Soil Moisture Balance Research Articles

Estimating basin scale evapotranspiration (ET) by water balance and remote sensing methods

AbstractEvapotranspiration (ET) is an important hydrological process that can be studied and estimated at multiple spatial scales ranging from a leaf to a river basin. We present a review of methods in estimating basin scale ET and its applications in understanding basin water balance dynamics. The review focuses on two aspects of ET: (i) how the basin scale water balance approach is used to estimate ET; and (ii) how ‘direct’ measurement and modelling approaches are used to estimate basin scale ET. Obviously, the basin water balance‐based ET requires the availability of good precipitation and discharge data to calculate ET as a residual on longer time scales (annual) where net storage changes are assumed to be negligible. ET estimated from such a basin water balance principle is generally used for validating the performance of ET models. On the other hand, many of the direct estimation methods involve the use of remotely sensed data to estimate spatially explicit ET and use basin‐wide averaging to estimate basin scale ET. The direct methods can be grouped into soil moisture balance modelling, satellite‐based vegetation index methods, and methods based on satellite land surface temperature measurements that convert potential ET into actual ET using a proportionality relationship. The review also includes the use of complementary ET estimation principles for large area applications. The review identifies the need to compare and evaluate the different ET approaches using standard data sets in basins covering different hydro‐climatic regions of the world. Copyright © 2011 John Wiley & Sons, Ltd.

Applying a SPA model to examine the impact of climate change on GPP of open woodlands and the potential for woody thickening

AbstractWoody thickening is a global phenomenon that influences landscape C density, regional ecohydrology and biogeochemical cycling. The aim of the work described here is to test the hypothesis that increased atmospheric CO2 concentration, with or without photosynthetic acclimation, can increase gross primary production (GPP) and that this can explain woody thickening. We examine mechanisms underlying the response of GPP and highlight the importance of changes in soil water content by applying a detailed soil–plant–atmosphere model. Through this model, we show that CO2 enrichment with decreased or increased D and photosynthetic acclimation results in decreased canopy water use because of reduced gs. The decline in water use coupled with increased photosynthesis resulted in increased GPP, water‐use efficiency and soil moisture content. This study shows that this is a valid mechanism for GPP increase because of CO2 enrichment coupled with either a decrease or an increase in D, in water‐limited environments. We also show that a large increase in leaf area index could be sustained in the future as a result of the increased soil moisture content arising from CO2 enrichment and this increase was larger if D decreases rather than increases in the future. Large‐scale predictions arising from this simple conceptual model are discussed and found to be supported in the literature. We conclude that woody thickening in Australia and probably globally can be explained by the changes in landscape GPP and soil moisture balance arising principally from the increased atmospheric CO2 concentration. Copyright © 2010 John Wiley & Sons, Ltd.

Major Mesoamerican droughts of the past millennium

[1] Ancient Montezuma baldcypress (Taxodium mucronatum) trees found in Barranca de Amealco, Queretaro, have been used to develop a 1,238-year tree-ring chronology that is correlated with precipitation, temperature, drought indices, and crop yields in central Mexico. This chronology has been used to reconstruct the spring-early summer soil moisture balance over the heartland of the Mesoamerican cultural province, and is the first exactly dated, annually resolved paleoclimatic record for Mesoamerica spanning the Late Classic, Post Classic, Colonial, and modern eras. The reconstruction indicates that the Terminal Classic drought extended into central Mexico, supporting other sedimentary and speleothem evidence for this early 10th century drought in Mesoamerica. The reconstruction also documents severe and sustained drought during the decline of the Toltec state (1149–1167) and during the Spanish conquest of the Aztec state (1514–1539), providing a new precisely dated climate framework for Mesoamerican cultural change.

Desert shrub stemflow and its significance in soil moisture replenishment

Abstract. Stemflow of xerophytic shrubs represents a significant component of water replenishment to the soil-root system influencing water utilization of plant roots at the stand scale, especially in water scarce desert ecosystems. In this study, stemflow of Caragana korshinskii was quantified by an aluminum foil collar collection method on re-vegetated sand dunes of the Shapotou restored desert ecosystem in northwestern China. Time domain reflectometry probes were inserted horizontally at 20 different soil profile depths under the C. korshinskii shrub to monitor soil moisture variation at hourly intervals. Results indicated that 2.2 mm precipitation was necessary for the generation of stemflow for C. korshinskii. Stemflow averaged 8% of the gross precipitation and the average funnelling ratio was as high as 90. The soil moisture in the uppermost soil profile was strongly correlated with individual rainfall and the stemflow strengthened this relationship. Therefore, it is favourable for the infiltrated water redistribution in the deeper soil profile of the root zone. Consequently, stemflow contributes significantly to a positive soil moisture balance in the root zone and the replenishment of soil moisture at deeper soil layers. This plays an important role in plant survival and the general ecology of arid desert environments.

