Modeling Surface Runoff and Evapotranspiration using SWAT and BEACH for a Tropical Watershed in North Vietnam, Compared to MODIS Products

Abstract

Accurate estimation of surface runoff (Q) and evapotranspiration (ET) is a challenging task but an important research topic because both Q and ET play vital roles in the study of the hydrological cycle, of climate change, water resources, flood management and so on. In this paper we will present the modeling method to estimate the daily Q and ET for a medium-sized watershed in the tropical region of the North of Vietnam using the Soil and Water Assessment Tool (SWAT) and Bridging Event and Continuous Hydrological (BEACH) models. The models were calibrated and validated for the river discharge for SWAT and evaporation (E) for BEACH in a 12 year period from 2001 to 2012. The simulated ETs by the models were compared with the satellite-based ET of MODIS products. Our simulation results show that the SWAT and BEACH models are capable of satisfactorily reproducing (with the NSE > 0.62 and R 2 > 0.78) the stream-gauged river discharge and the observed E, respectively. Daily ET varied from 0.3 to 14 mm day -1 and was highest from May to August and lowest from December to March. Although the monthly and yearly MODIS ETs were slightly higher than those of SWAT and BEACH, a strong relationship between them was found with a standard deviation ranging from three to 40 mm. A light decrease of ET values in the 12 years can be seen in the result analyses; however a longer simulation time might be needed to ensure this trend.

Hydrological Modeling and Runoff Mitigation in an Ungauged Basin of Central Vietnam Using SWAT Model

“…Petković et al [44] mentioned that relative humidity and a wind speed of two meters are two factors that play a role in the variation of ET. The same results were also presented by Nguyen and Kappas [3].…”

“…Petković et al [44] mentioned that relative humidity and a wind speed of two meters are two factors that play a role in the variation of ET. The same results were also presented by Nguyen and Kappas [3]. As Figure 8a,b shows, the lowest evapotranspiration is from November to February, when the average temperatures are lower than over the other months.…”

“…Among these, semi-distributed hydrological models can simulate water balance spatially based on various soils, land uses, topography and climate conditions. One of these hydrological models is SWAT [1] which is tested in various world climates from arid and semi-arid regions [2] to humid and tropical areas [3]. Moreover, it is able to simulate water resources in large scales to regional scales.…”

A Review of SWAT Studies in Southeast Asia: Applications, Challenges and Future Directions

“…Therefore, most of the SWAT studies include analyses of calibration and validation performance results. For example, SWAT model reliability assessments were conducted for the PoKo [162], Cong [148], and Nam Kim [151] watersheds in Vietnam. These studies reported the model performed well for overall streamflow simulation but did not match some peaks and base flows accurately.…”

Land-Use Land-Cover Change and Its Impact on Surface Runoff using Remote Sensing and GIS

“…Thomas (2015) used RINSPE model implemented in ArcView GIS 3.3 environment to model for estimating runoff in the Olifants river catchment area in north eastern South Africa as surface runoff and entering into the subsurface as infiltration. In another study, Hong Quang Nguyen and Martin Kappas (2015) used Soil and Water Assessment Tool (SWAT) and Bridging Event and Continuous Hydrological (BEACH) models for estimating surface runoff and evapotranspiration in a tropical watershed in North Vietnam. While estimating the runoff in Vindhyachal region, part of Mirzapur district, Uttar Pradesh, northern India, Topno et al (2015) observed an improvement in estimated runoff accuracies by using a curve number (CN) model developed by the United States Department of Agriculture (USDA).…”