Impact of Forest Conversion to Agriculture on Hydrologic Regime in the Large Basin in Vietnam

Nguyen Cung Que Truong,Hong Quan Nguyen,Dao Nguyen Khoi,Akihiko Kondoh

doi:10.3390/w14060854

Nguyen Cung Que Truong, Hong Quan Nguyen + Show 2 more

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https://doi.org/10.3390/w14060854

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Abstract

Deforestation due to agricultural land expansion occurred greatly during 1994 to 2005 with a high proportion of forests being converted into agriculture in the upstream Dong Nai river basin in Vietnam. Most of these conversions included expansions of coffee plantations in Dak Lak and Lam Dong provinces, which are in the world’s Robusta coffee production area. The aim of this study is to quantify the impact on the water cycle due to the conversion of forest to coffee plantations in a tropical humid climate region by the application of a hydrological model: soil and water assessment tool (SWAT). The model was calibrated with climate data from 1980–1994, validated with climate data from 1995–2010, and verified with statistical indicators such as Nash–Sutcliffe efficiency (NSE), percent bias (PBIAS), and ratio of the root mean square error (RSR). The simulations indicated that forest conversions into agriculture (expansion of coffee plantations) had significantly increased surface runoff (SUR) while actual evapotranspiration (ET), soil water content (SW), and groundwater discharge (GW) decreased. These changes are mainly related to the decrease in infiltration and leaf area index (LAI) post land cover changes. However, the soil was not thoroughly destroyed after deforestation due to the replacement of the lost forest with crops and vegetation. Therefore, changes in infiltration were marginal and not sufficient to bring large changes in the annual flow. Higher reductions in ET and SW were proposed, resulting in reduced streamflow in the dry season at the basin where the proportion of agricultural land was higher than the forest cover. Besides the plantation expansion, which resulted in streamflow reductions in the dry season, an existing problem was over-irrigation of coffee plantations that could likely deplete groundwater resources. Hence, balancing economic benefits by coffee production and mitigating groundwater depletion issues should be prioritized for land use management in the study area.

Highlights

IntroductionThe Vietnamese government initiated a series of economic reforms in the mid-1980s, which were aimed at stimulating economic growth, the most remarkable policy being the New Economic Zones program
The results indicated that deforestation increased the surface runoff and soil water content while actual evapotranspiration, water yield, and annual flow increased marginally
ET insignificantly decreased with a reduction of 2%, and soil water content (SW) decreased by 10% at Ta Lai station

Summary

Introduction

The Vietnamese government initiated a series of economic reforms in the mid-1980s, which were aimed at stimulating economic growth, the most remarkable policy being the New Economic Zones program. This policy resulted in large-scale displacement of residents to uninhabited areas due to expansion of the agricultural land. These factors led to the conversion of land use and land cover in Vietnam after mid-1980s [1]. Since 1998, the Vietnamese government implemented multiple national No programs for poverty reduction and programs for socio-economic development in mountainous areas; for

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