Estimation of Groundwater Recharge in Limestone Aquifer using an Improved Soil Moisture Balance Method: A Case Study in Jaffna District

Estimation of recharge is extremely important for proper management of groundwater systems. The main purpose of this paper is to study the possibility of estimation of potential recharge in limestone aquifer as a case study in Thirunelvely and Kondavil area of Jaffna district, Sri Lanka using an improved soil moisture balance model (SAMBA). This model was used to estimate the groundwater recharge for a permanent grass and a commonly cultivated vegetable crop chilli for the years 2007 and 2008 for which soil properties, crop characters and climatic conditions were considered. The new concept of near surface soil moisture storage was included in the model and it is used to represent continuing evaporation on the days following heavy rainfall even though the soil moisture deficit is high. Uncertainties and variation in parameter values were explored using sensitivity analysis. The potential recharge resulted from the model was compared with the real field conditions of actual recharge which was derived from the water table fluctuation method. DOI: http://dx.doi.org/10.4038/tar.v21i1.2586 Tropical Agricultural Research Vol. 21(1): 51-61 (2009)

The importance of preferential flow in controlling groundwater recharge in tropical Africa and implications for modelling the impact of climate change on groundwater resources

An improved water table fluctuation technique for estimating recharge is applied to a sustained (10-year) groundwater level monitoring record in Uganda, a rare dataset for tropical Africa, and compared against results from soil moisture balance models (SMBMs) and unsaturated flow models. The results show that recharge is directly proportional to rainfall (long-term average rainfall is around 1200 mm/a), even during times when high soil moisture deficits are anticipated. This indicates that preferential and/or localized flow mechanisms dominate the recharge behaviour. SMBMs and unsaturated flow models, based on uniform flow governed by the Richards equation, are shown to be inappropriate for estimating recharge in this location underlain by lateritic soils. Given the large spatial coverage of lateritic soils both globally and in tropical Africa, and despite the convenience of physically based uniform flow models and, in particular, SMBMs, concern is raised over the use of such models for recharge estimation, and thus for exploring future trends due to climate or land use change, unless backed up by sufficient hydraulic data to enable the recharge processes to be confirmed. More research is needed to assess how widespread preferential flow may be within other major soil groups and climate zones.

Common criteria for the redefinition of Intermediate Less Favoured Areas in the European Union

This article defines eight key climate, soil and terrain criteria that have been developed for the future delimitation of the Intermediate Less Favoured Areas (LFAs) support, a measure of the Common Agricultural Policy. The LFA scheme has existed since 1975 and is a broad mechanism for improving the viability of agriculture in areas with natural handicaps. The common criteria have been developed for the European Commission's Directorate-General for Agriculture and Rural Development to satisfy the objectives in the Rural Development Policy 2007–2013 (Axis II), which aim to improve the environment and the countryside by more sustainable land management. The criteria were developed by experts, coordinated by the European Commissions Joint Research Centre, to meet the requirement for a robust and harmonised approach of identifying areas that experience natural constraints to agriculture throughout the EU 27 Member States. The criteria proposed are: temperature, heat stress, drainage, soil texture and stoniness, soil rooting depth, soil chemical properties, soil moisture balance and slope. Each criterion is described and an indicative threshold for assessment of its impact on agriculture is provided. The criteria are currently being tested by the EU Member States for a future possible legislation.

