Hydrological Responses at Regional Scale to Landscape Dynamics
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© Kamla-Raj 2014 J Biodiversity, 5(1,2): 11-32 (2014) Hydrological Responses at Regional Scale to Landscape Dynamics T.V. Ramachandra Energy and Wetlands Research Group, Centre for Ecological Sciences Indian Institute of Science, Bangalore 560 012, India Fax: 91-080-23601428 / 23600085 / 23600683 [CES TVR] E-mail: [email protected], [email protected] KEYWORDS Land Use. Land Cover. Western Ghats. Tropical Ecosystems. Stream Flow ABSTRACT Western Ghats is the primary catchment for most of the rivers in peninsular India. Pristine forests in this region are rich in biodiversity and are being cleared due to unsound developmental activities. Rapid land-use changes have undermined the hydrological conditions, there by affecting all the components in the hydrological regime. The development programs based on ad-hoc decisions, is posing serious challenges in conserving fragile ecosystems. These changes have adversely affected the hydrological regime of river basins resulting in diminished river / stream flows. This necessitates conservation of ecosystems in order to sustain the biodiversity, hydrology and ecology. In this situation, in order to resolve present problems and to avoid a future crisis, a comprehensive assessment of land use changes, its spatial distribution and its impact on hydrological regime was carried out to explore appropriate remedial methods for the sustainable utilization management of natural resources. INTRODUCTION the hydrological cycle. This requires under- standing of hydrological components and its Developing countries in the tropics are fac- relation to the land use/land cover dynamics. ing threats of rapid deforestation due to un- The reactions or the results are termed hydro- planned developmental activities based on ad- logical response and depends on the interplay hoc approaches and also due to policies and between climatic, geological and land use vari- laws that considers forest as national resource ables (Ramachandra et al. 2014a). to be fully exploited. The land use changes, in- Hydrological responses can be understood volving conversion of natural forests to other by analysing land use changes using temporal land uses; agriculture (enhanced grazing pres- remote sensing data and traditional approach- sure and intensive cultivation practices) and plan- es. Traditional approaches considers spatial tation (widespread acacia and eucalyptus plant- variability by dividing a basin into smaller geo- ing) have led to soil compaction, reduced infil- graphical units such as sub-basins, terrain- tration, groundwater recharge and discharge, based units, land cover classes, or elevation and rapid and excessive runoff (Ray et al. 2015; zones on which hydrological model computa- Scott and Lesch 1997; Sikka et al. 1998; Van Lill tions are made, and by aggregating the results et al. 1980). The structural changes in the eco- to provide a simulation for the basin as a whole. system due to land cover changes, will influ- Modelling is thus simplified because areas of ence the functional aspects namely hydrology, the catchment within these units are assumed to bio-geo chemical cycles and nutrient cycling. behave similarly in terms of their hydrological These are evident in many regions in the form of response. Remote sensing and GIS techniques conversion of perennial streams to seasonal and have been used to determine some of the model disappearance of water bodies leading to a seri- parameters. The main applications of remote ous water crisis. Thus, it is imperative to under- sensing in hydrology are to, i) determine water- stand the causal factors responsible for chang- shed geometry, drainage network and other map es in order to improve the hydrologic regime in a type information for hydrological models, ii) pro- region. It has been observed that the hydrolog- vide input data such as land use/land cover, soil ical variables are complexly related with the veg- moisture, surface temperature etc. GIS on the etation present in the catchment. The presence other hand allows for the combination of spatial or absence of vegetation has a strong impact on data such as topography, soil maps and hydro- 12 T.V. RAMACHANDRA logic variables such as rainfall distribution or effects of land use changes on the ecology and soil moisture (Ramachandra et al. 2013c). hydrology. Earlier studies confirm the relation- Land cover is the observed physical cover ship among the watershed physical characteris- at a given location and time as might be seen on tics and the storm-based hydrologic indices in- the ground or from remote sensing. This includes dicated that the greatest impact of land manage- the vegetation (natural or planted) and human ment is found with statistically significant pre- constructions (buildings etc.), which cover the dictive models for indices of time base, response Earth surface. Land use is, in part a description lag, and time of rise of hydrograph (Ramachan- of function, the purpose for which the land is dra et al. 2015; Bhat et al. 2007). being used. Land use and cover