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Eco-Hydrological Footprint of a River Basin in Western Ghats |
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Results and Discussion
Land use assessment is carried out by classifying temporal remote sensing data into 10 categories for the time period between 1973 and 2016 and are depicted in Figure 4 and land use details are listed in Table 1, which highlight the reduction of forest cover from 84.69 percent (1973) to 54.94 percent (2016). The construction of a se-ries of dams on Kali river during 1980-2000 has resulted in large scale land use changes. The major change in ever-green forest cover was during 1973-1989 and 1989-2004. The evergreen forest has decreased from 61.79 percent to 38.50 percent and dry deciduous forest has reduced from 7.82 percent to 2.24 percent in the catchment from 1973 to 2016. Monoculture plantations of social forestry (Aca-cia sp.) and horticulture (Areca) has increased from 1.66 percent to 16.8 percent. Large scale conversion of forests to monoculture plantation near the eastern plains is due to the industrial demand by the Dandeli paper mill and other purposes. Agriculture has increased in plains of Haliyal, Kalgatgi, Yellapur, and Dharwad taluks, from 9.20 per-cent to 17.71 percent. Increase in water bodies from 0.41 percent to 3.65 percent is due to the construction of major reservoirs during this period, stretching their expanses in the forested landscape. Built up areas have increased from 0.39 percent to 1.69 percent, major increase in built areas can be observed at Yellapur, Dandeli, Kalgatgi, Kai-ga, Karwar, Ankola, Haliyal, Ramanagar, Londa, Khana-pura, Joida, etc. The overall accuracy (88 to 91 percent) and Kappa statistics (0.84 to 0.90) depict agreement of classified data with field and reference data.
Spatio-temporal pattern analyses of rainfall (Figure
5) show that nearly 84 percent of the rainfall occurs due to the South West monsoon between June to September and average rainfall in the catchment is about 2597 mm. Annually rainfall varies between 1000 mm at the plains of Dharwad to over 4500 mm at the Ghats of Supa, Yellapur taluks. The coastal belt of Karwar and Ankola receive annual rainfall of 2500 mm and 4500 mm.
Hydrological assessment was carried out to under-stand water availability and water demands (Figure 6). Interception loss in the basin ranges between 187 mm and 1248 mm with an average of 640 mm. Net rainfall in Kali basin is about 1944 mm i.e., about 9923 million cubic meters. River Kali has over 58 percent forest cover indicating higher percolation into the subsurfaces, this is explained by runoff and infiltration. Runoff in the basin is about 2227 million cubic meters and infiltration of 7696 million cubic meters. Presence of rich evergreen forest cover in the Ghats, has contributed to higher infiltration i.e., about 4035 million cubic meters. Ground water recharge in the catchment ranges between 125 mm to 880 mm in the plains and Ghats, on an average 460 mm contributed to ground water recharge accounting to 2360 million cubic meters. Water available in the hypomorhpic layer is about 5022 million cubic meters. Sub-surface flows as function of pipeflow and baseflow was estimated
considering the soil and geological characteristics of the region. Pipeflow in the basin is about 550 million cu-bic meters whereas base flow is about 514 million cubic meters both together contributing to a sub-surface flow of 1064 million cubic meters.
Agriculture water demand was estimated based on cropping pattern, growth stages, cropping cycle, etc. Ag-riculture water demand was found to be higher in sub-ba-sins 1, 2, 3, 4, 5, 6, 11 (Figure 6) with over 100 million cubic meters as against Ghats, and annual agriculture demand in the basin is about 2272 million cubic meters. Taluk level livestock census showed of higher population in plains compared to the Ghats or Coasts, with water demand of over 1000 kilo cubic meters. Annual livestock demand in the basin is about 10.2 million cubic meters. Domestic water requirement in the basin is about 27.1 million cubic meters across the basin. Both livestock and human population combined together has a domestic footprint of 37.3 million cubic meters.
Water demand of the forested landscapes and min-imum ecological flow requirements were computed as explained in the methods section. Terrestrial demand is a function of evapo-transpiration, which is about 3779 mil-lion cubic meters during non-monsoons which could be catered by the water in the hypomorphic layer. Ecological flow in the basin is assumed to be 30 percent of mean annual flow. Annual average flow in the basin considering runoff and sub-surface flows is about 3291 million cubic meters with the environmental flow of about 987 million cubic meters. Ecological footprint of the basin is about 7075 million cubic meters and of this 6088 million cubic
meters is the water footprint in agriculture, domestic, livestock, and evapotranspiration from forests.
