MODELING HYDROLOGIC RESPONSE OF SEONATH BASIN UNDER CHANGING CLIMATE AND LAND-USE SCENARIOS

Abstract

Hydrological response of a river basin is primarily governed by climatic factors and basin characteristics. Changes in these two may alter the various attributes of water resources and hydrology of the region. With the pronounced enrichment of carbon emission in the atmosphere, worldwide warming is leading to changes in many climatic variables. Impacts of changing climate have been witnessed on every sphere of our planet. The hydrosphere, which is vital for sustaining life on earth, is closely linked to the various climatic phenomenon. The evaluation of the impacts of climate change on the hydrologic responses of river basins is vital for optimised planning and management of water resources for the sustenance of the developmental projects. To meet the various demands such as food, water, settlement, etc. of the ever-growing population, the land-use and land cover (LULC) have changed drastically, i.e. urban sprawling. The LULC change can alter land surface interactive processes, thus affects the hydrological cycle. This research has examined the impacts of various scenarios of varying climate and land-use on the hydrologic responses of the Seonath River basin, India. As a first step, the trends and variability of regional climatic characteristics of the Seonath basin were carried out for the past and future under two climatic scenarios, i.e. representative concentration pathways (RCPs). Thus, the impact of changing future climate on rain is analyzed by way of assessing future rainfalls in terms of projected rainfalls for different time steps. The simulations of the changes of varying land-use for three periods in the coming future were performed for the study basin. Five bias-corrected and statistically downscaled GCM model variables with RCP 4.5 and RCP 8.5 were considered to ascertain the impacts of climate change. Precipitation and temperature for baseline (1981-2005) and three future periods: early of the 21st century (2016-2035), mid of the century (2046-2065) and end of the century (2081-2099) have been used for hydrological simulations using a semi-distributed hydrological model on a monthly time scale. An MLP-ANN-Markov process based land-use change model was applied to predict the land-use conditions for the year 2030, 2060 and 2090 in future. For hydrological simulation Soil and Water Assessment Tool (SWAT) model with GIS-based GUI was calibrated for the period of twenty-five years (1980-2005) including three years of warm-up period and validated for five years of period (2000-2005). The future precipitation and temperature are showing rising trends as compared to the baseline period under both the RCP scenarios. The projected average annual streamflow of the Seonath river under the changing climate and land-use scenarios are expected to decrease by 2% to 6.5% during the early period of the 21st century and expected to increase by 15.40% to 48.00% during the mid and end of the 21st century. The high-flows in wet seasons are getting more intensified with short durations and dry spells or lean season flows are projected to be prolonged with the lesser quantum of flows as compared to the baseline period. The study also includes the detailed uncertainty analysis to identify and quantify the various components for the assessment of hydrological response under changing climate and land-use of the basin. A two-way ANOVA method has been used to determine the percentage contribution by the climate, land-use scenarios and their interactive terms. The GCMs and GCM*RCP interaction was found to be the main causes of uncertainty in the simulation of flows for the future. The study identified the composite index based water resources vulnerability of the sub-basins of the Seonath basin for the past and future periods. It was found that two sub-basins (viz. Seonath main and Maniyari) are moderately vulnerable, four out of eight sub-basins (viz. Arpa, Hamp, Kharun and Upper Seonath) are vulnerable and remaining two (viz. Lower Seonath and Jamunia) are highly vulnerable regions from a water resources point of view. Along with general shortterm and long-term adaptive strategies, the Seonath basin specific adaptation strategies were suggested to cope with the impacts on the flow regime caused due to the projected changes in the climate and land-use. The major strategies include the development of water storage infrastructure, expansion of irrigated areas, efficient use of water and check on the growing water pollution. Results of the study indicate that the impacts of land-use changes are smaller as compared to those caused by climatic changes. The study results also provide the assessments of water availability in the future periods with various percentage of dependability and can aid policymakers for effective planning and implementation of different water resources strategies.