changes are the result of many interacting processes. Each of Remote Sensing and GIS Techniques in these processes operates over a range of spa- Hydrology tial, temporal, quantitative, or analytical dimen- sion used to measure and study objects and Remote sensing uses measurements of the processes. Land-use and land-cover are linked electromagnetic spectrum to characterize the to climate and weather in complex ways (Ram- landscape or infer properties of it (Ramachandra achandra et al. 2012). Key links between chang- et al. 2015; Schultz and Engman 2000; Schmugge es in land cover and climate include the exchange et al. 2002). Satellite observations are available of greenhouse gases (such as water vapour, car- since the early 1970’s and it is possible to relate bon dioxide, methane, and nitrous oxide) be- trends such as vegetation cover densities to tween land surface and atmosphere, the radia- stream flow. The land cover maps derived by tion (both short and long wave) balance of land remote sensing are the basis of hydrologic re- surface, the exchange of sensible heat between sponse units for modelling. Geographic infor- land surface and atmosphere. Artificial changes mation System (GIS) helps in the spatial data to the natural cycle of water have produced analysis, integration of a combination of spatial changes in aquatic, riparian, wetland habitats data (such as soil, topography, hydrologic vari- and agricultural landscape. These interferences ables, etc.) and modelling (Schultz and Engman have had both positive and negative impacts on 2000). GIS deals with information about features the problems that they were intended to solve. that is referenced by a geographical location. Some of these activities have greatly constrained These systems are capable of handling both lo- the degree of interactions between the river chan- cational data and attribute data about such fea- nel and the associated floodplain with cata- tures through database management system strophic effects on biodiversity. (DBMS). Land Use Changes and Its Effect on Hydrology Western Ghats Human activities have been recognized as a The Western Ghats comprise the mountain major force shaping the biosphere (Karthick and range that runs along the western coast of In- Ramachandra 2007; Turner and Meyer 1994). In dia, from the Vindhya-Satpura ranges in the the 1980’s, terrestrial ecosystems as carbon north to the southern tip. This range intercepts sources and sinks were highlighted and later the moisture laden winds of the southwest mon- the important contribution of local evapotrans- soon thereby determining the climate and vege- piration to the water cycle-that is precipitation tation of the southern peninsula. The steep gra- recycling-as a function of land use/land cover dients of altitude, aspect and rainfall make the highlighted yet another considerable impact of region ecologically rich in flora and fauna. There land use/land cover change on the climate. A is a great variety of vegetation all along the Ghats: much broader range of impacts of land use/land scrub jungles, grassland along the lower alti- cover change on ecosystem goods and servic- tudes, dry and moist deciduous forests, and es were further identified (Lambin et al. 2003). A semi-evergreen and evergreen forests. Out of most efficient way of capturing the spatial and the 13,500 species of flowering plants in India, temporal details is by remote sensing. Hydro- 4500 are found in the Western Ghats and of these logical models coupled with remote sensing data 742 are found in Sharavathi river basin (Ram- can efficiently characterize temporal and spatial achandra et al. 2004). Climax vegetation of the HYDROLOGICAL RESPONSES AT REGIONAL SCALE 13 wet tract consists of Cullenia, Persea, Dipter- Studies are thus required to quantify the hydro- carpus, Diospyros and Memecylon. The decid- logical responses in order to gain an understand- uous forest tract is dominated by Terminalia, ing of the effect of anthropogenic activities on Lagerstroemia, Xylia, Tectona and Anogeissus. the hydrological components and thus the veg- The region also contains potentially valuable etation of study area. spices and fruits such as wild pepper varieties, cardamom, mango, jackfruit and other widely Objectives cultivated plants. There is an equal diversity of animal and bird life. Noticeable reptile fauna in The objectives of the study are: the evergreen forests include burrowing snakes i. Quantification of hydrologic components (uropeltids) (Gadgil and Meher-Homji 1990) and of Sharavathi River Basin, Western Ghats the king cobra and among amphibians, the limb- using Remote Sensing and GIS. less frog (caecilians). The Nilgiri langur, lion- ii. Study the impact of land use/land cover tailed macaque, Nilgiri tahr and Malabar large changes on hydrologic components. spotted civet are some examples of endangered endemic mammals belonging to this area. Shara- Study Area vathi river valley lies in the Central Western 2 Ghats and represents an area of 2985 km . Shara- Sharavathi river (Fig. 1) originates at Ambu- vathi is a west flowing river originating at Am- teertha, near Kavaledurga in Tirthahalli taluk.