Modelling the impact of forest cover on groundwater resources: A case study of the Sherwood Sandstone aquifer in the East Midlands, UK

Land-use change from arable agriculture to forestry has become a focus in many European countries to control leaching of non-point agricultural pollutants such as nitrate to aquifers. However, a reduction in groundwater recharge beneath forest areas could potentially exacerbate water supply shortages. No direct study has previously been undertaken in the UK to assess the effect of increasing woodland cover on the quantity of groundwater resources. To address this knowledge gap, this study applied a groundwater flow model (MODFLOW) with a soil moisture balance recharge model to predict the effect of land-use change to forestry on groundwater recharge and levels by 2025 at two public supply borehole sites on the unconfined Sherwood Sandstone aquifer in Nottinghamshire. Four land-use change scenarios focusing on borehole capture zones were developed. The recharge calculations revealed a reduction of up to 45% in annual recharge as a result of an increase in woodland cover in the borehole capture zones, with the reduction more marked in winter than in summer at both borehole locations. However, the associated decrease in groundwater levels was limited owing to the high storage capacity of the sandstone aquifer. Even with an increase in woodland cover over the entire target zone, the simulated decrease in groundwater levels was less than 0.3 m. It is concluded that a quantitative analysis using a modelling approach can assist in the better targeting of pollution control strategies that include land-use change to woodland, helping decision-makers balance the expected improvements to groundwater quality while concurrently managing groundwater resources.

Assessment of groundwater storage depletion by overexploitation using simple indicators in an irrigated closed aquifer basin in Iran

Abstract In arid and semi-arid regions irrigation is usually needed to provide enough water for crop growth in cultivated areas. As surface waters are scarce, especially in summertime when the water is needed, groundwater is heavily used to supply the water demand. Overexploitation of the aquifer in dry years causes depletion of the groundwater storage and systematical lowering of the piezometric levels. This is a particular problem in aquifers developed in closed basins where lateral inflow is nearly absent and replenishment is constrained by rainfall recharge. In this paper, simple indicators derived from meteorological data, abstraction rates and piezometric time series are compared with the groundwater storage depletion as obtained from a calibrated groundwater flow model. Application of the method to the overexploited Shahrekord basin in Iran shows that for the simulated period 1989–2003 an accumulative index of the difference of aquifer recharge, as calculated by a soil moisture balance method, and groundwater abstraction has a correlation coefficient of nearly one with model calculated storage. Indicators based on the filling index derived from piezometric time series or on the ratio of aquifer discharge to recharge have slightly lower correlations. The accumulated index indicator can be used to follow aquifer storage in the future without the need to run the full groundwater flow model. This simple approximation is restricted to aquifer systems with a limited lateral inflow and outflow.

Combined effect of fire and water scarcity on vegetation patterns in arid lands

In many arid zones around the word, the vegetation spontaneously forms regular patterns to optimize the use of the scarce water resources. The patterns act as early warning signal that fragile ecosystems may suddenly undergo irreversible shifts, thus, interpreting the structural shape of vegetation patterns is crucial to deciphering the ecosystem history and its expected further development. The sudden and irreversible shift of delicate ecosystems as a consequence of minor variation of the climatic forcing has been studied extensively in the past. The attitude of the ecosystem to recover after a catastrophic event, such as fire, did not receive as much attention so far. Here we modelled fire, as a sudden shift of the ecosystem state variables and functionality and evaluated post-fire scenarios under the hypothesis that two major feedbacks shaped the vegetation patterns: a positive feedback between preferential infiltration and plant growth, and a second feedback between infiltration and vegetation burning. A simple model solving a set of partial differential equations for soil moisture, plant biomass, surface water and dead biomass balance predicted significantly diverse post-fire vegetation patterns depending on the fire severity and on the degree of soil water repellency induced by the vegetation burning.

Stochastic modeling of soil salinity

A minimalist stochastic model of primary soil salinity is proposed, in which the rate of soil salinization is determined by the balance between dry and wet salt deposition and the intermittent leaching events caused by rainfall events. The long term probability density functions of salt mass and concentration are found by reducing the coupled soil moisture and salt mass balance equation to a single stochastic differential equation driven by multiplicative Poisson noise. The novel analytical solutions provide insight on the interplay of the main soil, plant and climate parameters responsible for long‐term soil salinization. In particular, they show the existence of two distinct regimes, one where the mean salt mass remains nearly constant (or decreases) with increasing rainfall frequency, and another where mean salt content increases markedly with increasing rainfall frequency. As a result, relatively small reductions of rainfall in drier climates may entail dramatic shifts in long‐term soil salinization trends, with significant consequences e.g. for climate change impacts on rain‐fed agriculture.

