentation is computed to assess the amount of different types of patch, transitional, edge, perforated and interior forest. Finally a mathematical relationship is established between the number of streams as a function of LULC, rainfall and forest fragmentation to identify the important parameters that play a pivotal role in deciding the water retaining capacity of the streams which may be wither seasonal or perennial.

The objectives of this study are:

1. to delineate sub-basins based on drainage patterns in the main river basin.

2. to perform LU analysis of the river basin (subbasin wise).

3. to compute forest fragmentation in each subbasin.

4. to carry out multivariate statistical analysis and establish a regression model to find the linkages between the LU, forest fragmentation, order of streams, stream density, rainfall and infiltration of the river basin.

The analysis will reveal the role of LU, rainfall, number and types of streams and vegetation types in the catchments in deciding the seasonality and perenniality of the river.