Considering terrestrial demand is met by water in the hypomorphic layer, then total ecological footprint would be the aggregation of agriculture, livestock, domestic de-mands, and ecological flow i.e., about 3297 million cubic meters, whereas the supply footprint naturally available as flow would account to 3291 million cubic meters, al-most catering the annual demand.
Ecohydrological status (Figure 6, Table 2) assess-ment confirms the role of native vegetation (native for-ests) in retaining the water in the catchment. Hydrolog-ical footprint (Figure 6) shows water scarce situation in sub-basins 1, 2, 3, 5 and 6 located in the eastern plains whereas sub-basins in the Ghats and Coasts i.e., 4, 7, 8, 9, 10, 11, 12 and 13 show sufficient water availability to cater domestic, irrigation, horticulture, livestock, and ecological needs. Presence of dense forest cover in the Ghats make it more favorable to cater most of the envi-ronmental flow demands in each sub-basin and ecological flow demands in the river downstream.
Hydrological status of Kali river was calculated based on the interannual variability of water supply and demand (Figure 7). Kali river showed sufficient water in the Ghats and coasts, whereas the transition zones and plain lands with higher monoculture, agricultural activ-ities has led to water scarcity between 4 to 9 months. Based on flow in the river the sub-basins were classified into 4 categories (A, B, C, D). Perennial rivers are cate-gorized under A (with 12 months flow), intermittent river with 9 to 11 months flow (category B), 8 to 6 months (category C), whereas seasonal river stretches were classified under D category. Accordingly, the Ghats and coasts have perennial river system as against the upper plainlands.
Kali river catchment is a habitat to very rare and endangered wildlife and endemic flora. Ecology of Kali basin is assessed through biodiversity (such as endemic flora and fauna) based on field measurements, and re-view of published literature [50,52,80]. Figure 7 depicts the distribution of endemic flora and fauna in Kali river basin. The flora includes most threatened and vulnerable species such as Wisneria triandra, Holigarna beddomei, Holigarna grahamii, Garcinia gummi-gutta, Hopea ponga, Diospyros candolleana, Diospyros paniculata, Diospyros saldanhae, Cinnamomum malabatrum, Myris-tica malabarica, and Psydrax umbellate, etc. Wildlife in-cludes predators such as tiger (Panthera tigris), leopard, wild dog (Cuon alpinus) and the sloth bear. Prey animals are barking deer, spotted deer (Axis axis), wild boar, sambar (Cervus unicolor), gaur (Bos gaurus). The region has an important elephant corridor between Karnataka and Maharashtra for about 47 elephants. Birds include great hornbill (Buceros bicornis), malabar pied hornbill (Anthracoceros coronatus), blue winged parakeet, Nilgiri thrush, malabar lark, bulbul, thrush, etc. There are about 22 amphibians and 31 fish species, which are endemic to Western Ghats. This highlights the occurrence of endemic flora and fauna in catchments with the perennial water resource and sufficient hydrological footprint.
The information related to biodiversity and ecology of the region were compiled through literature review and field measurements. Ecological Sensitive Regions (ESR) were delineated based on the geo-climatic, land, ecolog-ical, hydrological parameters [80]. ESR spatial data is integrated with hydrological status of the river (perennial, seasonal) and is presented in Figure 8. The study confirms the ecological sensitiveness linkages with the hydrolog-ic regime of a region with the occurrence of perennial streams in ESR 1 and 2. Figure 7 and Figure 8 confirms the role of native forests (contiguous interior forests) in sustaining the water evident from the occurrence of pe-rennial streams compared to the seasonal streams in the catchment dominated by degraded forest patches. This highlights the linkages of hydrology, biodiversity, and ecology with the land use dynamics in a catchment.
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Citation :T.V. Ramachandra, S. Vinay, S. Bharath, A. Shashishankar, 2018. Eco-Hydrological Footprint of a River Basin in Western Ghats. Yale Journal of Biology and MEDICINE 91 (2018), pp.431-444.
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