Freshwater Situation in Kuwait-Remote Sensing Inputs on Possibility of Artificial Recharge

Problem statement: Kuwait is an arid country having per capita freshwater consumption of 485 l day-1. Almost the entire freshwater requirements are met through desalination. The water tariffs in the country are very low consequent to 60% subsidy provided by the government. The use of tertiary treated wastewater is restricted to irrigation and forestation; this leaves huge surplus that can be utilized for creation of shallow artificial aquifers. Approach: Remote sensing data provides information on existence of a paleo drainage network in north Kuwait which can be utilized for artificial recharge. Results: About 85% of treated wastewater which remains unutilized can be pumped into shallow aquifers creating future reserve. The shallow aquifers will also improve the soil moisture balance and shall support perennial vegetation, impeding dust transport. Conclusion: The pumping of tertiary treated wastewater into the paleo drainage network will create a future reserve besides improving the soil moisture index and vegetation cover in the area.

The impact of climate change on groundwater recharge and runoff in a humid, equatorial catchment: sensitivity of projections to rainfall intensity

Projected warming in equatorial Africa, accompanied by greater evaporation and more frequent heavy precipitation events, may have substantial but uncertain impacts on terrestrial hydrology. Quantitative analyses of climate change impacts on catchment hydrology require high-resolution (<50 km) climate data provided by regional climate models (RCMs). We apply validated precipitation and temperature data from the RCM PRECIS (Providing Regional Climates for Impact Studies) to a semi-distributed soil moisture balance model (SMBM) in order to quantify the impacts of climate change on groundwater recharge and runoff in a medium-sized catchment (2098 km2) in the humid tropics of southwestern Uganda. The SMBM explicitly accounts for changes in soil moisture, and partitions effective precipitation into groundwater recharge and runoff. Under the A2 emissions scenario (2070–2100), climate projections from PRECIS feature not only rises in catchment precipitation and modelled potential evapotranspiration by 14% and 53%, respectively, but also increases in rainfall intensity. We show that the common application of the historical rainfall distribution using delta factors to the SMBM grossly underestimates groundwater recharge (i.e. 55% decrease relative to the baseline period of 1961–1990). By transforming the rainfall distribution to account for changes in rainfall intensity, we project increases in recharge and runoff of 53% and 137%, respectively, relative to the baseline period.

The AMMA-CATCH Gourma observatory site in Mali: Relating climatic variations to changes in vegetation, surface hydrology, fluxes and natural resources

The Gourma site in Mali is one of the three instrumented meso-scale sites deployed in West-Africa as part of the African Monsoon Multi-disciplinary Analysis (AMMA) project. Located both in the Sahelian zone sensu stricto, and in the Saharo–Sahelian transition zone, the Gourma meso-scale window is the northernmost site of the AMMA-CATCH observatory reached by the West African Monsoon. The experimental strategy includes deployment of a variety of instruments, from local to meso-scale, dedicated to monitoring and documentation of the major variables characterizing the climate forcing, and the spatio-temporal variability of surface processes and state variables such as vegetation mass, leaf area index (LAI), soil moisture and surface fluxes. This paper describes the Gourma site, its associated instrumental network and the research activities that have been carried out since 1984. In the AMMA project, emphasis is put on the relations between climate, vegetation and surface fluxes. However, the Gourma site is also important for development and validation of satellite products, mainly due to the existence of large and relatively homogeneous surfaces. The social dimension of the water resource uses and governance is also briefly analyzed, relying on field enquiry and interviews. The climate of the Gourma region is semi-arid, daytime air temperatures are always high and annual rainfall amounts exhibit strong inter-annual and seasonal variations. Measurements sites organized along a north–south transect reveal sharp gradients in surface albedo, net radiation, vegetation production, and distribution of plant functional types. However, at any point along the gradient, surface energy budget, soil moisture and vegetation growth contrast between two main types of soil surfaces and hydrologic systems. On the one hand, sandy soils with high water infiltration rates and limited run-off support almost continuous herbaceous vegetation with scattered woody plants. On the other hand, water infiltration is poor on shallow soils, and vegetation is sparse and discontinuous, with more concentrated run-off that ends in pools or low lands within structured endorheic watersheds. Land surface in the Gourma is characterized by rapid response to climate variability, strong intra-seasonal, seasonal and inter-annual variations in vegetation growth, soil moisture and energy balance. Despite the multi-decadal drought, which still persists, ponds and lakes have increased, the grass cover has largely recovered, and there are signs of increased tree cover at least in the low lands.

