Introduction

Developing countries in the tropics are facing threats of rapid deforestation due to unplanned developmental activities based on ad-hoc approaches and also due to policies and laws that considers forest as national resource to be fully exploited. The land use changes, involving conversion of natural forests to other land uses; agriculture (enhanced grazing pressure and intensive cultivation practices) and plantation (widespread acacia and eucalyptus planting) have led to soil compaction, reduced infiltration, groundwater recharge and discharge, and rapid and excessive runoff (Ray et al. 2015; Scott and Lesch 1997; Sikka et al. 1998; Van Lill et al. 1980).The structural changes in the ecosystem due to land cover changes, will influence the functional aspects namely hydrology, bio-geo chemical cycles and nutrient cycling. These are evident in many regions in the form of conversion of perennial streams to seasonal and disappearance of water bodies leading to a serious water crisis. Thus, it is imperative to understand the causal factors responsible for changes in order to improve the hydrologic regime in a region. It has been observed that the hydrological variables are complexly related with the vegetation present in the catchment. The presence or absence of vegetation has a strong impact on the hydrological cycle. This requires understanding of hydrological components and its relation to the land use/land cover dynamics. The reactions or the results are termed hydrological response and depends on the interplay between climatic, geological and land use variables (Ramachandra et al., 2014a).

Hydrological responses can be understood by analysing land use changes using temporal remote sensing data and traditional approaches. Traditional approaches considers spatial variability by dividing a basin into smaller geographical units such as sub-basins, terrain-based units, land cover classes, or elevation zones on which hydrological model computations are made, and by aggregating the results to provide a simulation for the basin as a whole. Modelling is thus simplified because areas of the catchment within these units are assumed to behave similarly in terms of their hydrological response. Remote sensing and GIS techniques have been used to determine some of the model parameters. The main applications of remote sensing in hydrology are to i) determine watershed geometry, drainage network and other map type information for hydrological models ii) provide input data such as land use/land cover, soil moisture, surface temperature etc. GIS on the other hand allows for the combination of spatial data such as topography, soil maps and hydrologic variables such as rainfall distribution or soil moisture (Ramachandra et al., 2013c).
Land cover is the observed physical cover at a given location and time as might be seen on the ground or from remote sensing. This includes the vegetation (natural or planted) and human constructions (buildings etc.), which cover the Earth surface. Land use is, in part a description of function, the purpose for which the land is being used. Land use and cover changes are the result of many interacting processes. Each of these processes operates over a range of spatial, temporal, quantitative, or analytical dimension used to measure and study objects and processes. Land-use and land-cover are linked to climate and weather in complex ways (Ramachandra et al., 2012). Key links between changes in land cover and climate include the exchange of greenhouse gases (such as water vapour, carbon dioxide, methane, and nitrous oxide) between land surface and atmosphere, the radiation (both short and long wave) balance of land surface, the exchange of sensible heat between land surface and atmosphere. Artificial changes to the natural cycle of water have produced changes in aquatic, riparian, wetland habitats and agricultural landscape. These interferences have had both positive and negative impacts on the problems that they were intended to solve. Some of these activities have greatly constrained the degree of interactions between the river channel and the associated floodplain with catastrophic effects on biodiversity.

Land use changes and its effect on hydrology
Human activities have been recognized as a major force shaping the biosphere (Karthick and Ramachandra 2007; Turner and Meyer 1994). In the 1980’s, terrestrial ecosystems as carbon sources and sinks were highlighted and later the important contribution of local evapotranspiration to the water cycle-that is precipitation recycling-as a function of land use/land cover highlighted yet another considerable impact of land use/land cover change on the climate. A much broader range of impacts of land use/land cover change on ecosystem goods and services were further identified (Lambin et al. 2003). A most efficient way of capturing the spatial and temporal details is by remote sensing. Hydrological models coupled with remote sensing data can efficiently characterize temporal and spatial effects of land use changes on the ecology and hydrology. Earlier studies confirm the relationship among the watershed physical characteristics and the storm-based hydrologic indices indicated that the greatest impact of land management is found with statistically significant predictive models for indices of time base, response lag, and time of rise of hydrograph (Ramachandra et al. 2015; Bhat et al. 2007).

