Assessment on Hydrological Ecosystem Services in Da River Basin, Northern Vietnam

Abstract

Ecosystem services provide various benefits to humans. By assessing and valuing ecosystem services, it is possible to give incentives to ecosystem services suppliers to encourage proper forests management and alleviate the poverty in developing countries. Due to its increasing cognition of the ecosystem services assessment, the Vietnamese government adopted the Payment for Forest Ecosystem Services (PFES) policy that provides incentives to upper landowners for protecting their ecosystems. Since Vietnam is suffering from many hydrological problems accompanied with forest loss, such as an insufficient water supply in dry seasons and sediment loss from hilly areas, the current PFES policy is developed well on hydrological ecosystem services. However, implementing PFES in nationwide requires quantitative and spatially explicit assessments that are thus far lacking in Vietnam. In this study, to assess two hydrological ecosystem service, water yield and sediment retention, Da River basin was selected as it has the largest discharge to the delta, relatively rich forest, high vulnerability to forest degradation, and sufficient service payers such as water supplying company and hydro-electronic power companies. For a method, since ecosystem services highly depend on land cover, land cover was classified into seven classes, using both the dry and wet seasons Landsat images. Then, on the basis of previous ecosystem assessment methods, water balance theory and the Universal Soil Loss Equation (USLE) were adopted as the water yield and sediment retention analysis respectively, and MODIS Enhanced Vegetation Index (EVI) in 2012 was adopted to assess forest quality to support K-coefficient included in PFES policy in Vietnam. The land cover classification result for forest cover was 52%, which is lower than other referenced maps such as the MODIS land cover and FROM-GLC-agg map. This result might have been derived due to the site-specific land cover definition, higher resolution as compared to MODIS land cover and the consideration of both the dry and wet seasons in contrast to the one-scene classification of the FROM-GLC-agg map. Annual precipitation was 1,301 to 2,384 mm and actual evapotranspiration MODIS ET was 5-1,671 mm, resulting in a water yield of 2.5-1,472 mm per year. Spatially, Yen Bai province and southern Dien Bien province were high in water yield. Potential soil loss was up to 8,874 tons/cell and sediment retention per cell was up to 25.323 tons per cell per year. Fansipan Mountain, Phu Tra Mountain, Dien Bien province, and Yen Bai province were high in sediment retention. The average EVI in 2012 ranged from 0.0308 to 0.5786, and Dien Bien province, the middle of Da River basin, and Hoa Binh province were high in EVI. Finally, forest cover was extracted from the land cover classification results and clipped above the data to set prior forest region considering K coefficients that include both hydrological ecosystem services (K2 coefficient) and forest quality (K1 coefficient). After overlaying the data, in Dien Bien province, there was high forest quality with mid-high hydrological ecosystem services, showing the highest probability of achieving much incentives, according to the application of the K-coefficient described on PFES policy and acts. This study was intended to give current information of forests existence and suggest valid grounds for assessing ecosystem services and supporting K coefficients to set priority forests region in implementing PFES policy in a more accurate and systematic way.