Development of a Large‐Scale Hydrological Model TOPX and Its Coupling with Regional Integrated Environment Modeling System RIEMS

AbstractOn the basis of the improved SIMTOP runoff parameterization scheme and the calculating method of three‐layer soil moisture balance in Xinanjiang model, this paper developed a simple but highly‐efficient large‐scale hydrological model (TOPX), which can provide the function of scaling transformation on topographic index. Although the TOPX model has less data input and minimum parameters for calibrating, it can better describe the two‐dimensional hydrological processes. Then TOPX was coupled with the regional integrated environment modeling system (RIEMS) to enforce its ability of numerical simulation for the runoff in large‐scale watershed. The results of the off‐line test performed at Youshui River catchment indicate that the TOPX model produced better simulation effect of daily runoff in small sized catchment and it can describe the various hydrological processes of watershed. The off‐line test on Jinghe basin show that TOPX model has the better ability of distributed simulation at large‐scale and it can capture the major characteristics of land‐surface hydrological processes at regional‐scale. Then the coupling model of RIEMS and TOPX was still on‐line tested in Jinghe basin. By means of the scale transformation scheme on topographic index and the yielding and runoff routing theory, the coupling model use the meteorological data simulated by a regional climate model to drive the hydrological model for predicting the daily runoff at large‐scale watershed. A further analysis revealed that the accuracy of the distributed rainfall data simulated by the regional climate model (RIEMS) is the crucial factor to affect the modeled runoff in the coupling model (RIEMS_TOPX).

Quantification of groundwater recharge in a hard rock terrain of Orissa: a case study

A study was carried out to select the best method to estimate groundwater recharge in a hard rock terrain. Various standard empirical methods, soil-moisture balance method, water table fluctuation (WTF) method and commonly adopted norms set by Groundwater Estimation Committee (GEC), Govt of India were used to estimate recharge for the Munijhara watershed in the Nayagarh block of Orissa (India). The empirical formulae gave recharge rates ranging from 13 cm to 32 cm/year with average of 22.4 cm and standard deviation of 5.34, independent of other influencing factors like soil, topography and geology. The soil-moisture balance study indicated that recharge is more dependent on the continuous heavy rainfall total annual volume of rainfall. Recharge was limited at up to 10 mm per day, possibly due to presence of hard rock below the soil surface. The rise in water table depth was 3.45 m to 5.35 m with a mean rise of 4.5 m during the year 2006-2007. Annual groundwater recharge based on the WTF approach varied from 10.3 to 16.85 cm with a mean of 13.5 cm, standard deviation of 1.57 cm and coefficient of variation 11.57%. This recharge accounted for 8 to 14% of rainfall received. With a water budget approach based on GEC norms, recharge was calculated as 17 cm per year. The study showed that the magnitudes of annual groundwater recharge as estimated by the WST method and GEC norms are in conformity with other recent findings in India under the same climate conditions. Based on the results recharge structures could be planned in suitable locations to reduce fallow areas under the watershed.

Simulating the effect of capillary flux on the soil water balance in a stochastic ecohydrological framework

Groundwater uptake can play a major role in the survival of vegetation in semiarid areas, but this has not yet been included in an earlier developed ecohydrological stochastic framework. In this paper we provide a piecewise linear equation which includes capillary fluxes from shallow groundwater in the loss function of the ecohydrological stochastic model. The results indicate that this model is able to simulate the capillary fluxes, and the model also reflects the impact of the fluxes on the soil moisture balance. In addition, the results are analytically tractable and allow calculation of the probability density functions of soil water saturation and water stress for different groundwater depths below the root zone.

Impact of rainfall distribution on the parameterisation of a soil-moisture balance model of groundwater recharge in equatorial Africa

Summary Robust calibration of hydrological models, driven by gridded precipitation data derived from either Regional Climate Models or statistical downscaling of General Circulation Models, is essential to the quantitative analysis of the impacts of climate change on catchment hydrology and freshwater resources. Predicted warming in equatorial Africa, accompanied by greater evaporation and more frequent heavy precipitation events, may have substantial but uncertain impacts on terrestrial hydrology. In this study, we examine how the spatial representation of precipitation influences the parameterisation and calibration of a soil-moisture balance model (SMBM) in the humid tropics of equatorial Uganda. SMBMs explicitly account for changes in soil-moisture and partition effective precipitation into groundwater recharge and runoff. The semi-distributed SMBM, calibrated with daily station data over a 15 year period (1965–1979), estimates a mean annual recharge of 104 mm a −1 and mean annual surface runoff of 144 mm a −1 . Interpolation of station precipitation by inverse distance weighting produces a more uniform distribution, and a 7% increase, in mean annual catchment precipitation relative to point-based station data. Application of interpolated (gridded), uncorrected precipitation to the SMBM results in an underestimation of runoff and overestimation of recharge by 57% and 52%; respectively whereas use of corrected, gridded precipitation results in an underestimation of recharge and runoff by 10% and 64%; respectively. Recalibration of the SMBM using gridded precipitation data requires a 3% reduction in potential evapotranspiration, a 12% increase in the runoff-coefficient, and an 18% reduction in the rainfall threshold. These values are inconsistent with local, point-based observations of these parameters. Although current efforts seek to improve the distribution and duration of key hydrological measurements (e.g. soil-moisture, groundwater levels) in data-poor regions, the parameterisation of gridded hydrological models remains largely empirical due to the discrepancy between gridded and locally observed hydrological parameters.

