The water demand for various purposes is ever increasing worldwide, despite a sharp decline of available potable water worldwide including both surface and groundwater. The survey by the United Nations for the world population states that in 2030, about 40% of the Indian population is expected to reside in urban areas (McKinsey Global Institute, 2010). Similarly, in few other developing countries (Brazil, Indonesia, South Africa etc.), an increasing trend towards urbanization has been recorded mainly during the second half of the 21st century. Urbanization and rising population cause mismanagement of water resources leading to the water scarcity and, eventually affecting socio-economic status of the country (Mishra and Singh, 2010). It also affects by hydro-meteorological phenomena such as uneven distribution of precipitation and soil moisture. Consequently, it leads to unstable water resources condition in the developing countries (Goyal et al. 2018). Hence, understanding the hydrological responses on the catchment scale help better management of water resources, for which developing water balance models are often encouraged. The model requires the catchment characteristics such as the area, shape, Land Use and Land Cover (LULC), soil, topography, etc. This is primarily to study the response of a catchment to the hydrological processes, mainly in pre and post event of precipitation through water balance models (Liang et al. 2003). Water balance model has been in the use to assess the hydrological responses mainly to simulate the water balance components (WBCs) such as precipitation, evapotranspiration (ET), surface runoff, lateral flow, percolation and soil water (Lu et al. 2015). There are many computer-based codes are available to estimate WBCs and also many theoretical and experimental studies have been conducted in the past. The water balance model can be developed at various time scales: hourly, daily, monthly, seasonally, and yearly. The hourly to daily time scale models are generally accurate and most suitable for rainfall-runoff and flood studies. However, the availability of such a fine resolution data is rare in many parts of the world and thus daily and monthly scale water balance models are mostly preferred.
SWM (Stanford Watershed model) is the first computer coded physical-based water-balanced models developed during 1959-1966 (Crawford and Linsley, 1966). Since then, the wide range of modeling approaches are available varying from simple empirical, more data rigorous machine learning-based models and physically-based models. Parida et al. (2006) applied Artificial Neural Network (ANN) aided water balance model to forecast the catchment scale runoff coefficient over eastern Botswana. Kasiviswanathan et al. (2016) developed data-driven model to predict groundwater level over Amaravathi catchment, India. The physics-based model started evolving from the 19th century with the advancement of computational facility, better understanding of physical processes and availability of high-resolution data (Pandi et al. 2021). Pandi et al. (2021) have reviewed the applications and performances of empirical, data-driven, physical and hybrid models. The most commonly used physical-based water balance models are Variable Infiltration Capacity model (Hurkmans et al. 2008); Wapaba model (Wang et al. 2011); SimHyd (Chiew et al. 2002); Austrialian Water Balance model (Boughton, 2004); Soil and Water Assessment Tool (SWAT) (Patil and Ramsankaran, 2017; Swain and Patra, 2019); MIKE-SHE coupled MIKE-11 (Loliyana and Patel, 2018) etc. Xu and Singh, (1998) and Francesconi et al. (2016) reviewed the various applications of the SWAT model. Among several models developed, SWAT is well documented and applied in many countries worldwide. Murty et al. (2014) used SWAT to compute WBCs such as runoff, groundwater and ET over the Ken catchment. In general, selection the water balance models mainly depend on the purpose and availability of the number of input parameters and different hydro-meteorological variables along with their consistent spatiotemporal resolution. Presently high-spatiotemporal resolution meteorological data are not available in most of the developing countries. Many previous studies recommend that the water balance model at the monthly scale is reasonably good in water management studies at the catchment scale (Pal et al. 2021; Xu and Singh, 1998). Xu and Singh, (1998) have reviewed different monthly water balance models for their applications in the field and pointed out the data constraints.
The changes in LULC and meteorological variables are triggered mainly by the rising population, urbanization, climate change and environmental factors (Garg et al. 2017). The most commonly used LULC forecasting software package includes Celluar Automata (CA)-ANN, Dyna-CLUE, IDRISI’s CA-MARKOV etc. In this study, LULC were forecasted using the CA-ANN model. The CA-ANN model is a simple and widely used software package to forecast LULC (Rahman et al. 2017). Aarthi and Gnanappazham (2018) applied CA-ANN model to forecast the LULC over Sriperumbudur Taluk, Tamilnadu, India. They used historical data from 2009, 2013 and 2016 to forecast the urban sprawl and other classes for the years 2020. McCabe and Wolock (2011), and Pandžić et al. (2009) used the moving average method to forecast precipitation and temperature to estimate runoff and ET. Akrami et al. (2014) used the smoothing moving average and wavelet transform in short-term forecasting of precipitation over Klang River catchment, Malaysia. The meteorological variables are generally forecasted using the smoothing moving average method.
This paper used the data collected from Chittar catchment, Tirunelveli District, Tamilnadu, India to demonstrate the response of LULC and climate temporal changes in the WBCs. The rationale behind the selection of this catchment was to emphaise the importance of managing monsoon precipitation as it is the major source of water especially in the state Tamilnadu, located in the southern part of India. The average annual rainy day is about 60 days in the state. The annual average rainfall of Tamilnadu state is 980 mm out of which about 50% - 70% of total annual precipitation is losses through evapotranspiration process (Gosain et al. 2011). Hence, modeling of the WBCs is important for sustainable water management. It may be noted that most of the existing water balance studies over developing country like India are empirical or data driven or GIS based overlay analysis. Despite few studies reported development of water balance models (Swain and Patra, 2019), they are mostly biased input and output variables. Further, the impacts of LULC and meteorological variables changes are not incorporated in the model development (Swain and Patra, 2019). Thus, this paper focuses on developing a monthly and annual water balance model to simulate past and near-future period WBCs at catchment scale and to study the dynamics of water balance and changes occurred in different WBCs using SWAT model. The spatiotemporal variations in LULC and meteorological variables are also modeled and incorporated in the water balance model.