Agro Hydrological Characterization of River Basin in Tropical Monsoon Climatology under Changing Land Use and Climate Scenarios

Abstract

The present study assessed the impact of climate and land use change on agro-hydrological characteristics in the Anandapur catchment of Baitarani River basin, India using the Soil and Water Assessment Tool (SWAT) hydrological model. SWAT is a physically based semi-distributed hydrologic model and widely used for hydrological fluxes simulation and watershed management across the globe. The future climatic alterations under two Representative Concentration Pathways (RCPs 4.5 and 8.5) scenarios are quantified by an ensemble of two different CMIP5 models (CNRM-CM5.0 and GFDL-CM3.0). The future climatic alterations under two Representative Concentration Pathways (RCPs), i.e., 4.5 and 8.5 scenarios are quantified by an ensemble of two different CMIP5 models, i.e., CNRM-CM5.0, GFDL-CM3.0. The outcomes of this study reveal that the future rainfall and temperature may experience an increasing trend with gradual shifting of monsoon from mid-June to mid-May. The climate change impact on the considered three hydrological fluxes indicates that the streamflow and evapotranspiration (ET) exhibit significant increasing trend across all the future projections, whereas the groundwater recharge (GWR) is expected to have a comparatively slower increasing trend. The spatial discretization of streamflow and ET exhibits a linear association with the precipitation during the base period and future climate scenarios. The reduction in the GWR could be attributed to the increased urbanization and decreased forest cover in the coming time scales resulting in three major sub-basins to have only 0-20% increase with respect to the base period. The future LULC change scenarios are simulated using land change modeler (LCM). A land change modeler is a decision-making tool and it is facilitated with LULC change analysis, modeling, identification of transitions between LULC classes, and predict the future scenarios of the landscape by incorporating user-specified drivers of changes. The LCM uses Markov Chain model to compute the future land-use change of each land cover class for a specified date. The model is calibrated and validated at the catchment and sub-catchment level with an uncertainty analysis. After validation of model the future LULC change scenarios are predicted by the model in 2030 and 2040 using the transition matrix. Then combined effect of climate and land use change on hydrological components has been analysed onsidering both climatic and land use dataset. The variation of different hydrological components based on combined effect of both climate and land use change scenario are almost similar to variation found in the climate change only scenario. The crop yield is simulated in spatial and temporal scale considering different irrigation strategy. The performance of the model is found to be satisfactory for crop yield simulation during the calibration and validation periods. The optimal irrigation schedule could save more water leading to less groundwater exploitation, increase yield at par with full irrigation and higher crop water productivity (CWP) than other irrigation scenarios. The drought have been evaluated based on climate and land use change scenarion using different drought indices. The variation of standardized precipitation evapotranspiration index (SPI) and standardized precipitation evapotranspiration index (SPEI) are almost similar in annual time scale. Under moderate and severe conditions the number of drought events has increased based on SPEI compared to SPI. The number of drought months under moderate and severe conditions has increased after considering temperature along with precipitation. The influence of temperature is more in causing moderate and severe drought events. The performance of agricultural standardized precipitation evapotranspiration index (aSPEI) is better than SPEI for analysing the agricultural drought characteristics. The future drought events are identified which have negative impact on crop yield considering critical drought point of different regions. The characteristics of hydrological drought were evaluated considering climate variable along with catchment variables. The catchment variable, base flow index has higher influence on short term hydrological drought where, pastureland has significant control over medium term drought. The average precipitation during the spring has potential influence on the average drought duration, where, the average precipitation during the summer showed a significant control on the long term drought duration. Overall, the decreasing trend of water availability in the catchment is likely to intensify further with fewer runoff losses in the form of streamflow. On the other hand, the crop is expected to suffer from moisture stress owing to frequent alternate dry spells and unexpected inundation due to frequent flash floods, due to intensive rainfall across the basin during monsoon season. Frequent irrigation is required during the non-monsoon period because of increased ET in this period.