Climate and soil moisture environment during development of the fifth palaeosol in Guanzhong Plain

Based on weathering characteristics of the fifth palaeosol layer (S5) of four sections in Guanzhong Plain, the thickness of the weathered profile of the paleosol is determined to be greater than the ordinary soil, a weathered and leached loess layer thicker than 2 m. The distribution depth of the red argillans, the weathered and leached loess layer, Fe2O3, CaCO3 and Sr content under the S5 all indicate that the precipitation in Guanzhong Plain was over 900 mm at that time. The distribution depth of gravity water zone reached 4.2 m at least, and the soil moisture content was generally more than 20% within the range of 4.2 m. At that time there was sufficient soil moisture and no dried earth layer developed in Guanzhong Plain, suitable for the forest to develop. When this soil developed, the mean annual precipitation was more than the annual soil moisture evaporation. The value of soil moisture balance was positive and the atmospheric precipitation could supply the underground water normally. Soil water was weak acidic in the middle and late stages when S5 developed in Guanzhong Plain. It was a kind of subtropical climate and even more humid and warmer than the northern edge of the subtropical climate zone in Guanzhong Plain when the S5 developed. At that time the subtropical climate was prevailing over the northern side and southern side of Qingling Mountains, showing the Mountains no longer to be the boundary between the subtropical zone and the temperate zone in China. The summer monsoon acted intensely and could go over Qingling Mountains frequently bring abundant precipitation.

Geospatial estimation of soil moisture in rain-fed paddy fields using SCS-CN-based model

Paddy fields are characterized by standing water and saturation condition during the entire crop growth period. However, in sub-humid and semi-arid areas, scarce rainfall and intermittent dry spells often cause soil moisture depletion resulting in unsaturated condition in the fields. These distinctive characteristics of the paddy fields have significant influence on the runoff generation and soil moisture retention characteristics of the watershed. In this study, the objective is to extend the application of the Soil Conservation Services Curve Number (SCS-CN)-based models for the geospatial and temporal simulation of soil moisture to paddy field-dominated agricultural watersheds in the water scarce areas. Different SCS-CN-based models, integrated with the soil moisture balance equation, are used to estimate the surface runoff and soil moisture content wherein, the spatial variation in the soil hydraulic characteristics is used to calculate the geospatial variation in soil moisture content. Physical significance of the terms initial abstraction ( I a ) and potential maximum retention ( S) in these models and their influence on the estimation of runoff and soil moisture are analysed in detail. A new SCS-CN-based model for soil moisture simulation (SCS-CN-SMS), to improve the soil moisture estimation, is proposed in this paper. The proposed model is built up on the soil moisture balance equation to account for the effect of ponding condition and soil moisture variation between the dry and saturation condition. The method is tested with 3 years observed surface runoff data and crop production statistics from a part of the Gandeshwari sub-watershed in West Bengal, India. The entire study area is divided into cells of 20 m × 20 m. Various components of the soil moisture balance equation are estimated for each cell as a function of the soil moisture content. Remote Sensing Technique and Geographic Information System (GIS) are used to extract and integrate the spatially distributed land use and soil characteristics. The Hortonion overland flow concept adopted in the SCS-CN method is used to estimate the soil hydraulic characteristics of each cell in which the curve number is used to infer the spatial variation of the land use and soil characteristics. Even though the original SCS-CN method and the existing modified versions are efficient for runoff estimation, these models are found to be inappropriate for the estimation of soil moisture distribution. On the other hand, the proposed SCS-CN-SMS model gives better results for both runoff and soil moisture simulation and is, therefore, more suitable for the hydrological modeling of paddy field-dominated agricultural watersheds.