Remote sensing and GIS techniques in hydrology
Remote sensing uses measurements of the electromagnetic spectrum to characterize the landscape or infer properties of it (Ramachandra et al. 2015; Schultz and Engman 2000; Schmugge et al. 2002). Satellite observations are available since the early 1970’s and it is possible to relate trends such as vegetation cover densities to stream flow. The land cover maps derived by remote sensing are the basis of hydrologic response units for modelling. Geographic information System (GIS) helps in the spatial data analysis, integration of a combination of spatial data (such as soil, topography, hydrologic variables, etc.) and modeling (Schultz and Engman 2000). GIS deals with information about features that is referenced by a geographical location. These systems are capable of handling both locational data and attribute data about such features through database management system (DBMS).

Western Ghats
The Western Ghats comprise the mountain range that runs along the western coast of India, from the Vindhya-Satpura ranges in the north to the southern tip. This range intercepts the moisture laden winds of the southwest monsoon thereby determining the climate and vegetation of the southern peninsula. The steep gradients of altitude, aspect and rainfall make the region ecologically rich in flora and fauna. There is a great variety of vegetation all along the Ghats: scrub jungles, grassland along the lower altitudes, dry and moist deciduous forests, and semi-evergreen and evergreen forests. Out of the 13,500 species of flowering plants in India, 4500 are found in the Western Ghats and of these 742 are found in Sharavathi river basin (Ramachandra et al. 2004). Climax vegetation of the wet tract consists of Cullenia, Persea, Diptercarpus, Diospyros and Memecylon. The deciduous forest tract is dominated by Terminalia, Lagerstroemia, Xylia, Tectona and Anogeissus. The region also contains potentially valuable spices and fruits such as wild pepper varieties, cardamom, mango, jackfruit and other widely cultivated plants. There is an equal diversity of animal and bird life. Noticeable reptile fauna in the evergreen forests include burrowing snakes (uropeltids) (Gadgil and Meher-Homji 1990) and the king cobra and among amphibians, the limbless frog (caecilians). The Nilgiri langur, lion-tailed macaque, Nilgiri tahr and Malabar large spotted civet are some examples of endangered endemic mammals belonging to this area. Sharavathi river valley lies in the Central Western Ghats and represents an area of 2985 km2. Sharavathi is a west flowing river originating at Ambuthirtha in Shimoga district and during its course, falls from a height of around 253 m at the famed Jog Falls. It flows through Honnavar and eventually into the Arabian Sea.
Karnataka Power Cooperation Limited (KPCL) has set up a dam at Linganamakki across Sharavathi in 1964 to harness electricity, which has divided the river basin into upstream and downstream. The construction of this dam has made considerable hydrological and ecological alterations in the river basin. The dam resulted in the submergence of wetlands and forest areas of unmeasured biodiversity. The effects are particularly seen in the upstream of the river basin where the dam submerged many villages and forests to give rise to small isolated islands. These island and surrounding areas have created niches for 150 species of birds, 145 species of butterflies and 180 species of beetles along with mammals such as spotted deer, barking deer, civet, leopard and the Indian gaur. The reservoir has provided further impetus to farmers and plantation agriculturists. Large tracts of forestlands have been cleared for paddy cultivation and plantation trees such as areca and acacia. Apart from these, vast tracts of natural vegetation has been cleared and replaced with monoculture plantations of Acacia auriculiformis, Eucalyptus sp. and Tectona grandis. As a result of these activities, there is evidence of changes in runoff and stream flow regimes. There are instances where wells have ‘run dry’ in the wet spots of the basin, mainly because percolation of rainwater into the ground has decreased due to deforestation. Studies are thus required to quantify the hydrological responses in order to gain an understanding of the effect of anthropogenic activities on the hydrological components and thus the vegetation of study area.

Objectives

The objectives of the study are: