Effects of Land Use Dynamics on Hydrological Response of Watershed: a Case Study of Chittar Watershed, Vamanapuram River Basin, Thiruvananthapuram District, Kerala, India

Watersheds in the tropical regions of India are vulnerable to the effects of land use/land cover (LULC) change, transpiration and evaporation on groundwater resources. Understanding these changes is important to delineate the impacts on the hydrological cycle and thus helps to strengthen the efficiency of the water management system. A significant change in LULC and evapotranspiration has been observed in the Chittar watershed over the years. The present study involves the assessment of LULC changes during 1967–2001 and 2001–2015. The MODIS MOD 16 A3 data products were used to study evapotranspiration during the period. The groundwater level data of Central Ground Water Board (CGWB) have been used to study the water level changes from 2001 to 2015. The results of the LULC changes indicate that the natural vegetation is decreased significantly from 1967 to 2015. The aerial coverage of natural vegetation was 54% in 1967 which was reduced to 49% in 2001 and 30% in 2015. The most significant land use category is eucalyptus plantation which is decreased from 1967 (12 km2) to 2001 (9 km2). After the year 2011, eucalyptus plantations are converted into acacia plantations. The average annual evapotranspiration of the study area is 917 mm/year during the years 2001 to 2015. The overall evapotranspiration showed a decreasing trend with marked interannual fluctuations. Coming to the groundwater, the upstream of the study area exhibited shallow groundwater level (6.5 to 7.5). From 2001 to 2009, the groundwater level was significantly fluctuated; however, the fluctuation was minimal after 2009. To conclude, the study revealed that the LULC changes in the Chittar watershed have a pivotal role in the observed changes in evapotranspiration. The results reiterated that the changes in evapotranspiration (ET) have a strong bearing on the groundwater potential of the area.